Ceramic powder, ceramic powder production method and production method of ceramic structure using ceramic powder

Abstract

To provide a ceramic powder for obtaining a high-definition ceramic structure in a short time in the production of a ceramic structure using an additive manufacturing method in which modeling is performed by irradiating a raw material powder with laser light.SOLUTION: A ceramic powder used in an additive manufacturing method in which modeling is performed by irradiating a raw material powder with laser light, including a first particle group which consists of particles of a first inorganic compound, and whose average particle size is 10 μm or greater and 100 μm or less and a second particle group which consists of a second inorganic compound having an absorption band at the wavelength of the laser beam and having an average particle size smaller than the first particle group, and the particle included in the second particle group is disposed on a surface of the particle included in the first particle group.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to raw material powder used in producing a ceramic object by three-dimensional modeling using the melting and solidification (including sintering) of raw material powder by irradiation with laser light, and to a ceramic modeling method using the raw material powder. [Background technology]

[0002] In recent years, additive manufacturing (also known as three-dimensional modeling technology) using laser light has developed and its technological level has increased. In the metals field in particular, selective laser sintering (SLS) and selective laser melting (SLM), which are types of powder bed fusion (powder additive manufacturing), have made it possible to manufacture precise and diverse objects. These methods use laser drawing to melt and bond or sinter raw metal powder into the desired shape. Compact, high-power, and low-cost lasers in the near-infrared region, such as YAG lasers and fiber lasers, are the most commonly used for drawing.

[0003] In principle, SLS and SLM can also be applied to ceramic powders. However, most insulating ceramics are highly transparent to light in the visible to infrared range. In other words, the raw ceramic particles hardly absorb laser light in this wavelength range. Therefore, when additively manufacturing ceramics using SLS or SLM equipment, it is necessary to irradiate the material with laser light of a power greater than the thermal energy required to melt the material in the processing area. Furthermore, in this case, most of the irradiated laser light is transmitted and diffused through the ceramic particles, resulting in melting of an area larger than the diameter of the laser beam, making it difficult to form a clear boundary. For this reason, it has traditionally been difficult to produce high-resolution ceramics using SLS or SLM.

[0004] To address these issues, for example, Non-Patent Document 1 proposes additive manufacturing using laser light irradiation of eutectic oxide ceramics. Specifically, the melting point of the powder to be molded is lowered by using an Al2O3-ZrO2 eutectic system, thereby reducing the laser light power required for melting. This method has the advantage of being able to mold ceramic structures with high mechanical strength due to the formation of a microstructure unique to eutectic systems during solidification. While this method has shown some improvement in fineness, the molding accuracy is still insufficient, as numerous surface protrusions still occur. In addition, molding ceramic structures using laser light has the problem of being time-consuming due to slower heat transfer and reaction rates than metals. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Physics Procedia 5 (2010) 587-594 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention solves these problems by providing ceramic raw material powder for obtaining high-definition ceramic structures in a short time in additive manufacturing of ceramic structures using SLS and SLM equipment, as well as a method for producing such raw material powder and a method for obtaining high-definition ceramic structures using such raw material powder. [Means for solving the problem]

[0007] According to a first aspect of the present invention, there is provided a ceramic powder for use in an additive manufacturing method in which a raw material powder is irradiated with laser light to form a shape, the ceramic powder comprising: a first particle group consisting of particles of a first inorganic compound and having an average particle diameter of 10 μm or more and 100 μm or less; and a second particle group consisting of particles of a second inorganic compound having an absorption band at the wavelength of the laser light and having an average particle diameter smaller than that of the first particle group, wherein the particles in the second particle group are arranged on the surfaces of the particles in the first particle group.

[0008] According to a second aspect of the present invention, there is provided a method for producing the ceramic powder described above, which includes at least the steps of covering the surfaces of particles contained in the first particle group with a metal component-containing liquid that serves as a precursor for the second particle group, and heating the particles contained in the first particle group that are covered with the metal component-containing liquid to arrange particles contained in the second particle group on the surface portions of the particles.

