Tactile articles and uses using sintered articles prepared from molded gel compositions

Abstract

A tactile article using a sintered article prepared from a molded gel composition, a method for making the tactile article, and uses are provided. The tactile article includes a shaped zirconia ceramic plate and a piezoelectric actuator attached to the shaped zirconia ceramic plate to vibrate the shaped zirconia ceramic plate at ultrasonic frequencies.

Description

[Background technology]

[0001] Research has been conducted on ultrasonically driven variable friction surfaces, which can make rough surfaces feel smoother by vibrating the substrate at ultrasonic frequencies with amplitudes in the micrometer range. This may be due to a "squeezed air film" effect, in which a thin film of air is trapped between the input unit (e.g., a fingertip) and the surface, resulting in less contact between them and therefore lower friction. Later work applied this principle to larger surfaces, such as the glass on an LCD screen. Summary of the Invention

[0002] The present disclosure provides tactile articles, methods of making tactile articles, and uses that use sintered articles prepared from molded gel compositions.

[0003] In one aspect, the present disclosure describes a haptic device including a shaped zirconia ceramic plate including a plate body and an actuation surface thereof, and a piezoelectric actuator attached to the shaped zirconia ceramic plate and configured to generate standing waves on the actuation surface of the shaped zirconia ceramic plate at ultrasonic frequencies above 20 kHz. In some cases, the shaped zirconia ceramic plate is a product of drying and sintering a shaped gel article. The shaped gel article includes a polymerization product of a reaction mixture, the reaction mixture being positioned within a mold cavity during polymerization, and the shaped gel article retains both the same size and shape as the mold cavity (except for areas where the mold cavity is overfilled) when removed from the mold cavity.

[0004] In another aspect, the present disclosure describes a method for manufacturing a haptic device, the method including: providing a reaction mixture into a mold cavity, the reaction mixture including 20-60 wt % zirconia-based particles based on the total weight of the reaction mixture; polymerizing the reaction mixture to form a shaped gel plate in the mold cavity and in contact with a surface of the mold cavity; removing the shaped gel plate from the mold cavity, the shaped gel plate retaining the same size and shape as the mold cavity; removing the solvent medium to form a dried shaped gel plate; heating the dried shaped gel plate to form a shaped zirconia ceramic plate; and providing a piezoelectric actuator attached to the shaped zirconia ceramic plate and configured to generate a standing wave on an actuation surface of the shaped zirconia ceramic plate at an ultrasonic frequency above 20 kHz.

[0005] Various unexpected results and advantages are obtained with exemplary embodiments of the present disclosure. Advantages of exemplary embodiments of the present disclosure include, for example, tactile articles including shaped zirconia ceramic plates that exhibit high efficiency in converting electrical power to Z-axis displacement compared to conventional glass resonators. Furthermore, shaped zirconia ceramic plates can be prepared from corresponding shaped gel articles that can have intricate, fine features that can be retained in the sintered article.

[0006] The foregoing is a summary of various aspects and advantages of exemplary embodiments of the present disclosure. The above Summary is not intended to describe each illustrated embodiment or every implementation of certain exemplary embodiments of the present disclosure. The following figures and Detailed Description more particularly illustrate certain preferred embodiments that employ the principles disclosed herein. [Brief explanation of the drawings]

[0007] A more complete understanding of the present disclosure may be obtained from the following detailed description of various embodiments of the present disclosure when considered in conjunction with the accompanying drawings, in which:

[0008] [Figure 1] FIG. 1 is a schematic diagram of a haptic device including a shaped zirconia ceramic plate, according to one embodiment. [Figure 2] FIG. 1 is a perspective view of a shaped zirconia ceramic plate according to one embodiment. [Figure 3] FIG. 1 is a perspective view of a shaped zirconia ceramic plate according to another embodiment. [Figure 4] FIG. 1 is a plan view of a shaped zirconia ceramic plate according to another embodiment. [Figure 5] FIG. 10 is a side perspective view of a shaped zirconia ceramic plate according to another embodiment. [Figure 6] FIG. 10 is a side perspective view of a shaped zirconia ceramic plate according to another embodiment. [Figure 7] FIG. 1 is a flow diagram of a process for manufacturing a shaped zirconia ceramic plate, according to one embodiment.

[0009] In the drawings, like reference numerals refer to like elements. The above-identified drawings may not be drawn to scale and illustrate various embodiments of the present disclosure; however, as noted in the Detailed Description, other embodiments are also contemplated. In all cases, this disclosure describes the disclosure disclosed herein by representing exemplary embodiments, and not by express limitation. It should be understood that numerous other modifications and embodiments may be devised by those skilled in the art that are within the scope and spirit of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] With regard to the following glossary of defined terms, these definitions shall apply throughout this application, unless a different definition is provided in the claims or elsewhere in this specification.

[0011] Glossary Certain terms are used throughout this specification and claims, most of which are well known, but may require some explanation. It should be understood that: As used herein, the term "zirconia" refers to various stoichiometric formulas of zirconium oxide. The most typical stoichiometric formula is ZrO2, commonly referred to as either zirconium oxide or zirconium dioxide.

[0012] As used herein, the term "zirconia-based" means that the material is predominantly zirconia. For example, at least 70 mol%, at least 75 mol%, at least 80 mol%, at least 85 mol%, at least 90 mol%, at least 95 mol%, or at least 98 mol% of the material is zirconia. Zirconia is often doped with other inorganic oxides, such as, for example, lanthanide oxides and / or yttrium oxide.

[0013] As used herein, the term "inorganic oxide" includes, but is not limited to, oxides of various inorganic elements such as, for example, zirconium oxide, yttrium oxide, lanthanide element oxides, aluminum oxide, calcium oxide, and magnesium oxide.

[0014] As used herein, the term "lanthanide element" refers to an element in the lanthanide series of the periodic table of elements. The lanthanide series can have atomic numbers 57 (lanthanum) to 71 (lutetium). Elements included in this series are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). As used herein, the term "rare earth" refers to an element that is scandium (Sc), yttrium (Y), or a lanthanide element.

[0015] As used herein, the term "within the range" includes the endpoints of the range and all numbers between the endpoints. For example, a range of 1 to 10 includes the numbers 1, 10, and all numbers between 1 and 10.

[0016] As used herein, the term "associated" refers to a group of two or more primary particles that are aggregated and / or agglomerated. Similarly, the term "non-associated" refers to two or more primary particles that are free or substantially free of aggregation and / or agglomeration.

[0017] As used herein, the term "agglomeration" refers to a strong association of two or more primary particles. For example, the primary particles may be chemically bonded to each other. Generally, breaking down the agglomerates into smaller particles (e.g., primary particles) is difficult to achieve.

[0018] As used herein, the term "agglomeration" refers to a weak association of two or more primary particles. For example, the particles may be held together by charge or polarity. Breaking agglomerates into smaller particles (e.g., primary particles) is less difficult than breaking aggregates into smaller particles.

[0019] As used herein, the term "primary particle size" refers to the size of unassociated single crystal zirconia particles, which are considered primary particles. X-ray diffraction (XRD) is typically used to measure primary particle size.

[0020] As used herein, the term "hydrothermal" refers to a process in which an aqueous medium is heated to a temperature above the normal boiling point of the aqueous medium at or above the pressure necessary to prevent the aqueous medium from boiling.

[0021] As used herein, the term "sol" refers to a colloidal suspension of discrete particles in a liquid. The discrete particles often have an average size in the range of 1 to 100 nm.

[0022] As used herein, the term "gel" or "gel composition" refers to the polymerization product of a reaction mixture that is a casting sol, the casting sol including zirconia-based particles, a solvent medium, a polymerizable material, and a photoinitiator.

[0023] As used herein, the term "shaped gel" refers to a gel composition formed within a mold cavity, where the shaped gel (i.e., shaped gel article) has a shape and size determined by the mold cavity. In particular, a polymerization reaction mixture containing zirconia-based particles can be polymerized within the mold cavity to form a gel composition, which retains the size and shape of the mold cavity when removed from the mold cavity.

[0024] As used herein, the term "aerogel" refers to a three-dimensional low-density solid (e.g., less than 30% of theoretical density). Aerogels are porous materials derived from gels in which the liquid component of the gel has been replaced by a gas. This solvent removal is often carried out under supercritical conditions. During this process, the network does not substantially shrink, resulting in a highly porous, low-density material.

[0025] As used herein, the term "xerogel" refers to a gel composition that has been further processed to remove the solvent medium by evaporation under ambient conditions or at elevated temperatures.

[0026] As used herein, the term "isotropic shrinkage" refers to shrinkage that is essentially the same in the x, y, and z directions, i.e., the degree of shrinkage in one direction is within 5%, 2%, 1%, or 0.5% of the shrinkage in the other two directions.

[0027] As used herein, the term "net-shape process" refers to a process that produces an initial item that is substantially close to the desired final (net) shape, but with a high probability of larger dimensions corresponding to the degree of isotropic shrinkage possible. This reduces the need for traditional costly finishing methods, such as machining or grinding.

[0028] The present disclosure provides tactile articles, methods for manufacturing tactile articles, and uses using sintered articles prepared from molded gel compositions. The tactile article includes a shaped zirconia ceramic plate and a piezoelectric actuator attached to the shaped zirconia ceramic plate to vibrate the shaped zirconia ceramic plate at ultrasonic frequencies. The haptic devices described herein can include sintered articles prepared from the gel compositions.

[0029] 1 is a schematic diagram of a haptic device 100 including a shaped zirconia ceramic plate 110, according to one embodiment. The shaped zirconia ceramic plate 110 includes a plate body 112 and an actuation surface 114 thereof. A piezoelectric actuator 120 is coupled to a rear surface 116 of the shaped zirconia ceramic plate 110. The piezoelectric actuator 120 is configured to generate vibrations (e.g., standing waves) on the actuation surface 114 of the shaped zirconia ceramic plate 110 at ultrasonic frequencies, e.g., greater than 20 kHz, greater than 40 kHz, or greater than 60 kHz, with amplitudes greater than 0.1 μm, greater than 0.2 μm, or greater than 0.3 μm.

[0030] 1, the piezoelectric actuator 120 is attached to the edge of the shaped zirconia ceramic plate 110 on the rear surface 116 via epoxy 102. It should be understood that the piezoelectric actuator 120 may be coupled to the shaped zirconia ceramic plate 110 at any desired location by any suitable mechanism. The piezoelectric actuator 120 may be any suitable vibration actuator that couples to the shaped zirconia ceramic plate and causes the zirconia ceramic plate to vibrate at the desired ultrasonic frequency.

[0031] In some embodiments, the piezoelectric actuator 120 may include a signal generator or amplifier that generates an alternating electric field to drive the piezoelectric transducer to vibrate. The signal generator or amplifier may use frequency and amplitude information sent from the controller and generate a corresponding electrical signal whose voltage varies with the received frequency. The controller may be integrated with the signal generator or amplifier, for example, on a printed circuit board (PCB). The controller may be a processor or computing device, and may include, for example, one or more general-purpose microprocessors, specially designed processors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), collections of discrete logic, and / or any type of processing device capable of performing the techniques described herein.

[0032] When the piezoelectric actuators 120 are actuated, the haptic device 100 provides a vibrating actuation surface 114, which can reduce the frictional force between a sensed object (e.g., a user's fingertip 2) and the actuation surface 114. This is due to a "squeezed air film" effect, where a thin film of air is trapped between the fingertip and the actuation surface, creating less contact between them and resulting in lower frictional forces. The variation in frictional force is related to the tactile feel of the actuation surface 114 and can be utilized to create a variable friction surface.

[0033] The ultrasonic friction reduction described herein can use various forms of vibration (e.g., sinusoidal or other complex forms) at high frequencies (e.g., ultrasonic frequencies above 20 kHz) to drive one or more piezoelectric actuators, creating standing waves on the actuation surface. The vibration frequency can be selected to match the resonant modes of the haptic device 100 to achieve a peak displacement, such as 700 nm or greater, for detectable friction reduction. Unlike low-frequency vibratory haptic devices, the ultrasonic frequencies applied here (e.g., >25 kHz) may not be perceived as vibrations because ultrasonic frequency vibrations may be outside the response range of the user's skin mechanoreceptors. Instead, the actuation surface feels "slippery" due to the reduced friction force.

[0034] In some embodiments, the resonant frequency can be used as a carrier signal to create sophisticated tactile emulation effects that can be modulated at low frequencies (e.g., below 400 Hz) that fall within the range that can be perceived as vibration.

[0035] In the present disclosure, the generated vibrations are controlled so that surface waves on the actuating surface with a suitable amplitude, frequency, and vibration mode can produce a perceptible friction-reducing effect. Without wishing to be bound by theory, it is believed that standing waves with a half-wavelength less than the width of a fingertip can minimize the perceptible effect of "dead spots" (nodes) on the vibrating surface (i.e., actuating surface), or are wide enough that the actuating surface may otherwise be on a single antinode. Minimizing "dead spots" may not be necessary to achieve a perceptible effect. In some embodiments, vibrations with a maximum displacement greater than 0.5 or 1 μm may be required to produce a perceptible effect.

[0036] 1, a shaped zirconia ceramic plate 110 has one or more edges mounted on a frame 12 in which a touch device 14 is housed. The plate 110 may include a low-friction surface 124b that allows the plate body 112 to slide or move on structural supports 124a within the frame 12 that support the plate body 112. An additional touch surface (e.g., a protective glass plate not shown in FIG. 1) may be attached to the touch device 14 via an adhesive 122 (e.g., an optically clear adhesive).

[0037] The shaped zirconia ceramic plate 110 further includes one or more intricate features formed on the plate body 112 as a unitary structure. The term "unitary structure" means that the intricate features are formed with the shaped zirconia ceramic plate as an integral structure without adding or subtracting material from the plate to form the features. The intricate features may include, for example, one or more slots, one or more grooves, one or more tabs, one or more holes, one or more bosses, one or more sockets, and combinations thereof.

[0038] Shaped zirconia ceramic plates can be of various shapes or geometries, such as flat, curved, or undulating structures. The size of the plates can vary depending on the application. In some embodiments, the various shapes can have in-plane (e.g., XY plane in a Cartesian coordinate system) dimensions ranging from 1.0 mm to 10 cm, and thicknesses (e.g., dimensions in the Z axis of a Cartesian coordinate system) ranging from 10 μm to 1 mm. In some embodiments, plates can be manufactured from sintered articles by processes described further below. Sintered articles of any desired size and shape can be prepared. The longest dimension can be up to 1 cm, up to 2 cm, up to 5 cm, or up to 10 cm or even longer. The longest dimension can be at least 1 cm, at least 2 cm, at least 5 cm, at least 10 cm, at least 20 cm, at least 50 cm, or at least 100 cm.

[0039] The intricate features can have very fine geometries. The maximum dimension (e.g., depth, width, length, diameter, etc.) of the fine geometries can be, for example, about 5 mm or less, about 2 mm or less, about 1 mm or less, about 0.5 mm or less, about 0.1 mm or less, about 0.05 mm or less, or even less. In some embodiments, the maximum dimension of the fine geometries can be, for example, less than about 1 / 10, 1 / 20, 1 / 50, 1 / 100, 1 / 200, 1 / 500, or 1 / 1000 of the maximum dimension of the shaped zirconia ceramic plate 110.

[0040] The shaped zirconia ceramic plates described herein may comprise at least 70 mol%, at least 75 mol%, at least 80 mol%, at least 85 mol%, at least 90 mol%, at least 95 mol%, or at least 98 mol% zirconia-based material, wherein at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, or at least 99.5 wt% of the zirconia-based material has a cubic crystal structure, a tetragonal crystal structure, or a combination thereof.