[0009] According to a third aspect of the present invention, there is provided a method for manufacturing a ceramic structure using an additive manufacturing method in which a raw material powder is irradiated with laser light to form a shape, the method comprising: (i) a step of placing the above-described ceramic powder in a laser irradiation section; and (ii) a step of selectively irradiating the ceramic powder placed in the laser irradiation section with laser light, thereby melting and then solidifying the portions of the ceramic powder irradiated with the laser light, wherein the method for manufacturing a ceramic structure is provided by repeating the steps (i) and (ii). [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional schematic view showing an example of an apparatus for irradiating laser light onto the ceramic powder of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of an apparatus for irradiating the ceramic powder of the present invention with laser light, which is different from that shown in FIG. 1. [Figure 3]3A and 3B are schematic diagrams showing enlarged portions of the ceramic powders of the present invention and a comparative example, where FIG. 3A shows a case where the second particle group is relatively small, and FIG. 3B shows a case where the second particle group is relatively large. [Figure 4] 1 is a photograph showing an electron microscope image of a part (one particle) of an example of the ceramic powder of the present invention, which is observed under magnification. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described. The present invention relates to a ceramic powder suitable for use as a raw material powder for obtaining ceramic structures (shaped objects) by additive manufacturing techniques using laser light. The ceramic powder of the present invention includes a first particle group consisting of particles of a first inorganic compound that serve as aggregates for the ceramic structure, and a second particle group consisting of particles of a second inorganic compound that serve as laser light absorbers and has an average particle diameter smaller than that of the first particle group. The particles in the second particle group (usually multiple particles) are arranged on the surface of the particles in the first particle group. Such ceramic powders are heated by absorbing laser light through the second particle group, and can efficiently transfer that heat to the first particle group. As a result, they can be melted by scanning the laser light at high speed, thereby increasing the manufacturing speed.

[0012] The ceramic powder of the present invention has the following characteristics. (1) Laser light irradiation causes melting and solidification, which allows the formation of ceramic structures. (2) The first particle group is made of particles of a first inorganic compound and has an average particle size of 10 μm or more and 100 μm or less. (3) A second particle group is included, which is made of particles of a second inorganic compound and has an average particle size smaller than that of the first particle group. (4) The particles contained in the second particle group are arranged on the surfaces of the particles contained in the first particle group, and the second inorganic compound is an absorber having an absorption band at the wavelength of the laser light. The features of each are described in detail below.

[0013] (Feature 1) The ceramic powder of the present invention is a raw material for obtaining a ceramic structure and contains ceramic as a main component. Furthermore, the powder has the property of melting at the irradiated portion when irradiated with laser light and solidifying when the laser light irradiation is stopped. In this invention, the phrase "melt and solidify" not only refers to the case where the powder becomes completely liquid (viscous fluid) and then solidifies, but also includes the case where the particles (surfaces) constituting the powder soften and bond to each other (so-called sintering). This property is preferably exhibited when the powder has Features 2, 3, and 4 described below.

[0014] There are no restrictions on the type of laser used, but lasers used in metal 3D modeling equipment can be used as is. For example, small, high-power, relatively inexpensive fiber lasers and solid-state lasers such as YAG lasers used in SLS and SLM equipment can be used. The oscillation wavelength of a typical solid-state laser is 800 nm to 1200 nm, which is within the so-called near-infrared region (0.75 to 2.5 μm). The laser oscillation method can be either continuous or pulsed.

[0015] When attempting to obtain a high-definition ceramic structure (modeled object), the irradiation diameter of the laser beam is preferably 10 μm or more and 200 μm or less. On the other hand, when prioritizing the speed of modeling and attempting to obtain a large modeled object in a short time, the irradiation diameter of the laser beam is preferably 200 μm or more and 2000 μm or less.

[0016] FIG. 1 is a schematic cross-sectional view showing an example of an apparatus for irradiating a ceramic powder of the present invention with laser light. FIG. 1 shows the configuration of the apparatus for selective laser sintering (SLS), a type of powder bed fusion method. This method is also called powder bed direct fabrication. The apparatus in FIG. 1 is composed of a powder container 11, a build stage 12, a recoater 13, a scanner 14, and a laser 15. The ceramic powder of the present invention is filled into the powder container 11. The powder container 11 and the build stage 12 have mechanisms for moving vertically, and the recoater 13 can transfer the ceramic powder from the powder container 11 to the build stage 12. In the build stage 12, the ceramic powder is spread over an area wider than the maximum horizontal cross section of the desired ceramic object.

[0017] Next, the laser 15 and scanner unit 14 irradiate the ceramic powder (the top layer) on the modeling stage 12 with laser light to create a pattern on the desired solidification area. In the ceramic powder irradiated with the laser light, the second particle group absorbs the laser light and converts the energy into heat, melting the second particle group. The heat is then transferred to the first particle group, melting them. When the laser light is then moved to another location, the molten area cools and solidifies. This process results in a single layer of modeled object. The unmelted ceramic powder remains in the same layer. A new layer of ceramic powder is laid on top of this layer, and laser light is irradiated to melt and solidify the powder in the desired locations, forming a model integrated with the previously modeled object. By repeating this process, ceramic structures (modeled objects) with any desired three-dimensional shape can be manufactured.

[0018] FIG. 2 is a cross-sectional schematic diagram showing an example of another type of apparatus for irradiating the ceramic powder of the present invention with laser light. FIG. 2 is a diagram illustrating a modeling method known as directed energy deposition (DED) or cladding. A cladding nozzle 21 has multiple powder supply holes 22 and functions to eject the ceramic powder of the present invention from these powder supply holes 22 at a desired flow rate. A laser 23 is irradiated onto the region where the beam of the ejected ceramic powder is focused, allowing a ceramic object to be additionally formed at a desired location on the substrate 20. In other words, in this case, the ceramic powder is ejected (placed) from the cladding nozzle 21 onto the laser irradiation area, and the focused region is selectively irradiated with laser light. Unlike the powder layering method, this method has the advantage of being able to model on curved surfaces.

[0019] (Feature 2) The ceramic powder of the present invention includes a first particle group having an average particle diameter of 10 μm to 100 μm. By setting the average size of the first particle group, which serves as the aggregate for a ceramic shaped product, to 10 μm to 100 μm, the fluidity required for powder transfer by a recoater or cladding nozzle during shaping (e.g., 40 seconds / 50 g or less) can be met, and the shaped product can be provided with sufficient strength. From the same perspective, the average particle diameter of the first particle group is more preferably 15 μm to 40 μm. From the viewpoint of fluidity, each particle in the first particle group is preferably spherical, but may also be irregular or have an anisotropic shape such as a plate or needle shape. The average particle diameter can be calculated as the circle-equivalent diameter of a projected image of the powder from a micrograph. For example, the average particle diameter can be obtained by randomly selecting 100 or more particles from the first particle group that constitute the powder, excluding particles in the second particle group located at the surface, and averaging the circle-equivalent diameter for each particle. If there is variation in the size of each particle, it is possible to combine microscopic photographs taken at different magnifications, but it is more preferable that the variance in the equivalent circle diameter of each first particle is small and that the particle diameter (equivalent circle diameter) of 99% or more of the particles by number is 10 μm or more and 100 μm or less.

[0020] In the present invention, the term "powder" refers to an aggregate of particles that can be recognized as isolated particles. Furthermore, the term "particle group" refers to an aggregate of particles that meets a predetermined condition. The first particle group does not have to be composed of particles of a single composition, and may be a mixture of multiple types of particles with different compositions, as long as the first particle group has the predetermined average particle diameter.

[0021] In the present invention, the term "inorganic compound" refers to an oxide, nitride, oxynitride, carbide, or boride containing one or more elements from the group consisting of antimony and bismuth in addition to elements from Groups 1 to 14 of the Periodic Table (excluding hydrogen). Furthermore, particles made of an inorganic compound may be composed of a single type of inorganic compound, or may be a composite of two or more types of inorganic compounds. By using inorganic compound particles as the main component of the powder for shaping, the resulting product from the melting and solidification reaction upon irradiation with laser light can be made into a ceramic-like substance.