[0041] The shaped zirconia ceramic plates described herein may have a higher density than standard glass plates, such as borosilicate glass plates of similar dimensions, available from Swift Glass Co. (Elmira Heights, NY). Borosilicate glass may have a theoretical density of approximately 2.23 g / cc. Tetragonal zirconia may have a theoretical density of approximately 6.10 g / cc. In some embodiments, the shaped zirconia ceramic plates may have a relative density of at least 90%, at least 95%, at least 97%, at least 99%, or even higher than the theoretical density of crystalline zirconia in the cubic or tetragonal phase. Theoretical density is defined as the maximum density of crystalline zirconia in the pore-free cubic or tetragonal phase.

[0042] In some embodiments, the shaped zirconia ceramic plate can be the product of drying and sintering a shaped gel article. The shaped gel article can include the polymerization product of a reaction mixture. The reaction mixture is positioned within a mold cavity during polymerization, and the shaped gel article retains both the same size and shape as the mold cavity (except for areas where the mold cavity is overfilled) when removed from the mold cavity. The reaction mixture can include: a. 20-60 wt. % zirconia-based particles, based on the total weight of the reaction mixture, having an average particle size of 100 nm or less and containing at least 70 mol. % ZrO; b. 30-75% by weight of a solvent medium based on the total weight of the reaction mixture, the solvent medium comprising at least 60% of an organic solvent having a boiling point at least equal to 150°C; c. 2-30 wt. % of a polymerizable material, based on the total weight of the reaction mixture, the polymerizable material comprising: (1) a first surface modifier having free-radically polymerizable groups; d. a photoinitiator for a free radical polymerization reaction; Includes.

[0043] The shaped zirconia ceramic plate 110 can be provided as a tactile feedback device in various forms, such as, for example, a button, a knob, or a touchpad. In some embodiments, one or more haptic devices described herein can be combined with another electronic device, such as, for example, a touch device. The "squeezed membrane effect" created by the haptic device can be utilized to add a touch feedback dimension to interactions with the electronic device. This additional dimension can add enhanced realism that can potentially improve performance.

[0044] In some applications, the (X,Y) position of a user's fingertip on the working surface 114 of the shaped zirconia ceramic plate 110 can be determined. The finger position can be tracked using various devices, such as a touch sensor. The touch device or sensor can be a capacitive touch sensor that uses a layer of indium tin oxide (ITO) attached below the resonant surface. The (X,Y) position of the fingertip on the plate can be sent to a controller that controls signal generation for the piezoelectric actuators. The (X,Y) position can be mapped to varying amplitude and / or frequency levels of a signal generator or amplifier to create the tactile illusion of changing surface features as the fingertip moves over the working surface of the shaped zirconia ceramic plate.

[0045] Exemplary shaped zirconia ceramic plates having various shaped structures with attachment features and / or additional features are shown in FIGS. 2-6. In the embodiment shown in FIG. 2, shaped zirconia ceramic plate 110a has a flat plate body 112a defining its working surface 114a and one or more features, such as through-holes 21, bosses 22, or conduits 23, formed in plate body 112a. In the embodiment shown in FIG. 3, shaped zirconia ceramic plate 110b has a curved plate body 112b defining its working surface 114b and one or more features, such as through-holes or bosses 31, formed in plate body 112b. In the embodiment shown in FIG. 4, shaped zirconia ceramic plate 110c has a plate body 112c defining its working surface 114c and one or more features, such as tabs 41, formed at the corners of plate body 112c. In the embodiment shown in Figure 5, the shaped zirconia ceramic plate 110d has a plate body 112d defining an actuation surface 114d and one or more slots 51 formed on a side surface 116d of the plate body 112d. In the embodiment shown in Figure 6, the shaped zirconia ceramic plate 110e has a plate body 112e defining an actuation surface 114e and one or more sockets 61 formed on a side surface 116e of the plate body 112e.

[0046] The shaped zirconia ceramic plates described herein can be fabricated by process 700, shown in FIG. 7. Process 700, shown in FIG. 7, provides a route to producing precise net-shaped ceramics from nanoparticles and / or microparticles, enabling unique geometries and properties without the high cost of machining. In 710, a reaction mixture or casting sol containing zirconia-based particles is prepared. The reaction mixture further includes one or more polymerizable materials having polymerizable groups capable of undergoing free radical polymerization (i.e., the polymerizable groups are free radically polymerizable). The reaction mixture is typically placed in a mold. Thus, in 710, an article is provided that includes (a) a mold having a mold cavity and (b) the reaction mixture positioned within the mold cavity and in contact with the surface of the mold cavity. In 720, a gel composition is formed within the mold cavity by curing the reaction mixture. In some embodiments, the gel composition may include the polymerization product of the reaction mixture (i.e., the casting sol). The gel composition may assume a shape defined by the mold cavity. In some embodiments, the gel composition may be formed as a shaped gel plate including a plate body and one or more attachment features formed on the plate body when it contacts the inner surface of the mold cavity. At 730, the shaped gel article is removed from the mold cavity, and the shaped gel article is treated to remove its organic solvent. This can be referred to as drying the gel composition or shaped gel article. Shaped gel articles of any size and complexity can be dried into aerogel articles. At 740, the aerogel article is heated to remove polymeric materials or any other organic materials that may be present and to achieve strength through densification. After organic burnout and optional soaking in aqueous ammonium hydroxide, the dried article is sintered.

[0047] Reaction mixture (casting sol) 1. Zirconia-based particles The reaction mixture contains zirconia-based particles. Any suitable process can be used to form the zirconia-based particles. In particular, the zirconia-based particles have an average particle size of 100 nm or less and contain at least 70 mole % ZrO. The zirconia-based particles are crystalline, with the crystalline phase being predominantly cubic and / or tetragonal. The zirconia-based particles are preferably non-associated, making them suitable for forming high-density sintered articles. Non-associated particles result in low viscosity and high optical transparency of the reaction mixture. Furthermore, non-associated particles result in a more uniform pore structure within the aerogel or xerogel, resulting in a more homogeneous sintered article.

[0048] In many embodiments, a hydrothermal process (hydrothermal reactor system) is used to produce crystalline, non-associated zirconia-based particles. A feedstock for the hydrothermal reactor system is used containing zirconia salts and other optional salts dissolved in an aqueous medium. Suitable optional salts include, for example, rare earth salts, transition metal salts, alkaline earth metal salts, and post-transition metal salts. Examples of rare earth salts include, for example, salts containing scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Examples of transition metals include, but are not limited to, salts of iron, manganese, cobalt, chromium, nickel, copper, tungsten, vanadium, and hafnium. Examples of alkaline earth metal salts include, but are not limited to, salts of calcium and magnesium. Examples of post-transition metal salts include, but are not limited to, aluminum, gallium, and bismuth salts. In many embodiments, the post-transition metal salt is an aluminum salt. In many embodiments, the optional salt is an yttrium salt, a lanthanum salt, a calcium salt, a magnesium salt, an aluminum salt, or a mixture thereof. In some preferred embodiments, the optional salt is an yttrium salt and a lanthanum salt. The metal is typically incorporated into the zirconia-based particles rather than being present as a separate particle.

[0049] The dissolved salts contained in the feedstock for a hydrothermal reactor system are typically selected to have anions that are removable and non-corrosive in subsequent processing steps. The dissolved salts are typically carboxylates, such as those having a carboxylate anion with four or fewer carbon atoms, such as formate, acetate, propionate, butyrate, or a combination thereof. In many embodiments, the carboxylate is acetate. That is, the feedstock often contains dissolved zirconium acetate and other optional acetates, such as yttrium acetate and acetates of lanthanide elements (e.g., lanthanum acetate). The feedstock may further contain a carboxylic acid of the corresponding carboxylate anion. For example, feedstocks prepared from acetates often contain acetic acid. The pH of the feedstock is typically acidic. For example, the pH is often at most 6, at most 5, or at most 4 and at least 2 or at least 3.

[0050] One exemplary zirconium salt is zirconium acetate, ZrO ((4-n) / 2) n+ (CH3COO - ) n (where n is in the range of 1 to 2). Zirconium ions can exist in various structures, depending, for example, on the pH of the feed material. Methods for producing zirconium acetate are described, for example, in W.B. Blumenthal, "The Chemical Behavior of Zirconium," pp. 311-338, D. Van Nostrand Company, Princeton, NJ (1958). Suitable aqueous zirconium acetate solutions are commercially available, for example, from Magnesium Elektron, Inc. (Flemington, NJ, USA), and contain, for example, up to 17 wt. % zirconium, up to 18 wt. % zirconium, up to 20 wt. % zirconium, up to 22 wt. % zirconium, up to 24 wt. % zirconium, up to 26 wt. % zirconium, or up to 28 wt. % zirconium, based on the total weight of the solution.

[0051] The feedstock is often selected to avoid or minimize the use of anions other than carboxylate anions. That is, the feedstock is selected to avoid or minimize the use of halide salts, oxyhalide salts, sulfate salts, nitrate salts, or oxynitrate salts. Halide and nitrate anions tend to result in the formation of zirconia-based particles that are primarily monoclinic phase, rather than the more desirable tetragonal or cubic phase. Because the optional salts are used in relatively small amounts compared to the amount of zirconium salt, the optional salts can have anions that are not carboxylate. In many embodiments, it is preferred that all salts added to the feedstock be acetate salts.

[0052] The amount of various salts dissolved in the feed material can be readily determined based on the percent solids selected for the feed material and the desired composition of the zirconia-based particles. Typically, the feed material is a solution and does not contain dispersed or suspended solids. For example, seed particles are not present in the feed material. The feed material usually has more than 5 weight percent solids, and these solids are typically dissolved. "Weight percent solids" can be calculated by drying a sample to a constant weight at 120°C and refers to the portion of the feed material that is not water, a water-miscible cosolvent, or another compound that can be evaporated at temperatures up to 120°C. Weight percent solids is calculated by dividing the dry weight by the wet weight and then multiplying by 100. Wet weight refers to the weight of the feed material before drying, and dry weight refers to the weight of the sample after drying. In many embodiments, the feed material is at least 5 weight percent, at least 10 weight percent, at least 12 weight percent, or at least 15 weight percent solids. Some feed materials have up to 20 weight percent solids, up to 25 weight percent solids, or even more than 25 weight percent solids.

[0053] Once the percent solids is selected, the amount of each dissolved salt can be calculated based on the desired composition of the zirconia-based particles. The zirconia-based particles are at least 70 mol% zirconium oxide. For example, the zirconia-based particles can be at least 75 mol%, at least 80 mol%, at least 85 mol%, at least 90 mol%, or at least 95 mol% zirconium oxide. The zirconia-based particles can be up to 100 mol% zirconium oxide. For example, the zirconia-based particles can be up to 99 mol%, up to 98 mol%, up to 95 mol%, up to 90 mol%, or up to 85 mol% zirconium oxide.

[0054] In addition to zirconium oxide, other inorganic oxides may be included in the zirconia-based particles depending on the intended use of the final sintered article. Up to 30 mol%, up to 25 mol%, up to 20 mol%, up to 10 mol%, up to 5 mol%, up to 2 mol%, or up to 1 mol% of the zirconia-based particles may be Y2O3, La2O3, Al2O3, CeO2, Pr2O3, Nd2O3, Pm2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Fe2O3, MnO2, Co2O3, Cr2O3, NiO, CuO, VO3, Bi2O3, Ga2O3, Lu2O3, HfO2, or mixtures thereof. Inorganic oxides such as Fe2O3, MnO2, Co2O3, Cr2O3, NiO, CuO, Bi2O3, Ga2O3, Er2O3, Pr2O3, Eu2O3, Dy2O3, Sm2O3, V2O3, or W2O3 may be added to change the color of the zirconia-based particles, for example.

[0055] When zirconia-based particles do not contain inorganic oxides other than zirconium oxide, some monoclinic crystalline phase is likely to be present. Because the monoclinic phase is less stable than either the tetragonal or cubic phases when heated, minimizing the amount of monoclinic phase is considered desirable for many applications. For example, the monoclinic phase may transform to the tetragonal phase when heated above 1200°C, but may revert to the monoclinic phase upon cooling. This transformation may be accompanied by volume expansion, which can lead to cracking or crazing of the material. In contrast, the tetragonal and cubic phases can be heated to approximately 2370°C or higher without undergoing a phase transformation.

[0056] In many embodiments, when a rare earth oxide is included in the zirconia-based oxide, the rare earth element is yttrium or a combination of yttrium and lanthanum. The presence of yttrium or both yttrium and lanthanum can prevent the tetragonal or cubic phase from undergoing a destructive transformation to the monoclinic phase upon cooling from high temperatures, such as above 1200° C. The addition of yttrium or both yttrium and lanthanum can increase or maintain the physical integrity, toughness, or both, of the sintered article.

[0057] The zirconia-based particles may contain 0 to 30 weight percent yttrium oxide, based on the total moles of inorganic oxides present. When yttrium oxide is added to the zirconia-based particles, it is often added in an amount equal to at least 1 mole percent, at least 2 mole percent, or at least 5 mole percent. The amount of yttrium oxide may be up to 30 mole percent, up to 25 mole percent, up to 20 mole percent, or up to 15 mole percent. For example, the amount of yttrium oxide may range from 1 to 30 mole percent, 1 to 25 mole percent, 2 to 25 mole percent, 1 to 20 mole percent, 2 to 20 mole percent, 1 to 15 mole percent, 2 to 15 mole percent, 5 to 30 mole percent, 5 to 25 mole percent, 5 to 20 mole percent, or 5 to 15 mole percent. The mole percent amounts are based on the total moles of inorganic oxides in the zirconia-based particles.

[0058] The zirconia-based particles may contain 0 to 10 mol% lanthanum oxide, based on the total moles of inorganic oxides present. When lanthanum oxide is added to the zirconia-based particles, it can be used in an amount equal to at least 0.1 mol%, at least 0.2 mol%, or at least 0.5 mol%. The amount of lanthanum oxide can be up to 10 mol%, up to 5 mol%, up to 3 mol%, up to 2 mol%, or up to 1 mol%. For example, the amount of lanthanum oxide can range from 0.1 to 10 mol%, 0.1 to 5 mol%, 0.1 to 3 mol%, 0.1 to 2 mol%, or 0.1 to 1 mol%. The mol% amounts are based on the total moles of inorganic oxides in the zirconia-based particles.

[0059] In some embodiments, the zirconia-based particles contain 70-100 mol% zirconium oxide, 0-30 mol% yttrium oxide, and 0-10 mol% lanthanum oxide. For example, the zirconia-based particles contain 70-99 mol% zirconium oxide, 1-30 mol% yttrium oxide, and 0-10 mol% lanthanum oxide. In other examples, the zirconia-based particles contain 75-99 mol% zirconium oxide, 1-25 mol% yttrium oxide, and 0-5 mol% lanthanum oxide, or 80-99 mol% zirconium oxide, 1-20 mol% yttrium oxide, and 0-5 mol% lanthanum oxide, or 85-99 mol% zirconium oxide, 1-15 mol% yttrium oxide, and 0-5 mol% lanthanum oxide. In yet another embodiment, the zirconia-based particles contain 85-95 mol % zirconium oxide, 5-15 mol % yttrium oxide, and 0-5 mol % (e.g., 0.1-5 mol % or 0.1-2 mol %) lanthanum oxide, where the mol % amounts are based on the total moles of inorganic oxides in the zirconia-based particles.

[0060] Other inorganic oxides can be used in combination with or in place of the rare earth elements. For example, calcium oxide, magnesium oxide, or mixtures thereof may be added in amounts ranging from 0 to 30 mol%, based on the total moles of inorganic oxides present. The presence of these inorganic oxides tends to reduce the amount of monoclinic phase formed. When calcium oxide and / or magnesium oxide are added to the zirconia-based particles, the total amount added is often at least 1 mol%, at least 2 mol%, or at least 5 mol%. The amount of calcium oxide, magnesium oxide, or mixtures thereof can be up to 30 mol%, up to 25 mol%, up to 20 mol%, or up to 15 mol%. For example, the amount can be in the range of 1 to 30 mol%, 1 to 25 mol%, 2 to 25 mol%, 1 to 20 mol%, 2 to 20 mol%, 1 to 15 mol%, 2 to 15 mol%, 5 to 30 mol%, 5 to 25 mol%, 5 to 20 mol%, or 5 to 15 mol%. The mole percent amounts are based on the total moles of inorganic oxides in the zirconia-based particles.

[0061] Furthermore, aluminum oxide may be included in an amount ranging from 0 to less than 1 mol % based on the total moles of inorganic oxides in the zirconia-based particles. In some examples, the zirconia-based particles contain 0 to 0.5 mol %, 0 to 0.2 mol %, or 0 to 0.1 mol % of the inorganic oxide.

[0062] The liquid medium of the feedstock for the hydrothermal reactor is typically primarily water (i.e., the liquid medium is an aqueous medium). The water is preferably deionized to minimize the introduction of other metal species, such as alkali metal ions, alkaline earth ions, or both, into the feedstock. A water-miscible organic co-solvent may be included in the solvent medium phase in an amount of up to 20 wt. % based on the weight of the solvent medium phase. Suitable co-solvents include, but are not limited to, 1-methoxy-2-propanol, ethanol, isopropanol, ethylene glycol, N,N-dimethylacetamide, and N-methylpyrrolidone. In most embodiments, no organic solvent is added to the aqueous medium.

[0063] Upon hydrothermal treatment, various dissolved salts in the feedstock undergo hydrolysis and condensation reactions to form zirconia-based particles. These reactions are often accompanied by the liberation of acidic by-products, which are often one or more carboxylic acids corresponding to the zirconium carboxylate salts plus any other carboxylate salts in the feedstock. For example, if the salt is acetate, acetic acid is formed as a by-product of the hydrothermal reaction.

[0064] Any suitable hydrothermal reactor system can be used to prepare zirconia-based particles. The reactor can be a batch or continuous reactor. In a continuous hydrothermal reactor, heating times are typically shorter and temperatures are typically higher compared to a batch hydrothermal reactor. The duration of the hydrothermal treatment can vary depending on the type of reactor, the reactor temperature, and the concentration of the feedstock. The pressure within the reactor can be autogenous (i.e., the vapor pressure of water at the reactor temperature), hydraulic (i.e., pressure generated by pumping a fluid against a constraint), or generated from the addition of an inert gas such as nitrogen or argon. Suitable batch hydrothermal reactors are available, for example, from Parr Instruments Co. (Moline, IL, USA). Some suitable continuous hydrothermal reactors are described, for example, in U.S. Pat. Nos. 5,453,262 (Dawson et al.) and 5,652,192 (Matson et al.), Adschiri et al., J. Am. Ceram. Soc., 75, 1019-1022 (1992), and Dawson, Ceramic Bulletin, 67(10), 1673-1678 (1988).

[0065] When a batch reactor is used to form zirconia-based particles, the temperature is often within the range of 160°C to 275°C, 160°C to 250°C, 170°C to 250°C, 175°C to 250°C, 200°C to 250°C, 175°C to 225°C, 180°C to 220°C, 180°C to 215°C, or 190°C to 210°C. The feedstock is typically placed in the batch reactor at room temperature. The feedstock in the batch reactor is heated to a specified temperature and held at that temperature for at least 30 minutes, at least 1 hour, at least 2 hours, or at least 4 hours. The temperature can be held for up to 24 hours, up to 20 hours, up to 16 hours, or up to 8 hours. For example, the temperature can be held for 0.5 to 24 hours, 1 to 18 hours, 1 to 12 hours, or 1 to 8 hours. Any size of batch reactor can be used. For example, the volume of the batch reactor may range from a few mL to several liters or more.

[0066] In many embodiments, the feedstock passes through a continuous hydrothermal reactor. As used herein, the term "continuous" in reference to a hydrothermal reactor system means that the feedstock is continuously introduced and the effluent is continuously removed from the heated zone. The introduction of the feedstock and the removal of the effluent typically occur at different locations in the reactor. The continuous introduction and removal may be continuous or intermittent.

[0067] In many embodiments, the continuous hydrothermal reactor system includes a tubular reactor. As used herein, the term "tubular reactor" refers to the heated portion (i.e., the heating zone) of a continuous hydrothermal reactor system. The shape of the tubular reactor is often selected based on the desired length of the tubular reactor and the method used to heat the tubular reactor. For example, the tubular reactor can be straight, U-shaped, or coiled. The interior of the tubular reactor can be empty or can contain baffles, balls, or other known mixing means. An example of a hydrothermal reactor system with a tubular reactor is described in International Application PCT / WO2011 / 082031 (Kolb et al.).

[0068] In some embodiments, the tubular reactor has an inner surface containing a fluorinated polymer material. The fluorinated polymer material can include, for example, a fluorinated polyolefin. In some embodiments, the polymer material is polytetrafluoroethylene (PTFE), such as that available from DuPont (Wilmington, DE, USA) under the trade name "Teflon." Some tubular reactors have a PTFE hose within a metal housing, such as a braided stainless steel housing. Carboxylic acids that may be present in the feedstock do not leach metals from such tubular reactors.

[0069] The dimensions of the tubular reactor can vary and can be selected to, together with the feed flow rate, provide a suitable residence time for the reactants within the tubular reactor. A tubular reactor of any suitable length can be used, so long as the residence time and temperature are sufficient to convert the zirconium in the feed to zirconia-based particles. The tubular reactor often has a length of at least 0.5 m, at least 1 m, at least 2 m, at least 5 m, at least 10 m, at least 15 m, at least 20 m, at least 30 m, at least 40 m, or at least 50 m. In some embodiments, the length of the tubular reactor is less than 500 m, less than 400 m, less than 300 m, less than 200 m, less than 100 m, less than 80 m, less than 60 m, less than 40 m, or less than 20 m.

[0070] Typically, tubular reactors with relatively small internal diameters are preferred. For example, tubular reactors with internal diameters of about 3 cm or less are often used because of the rapid heating of the feedstock that can be achieved in these tubular reactors. Furthermore, the temperature gradient across the tubular reactor is smaller in reactors with smaller internal diameters compared to those with larger internal diameters. The larger the internal diameter of the tubular reactor, the more similar the reactor becomes to a batch reactor. However, if the internal diameter of the tubular reactor is too small, the reactor is more likely to become clogged or partially clogged during operation due to material adhering to the reactor walls. The internal diameter of the tubular reactor is often at least 0.1 cm, at least 0.15 cm, at least 0.2 cm, at least 0.3 cm, at least 0.4 cm, at least 0.5 cm, or at least 0.6 cm. In some embodiments, the diameter of the tubular reactor is 3 cm or less, 2.5 cm or less, 2 cm or less, 1.5 cm or less, or 1.0 cm or less. Some tubular reactors have an inner diameter in the range of 0.1 to 3.0 cm, in the range of 0.2 to 2.5 cm, in the range of 0.3 to 2 cm, in the range of 0.3 to 1.5 cm, or in the range of 0.3 to 1.0 cm.

[0071] In a continuous hydrothermal reactor system, the temperature and residence time, along with the dimensions of the tubular reactor, are selected to convert at least 90 mole percent of the zirconium in the feed material to zirconia-based particles using a single hydrothermal treatment, i.e., at least 90 mole percent of the zirconium dissolved in the feed material is converted to zirconia-based particles during a single pass through the continuous hydrothermal reactor system.

[0072] Alternatively, a multi-step hydrothermal process can be used. For example, a feedstock can be subjected to a first hydrothermal treatment to form a zirconium-containing intermediate and by-products such as carboxylic acids. A second feedstock can be formed by removing at least a portion of the by-products of the first hydrothermal treatment from the zirconium-containing intermediate. The second feedstock can then be subjected to a second hydrothermal treatment to form a sol containing zirconia-based particles. This process is further described in U.S. Pat. No. 7,241,437 (Davidson et al.).

[0073] When a two-step hydrothermal process is used, the conversion rate of the zirconium-containing intermediate is typically 40 to 75 mole percent. The conditions used in the first hydrothermal treatment can be adjusted to achieve a conversion within this range. Any suitable method can be used to remove at least a portion of the by-products of the first hydrothermal treatment. For example, carboxylic acids such as acetic acid can be removed by various methods, including evaporation, dialysis, ion exchange, precipitation, and filtration.

[0074] When referring to a continuous hydrothermal reactor system, the term "residence time" refers to the average length of time that the feed material is within the heated portion of the continuous hydrothermal reactor system. Any suitable flow rate for the feed material through the tubular reactor can be used, so long as the residence time is long enough to convert the dissolved zirconium to zirconia-based particles. That is, the flow rate is often selected based on the residence time required to convert the zirconium in the feed material to zirconia-based particles. Higher flow rates are desirable to increase throughput and minimize material buildup on the walls of the tubular reactor. Higher flow rates can often be used when increasing the reactor length, or when increasing both the reactor length and diameter. The flow through the tubular reactor can be either laminar or turbulent.

[0075] In some exemplary continuous hydrothermal reactors, the reactor temperature is in the range of 170°C to 275°C, 170°C to 250°C, 170°C to 225°C, 180°C to 225°C, 190°C to 225°C, 200°C to 225°C, or 200°C to 220°C. If the temperature exceeds about 275°C, the pressure may become unacceptably high for some hydrothermal reactor systems. However, if the temperature is below about 170°C, the conversion of zirconium in the feedstock to zirconia-based particles may be less than 90 wt% using typical residence times.

[0076] The effluent of the hydrothermal treatment (i.e., the product of the hydrothermal treatment) is a zirconia-based sol and can be referred to as a "sol effluent." The sol effluent is a dispersion or suspension of zirconia-based particles in an aqueous medium. The sol effluent contains at least 3 wt. % zirconia-based particles, dispersed, suspended, or a combination thereof, based on the weight of the sol. In some embodiments, the sol effluent contains at least 5 wt. %, at least 6 wt. %, at least 8 wt. %, or at least 10 wt. % zirconia-based particles based on the weight of the sol. The wt. % zirconia-based particles can be up to 16 wt. % or more, up to 15 wt. %, up to 12 wt. %, or up to 10 wt. %.

[0077] The zirconia-based particles in the sol effluent are crystalline and have an average primary particle size of 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, 15 nm or less, or 10 nm or less. The zirconia-based particles typically have an average primary particle size of at least 1 nm, at least 2 nm, at least 3 nm, at least 4 nm, or at least 5 nm.

[0078] Sol effluents usually contain unassociated zirconia-based particles. Sol effluents are typically clear or slightly hazy. In contrast, zirconia-based sols containing agglomerated or aggregated particles usually tend to have a milky or cloudy appearance. Sol effluents often have high light transmittance due to the small size and unassociated morphology of the primary zirconia particles in the sol. High light transmittance of the sol effluent may be desirable in the preparation of transparent or translucent sintered articles. As used herein, "light transmittance" refers to the amount of light passing through a sample (e.g., sol effluent or casting sol) divided by the total amount of light incident on the sample. The percentage of light transmittance is calculated using the formula: [ka] where I is the intensity of light passing through the sample and I OThe transmittance of light through the sol effluent is often related to the transmittance of light through the casting sol (the reaction mixture used to form the gel composition). Good transmittance helps ensure that sufficient curing occurs during the formation of the gel composition, resulting in greater cure depth within the gel composition.

[0079] Light transmittance may be determined, for example, using a UV / Vis spectrophotometer set at a wavelength of 420 nm or 600 nm with a 1 cm path length. Light transmittance is a function of the amount of zirconia in the sol. For a sol effluent containing about 1 wt. % zirconia, the light transmittance is typically at least 70%, at least 80%, at least 85%, or at least 90% at either 420 nm or 600 nm. For a sol effluent containing about 10 wt. % zirconia, the light transmittance is typically at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, or at least 70% at either 420 nm or 600 nm.

[0080] The zirconia-based particles in the sol effluent are crystalline and can be cubic, tetragonal, monoclinic, or a combination thereof. Because the cubic and tetragonal phases are difficult to distinguish using X-ray diffraction techniques, these two phases are typically lumped together and referred to as the "cubic / tetragonal" phase for quantitative purposes. The proportion of cubic / tetragonal phase can be determined, for example, by measuring the peak area of ​​the X-ray diffraction peaks for each phase and using the following equation: [ka] In this equation, "C / T" refers to the diffraction peak area of ​​the cubic / tetragonal phase, "M" refers to the diffraction peak area of ​​the monoclinic phase, and "%C / T" refers to the weight percent of the cubic / tetragonal crystalline phase. Details of the X-ray diffraction measurements are further described in the Examples section below.

[0081] Typically, at least 50% by weight of the zirconia-based particles in the sol effluent have a cubic structure, a tetragonal structure, or a combination thereof. A higher content of cubic / tetragonal phase is usually desired. The amount of cubic / tetragonal phase is often at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% by weight, based on the total weight of all crystalline phases present in the zirconia-based particles.

[0082] For example, cubic / tetragonal crystals have been found to be associated with the formation of low-aspect-ratio primary particles with a cube-like shape when viewed under an electron microscope. This particle shape tends to disperse relatively easily in a liquid matrix. Typically, zirconia particles have an average primary particle size of up to 50 nm, although larger particle sizes can also be useful. For example, the average primary particle size can be up to 40 nm, up to 35 nm, up to 30 nm, up to 25 nm, up to 20 nm, up to 15 nm, or even up to 10 nm. The average primary particle size is often at least 1 nm, at least 2 nm, at least 3 nm, or at least 5 nm. The average primary particle size, which refers to the unassociated particle size of the zirconia particles, can be determined by X-ray diffraction, as described in the Examples section. The zirconia sols described herein typically have a primary particle size in the range of 2 to 50 nm. In some embodiments, the average primary particle size is in the range of 5 to 50 nm, 2 to 40 nm, 5 to 40 nm, 2 to 25 nm, 5 to 25 nm, 2 to 20 nm, 5 to 20 nm, 2 to 15 nm, 5 to 15 nm, or 2 to 10 nm.

[0083] In some embodiments, the particles in the sol effluent are not associated, and the average particle size is the same as the primary particle size. In some embodiments, the particles aggregate or agglomerate to a size of up to 100 nm. The degree of association between primary particles can be determined from the volume average particle size. The volume average particle size can be measured using photon correlation spectroscopy, which is described in more detail in the Examples section below. Briefly, the volume distribution of particles (the percentage of the total volume corresponding to a given size range) is measured. The volume of a particle is proportional to the cube of its diameter. The volume average size is the size of the particle corresponding to the mean of the volume distribution. If the zirconia-based particles are associated, the volume average particle size provides a measure of the size of the aggregates and / or agglomerates of the primary particles. If the zirconia particles are not associated, the volume average particle size provides a measure of the size of the primary particles. Zirconia-based particles typically have a volume average size of up to 100 nm. For example, the volume average size can be at most 90 nm, at most 80 nm, at most 75 nm, at most 70 nm, at most 60 nm, at most 50 nm, at most 40 nm, at most 30 nm, at most 25 nm, at most 20 nm, or at most 15 nm, or even at most 10 nm.

[0084] A quantitative measure of the degree of association between primary particles in the sol effluent is the dispersion index. As used herein, "dispersion index" is defined as the volume average particle size divided by the primary particle size. The primary particle size (e.g., weighted average crystallite size) is determined using X-ray diffraction techniques, and the volume average particle size is determined using photon correlation spectroscopy. As the association between primary particles decreases, the dispersion index approaches a value of 1, but may be slightly higher or lower. Zirconia-based particles typically have a dispersion index in the range of 1 to 7. For example, the dispersion index is often in the range of 1 to 5, 1 to 4, 1 to 3, 1 to 2.5, or even 1 to 2.