[0022] The particles of the first inorganic compound contained in the first particle group are preferably composed primarily of a metal oxide. By using a ceramic powder containing a metal oxide as the primary component, a shaped object with high strength can be obtained. Here, "metal oxide" refers to an oxide containing one or more elements from the group of elements excluding boron, carbon, silicon, germanium, and elements in Group 13 (nitrogen group) and Group 14 (oxygen group) from the above-mentioned element group. The particles contained in the first particle group are preferably composed primarily of aluminum oxide, silicon dioxide, or zirconium oxide, among metal oxides. By using aluminum oxide, silicon dioxide, or zirconium oxide as the primary component and aggregate of the shaped object, a shaped object with excellent mechanical strength, heat resistance, electrical insulation, and environmental compatibility can be produced.

[0023] The particles in the first particle group may be composed of a single metal oxide, but using them in combination with other substances may exhibit new functions and become even more desirable. Examples include a combination of aluminum oxide and zirconium oxide, or a combination of aluminum oxide and a rare earth metal oxide such as gadolinium oxide or yttrium oxide. When the particles in the first particle group are composed of these metal oxides, a eutectic is formed upon heating, lowering the melting temperature compared to a single metal oxide, making the melting and solidification reactions upon laser irradiation relatively easy. Furthermore, a eutectic structure may appear in the shaped object solidified after melting, resulting in higher mechanical strength than a single metal oxide. From this perspective, it is desirable for the particles in the first particle group to contain aluminum oxide and gadolinium oxide. Furthermore, the particles in the first particle group may contain the above metal oxide and aluminum nitride or boron nitride. Using a combination of these compositions as the first particle group may result in lighter weight and higher strength than using oxides alone.

[0024] (Feature 3) The ceramic powder of the present invention includes a first particle group consisting of particles of a first inorganic compound, and a second particle group consisting of particles of a second inorganic compound, the second particle group having a smaller average particle diameter than the first particle group. The second inorganic compound has light absorption ability for laser light of a wavelength used in additive manufacturing. The particles in the second particle group are arranged on the surface of the particles in the first particle group. In other words, the first particle group consisting of the first inorganic compound and the second particle group consisting of the second inorganic compound have different chemical compositions, but both are the main components of the ceramic powder of the present invention.

[0025] A particle included in the first particle group usually has a plurality of particles included in the second particle group, which have an average particle diameter smaller than that of the first particle group, arranged on the surface thereof. Figures 3(a) and 3(b) are enlarged schematic diagrams showing a particle 1 included in the first particle group and a plurality of particles 2 or 3 included in the second particle group arranged on its surface, which constitute the ceramic powder of the present invention. The ceramic powder of the present invention is an aggregate of a large number of particles having the shape shown in Figures 3(a) and 3(b).

[0026] In Figures 3(a) and 3(b), particle 1 is approximately spherical, but the shape is not particularly limited for achieving the effects of the present invention. Numerous particles 2 and 3 are present on the surface of particle 1, and these particles 2 and 3 are particles contained in the second particle group. The particle diameter of the particles contained in the second particle group, which is strongly related to the effect of the present invention, is smaller than that of the particles contained in the first particle group in terms of average particle diameter. However, a small amount of particles contained in the second particle group equal to or larger than the particles contained in the first particle group may be present in the ceramic powder. In this case, a small amount of composite particles, in which particles contained in the second particle group are not necessarily located on the surface of particles contained in the first particle group, will be present in the ceramic powder. However, this is not a problem as long as it does not impair the effect of the present invention. The particle diameter can be calculated as the circle-equivalent diameter of the projected image from a micrograph of the powder. As described in detail in Feature 4 below, the second particle group has the function of absorbing laser light and generating heat. It is more preferable that the average particle size of the second particle group is 0.05 μm or more and 2 μm or less, since the rate of heat transfer to the particles 1 is further increased.

[0027] FIG. 3(a) shows a state in which particles 2 having an average particle diameter of 0.05 μm or more and 2 μm or less are arranged on the surface of particle 1. When the average particle diameter of particles 2 is 0.05 μm or more, the efficiency of energy absorption by particles 2 when irradiated with laser light increases. On the other hand, when the average particle diameter of particles 2 is 2 μm or less, the contact area between particles 1 and 2 increases, and the rate of heat transfer from particles 2 to particles 1 increases. More preferably, the average particle diameter of particles 2 is 0.05 μm or more and less than 1 μm.