[0085] Photon correlation spectroscopy can also be used to calculate the Z-average primary particle size. The Z-average size is calculated from the fluctuation in the intensity of scattered light using cumulative analysis and is proportional to the sixth power of the particle diameter. The volume-average size is typically smaller than the Z-average size. Zirconia-based particles tend to have a Z-average size of up to 100 nm. For example, the Z-average size can be up to 90 nm, up to 80 nm, up to 70 nm, up to 60 nm, up to 50 nm, up to 40 nm, up to 35 nm, up to 30 nm, up to 20 nm, or even up to 15 nm.

[0086] Depending on the method of preparation of the zirconia-based particles, the particles may contain at least some organic material in addition to inorganic oxides. For example, if the particles are prepared using a hydrothermal technique, there may be some organic material attached to the surface of the zirconia-based particles. Without wishing to be bound by theory, it is believed that the organic material originates from carboxylate species (anions, acids, or both) contained in the feedstock or formed as by-products of the hydrolysis and condensation reactions (i.e., the organic material is often adsorbed onto the surface of the zirconia-based particles). For example, the zirconia-based particles contain up to 15 wt%, up to 12 wt%, up to 10 wt%, up to 8 wt%, or even up to 5 wt% organic material, based on the total weight of the zirconia-based particles.

[0087] The reaction mixture (casting sol) used to form the gel composition typically contains 20-60 wt% zirconia-based particles, based on the total weight of the reaction mixture. The amount of zirconia-based particles can be at least 25 wt%, at least 30 wt%, at least 35 wt%, or at least 40 wt%, and can be up to 55 wt%, up to 50 wt%, or up to 45 wt%. In some embodiments, the amount of zirconia-based particles ranges from 25-55 wt%, 30-50 wt%, 30-45 wt%, 35-50 wt%, 40-50 wt%, or 35-45 wt%, based on the total weight of the reaction mixture used in the gel composition.

[0088] 2. Solvent medium The sol effluent is the effluent from the hydrothermal reactor and contains zirconia-based particles suspended in an aqueous medium. The aqueous medium is primarily water but may contain carboxylic acids and / or carboxylate anions. In the reaction mixture (casting sol) used to form the gel composition and shaped gel article, the aqueous medium is replaced with a solvent medium containing at least 60% by weight of an organic solvent having a boiling point equal to at least 150°C. In some embodiments, the solvent medium contains at least 70%, at least 80%, at least 90%, at least 95%, at least 97%, at least 98%, or at least 99% by weight of an organic solvent having a boiling point equal to at least 150°C. The boiling point is often at least 160°C, at least 170°C, at least 180°C, or at least 190°C.

[0089] Any suitable method can be used to replace the aqueous medium from the sol effluent with a solvent medium that is predominantly an organic solvent having a boiling point equal to at least 150° C. In many embodiments, the sol effluent from the hydrothermal reactor system is concentrated to remove at least a portion of the water and carboxylic acids and / or carboxylate anions. The aqueous medium is often concentrated using methods such as drying or evaporation, solvent exchange, dialysis, diafiltration, ultrafiltration, or a combination thereof.

[0090] In some embodiments, the sol effluent of the hydrothermal reactor is concentrated by a drying process. Any suitable drying method can be used, such as spray drying or oven drying. For example, the sol effluent can be dried in a conventional oven at a temperature equal to at least 80°C, at least 90°C, at least 100°C, at least 110°C, or at least 120°C. The drying time is often more than 1 hour, more than 2 hours, or more than 3 hours. The dried effluent can then be resuspended in an organic solvent having a boiling point equal to at least 150°C.

[0091] In other embodiments, the sol effluent from the hydrothermal treatment can be subjected to ultrafiltration, dialysis, diafiltration, or a combination thereof to form a concentrated sol. Ultrafiltration results in concentration only. Both dialysis and diafiltration tend to remove at least a portion of the carboxylic acids and / or carboxylate anions dissolved in the sol effluent. In dialysis, a sample of the sol effluent can be placed in a closed membrane bag and then placed in a water bath. The carboxylic acids and / or carboxylate anions diffuse out of the sample into the membrane bag. That is, these species are believed to diffuse from the sol effluent through the membrane bag into the water bath to equalize the concentration inside the membrane bag with the concentration in the water bath. The water in the water bath is typically changed several times to reduce the concentration of the species in the bag. The membrane bag is typically selected to allow the carboxylic acids and / or their anions to diffuse out of the membrane bag but not the zirconia-based particles.

[0092] In diafiltration, a sample is filtered using a permeable membrane. Zirconia particles can be retained by the filter if the pore size of the filter is appropriately selected. Dissolved carboxylic acids and / or their anions pass through the filter. Any liquid that passes through the filter is replaced with fresh water. In discontinuous diafiltration methods, the sample is often diluted to a predetermined volume and then concentrated back to the original volume by ultrafiltration. The dilution and concentration steps are repeated one or more times until the carboxylic acids and / or their anions are removed or reduced to an acceptable concentration level. In continuous diafiltration methods (often called constant volume diafiltration methods), fresh water is added at the same rate as the liquid is removed by filtration. The dissolved carboxylic acids and / or their anions are in the liquid that is removed.

[0093] Although most of the inorganic oxides in the zirconia-based particles are incorporated into the crystalline material, there may be a fraction that can be removed during diafiltration or dialysis. The actual composition of the zirconia-based particles after diafiltration or dialysis may differ from the composition expected based on the various salts contained in the sol effluent from the hydrothermal reactor or in the feed material for the hydrothermal reactor. For example, a sol effluent prepared to have a composition of 89.9 / 9.6 / 0.5 ZrO2 / YO3 / La2O3 had the following composition after diafiltration: 90.6 / 8.1 / 0.24 ZrO2 / YO3 / La2O3, and a sol effluent prepared to have a composition of 97.7 / 2.3 ZrO2 / YO3 had the same composition after diafiltration.

[0094] Concentrated sols, whether by ultrafiltration, dialysis, diafiltration, or a combination thereof, often have a weight percent solids equal to at least 10%, at least 20%, 25%, or at least 30% by weight, and up to 60%, up to 55%, up to 50%, or up to 45% by weight solids. For example, the weight percent solids is often in the range of 10-60%, 20-50%, 25-50%, 25-45%, 30-50%, 35-50%, or 40-50% by weight, based on the total weight of the concentrated sol.

[0095] The carboxylic acid content (e.g., acetic acid content) of the concentrated sol is often at least 2 wt. % and can be up to 15 wt. %. In some embodiments, the carboxylic acid content can be at least 3 wt. %, at least 5 wt. % and up to 12 wt. %, or up to 10 wt. %. For example, the carboxylic acid can be present in an amount ranging from 2 to 15 wt. %, 3 to 15 wt. %, 5 to 15 wt. %, or 5 to 12 wt. % based on the total weight of the concentrated sol.

[0096] Typically, most of the aqueous medium is removed from the concentrated sol prior to forming the gel composition. Additional water is often removed using a solvent exchange process. For example, an organic solvent having a boiling point at least equal to 150°C can be added to the concentrated sol, and the water and any residual carboxylic acid can be removed by distillation. A rotary evaporator is often used for the distillation process.

[0097] Suitable organic solvents having a boiling point equal to 150°C are typically selected to be miscible with water. Furthermore, these organic solvents are often selected to be soluble in supercritical carbon dioxide or liquid carbon dioxide. The molecular weight of the organic solvent is usually at least 25 g / mol, at least 30 g / mol, at least 40 g / mol, at least 45 g / mol, at least 50 g / mol, at least 75 g / mol, or at least 100 g / mol. The molecular weight can be up to 300 g / mol or more, up to 250 g / mol, up to 225 g / mol, up to 200 g / mol, up to 175 g / mol, or up to 150 g / mol. The molecular weight is often in the range of 25 to 300 g / mol, 40 to 300 g / mol, 50 to 200 g / mol, or 75 to 175 g / mol.

[0098] The organic solvent is often a glycol or polyglycol, a monoether glycol or monoether polyglycol, a diether glycol or diether polyglycol, an ether ester glycol or ether ester polyglycol, a carbonate, an amide, or a sulfoxide (e.g., dimethyl sulfoxide). The organic solvent usually has one or more polar groups. The organic solvent does not have a polymerizable group, i.e., the organic solvent does not contain a group capable of undergoing free radical polymerization. Furthermore, none of the components of the solvent medium have a polymerizable group capable of undergoing free radical polymerization.

[0099] Suitable glycols or polyglycols, monoether glycols or monoether polyglycols, diether glycols or diether polyglycols, and ether ester glycols or ether ester polyglycols are often of formula (I): [ka] In formula (I), each R 1 are independently hydrogen, alkyl, aryl, or acyl. Suitable alkyl groups often have 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms. Suitable aryl groups often have 6 to 10 carbon atoms and are often phenyl or phenyl substituted with an alkyl group having 1 to 4 carbon atoms. Suitable acyl groups often have the formula -(CO)R a [In the formula, R a is alkyl having 1 to 10 carbon atoms, 1 to 6 carbon atoms, 1 to 4 carbon atoms, 2 carbon atoms, or 1 carbon atom. Acyl is often an acetate group (—(CO)CH3). In formula (I), each R 2 is typically ethylene or propylene. The variable n is at least 1 and can range from 1 to 10, 1 to 6, 1 to 4, or 1 to 3.

[0100] The glycol or polyglycol of formula (I) is a glycol or polyglycol having two R groups which are hydrogen. 1 Examples of glycols include, but are not limited to, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol.

[0101] The monoether glycol or monoether polyglycol of formula (I) is a monoether polyglycol having a first R 1 a group and a second R which is alkyl or aryl 1Examples of monoether glycols or monoether polyglycols include, but are not limited to, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, propylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether.

[0102] The diether glycol or diether polyglycol of formula (I) comprises two R groups which are alkyl or aryl. 1 Examples of diether glycols or diether polyglycols include, but are not limited to, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, dipropylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and pentaethylene glycol dimethyl ether.

[0103] The ether ester glycol or ether ester polyglycol of formula (I) comprises a first R 1 a group and a second R which is acyl 1 Examples of ether ester glycols or ether ester polyglycols include, but are not limited to, ethylene glycol butyl ether acetate, diethylene glycol butyl ether acetate, and diethylene glycol ethyl ether acetate.

[0104] Other suitable organic solvents are carbonates of formula (II). [ka] In formula (II), R 3 is hydrogen or alkyl, such as alkyl having 1 to 4 carbon atoms, 1 to 3 carbon atoms, or 1 carbon atom. Examples include ethylene carbonate and propylene carbonate.

[0105] Still other suitable organic solvents are the amides of formula (III). [ka] In formula (III), the group R 4 is hydrogen, alkyl, or R 5 In combination with R 4 Carbonyl and R bonded to 5 The group R forms a five-membered ring containing the nitrogen atom bonded to 5 is hydrogen, alkyl, or R 4 In combination with R 4 Carbonyl and R bonded to 5 The group R forms a five-membered ring containing the nitrogen atom bonded to 6 is hydrogen or alkyl. 4 , R 5 , and R 6 Suitable alkyl groups have 1 to 6 carbon atoms, 1 to 4 carbon atoms, 1 to 3 carbon atoms, or 1 carbon atom. Examples of amide organic solvents of formula (III) include, but are not limited to, formamide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone.

[0106] The solvent medium typically contains less than 15% water by weight, less than 10% water, less than 5% water, less than 3% water, less than 2% water, less than 1% by weight, or even less than 0.5% water by weight after the solvent exchange (e.g., distillation) process.

[0107] The reaction mixture often contains at least 30 wt% of the solvent medium. In some embodiments, the reaction mixture contains at least 35 wt% or at least 40 wt% of the solvent medium. The reaction mixture may contain up to 75 wt%, up to 70 wt%, up to 65 wt%, up to 60 wt%, up to 55 wt%, up to 50 wt%, or up to 45 wt% of the solvent medium. For example, the reaction mixture may contain 30-75 wt%, 30-70 wt%, 30-60 wt%, 30-50 wt%, 30-45 wt%, 35-60 wt%, 35-55 wt%, 35-50 wt%, or 40-50 wt% of the solvent medium. The weight percentage values ​​are based on the total weight of the reaction mixture.

[0108] The optional surface modifier (which can be referred to as a non-polymerizable surface modifier) ​​is often dissolved in an organic solvent before the solvent exchange process. The optional surface modifier typically does not contain a polymerizable group capable of undergoing a free radical polymerization reaction. The optional surface modifier is usually a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, a phosphoric acid or a salt thereof, a phosphonic acid or a salt thereof, or a silane that can be bonded to the surface of the zirconia-based particles. In many embodiments, the optional surface modifier is a carboxylic acid that does not contain a polymerizable group capable of undergoing a free radical polymerization reaction.

[0109] In some embodiments, the optional non-polymeric surface modifier is a carboxylic acid and / or anion thereof, having a compatible group that imparts polar character to the zirconia-based nanoparticles. For example, the surface modifier can be a carboxylic acid and / or anion thereof with an alkylene oxide or polyalkylene oxide group. In some embodiments, the carboxylic acid surface modifier is of the formula: [ka] In this formula, Q is a divalent organic linking group, z is an integer ranging from 1 to 10, and y is an integer ranging from 1 to 4. The group Q contains at least one alkylene or arylene group and may further contain one or more oxy, thio, carbonyloxy, or carbonylimino groups. Representative examples of this formula include, but are not limited to, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) and 2-(2-methoxyethoxy)acetic acid (MEAA). Still other representative carboxylic acids are the reaction products of aliphatic anhydrides with polyalkylene oxide monoethers, such as succinic acid mono-[2-(2-methoxyethoxy)-ethyl] ester and glutaric acid mono-[2-(2-methoxyethoxy)-ethyl] ester.

[0110] In other embodiments, the optional non-polymerizable surface modifier is a carboxylic acid and / or anion thereof, and the compatibilizing group can impart non-polar character to the zirconia-containing nanoparticles. For example, the surface modifier can be represented by the formula R c -COOH(where R c R may be a carboxylic acid or salt thereof, wherein R is an alkyl group having at least 5 carbon atoms, at least 6 carbon atoms, at least 8 carbon atoms, or at least 10 carbon atoms. c often have up to 20 carbon atoms, up to 18 carbon atoms, or up to 12 carbon atoms. Illustrative examples include octanoic acid, lauric acid, dodecanoic acid, stearic acid, and combinations thereof.

[0111] In addition to modifying the surface of the zirconia-based particles to minimize the possibility of agglomeration and / or aggregation when the sol is concentrated, the optional non-polymeric surface modifier can be used to adjust the viscosity of the sol.

[0112] Any suitable amount of optional non-polymeric surface modifier can be used. When present, the optional non-polymeric surface modifier is typically added in an amount equal to at least 0.5 wt.% based on the weight of the zirconia-based particles. For example, the amount can be equal to at least 1 wt.%, at least 2 wt.%, at least 3 wt.%, at least 4 wt.%, or at least 5 wt.%, and can be up to 15 wt.% or more, up to 12 wt.%, up to 10 wt.%, up to 8 wt.%, or up to 6 wt.%. The amount of optional non-polymeric surface modifier typically ranges from 0 to 15 wt.%, 0.5 to 15 wt.%, 0.5 to 10 wt.%, 1 to 10 wt.%, or 3 to 10 wt.% based on the weight of the zirconia-based particles.

[0113] Stated another way, the amount of optional non-polymerizable surface modifier is often in the range of 0 to 10 wt % based on the total weight of the reaction mixture, and often is at least 0.5 wt %, at least 1 wt %, at least 2 wt %, or at least 3 wt %, and can be up to 10 wt %, up to 8 wt %, up to 6 wt %, or up to 5 wt %, based on the total weight of the reaction mixture.

[0114] 3. Polymerizable materials The reaction mixture includes one or more polymerizable materials having polymerizable groups capable of undergoing free radical polymerization (i.e., the polymerizable groups are free radically polymerizable). In many embodiments, the polymerizable groups are ethylenically unsaturated groups, such as (meth)acryloyl groups, having the formula -(CO)-CR b =CH2 group (in the formula, R b is hydrogen or methyl). In some embodiments, the polymerizable group is a vinyl group (-CH=CH2) that is not a (meth)acryloyl group. The polymerizable material is typically selected to be soluble or miscible in an organic solvent having a boiling point at least equal to 150°C.

[0115] The polymerizable material includes a first monomer that is a surface modifier having a free-radically polymerizable group. The first monomer typically modifies the surface of the zirconia-based particle. Suitable first monomers have a surface-modifying group that can bond to the surface of the zirconia-based particle. The surface-modifying group is typically a carboxyl group (—COOH or its anion) or a group of the formula —Si(R 7 ) x (R 8 ) 3-x (In the formula, R 7 is a non-hydrolyzable group, and R 8 is a hydroxyl group or a hydrolyzable group, and the variable x is an integer equal to 0, 1, or 2. Suitable non-hydrolyzable groups are often alkyl groups, such as those having 1 to 10, 1 to 6, 1 to 4, or 1 to 2 carbon atoms. Suitable hydrolyzable groups are often halo groups (e.g., chloro groups), acetoxy groups, alkoxy groups having 1 to 10, 1 to 6, 1 to 4, or 1 to 2 carbon atoms, or silyl groups of the formula -OR d -OR e (In the formula, R d is alkylene having 1 to 4 or 1 to 2 carbon atoms, and R e is alkyl having 1 to 4 or 1 to 2 carbon atoms).

[0116] In some embodiments, the first monomer has a carboxyl group. Examples of first monomers having a carboxyl group include, but are not limited to, (meth)acrylic acid, itaconic acid, maleic acid, crotonic acid, citraconic acid, oleic acid, and β-carboxyethyl acrylate. Other examples of first monomers having a carboxyl group are reaction products of hydroxyl-containing polymerizable monomers with cyclic anhydrides such as maleic anhydride, succinic anhydride, or phthalic anhydride. Suitable hydroxyl-containing polymerizable monomers include, for example, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate. Specific examples of these reaction products include, but are not limited to, mono-2-(methacryloxyethyl)succinate (e.g., often referred to as hydroxyethyl acrylate succinate). In many embodiments, the first monomer is (meth)acrylic acid.

[0117] In other embodiments, the first monomer has the formula —Si(R 7 ) x (R 8 ) 3-xExamples of the first monomer having a silyl group include, but are not limited to, (meth)acryloxyalkyltrialkoxysilanes (e.g., 3-(meth)acryloxypropyltrimethoxysilane and 3-(meth)acryloxypropyltriethoxysilane), (meth)acryloxyalkylalkyldialkoxysilanes (e.g., 3-(meth)acryloxypropylmethyldimethoxysilane), (meth)acryloxy(acrloxy)alkyldialkylalkoxysilanes (e.g., 3-(meth)acryloxypropyldimethylethoxysilane), styrylalkyltrialkoxysilanes, Examples of suitable silanes include vinylsilanes (e.g., styrylethyltrimethoxysilane), vinyltrialkoxysilanes (e.g., vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriisopropoxysilane), vinylalkyldialkoxysilanes (e.g., vinylmethyldiethoxylsilane), and vinyldialkylalkoxysilanes (e.g., vinyldimethylethoxysilane), vinyltriacetoxysilane, vinylalkyldiacetoxysilanes (e.g., vinylmethyldiacetoxysilane), and vinyltris(alkoxyalkoxy)silanes (e.g., vinyltris(2-methoxyethoxy)silane).

[0118] The first monomer can function as a polymerizable surface modifier. Multiple first monomers can be used. The first monomer can be a single surface modifier or can be combined with one or more non-polymerizable surface modifiers, such as those described above. In some embodiments, the amount of the first monomer is at least 20% by weight based on the total weight of the polymerizable material. For example, the amount of the first monomer is often at least 25%, at least 30%, at least 35%, or at least 40% by weight. The amount of the first monomer can be up to 100%, up to 90%, up to 80%, up to 70%, up to 60%, or up to 50% by weight. Some reaction mixtures contain 20-100%, 20-80%, 20-60%, 20-50%, or 30-50% by weight of the first monomer based on the total weight of the polymerizable material.

[0119] The first monomer (i.e., the polymerizable surface-modifying monomer) may be the only monomer in the polymerizable material or may be combined with one or more second monomers that are soluble in the solvent medium. Any suitable second monomer that does not have a surface-modifying group can be used. That is, the second monomer does not have a carboxyl group or a silyl group. The second monomer is often a polar monomer (e.g., a non-acidic polar monomer), a monomer with multiple polymerizable groups, an alkyl (meth)acrylate, or a mixture thereof.

[0120] The overall composition of the polymerizable material is often selected so that the polymer of the material is soluble in the solvent medium. Homogeneity of the organic phase is often preferred to avoid phase separation of the organic components in the gel composition. This tends to result in the formation of smaller, more uniform pores (pores with a narrower pore size distribution) in the subsequently formed xerogel or aerogel. Furthermore, the overall composition of the polymerizable material can be selected to adjust compatibility with the solvent medium and to adjust the strength, flexibility, and uniformity of the gel composition. Furthermore, the overall composition of the polymerizable material can be selected to adjust the burnout characteristics of the organic material before sintering.

[0121] In many embodiments, the second monomer comprises a monomer having multiple polymerizable groups. The number of polymerizable groups can range from 2 to 6 or more. In many embodiments, the number of polymerizable groups ranges from 2 to 5 or 2 to 4. The polymerizable groups are typically (meth)acryloyl groups.

[0122] Exemplary monomers having two (meth)acryloyl groups include 1,2-ethanediol diacrylate, 1,3-propanediol diacrylate, 1,9-nonanediol diacrylate, 1,12-dodecanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, butylene glycol diacrylate, bisphenol A diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, polyethylene / polypropylene copolymer diacrylate, polybutadiene di(meth)acrylate, propoxylated glycerin tri(meth)acrylate, and neopentyl glycol hydroxypivalate diacrylate modified caprolactone.

[0123] Exemplary monomers having three or four (meth)acryloyl groups include, but are not limited to, trimethylolpropane triacrylate (e.g., Cytec and those commercially available from Sartomer (Exton, PA, USA) under the trade name SR-351), pentaerythritol triacrylate (e.g., those commercially available from Sartomer under the trade name SR-444), ethoxylated (3) trimethylolpropane triacrylate (e.g., those commercially available from Sartomer under the trade name SR-454), ethoxylated (4) pentaerythriol tetraacrylate (e.g., those commercially available from Sartomer under the trade name SR-494), tris(2-hydroxyethyl isocyanurate) triacrylate (e.g., those commercially available from Sartomer under the trade name SR-368), mixtures of pentaerythritol triacrylate and pentaerythritol tetraacrylate (e.g., those commercially available from Cytec and those containing a tetraacrylate to triacrylate ratio of approximately 3:1, available under the trade name PETA-K from Sartomer Industries, Inc.; pentaerythritol tetraacrylate (e.g., available under the trade name SR-295 from Sartomer); and di-trimethylolpropane tetraacrylate (e.g., available under the trade name SR-355 from Sartomer).

[0124] Exemplary monomers having five or six (meth)acryloyl groups include, but are not limited to, dipentaerythritol pentaacrylate (e.g., commercially available from Sartomer under the trade name SR-399) and hexafunctional urethane acrylate (e.g., commercially available from Sartomer under the trade name CN975).

[0125] Some polymerizable compositions contain 0-80 wt % of a monomer having multiple polymerizable groups, based on the total weight of the polymerizable material. For example, the amount can range from 10-80 wt %, 20-80 wt %, 30-80 wt %, 40-80 wt %, 10-70 wt %, 10-50 wt %, 10-40 wt %, or 10-30 wt %. The presence of a monomer having multiple polymerizable groups tends to enhance the strength of the gel composition formed when the reaction mixture is polymerized. Such a gel composition can be more easily removed from a mold without cracking. The above amounts of the monomer having multiple polymerizable groups can be used to adjust the flexibility and strength of the gel composition.

[0126] In some embodiments, the optional second monomer is a polar monomer. As used herein, the term "polar monomer" refers to a monomer having a free-radically polymerizable group and a polar group. The polar group is typically non-acidic and often contains a hydroxyl group, a primary amide group, a secondary amide group, a tertiary amide group, an amino group, or an ether group (i.e., a group containing at least one alkylene-oxy-alkylene group of the formula -ROR-, where each R is an alkylene having 1 to 4 carbon atoms).

[0127] Suitable optional polar monomers having a hydroxyl group include, but are not limited to, hydroxyalkyl (meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate), and hydroxyalkyl (meth)acrylamides (e.g., 2-hydroxyethyl (meth)acrylamide or 3-hydroxypropyl (meth)acrylamide), ethoxylated hydroxyethyl (meth)acrylates (e.g., monomers commercially available from Sartomer (Exton, PA, USA) under the trade names CD570, CD571, and CD572), and aryloxy-substituted hydroxyalkyl (meth)acrylates (e.g., 2-hydroxy-2-phenoxypropyl (meth)acrylate).

[0128] Exemplary polar monomers having a primary amide group include (meth)acrylamide. Exemplary polar monomers having a secondary amide group include, but are not limited to, N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-tert-octyl(meth)acrylamide, and N-octyl(meth)acrylamide. Exemplary polar monomers having a tertiary amide group include, but are not limited to, N-vinylcaprolactam, N-vinyl-2-pyrrolidone, (meth)acryloylmorpholine, and N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, and N,N-dibutyl(meth)acrylamide.

[0129] The polar monomer having an amino group includes various N,N-dialkylaminoalkyl(meth)acrylates and N,N-dialkylaminoalkyl(meth)acrylamides. Examples include, but are not limited to, N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylate, and N,N-diethylaminopropyl(meth)acrylamide.

[0130] Exemplary polar monomers having an ether group include, but are not limited to, alkoxylated alkyl (meth)acrylates such as ethoxyethoxyethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate, and poly(alkylene oxide) (meth)acrylates such as poly(ethylene oxide) (meth)acrylate and poly(propylene oxide) (meth)acrylate. Poly(alkylene oxide) acrylates are often referred to as poly(alkylene glycol) (meth)acrylates. These monomers can have any suitable terminal group, such as a hydroxyl group or an alkoxy group. For example, if the terminal group is a methoxy group, the monomer can be referred to as a methoxypoly(ethylene glycol) (meth)acrylate.

[0131] Suitable alkyl (meth)acrylates that can be used as the second monomer can have alkyl groups with a linear, branched, or cyclic structure. Examples of suitable alkyl (meth)acrylates include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-methylhexyl (meth)acrylate, n-octyl (meth)acrylate, and isooctyl (meth)acrylate. (meth)acrylate, 2-octyl (meth)acrylate, isononyl (meth)acrylate, isoamyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, isobornyl (meth)acrylate, 2-propylheptyl (meth)acrylate, isotridecyl (meth)acrylate, isostearyl (meth)acrylate, octadecyl (meth)acrylate, 2-octyldecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, and heptadecanyl (meth)acrylate.

[0132] The amount of the second monomer, which is a polar monomer and / or an alkyl (meth)acrylate monomer, is often in the range of 0 to 40 wt%, 0 to 35 wt%, 0 to 30 wt%, 5 to 40 wt%, or 10 to 40 wt%, based on the total weight of the polymerizable material.

[0133] Overall, the polymerizable material typically contains 20-100 wt% of the first monomer and 0-80 wt% of the second monomer, based on the total weight of the polymerizable material. For example, the polymerizable material may contain 30-100 wt% of the first monomer and 0-70 wt% of the second monomer, 30-90 wt% of the first monomer and 10-70 wt% of the second monomer, 30-80 wt% of the first monomer and 20-70 wt% of the second monomer, 30-70 wt% of the first monomer and 30-70 wt% of the second monomer, 40-90 wt% of the first monomer and 10-60 wt% of the second monomer, 40-80 wt% of the first monomer and 20-60 wt% of the second monomer, 50-90 wt% of the first monomer and 10-50 wt% of the second monomer, or 60-90 wt% of the first monomer and 10-40 wt% of the second monomer.

[0134] In some applications, it may be advantageous to minimize the weight ratio of polymerizable material to zirconia-based particles in the reaction mixture. This tends to reduce the amount of decomposition products of the organic material that must be combusted prior to forming the sintered article. The weight ratio of polymerizable material to zirconia-based particles is often at least 0.05, at least 0.08, at least 0.09, at least 0.1, at least 0.11, or at least 0.12. The weight ratio of polymerizable material to zirconia-based particles can be up to 0.80, up to 0.6, up to 0.4, up to 0.3, up to 0.2, or up to 0.1. For example, this ratio can be in the range of 0.05-0.8, 0.05-0.6, 0.05-0.4, 0.05-0.2, 0.05-0.1, 0.1-0.8, 0.1-0.4, or 0.1-0.3.

[0135] 4. Photoinitiators The reaction mixture used to form the gel composition contains a photoinitiator. The reaction mixture is advantageously initiated by the application of actinic radiation. That is, the polymerizable material is polymerized using a photoinitiator rather than a thermal initiator. Surprisingly, the use of a photoinitiator rather than a thermal initiator results in a more uniform cure throughout the gel composition, which tends to ensure uniform shrinkage in subsequent steps involved in forming a sintered article. Furthermore, when a photoinitiator rather than a thermal initiator is used, the exterior surface of the cured part is more uniform and has fewer defects.

[0136] Photoinitiated polymerization reactions often result in shorter cure times and fewer competing inhibitory reactions than thermally initiated polymerization reactions, and cure times can be more easily controlled than thermally initiated polymerization reactions, which require the use of opaque reaction mixtures.

[0137] In most embodiments, the photoinitiator is selected to be responsive to ultraviolet and / or visible light. Stated differently, the photoinitiator typically absorbs light at wavelengths ranging from 200 to 600 nm, 300 to 600 nm, or 300 to 450 nm. Some exemplary photoinitiators are benzoin ethers (e.g., benzoin methyl ether or benzoin isopropyl ether) or substituted benzoin ethers (e.g., anisoin methyl ether). Other exemplary photoinitiators are 2,2-diethoxyacetophenone or substituted acetophenones such as 2,2-dimethoxy-2-phenylacetophenone (commercially available under the trade name IRGACURE 651 from BASF Corp., Florham Park, NJ, USA, or under the trade name ESACURE KB-1 from Sartomer, Exton, PA, USA). Other exemplary photoinitiators are substituted benzophenones such as 1-hydroxycyclohexylbenzophenone (e.g., available under the trade designation "IRGACURE 184" from Ciba Specialty Chemicals Corp., Tarrytown, NY). Still other exemplary photoinitiators are substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oximes such as 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime. Other suitable photoinitiators include camphoquinone, 1-hydroxycyclohexylphenyl ketone (IRGACURE 184), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IRGACURE 819), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone (IRGACURE 369), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (IRGACURE 907), and 2-hydroxy-2-methyl-1-phenylpropan-1-one (DAROCUR 1173).

[0138] The photoinitiator is typically present in the range of 0.01 to 5 wt %, 0.01 to 3 wt %, 0.01 to 1 wt %, or 0.01 to 0.5 wt %, based on the total weight of the polymerizable materials in the reaction mixture.

[0139] 5. Inhibitors The reaction mixture used to form the gel composition may contain an optional inhibitor. The inhibitor may prevent undesired side reactions and moderate the polymerization reaction. Suitable inhibitors are often 4-hydroxy-TEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy) or phenol derivatives such as butylhydroxytoluene or p-methoxyphenol. The inhibitor is often used in an amount ranging from 0 to 0.5% by weight based on the weight of the polymerizable material. For example, the inhibitor may be present in an amount equal to at least 0.001%, at least 0.005%, or at least 0.01% by weight. The amount may be up to 1%, at most 0.5%, or at most 0.1% by weight.