[0028] Figure 3(b) is a schematic diagram showing one particle 1 from the first particle group constituting the ceramic powder of the present invention and one particle 3 from the second particle group arranged on its surface. Particle 3 is relatively larger than particle 2 in Figure 3(a), with a particle diameter of greater than 2 μm (but less than 10 μm). In Figures 3(a) and 3(b), particles 2 and 3 differ only in their particle diameters; their chemical compositions and crystalline structures are identical. Furthermore, the same particle 1 is used, and the mass of particles 2 and 3 attached to particle 1 is also equivalent. When the ceramic powders in Figures 3(a) and 3(b) are irradiated with laser light under the same conditions, the amount of heat generated by particles 2 and 3 in each ceramic powder is approximately equivalent.

[0029] However, in the ceramic powder of Figure 3(a), the total contact area between particle 2 and particle 1 is large, so the heat generated by particle 2 is quickly transferred to particle 1, and particle 1 begins to melt quickly and efficiently. On the other hand, in the ceramic powder of Figure 3(b), the contact area between particle 3 and particle 1 is relatively small, so the heat transfer rate is slow and much of the heat is lost by diffusion into the surrounding environment. As a result, melting is slower, and the printing speed is slower compared to the case of Figure 3(a).

[0030] However, the comparison of heat transfer rates using Figures 3(a) and 3(b) is a comparison within the range of the molding powder of the present invention, and even with the configuration of Figure 3(b), molding is possible in a shorter time than with conventional molding powders.

[0031] The strength and method of adsorption are not important, as the effect of the present invention can be obtained as long as particles 2 and 3 are in contact with the surface of particle 1. Furthermore, particle 1 may be chemically bonded to particle 2 or particle 3, so that particle 2 or particle 3 partially penetrates into particle 1.

[0032] When these particles 2 and 3 are arranged on the surface of particle 1, it is desirable that they adhere to particle 1 with as high a coverage rate as possible. For example, when particle 1 is observed two-dimensionally under a microscope, it is desirable that the coverage rate of particles 2 or 3 is 10 area % or more. The ideal coverage rate is 100 area %.

[0033] The surface of particle 1 may be provided with not only particles 2 having an average particle diameter of 0.05 μm or more and 2 μm or less, but also particles 3 having an average particle diameter exceeding 2 μm together with particles 2, but it is preferable that the area covered by particles 2 exceeds the area covered by particles 3.

[0034] The mass ratio of the first particle group to the second particle group contained in the ceramic powder is not limited, but for example, if the mass of the second particle group is 2% or more and 20% or less of the first particle group, the molding speed, molding accuracy, and strength of the molded product are all favorable, which is preferable. Hereinafter, particles 2 and 3 will not be distinguished from each other and will be collectively referred to as particles 2.

[0035] The ceramic powder of the present invention may contain particle groups other than the first particle group and the second particle group for the purpose of improving the properties of the ceramic powder itself or the ceramic structure formed therefrom. However, to fully obtain the effects of the present invention, the total proportion of the first particle group and the second particle group in the ceramic powder of the present invention is preferably 80 mass% or more, more preferably 90 mass% or more. Furthermore, the proportion of only the first particle group in the ceramic powder of the present invention is preferably 70 mass% or more.

[0036] (Feature 4) The second particle group is composed of particles of a second inorganic compound that is an absorber having an absorption band at the wavelength of the laser light. An absorber suitable for the second particle group efficiently absorbs the laser light, causing its own temperature to rise, which then spreads to the surrounding non-absorbing composition, causing a temperature rise. This achieves localized heating in the laser light irradiated area, forming an interface between the irradiated and non-irradiated areas, enabling highly accurate modeling.

[0037] The particles of the second inorganic compound contained in the second particle group preferably have a property that a composition change occurs upon laser light irradiation, and the laser light absorption rate in the solidified shaped object is lower than that before laser light irradiation. If the laser light absorption rate is lower in the region after the shaping process is completed by irradiating the laser light, it is possible to prevent the ceramic in the shaped region from being altered when an adjacent region is subsequently irradiated with laser light.