[0140] Gel Composition A gel composition (i.e., a casting sol) comprising the polymerization product of the reaction mixture described above is provided, namely, the gel composition is the polymerization product of a reaction mixture comprising: (a) 20-60 wt. % zirconia-based particles, based on the total weight of the reaction mixture, having an average particle size of 100 nm or less and comprising at least 70 mol. % ZrO; (b) 30-75 wt. % solvent medium, including at least 60% organic solvent having a boiling point equal to at least 150°C; (c) 2-30 wt. % polymerizable material, based on the total weight of the reaction mixture, including a first surface modifier having free-radical polymerizable groups; and (d) a photoinitiator for the free-radical polymerization reaction.

[0141] The reaction mixture is typically placed in a mold. Thus, an article is provided that includes (a) a mold having a mold cavity, and (b) a reaction mixture positioned within the mold cavity and in contact with a surface of the mold cavity. The reaction mixture is the same as described above.

[0142] Each mold has at least one mold cavity. The reaction mixture is typically exposed to ultraviolet and / or visible light while in contact with the surface of the mold cavity. The polymerizable material in the reaction mixture undergoes free radical polymerization. The first monomer functions as a surface modifier for the zirconia-based particles in the reaction mixture and bonds to the surface of the zirconia-based particles, thereby forming a three-dimensional gel composition that binds the zirconia-based particles together upon polymerization. This typically results in a strong, resilient gel composition. It also results in a homogeneous gel composition with small pore sizes that can be sintered at relatively low temperatures.

[0143] The gel composition is formed in the mold cavity. Thus, an article is provided that includes (a) a mold having a mold cavity, and (b) a gel composition positioned within the mold cavity and in contact with a surface of the mold cavity. The gel composition includes the polymerization product of a reaction mixture, the reaction mixture being the same as described above.

[0144] Because the gel composition is formed within the mold cavity, it assumes the shape defined by the mold cavity. That is, a shaped gel article is provided that is the polymerization product of the reaction mixture, which is positioned within the mold cavity during polymerization, and which retains both the same size and shape as the mold cavity (except for areas where the mold cavity is overfilled) upon removal from the mold. The reaction mixture is the same as described above.

[0145] The reaction mixture (casting sol) is typically transparent to ultraviolet / visible light. The percent transmission of a casting sol composition containing 40 wt. % zirconia-based particles is typically at least 5% when measured at 420 nm in a 1 cm sample cell (i.e., a spectrophotometer with a 1 cm path length). In some instances, the percent transmission under the same conditions is at least 7%, at least 10%, and can be up to 20% or more, up to 15%, or up to 12%. The percent transmission of a casting sol composition containing 40 wt. % zirconia-based particles is typically at least 20% when measured at 600 nm in a 1 cm sample cell. In some instances, the percent transmission under the same conditions is at least 30%, at least 40%, and can be up to 80% or more, up to 70%, or up to 60%. The reaction mixture is translucent, not opaque. In some embodiments, the cured gel composition is translucent.

[0146] The UV / visible light transmittance must be high enough to form a uniform gel composition. The transmittance must be sufficient to allow polymerization to occur uniformly throughout the mold cavity; that is, the rate of cure must be uniform or fairly uniform throughout the gel composition formed in the mold cavity. The cure depth is often at least 5 mm, at least 10 mm, or at least 20 mm when cured for 12 minutes in a chamber with eight UV / visible lamps using 0.2 wt. % photoinitiator based on the weight of inorganic oxide, as described below in the Examples section.

[0147] The reaction mixture (casting sol) typically has a viscosity low enough to effectively fill the small, intricate features of the mold cavity. In many embodiments, the reaction mixture has a viscosity that is Newtonian or near-Newtonian. That is, the viscosity is independent of shear rate or has only a slight dependence on shear rate. The viscosity can vary depending on the percent solids of the reaction mixture, the size of the zirconia-based particles, the composition of the solvent medium, the presence or absence of optional non-polymerizable surface modifiers, and the composition of the polymerizable material. In some embodiments, the viscosity is at least 2 centipoise, at least 5 centipoise, at least 10 centipoise, at least 25 centipoise, at least 50 centipoise, at least 100 centipoise, at least 150 centipoise, or at least 200 centipoise. The viscosity can be up to 500 centipoise, up to 300 centipoise, up to 200 centipoise, up to 100 centipoise, up to 50 centipoise, up to 30 centipoise, or up to 10 centipoise. For example, the viscosity can be in the range of 2 to 500 centipoise, 2 to 200 centipoise, 2 to 100 centipoise, 2 to 50 centipoise, 2 to 30 centipoise, 2 to 20 centipoise, or 2 to 10 centipoise.

[0148] The combination of low viscosity and the small particle size of the zirconia-based particles advantageously allows the reaction mixture (casting sol) to be filtered before polymerization. The reaction mixture is often filtered before being placed into the mold cavity. Filtration can be beneficial in removing debris and impurities that can adversely affect the properties of the gel composition and the sintered article, such as light transmittance and strength. Suitable filters often retain materials with sizes greater than 0.22 μm, greater than 0.45 μm, greater than 1 μm, greater than 2 μm, or greater than 5 μm. Conventional ceramic molding compositions cannot be easily filtered due to particle size and / or viscosity.

[0149] In some embodiments, the mold can have multiple mold cavities, or multiple molds with one mold cavity can be arranged to form a belt, sheet, continuous web, or die that can be used in a continuous process for preparing shaped gel articles.

[0150] The mold can be constructed of any material commonly used for molds. That is, the mold can be made of metallic materials, including alloys, ceramic materials, glass, quartz, or polymeric materials. Suitable metallic materials include, but are not limited to, nickel, titanium, chromium, iron, carbon steel, or stainless steel. Suitable polymeric materials include, but are not limited to, silicone, polyester, polycarbonate, poly(ether sulfone), poly(methyl methacrylate), polyurethane, polyvinyl chloride, polystyrene, polypropylene, or polyethylene. In some cases, the entire mold is constructed of one or more polymeric materials. In other cases, only the surfaces of the mold designed to come into contact with the casting sol, e.g., the surfaces of one or more mold cavities, are constructed of one or more polymeric materials. For example, when the mold is made of metal, glass, ceramic, or the like, one or more surfaces of the mold can optionally have a coating of a polymeric material.

[0151] A mold having one or more mold cavities can be replicated from the master tool. The master tool can have a pattern that is the inverse of the pattern on the working mold, i.e., the master tool can have protrusions that correspond to the cavities on the mold. The master tool can be made of a metal such as nickel or its alloy. To create the mold, a polymer sheet can be heated and placed next to the master tool. The polymer sheet can then be pressed against the master tool to emboss the polymer sheet, thereby forming the working mold. It is also possible to prepare the working mold by extruding or casting one or more polymeric materials onto the master tool. Many other types of mold materials, such as metals, can be embossed by the master tool in a similar manner. Disclosures relating to the formation of working molds from master tools include U.S. Pat. Nos. 5,125,917 (Pieper), 5,435,816 (Spurgeon), 5,672,097 (Hoopman), 5,946,991 (Hoopman), 5,975,987 (Hoopman), and 6,129,540 (Hoopman).

[0152] The mold cavity can have any desired three-dimensional shape. Some molds have multiple uniform mold cavities of the same size and shape. The mold cavities can have smooth (i.e., featureless) surfaces or can have features of any desired shape and size. The resulting shaped gel article can replicate mold cavity features, even if their dimensions are extremely small. This is possible due to the relatively low viscosity of the reaction mixture (casting sol) and the use of zirconia-based particles having an average particle size of 100 nm or less. For example, the shaped gel article can replicate mold cavity features having dimensions of less than 100 μm, less than 50 μm, less than 20 μm, less than 10 μm, less than 5 μm, or less than 1 μm.

[0153] The mold cavity has at least one surface through which ultraviolet and / or visible light can be transmitted to initiate polymerization of the reaction mixture within the mold cavity. In some embodiments, this surface is selected to be constructed of a material expected to transmit at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of incident ultraviolet and / or visible light. Higher transmittance may be required as the thickness of the molded part increases. This surface is often glass or a polymeric material such as polyethylene terephthalate, poly(methyl methacrylate), or polycarbonate.

[0154] In some cases, the mold cavity does not contain a release agent, which can be beneficial because it can help ensure that the contents of the mold stick to the walls of the mold and maintain the shape of the mold cavity. In other cases, a release agent can be applied to the surfaces of the mold cavity to ensure clean release of the shaped gel article from the mold.

[0155] The mold cavities can be filled with the reaction mixture (casting sol), whether or not it is coated with a mold release agent. The reaction mixture can be introduced into the mold cavities by any suitable method. Examples of suitable methods include pumping through a hose, using a knife roll coater, or using a die such as a vacuum slot die. A scraper or leveling rod can be used to force the reaction mixture into one or more cavities to remove any reaction mixture that does not fit into the mold cavities. Any portion of the reaction mixture that does not fit into one or more mold cavities can be recycled and reused later, if desired. In some embodiments, it may be desirable to form a shaped gel article formed from multiple adjacent mold cavities. That is, it may be desirable for the reaction mixture to cover the area between two mold cavities to form the desired shaped gel article.

[0156] The casting sol's low viscosity allows it to effectively fill small gaps or features within the mold cavity. These small gaps or features can be filled even at low pressure. The mold cavity may have a smooth surface or a complex surface with one or more features. The features can have any desired shape, size, regularity, and complexity. The casting sol typically flows effectively to cover the surface of the mold cavity, regardless of the complexity of the surface's shape. The casting sol usually contacts all surfaces of the mold cavity.

[0157] Polymerization of the reaction mixture occurs upon exposure to ultraviolet and / or visible light, resulting in the formation of a gel composition, which is the polymerized (cured) product of the reaction mixture. The gel composition is a shaped gel article having the same shape as the mold (e.g., mold cavity). The gel composition is a solid or semi-solid matrix with a liquid entrapped therein. The solvent medium in the gel composition is primarily an organic solvent having a boiling point at least equal to 150°C.

[0158] Due to the homogeneous nature of the casting sol and the use of UV / visible light to cure the polymeric material, the resulting gel composition tends to have a homogeneous structure that advantageously results in isotropic shrinkage during further processing to form a sintered article.

[0159] The reaction mixture (casting sol) typically hardens (i.e., polymerizes) with little or no shrinkage, which is beneficial for maintaining the fidelity of the gel composition to the template. Without being bound by theory, it is believed that the low shrinkage rate can be attributed to a combination of a high solvent medium concentration in the gel composition and bonding of the zirconia-based particles to each other via the polymerized surface modifier attached to the surface of the particles.

[0160] Preferably, the gelation process (i.e., the process of forming the gel composition) allows for the formation of shaped gel articles of any desired size that can be subsequently processed without inducing crack formation. For example, preferably, the gelation process results in shaped gel articles having a structure that does not collapse when removed from the mold. Preferably, the shaped gel articles are stable and strong enough to withstand drying and sintering.

[0161] Xerogel or aerogel formation After polymerization, the shaped gel article is removed from the mold cavity and the shaped gel article is treated to remove the organic solvent having a boiling point at least equal to 150° C. and any other organic solvents or water that may be present. This can be referred to as drying the gel composition or shaped gel article, regardless of the method used to remove the organic solvent.

[0162] In some embodiments, removal of the organic solvent is accomplished by drying the shaped gel article at room temperature (e.g., 20°C to 25°C) or at an elevated temperature. Any desired drying temperature can be used, up to 200°C. At higher drying temperatures, the rate of organic solvent removal may be too high, resulting in cracking. The temperature is often no greater than 175°C, no greater than 150°C, no greater than 125°C, or no greater than 100°C. The temperature for drying is typically at least 25°C, at least 50°C, or at least 75°C. A xerogel results from this organic solvent removal process.

[0163] Xerogel formation can be used to dry shaped gel articles of any size, but is most frequently used to prepare relatively small sintered articles. As the gel composition dries, either at room temperature or elevated temperatures, the density of the structure increases. Capillary forces draw the structure together, resulting in some linear shrinkage, such as up to about 25%, up to 20%, or up to 15%. The shrinkage typically depends on the amount of inorganic oxides present and the overall composition. Linear shrinkage is often in the range of 5-25%, 10-25%, or 5-15%. Because drying typically occurs most rapidly at the outer surfaces, a density gradient is often established throughout the structure. Density gradients can lead to crack formation. The likelihood of crack formation increases with the size and complexity of the shaped gel article and the complexity of the structure. In some embodiments, xerogels are used to prepare sintered bodies having a longest dimension of about 1 cm or less.

[0164] In some embodiments, the xerogel contains some residual organic solvent having a boiling point at least equal to 150° C. The residual solvent can be up to 6 wt %, based on the total weight of the aerogel. For example, the xerogel can contain up to 5 wt %, up to 4 wt %, up to 3 wt %, up to 2 wt %, or up to 1 wt % of organic solvent having a boiling point at least equal to 150° C.

[0165] When shaped gel articles have microfeatures that can easily break or crack, it is often preferable to form an aerogel intermediate rather than a xerogel. Shaped gel articles of any size and complexity can be dried to form aerogels. Aerogels are formed by drying the shaped gel article under supercritical conditions. A supercritical fluid, such as supercritical carbon dioxide, can be contacted with the shaped gel article to remove solvents that are soluble or miscible in the supercritical fluid. Organic solvents with boiling points at least equal to 150°C can be removed by supercritical carbon dioxide. This type of drying lacks capillary effects, and linear shrinkage is often in the range of 0-25%, 0-20%, 0-15%, 5-15%, or linearly 0-10%. Volumetric shrinkage is often in the range of 0-50%, 0-40%, 0-35%, 0-30%, 0-25%, 10-40%, or 15-40%. Both the linear and volumetric shrinkage rates depend on the proportion of inorganic oxides present in the structure. Density typically remains uniform throughout the structure. Supercritical fluid extraction is discussed in detail in van Bommel et al., J. Materials Sci., 29, 943-948 (1994); Francis et al., J. Phys. Chem., 58, 1099-1114 (1954); and McHugh et al., Supercritical Fluid Extraction: Principles and Practice, Butterworth-Heinemann, Stoneham, MA, 1986.

[0166] The use of an organic solvent having a boiling point at least equal to 150°C advantageously eliminates the need to soak the shaped gel article in a solvent such as alcohol (e.g., ethanol) to replace the water prior to supercritical extraction. This replacement is necessary to provide a liquid that is soluble in (and can be extracted with) the supercritical fluid. The soaking process often results in the formation of a rough surface on the shaped gel article. The rough surface caused by the soaking process can result from residue deposition (e.g., organic residue) during the soaking process. In the absence of the soaking process, the shaped gel article can better retain its original glossy surface when removed from the mold cavity.

[0167] Supercritical extraction can remove all or most of the organic solvent having a boiling point at least equal to 150° C. Removal of the organic solvent results in the formation of pores in the dried structure. Preferably, the pores are large enough to allow gases from the decomposition products of the polymeric material to escape without cracking the structure when the dried structure is further heated to burn out the organic material and form a sintered article.

[0168] In some embodiments, the aerogel contains some residual organic solvent having a boiling point at least equal to 150° C. The residual solvent can be up to 6 wt %, based on the total weight of the aerogel. For example, the aerogel can contain up to 5 wt %, up to 4 wt %, up to 3 wt %, up to 2 wt %, or up to 1 wt % organic solvent having a boiling point at least equal to 150° C.

[0169] In some embodiments, the aerogel is 50 ml 2 / g~400m 2 / g. For example, the surface area is at least 75 m 2 / g, at least 100m 2 / g, at least 125m 2 / g, at least 150m 2 / g, or at least 175m 2 / g. The surface area is up to 350m 2 / g, up to 300m 2 / g, up to 275m 2 / g, up to 250m 2 / g, up to 225m 2 / g, or up to 200m 2 / g.

[0170] The volume percent of inorganic oxide in aerogels is often in the range of 3 to 30 volume percent. For example, the volume percent of inorganic oxide is often at least 4 volume percent or at least 5 volume percent. Aerogels with lower volume percent of inorganic oxide tend to be very brittle and may crack during supercritical extraction or subsequent processing. Furthermore, if too much polymeric material is present, the pressure during subsequent heating may become unacceptably high, resulting in crack formation. Aerogels with inorganic oxide contents greater than 30 volume percent tend to crack when the polymeric material decomposes and evaporates during the calcination process. Decomposition products may be less likely to be released from a denser structure. The volume percent of inorganic oxide is often up to 25 volume percent, up to 20 volume percent, up to 15 volume percent, or up to 10 volume percent. The volume percent is often in the range of 3 to 25 volume percent, 3 to 20 volume percent, 3 to 15 volume percent, 4 to 20 volume percent, or 5 to 20 volume percent.

[0171] Organic Burnout and Pre-Sintering After removal of the solvent medium, the resulting xerogel or aerogel is heated to remove polymeric materials or any other organic materials that may be present and to achieve strength through densification. Temperatures are often raised to as high as 1000°C or 1100°C during this process. The rate at which the temperature is increased is usually carefully controlled so that the pressures resulting from the decomposition and evaporation of the organic materials are not sufficient to induce cracks in the structure.

[0172] The rate at which the temperature is increased can be constant or can vary over time. The temperature can be increased to a specific temperature, held at that temperature for a period of time, and then increased further at the same or a different rate. This process can be repeated multiple times, if desired. The temperature is gradually increased to about 1000°C or about 1100°C. In some embodiments, the temperature is first increased at a moderate rate from about 20°C to about 200°C, e.g., at a rate ranging from 10°C / hr to 30°C / hr. The temperature is then increased relatively slowly (e.g., at a rate of 1°C / hr to less than 10°C / hr) to about 400°C, about 500°C, or about 600°C. This slow heating rate promotes evaporation of the organic material without cracking the structure. After removing most of the organic material, the temperature can be rapidly increased to about 1000°C or about 1100°C, e.g., at a rate greater than 50°C / hr (e.g., 50°C / hr to 100°C / hr). The temperature may be held at any temperature for up to 5 minutes, up to 10 minutes, up to 20 minutes, up to 30 minutes, up to 60 minutes, or up to 120 minutes or even longer.

[0173] Thermogravimetric analysis and dilatometry can be used to determine the appropriate rate of heating. These techniques track the weight loss and shrinkage that occurs at different heating rates. The heating rate can be adjusted over different temperature ranges to maintain a slow and fairly constant rate of weight loss and shrinkage until the organic material is removed. Careful control of organic removal promotes the formation of a sintered article with minimal or no cracks.

[0174] The article is often cooled to room temperature after organic burnout. The cooled article may optionally be immersed in a basic solution, such as aqueous ammonium hydroxide. Immersion can be effective in removing undesirable ionic species, such as sulfate ions, due to the porous nature of the article at this stage of the process. Sulfate ions can be ion-exchanged with hydroxyl ions. If sulfate ions are not removed, they can create small pores in the sintered article that tend to reduce translucency and / or strength.

[0175] More specifically, the ion exchange process often involves immersing the heated article in a 1N aqueous ammonium hydroxide solution to remove the organic material. This immersion step is often for at least 8 hours, at least 16 hours, or at least 24 hours. After immersion, the article is removed from the ammonium hydroxide solution and thoroughly washed with water. The article may be immersed in water for any desired period of time, such as at least 30 minutes, at least 1 hour, at least 2 hours, or at least 4 hours. The immersion in water may be repeated several times, if desired, by replacing the water with fresh water.

[0176] After immersion, the article is typically dried in an oven to remove water. For example, the article can be dried by heating in an oven set at a temperature equal to at least 80° C., at least 90° C., or at least 100° C. For example, the temperature can range from 80° C. to 150° C., 90° C. to 150° C., or 90° C. to 125° C. for at least 30 minutes, at least 60 minutes, or at least 120 minutes.

[0177] Sintering After organic burnout and optional soaking in aqueous ammonium hydroxide, the dried article is sintered. Sintering typically occurs at temperatures above 1100°C, such as at least 1200°C, at least 1250°C, at least 1300°C, or at least 1320°C. The rate of heating is typically very fast, such as at least 100°C / hr, at least 200°C / hr, at least 400°C / hr, or at least 600°C / hr. The temperature can be held for any desired time to produce a sintered article of the desired density. In some embodiments, the temperature is held for at least 1 hour, at least 2 hours, or at least 4 hours. The temperature may be held for 24 hours or even longer, if desired.

[0178] The density of the dried article increases during the sintering process, while the porosity is substantially reduced. When a sintered article is free of pores (i.e., voids), it is considered to have the maximum density possible for that material. This maximum density is called the "theoretical density." When pores are present in the sintered article, the density will be less than the theoretical density. The percentage of theoretical density can be determined from an electron micrograph of a cross section of the sintered article. The percentage of the area of ​​the electron micrograph that is attributable to pores in the sintered article can be calculated. In other words, the percentage of theoretical density can be calculated by subtracting the percentage of voids from 100%. That is, if 1% of the area of ​​an electron micrograph of a sintered article is attributable to pores, the sintered article is considered to have a density equal to 99%. Density can also be determined by the Archimedes method.

[0179] In many embodiments, the sintered article has a density of at least 99% of theoretical. For example, the density can be at least 99.2%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, at least 99.9%, or at least 99.95%, or even at least 99.99% of theoretical. As the density approaches theoretical density, the translucency of the sintered article tends to improve. Sintered articles having a density of at least 99% of theoretical often appear translucent to the human eye.

[0180] The sintered article contains a crystalline zirconia-based material. Crystalline zirconia-based materials are often predominantly cubic and / or tetragonal. Tetragonal materials can undergo phase transformation strengthening upon cracking; that is, some of the tetragonal phase material can transform to monoclinic phase material within the crack area. The monoclinic phase material tends to occupy a larger volume than the tetragonal phase material, which tends to inhibit crack propagation.

[0181] In many embodiments, at least 80% of the zirconia-based material in the initially prepared sintered article is present in the cubic and / or tetragonal crystalline phase. That is, at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or at least 99.5% of the initially prepared zirconia-based material is in the cubic and / or tetragonal phase. The remainder of the zirconia-based material is typically monoclinic. In terms of the amount of monoclinic phase, up to 20% of the zirconia-based material is monoclinic.

[0182] The zirconia-based material in the sintered article is typically 80-100% cubic and / or tetragonal and 0-20% monoclinic, 85-100% cubic and / or tetragonal and 0-15% monoclinic, 90-100% cubic and / or tetragonal and 0-10% monoclinic, or 95-100% cubic and / or tetragonal and 0-5% monoclinic.

[0183] The average grain size is often in the range of 75 nm to 400 nm, or in the range of 100 nm to 400 nm. The grain size is typically 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, or 150 nm or less. This grain size contributes to the high strength of the sintered article.

[0184] The sintered material can have, for example, an average biaxial flexural strength of at least 300 MPa. For example, the average biaxial flexural strength can be at least 400 MPa, at least 500 MPa, at least 750 MPa, at least 1000 MPa, or even at least 1300 MPa.

[0185] The sintered material may have a total transmittance of at least 65% at a thickness of 1 mm.

[0186] The shape of the sintered article is typically the same as the shape of the shaped gel article. Compared to the shaped gel article, the sintered article undergoes an isotropic reduction in size (i.e., isotropic shrinkage). That is, the degree of shrinkage in one direction is within 5%, 2%, 1%, or 0.5% of the shrinkage in the other two directions. Stated differently, a net-shaped sintered article can be prepared from the shaped gel article. The shaped gel article can have intricate features that can be retained in the sintered article but have smaller dimensions based on the degree of isotropic shrinkage. That is, a net-shaped sintered article can be formed from the shaped gel article.

[0187] The amount of isotropic linear shrinkage between the shaped gel article and the sintered article is often in the range of 40-70% or 45-55%. The amount of isotropic volumetric shrinkage is often in the range of 80-97%, 80-95%, or 85-95%. These large amounts of isotropic shrinkage are due to the relatively low amount (3-30 volume %) of zirconia-based particles in the reaction mixture used to form the gel composition (shaped gel article). Previous teachings required a high volume fraction of inorganic oxides to obtain a fully dense sintered article. Surprisingly, a gel composition can be obtained from a casting sol with a relatively low amount of zirconia-based particles that is strong enough to undergo demolding (even in molds with intricate shapes and surfaces), drying, heating to burn out organics, and sintering without cracking (even in molds with intricate shapes and surfaces). Also surprising is that the shape of the sintered article can match the shape of the shaped gel article and mold cavity very well, despite the large percentage of shrinkage. This large rate of shrinkage can be advantageous for some applications, for example, allowing for the production of smaller parts than can be obtained using many other ceramic forming processes.

[0188] Isotropic shrinkage tends to lead to the formation of a sintered article that is typically crack-free and has a uniform density throughout. Any cracks that form are often related to cracks resulting from removal of the shaped gel article from the mold cavity, rather than cracks formed during aerogel or xerogel formation, burnout of the organic material, or the sintering process. In some embodiments, particularly for large articles or articles with intricate features, it may be preferable to form an aerogel rather than a xerogel intermediate.

[0189] Sintered articles of any desired size and shape can be prepared. The longest dimension can be up to 1 cm, up to 2 cm, up to 5 cm, or up to 10 cm or even longer. The longest dimension can be at least 1 cm, at least 2 cm, at least 5 cm, at least 10 cm, at least 20 cm, at least 50 cm, or at least 100 cm.

[0190] The sintered article can have a smooth surface or a surface containing a variety of features. The features can have any desired shape, depth, width, length, and complexity. For example, the features can have a longest dimension of less than 500 μm, less than 100 μm, less than 50 μm, less than 25 μm, less than 10 μm, less than 5 μm, or less than 1 μm. In other words, a sintered article having a complex surface or multiple complex surfaces can be formed from a shaped gel article that has undergone isotropic shrinkage.

[0191] A sintered article is a net shaped article formed from a shaped gel article formed in a mold cavity. The sintered article closely mimics the shape of a shaped gel article that has the same shape as the mold cavity used to form it, although it has smaller dimensions in terms of the amount of isotropic shrinkage, and can often be used without further milling or processing.

[0192] Sintered articles are typically strong and translucent. These properties are a result of starting, for example, from a zirconia-containing sol effluent containing unassociated zirconia-based nanoparticles. These properties are also a result of preparing a homogeneous gel composition; that is, the density and composition of the gel composition are uniform throughout the shaped gel article. These properties are also a result of preparing a dried gel shaped article (either a xerogel or aerogel) with small, uniform pores throughout. These pores are eliminated by sintering to form the sintered article. The sintered article has a high theoretical density while possessing extremely small grain sizes. Small grain sizes lead to high strength and high translucency. Various inorganic oxides, such as yttrium oxide, are often added to adjust translucency by, for example, adjusting the amount of cubic and tetragonal phases in the sintered article.

[0193] Unless otherwise indicated, all numbers expressing quantities or ingredients, property measurements, and the like used in the specification and embodiments are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and accompanying listings of embodiments may be varied depending upon the desired properties desired to be obtained by one of ordinary skill in the art utilizing the teachings of the present disclosure. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques; however, this is not intended to limit the application of the doctrine of equivalents to the scope of the claimed embodiments.

[0194] Various modifications and variations can be made to the exemplary embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. Accordingly, it should be understood that embodiments of the present disclosure are not limited to the exemplary embodiments described below, but are instead governed by the limitations set forth in the claims and any equivalents thereof.

[0195] List of Exemplary Embodiments Exemplary embodiments are listed below: It should be understood that any one of embodiments 1 to 11 and 12 to 21 can be combined.

[0196] Embodiment 1 is a shaped zirconia ceramic plate including a plate body and a working surface thereof; a piezoelectric actuator attached to the shaped zirconia ceramic plate and configured to generate standing waves on the actuation surface of the shaped zirconia ceramic plate at ultrasonic frequencies above 20 kHz; A haptic device comprising:

[0197] Embodiment 2 is the haptic device of embodiment 1, wherein the shaped zirconia ceramic plate further comprises one or more attachment features integrally formed on the plate body.

[0198] Embodiment 3 is a tactile device described in embodiment 2, wherein the one or more attachment features include at least one of one or more slots, one or more grooves, one or more tabs, one or more holes, one or more bosses, or one or more sockets.

[0199] Embodiment 4 is the haptic device of any one of Embodiments 1-3, wherein the shaped zirconia ceramic plate is a product of drying and sintering a shaped gel article.

[0200] Embodiment 5 is a method for preparing a shaped gel article comprising the polymerization product of a reaction mixture positioned within a mold cavity during polymerization, the shaped gel article retaining both the same size and shape as the mold cavity (except for areas where the mold cavity is overfilled) upon removal from the mold cavity, and the reaction mixture being a. 20-60 wt. % zirconia-based particles, based on the total weight of the reaction mixture, having an average particle size of 100 nm or less and containing at least 70 mol. % ZrO; b. 30-75% by weight of a solvent medium based on the total weight of the reaction mixture, the solvent medium comprising at least 60% of an organic solvent having a boiling point at least equal to 150°C; c. 2-30 wt. % of a polymerizable material, based on the total weight of the reaction mixture, the polymerizable material comprising: (1) a first surface modifier having free-radically polymerizable groups; d. a photoinitiator for a free radical polymerization reaction; 5. A haptic device according to embodiment 4, comprising:

[0201] Embodiment 6 is a haptic device described in any one of embodiments 1 to 5, wherein the shaped zirconia ceramic plate comprises at least 70 mole % zirconia-based material, and at least 80 weight % of the zirconia-based material has a cubic crystal structure, a tetragonal crystal structure, or a combination thereof.

[0202] Embodiment 7 is a haptic device described in embodiment 6, wherein the shaped zirconia ceramic plate has a density of at least 99% of the theoretical density of crystalline zirconia in the cubic or tetragonal phase, the theoretical density being the maximum density of crystalline zirconia in the cubic or tetragonal phase without pores.

[0203] Embodiment 8 is a haptic device according to any one of embodiments 1 to 7, wherein the plate body includes at least one of a flat structure, a curved structure, or an undulating structure.

[0204] Embodiment 9 is a haptic device according to any one of embodiments 1 to 8, further comprising a display covered with a shaped zirconia ceramic plate.

[0205] Embodiment 10 is a haptic device according to embodiment 9, wherein the display is received by a frame and the shaped zirconia ceramic plate is mounted on the frame via one or more mounting features thereof.

[0206] Embodiment 11 is a tactile device described in any one of embodiments 1 to 10, further including a processor configured to control the frequency and amplitude of the standing wave generated by the piezoelectric actuator based on detection of the position of the input unit on the actuation surface.

[0207] Embodiment 12 is a method for manufacturing a haptic device, comprising: providing a reaction mixture into a mold cavity, the reaction mixture comprising 20 to 60 weight percent zirconia-based particles, based on a total weight of the reaction mixture; polymerizing the reaction mixture to form a shaped gel plate within the mold cavity and in contact with the surface of the mold cavity; removing the shaped gel plate from the mold cavity, wherein the shaped gel plate retains the same size and shape as the mold cavity; removing the solvent medium to form a dried, shaped gel plate; heating the dried, shaped gel plate to form a shaped zirconia ceramic plate; providing a piezoelectric actuator attached to the shaped zirconia ceramic plate and configured to generate standing waves on the actuation surface of the shaped zirconia ceramic plate at ultrasonic frequencies above 20 kHz; The method includes:

[0208] Embodiment 13 is the method of embodiment 12, wherein the zirconia-based particles have an average particle size of 100 nm or less and comprise at least 70 mole % ZrO2.

[0209] Embodiment 14 is the method of embodiment 13, wherein the zirconia-based particles are crystalline, and at least 80% by weight of the zirconia-based particles have a cubic structure, a tetragonal structure, or a combination thereof.

[0210] Embodiment 15 is the method of embodiment 13 or 14, wherein the zirconia-based particles comprise 80-99 mol % zirconium oxide, 1-20 mol % yttrium oxide, and 0-5 mol % lanthanum oxide.

[0211] Embodiment 16 is a method for preparing a reaction mixture comprising: 30-75% by weight of a solvent medium based on the total weight of the reaction mixture, the solvent medium comprising at least 60% of an organic solvent having a boiling point at least equal to 150°C; 2 to 30 wt. % of a polymerizable material, based on the total weight of the reaction mixture, the polymerizable material comprising: (1) a first surface modifier having free-radically polymerizable groups; a photoinitiator for a free radical polymerization reaction; 16. The method according to any one of embodiments 12 to 15, further comprising:

[0212] Embodiment 17 is the method of any one of embodiments 12-16, wherein the shaped zirconia ceramic plate comprises at least 70 mole percent zirconia-based material, and at least 80 weight percent of the zirconia-based material has a cubic crystal structure, a tetragonal crystal structure, or a combination thereof.

[0213] Embodiment 18 is a method according to any one of embodiments 12 to 17, wherein the shaped gel plate comprises a plate body and one or more attachment features formed on the plate body when it contacts the surface of the mold cavity.

[0214] Embodiment 19 is the method of any one of embodiments 12 to 18, further comprising removing the shaped gel plate from the mold cavity, wherein the shaped gel article retains the same size and shape as the mold cavity (except for areas where the mold cavity is overfilled).

[0215] Example 20 is the method of any one of Examples 12-19, further comprising providing a display covered with a shaped zirconia ceramic plate.

[0216] Example 21 is the method of example 20, further comprising attaching the shaped zirconia ceramic plate to a frame of a display via the attachment features of the shaped zirconia ceramic plate.

[0217] The operation of the present disclosure will be further described with reference to the following detailed examples. These examples are provided to further illustrate various specific preferred embodiments and techniques. However, it should be understood that many variations and modifications can be made while remaining within the scope of the present disclosure. [Example]

[0218] These examples are for illustrative purposes only and are not intended to unduly limit the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques; this is not intended to limit the application of the doctrine of equivalents to the scope of the claims. material [Table 1]

[0219] Preparation of Casting Sol - CS1 Sol-1a had a composition of ZrO (97.7 mol%) / YO (2.3 mol%) in terms of inorganic oxides and was prepared and processed as described for Sol-S2 in the Examples section of U.S. Patent Application Publication No. 20180044245 A1.

[0220] A diethylene glycol monoethyl ether-based sol, Sol-1b, was prepared by adding 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) (3.56 wt % based on the gram of oxide in the sol) and an appropriate amount of diethylene glycol monoethyl ether (adjusted to the intended final oxide concentration in the sol, e.g., 60 wt %) to a portion of Sol-1a and concentrating the sol via rotary evaporation. The resulting sol was 60.14 wt % oxide and 9.28 wt % acetic acid.

[0221] To prepare casting sol CS1, a portion of Sol-1b (1844.05 g) was placed in a 2 L bottle and combined with diethylene glycol monoethyl ether (56.48 g), acrylic acid (119.87 g), hydroxyethyl acrylate (HEA) (22.75 g), octyl acrylate (11.33 g), trimethylolpropane triacrylate ("SR351 H") (200.40 g), and hexafunctional urethane acrylate ("CN975") (100.00 g). Diphenyliodonium chloride (DPICl) (0.99 g) was added to the bottle and dissolved in the sol. OMNIRAD 819 (11.09 g), camphorquinone (CPQ) (3.55 g), and ethyl 4-(dimethylamino)benzoate (EDMAB) (17.74 g) were dissolved in diethylene glycol monoethyl ether (407.62 g) and added to the bottle. The resulting casting sol was passed through a 1 micron filter.

[0222] Preparation of gel bodies Gel bodies were fabricated by placing casting sol CS1 into a mold cavity in a manner similar to that described in the "Description of the Invention" section of U.S. Patent Application Publication No. 20180044245(A1). The mold cavity was formed by clamping a Delrin® frame with an open area (184.15 mm x 116.23 mm x 1.20 mm) between a P20 stainless steel plate and an acrylic plate with a protective film on the mold cavity side. The casting sol CS1 in the mold cavity was then polymerized to form a gel body over 90 seconds using a 450 nm LED array at approximately 0.4 W / cm², as measured using a Thorlabs Model PM100A (analog needle and LCD power meter console (SN: P1002769) with detector model number S12C, 400-1100 nm, 500 mW (SN: 17062804)).

[0223] Preparation of aerogels The gel body was dried and an aerogel was formed using supercritical CO2 extraction as described in the Examples section of US Patent Application Publication No. 20180044245(A1).

[0224] Preparation of pre-sintered body The dried aerogel body was placed on a layer of zirconia beads in an alumina crucible, which was then covered with an alumina crucible and fired in air according to the following schedule: 1- Heat from 20℃ to 220℃ at a rate of 18℃ / hour 2- Heat from 220°C to 244°C at a rate of 1°C / hour. 3- Heat from 244°C to 400°C at a rate of 6°C / hour. 4- Heat from 400℃ to 1020℃ at a rate of 60℃ / hour. 5- Cool from 1020°C to 20°C at a rate of 120°C / hour.

[0225] Preparation of sintered bodies The pre-sintered body was placed on a layer of zirconia beads in an alumina crucible. After covering the crucible with an alumina crucible, the sample was sintered in air according to the following schedule: 1- Heat from 25℃ to 1020℃ at a rate of 500℃ / hour. 2- Heat from 1020℃ to 1320℃ at a rate of 120℃ / hour. 3- 1320℃ for 2 hours, 4- Cool from 1320°C to 25°C at a rate of 500°C / hour.

[0226] After sintering, the part was not flat, so it was sintered a second time using the above schedule, except that it was sandwiched between two alumina plates and a 977 g weight was applied to promote creep, which resulted in flattening of the part.

[0227] Preparation of Casting Sol - CS2 Sol-1a had a composition of ZrO (97.7 mol%) / YO (2.3 mol%) in terms of inorganic oxides and was prepared and processed as described for Sol-S2 in the Examples section of U.S. Patent Application Publication No. 20180044245 A1.

[0228] A diethylene glycol monoethyl ether-based sol, Sol-1c, was prepared by adding 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) (3.56 wt % based on the gram of oxide in the sol) and an appropriate amount of diethylene glycol monoethyl ether (adjusted to the intended final oxide concentration in the sol, e.g., 60 wt %) to a portion of Sol-1a and concentrating the sol via rotary evaporation. The resulting Sol-1c was 61.50 wt % oxide and 8.11 wt % acetic acid.

[0229] To prepare casting sol CS2, a portion of Sol-1c (1238.15 g) was placed in a 1 L jar and combined with diethylene glycol monoethyl ether (93.89 g), 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) (13.57 g), acrylic acid (82.31 g), hydroxyethyl acrylate (HEA) (8.20 g), octyl acrylate (4.08 g), trimethylolpropane triacrylate ("SR351 H") (72.24 g), and hexafunctional urethane acrylate ("CN975") (36.05 g). OMNIRAD 819 (5.48 g), camphorquinone (CPQ) (1.75 g), ethyl 4-(dimethylamino)benzoate (EDMAB) (8.77 g), and diphenyliodonium chloride (DPICl) (0.58 g) were placed in a jar and dissolved into a sol.

[0230] Preparation of gel bodies Gel bodies were fabricated by placing casting sol CS2 into a mold cavity in a manner similar to that described in the "Description of the Invention" section of U.S. Patent Application Publication No. 20180044245(A1). The mold cavity was formed by clamping a Delrin™ frame with an open area (203.2 mm x 114.3 mm x 3.175 mm) between a P20 stainless steel plate and an acrylic plate with a protective film on the mold cavity side. The casting sol CS2 in the mold cavity was then polymerized to form a gel body over 30 seconds using a 450 nm LED array at approximately 0.4 W / cm², as measured using a Thorlabs Model PM100A (analog needle and LCD power meter console (SN: P1002769) with detector model number S12C, 400-1100 nm, 500 mW (SN: 17062804)).

[0231] Preparation of aerogels The gel body was dried and an aerogel was formed using supercritical CO2 extraction in a manner similar to that described in the Examples section of US Patent Application Publication No. 20180044245(A1).

[0232] Preparation of pre-sintered body The dried aerogel bodies were placed on alumina plates and then baked in air according to the following schedule: 1- Heat from 20℃ to 220℃ at a rate of 18℃ / hour 2- Heat from 220°C to 244°C at a rate of 1°C / hour. 3- Heat from 244°C to 400°C at a rate of 6°C / hour. 4- Heat from 400℃ to 1020℃ at a rate of 60℃ / hour. 5- Cool from 1020°C to 20°C at a rate of 120°C / hour.

[0233] Preparation of sintered bodies The pre-sintered body was ion-exchanged in a manner similar to that described in the Examples section of U.S. Patent Application Publication No. 20180044245(A1).

[0234] The pre-sintered bodies were then placed on alumina plates and sintered in air according to the following schedule: 1- Heat from 25℃ to 1020℃ at a rate of 500℃ / hour. 2- Heat from 1020℃ to 1320℃ at a rate of 120℃ / hour. 3- 1320℃ for 2 hours, 4- Cool from 1320°C to 25°C at a rate of 500°C / hour.

[0235] After sintering, the part was not flat, so it was sintered a second time using the above schedule, except that it was sandwiched between two alumina plates and a 2500 g weight was applied to promote creep, which resulted in flattening of the part.

[0236] Measurement of Example Three sintered bodies, EX-1, EX-2, and EX-3 (104.1 mm x 59.3 mm x 1.62 mm thick, 104.0 mm x 59.4 mm x 1.64 mm thick, and 106.7 mm x 59.6 mm x 1.63 mm thick, respectively, with an average thickness of 104.9 mm x 59.4 mm x 1.63 mm) were fabricated as described above. The density of each sample was approximately 6100.0 kg / m 3 The tactile resonators were fabricated by attaching a 60 mm × 5 mm × 2 mm thick piezoelectric resonator (STEMiNC part number SMPL60W05T21F27R) (Steiner & Martins Inc., Doral, FL, USA) to the short edge of each sintered body using conductive epoxy (Epo-Tek H20E, Epoxy Technology, Inc., Billerica, MA, USA). Positive and negative leads were attached to each terminal of the piezoelectric resonator and terminated with BNC connectors.

[0237] Four tactile resonators, CE-1, CE-2, CE-3, and CE-4, were fabricated by attaching piezoelectric resonators (STEMiNC part number SMPL60W05T21F27R) (Steiner & Martins Inc., Doral, FL USA) to four amorphous glass plates measuring 105.7 mm × 60.0 mm × 1.70 mm thick. The density of each sample was approximately 2764.0 kg / m. 3 A 60 mm × 5 mm × 2 mm thick piezoelectric resonator was bonded to the short side of each glass plate using conductive epoxy (Epo-Tek H20E, Epoxy Technology, Inc., Billerica, MA USA). Positive and negative leads were attached to each terminal of the piezoelectric resonator and terminated with BNC connectors.

[0238] Each of the seven tactile resonators, EX-1, EX-2, EX-3, CE-1, CE-2, CE-3, and CE-4, was coupled to a Trek PZD350A M / S piezoelectric amplifier (Trek Inc., Lockport, NY, USA) via an attached BNC connector. The resonators were driven at peak resonant frequencies between 20 kHz and 40 kHz. Input power was measured using a Tektronix PA1000 power analyzer (Tektronix, Inc., Beaverton, OR, USA), and the maximum z-axis displacement of the resonators at the resonant frequency was measured using a Polytec (PV-500) laser scanning vibrometer (Polytec, Inc., Irvine, CA, USA) at approximately 500 sample points distributed in a triangular lattice pattern across the resonator surface. The reported average z-axis displacement is the average of these sample points.

[0239] Table 2 below shows the maximum z-axis displacement and associated input power for each of the tactile resonators. The data in Table 2 indicates that the ZrO2 sample requires approximately 1 / 2 to 2 / 3 the power of the glass sample to achieve a similar level of Z-axis displacement. This indicates a more efficient transfer of power to Z-axis displacement in the ZrO2 sample compared to the glass sample. [Table 2]

[0240] Throughout this specification, references to "one embodiment," "a particular embodiment," "one or more embodiments," or "an embodiment" mean that the particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one of the particular exemplary embodiments of the present disclosure, regardless of whether the term "embodiment" is preceded by the term "embodiment." Thus, the appearances of phrases such as "in one or more embodiments," "a particular embodiment," "in one embodiment," or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same particular exemplary embodiments of the present disclosure. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0241] While certain exemplary embodiments have been described in detail herein, it will be understood that those skilled in the art will be able to readily conceive of modifications, variations, and equivalents to these embodiments upon reading the foregoing description. Accordingly, it should be understood that the present disclosure is not intended to be unduly limited to the exemplary embodiments described thus far. In particular, as used herein, the recitation of numerical ranges by endpoints is intended to include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). Additionally, all numbers used herein are intended to be modified by the term "about." Furthermore, various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims.

Claims

1. a shaped zirconia ceramic plate including a plate body and a working surface thereof; a piezoelectric actuator attached to the shaped zirconia ceramic plate and configured to generate standing waves on the actuation surface of the shaped zirconia ceramic plate at ultrasonic frequencies above 20 kHz; Including, A haptic device wherein the shaped zirconia ceramic plate includes a low-friction surface that has lower friction than the surface of the plate body, allowing the plate body to slide or move on a structural support that supports the plate body.

2. The haptic device of claim 1 , wherein the shaped zirconia ceramic plate further comprises one or more attachment features integrally formed on the plate body.

3. The haptic device of claim 2 , wherein the one or more mounting features include at least one of one or more slots, one or more grooves, one or more tabs, one or more holes, one or more bosses, or one or more sockets.

4. The haptic device of claim 1 , wherein the shaped zirconia ceramic plate is a product of drying and sintering a shaped gel article.

5. the shaped gel article comprises a polymerization product of a reaction mixture, the reaction mixture being positioned within a mold cavity during polymerization, the shaped gel article retaining both the same size and shape as the mold cavity (except for areas where the mold cavity is overfilled) upon removal from the mold cavity, and the reaction mixture a. 20 to 60 wt. % zirconia-based particles, based on the total weight of the reaction mixture, having an average particle size of 100 nm or less and at least 70 mol. % ZrO ２ Zirconia-based particles comprising: b. 30 to 75% by weight of a solvent medium, based on the total weight of the reaction mixture, comprising at least 60% of an organic solvent having a boiling point at least equal to 150° C.; c. 2 to 30 wt. % of a polymerizable material, based on the total weight of the reaction mixture, the polymerizable material comprising: (1) a first surface modifier having free-radically polymerizable groups; d. a photoinitiator for the free radical polymerization reaction; The haptic device of claim 4 , comprising:

6. 10. The haptic device of claim 1, wherein the shaped zirconia ceramic plate comprises at least 70 mole percent zirconia-based material, and at least 80 weight percent of the zirconia-based material has a cubic crystal structure, a tetragonal crystal structure, or a combination thereof.

7. The haptic device of claim 6, wherein the shaped zirconia ceramic plate has a density of at least 99% of the theoretical density of crystalline zirconia in a cubic or tetragonal phase, the theoretical density being the maximum density of crystalline zirconia in a pore-free cubic or tetragonal phase.

8. The haptic device of claim 1 , wherein the plate body includes at least one of a flat structure, a curved structure, or an undulating structure.

9. The haptic device of claim 1 further comprising a display covered by the shaped zirconia ceramic plate.

10. The haptic device of claim 9 , wherein the display is received by a frame, and the shaped zirconia ceramic plate is mounted on the frame via one or more mounting features thereof.

11. The haptic device of claim 1 , further comprising a processor configured to control a frequency and an amplitude of the standing wave generated by the piezoelectric actuator based on detection of a position of an input unit on the actuation surface.

Images