[0038] Preferably, the particles of the second inorganic compound contained in the second particle group are made of a metal oxide, and the change in laser light absorptance is due to a change in the valence of the metal element. When the laser light absorptance changes due to a change in valence, no change in volume occurs. In contrast, when the absorptance changes due to the release of volatiles from the absorber particles, the volume change has a significant effect. Examples of metal oxides whose valence changes upon laser light irradiation, resulting in a decrease or loss of laser light absorptance, include oxides of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta, W, In, Sn, Bi, Ce, Pr, Sm, Eu, Tb, and Yb. A combination of particles made of these metal oxides may also be used as the second particle group.

[0039] As the laser light used for ceramics molding, lasers with wavelengths around 1000 nm, such as Nd:YAG lasers and Yb fiber lasers, are preferred from the viewpoints of availability and controllability of irradiation energy. Materials that have high absorption of laser light in this wavelength range and that cause a decrease in absorption include terbium oxide (Tb4O7) containing tetravalent terbium, and praseodymium oxide (Pr6O 11 When the second particle group of the present invention contains terbium oxide containing tetravalent terbium or praseodymium oxide containing tetravalent praseodymium as the main component, it effectively generates heat by absorbing laser light, and then loses its absorption ability due to a decrease in valence.

[0040] Terbium oxide and praseodymium oxide have various valence states of the metal part. Taking terbium oxide as an example, there are two typical states: Tb4O7 and Tb2O3. The former state is expressed as Tb4O7 in the molecular formula, but the ratio of metal to oxygen is not strict and includes compositions around 4:7. The metal part of Tb4O7 in the former state is Tb 4+ and Tb 3+ In the latter state, the metallic part of Tb2O3 is composed of Tb 3+ It consists only of

[0041] Tb4O7 has a high infrared absorption rate around 1000 nm, exceeding 60% and sometimes reaching 70%. 4+ As the fraction of Tb decreases, the absorption rate decreases. 3+ In the case of Tb2O3, which is composed only of terbium, the absorption rate is about 7%. Therefore, terbium oxide (Tb4O7), in which the absorber contains tetravalent terbium, is suitable as the main component of inorganic compound particle B for realizing the present invention. Similarly, praseodymium oxide (Pr6O 11 ) is also suitable as the main component of the inorganic compound particles B that realize the present invention.

[0042] X-ray absorption fine structure (XAFS) analysis can be used to evaluate the valence state. The rise energy of the absorption edge differs depending on the valence state, and the valence state can be evaluated from the profile.

[0043] (Manufacturing method) Although there are no particular limitations on the method for producing the ceramic powder having the above characteristics, a preferred method will be described below. The method for producing the ceramic powder of the present invention has the following characteristics. (5) A step of covering the surfaces of the particles contained in the first particle group with a metal component-containing liquid that will serve as a precursor of the particles contained in the second particle group. (6) A step of heating the particles contained in the first particle group that have been covered with the metal component-containing liquid by the above step, thereby disposing particles contained in the second particle group on the surfaces of the particles contained in the first particle group.

[0044] (Feature 5) A manufacturing method suitable for producing the ceramic powder of the present invention includes a step of covering the surface of particles 1 contained in a first particle group with a metal component-containing liquid that serves as a precursor for particles 2 contained in a second particle group.

[0045] Suitable materials for the particles 1 are as described above, and for example, commercially available metal oxide particles can also be used. The surfaces of the particles 1 may be modified to improve the wettability and adhesiveness of the surfaces of the particles 1. Examples of methods for surface modification include irradiation with energy rays, such as ultraviolet rays, and coating or immersion treatment with a surface modifier such as a silane coupling agent or a phosphonic acid derivative.

[0046] The metal oxide-containing liquid, which serves as the precursor of particles 2, is a solution or dispersion of a composition that can become particles 2 upon heating. Examples of such compositions include hydrolyzable or thermally decomposable organometallic compounds. More specifically, metal alkoxides of the above metals, organic acid salts, and metal complexes such as β-diketone complexes can be used. Another example of a metal complex is an amine complex. Examples of β-diketones include acetylacetone (=2,4-pentanedione), heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, and benzoylacetone. β-diketone complexes can also be considered a form of metal alkoxide because oxygen elements are coordinated to the metal.

[0047] For example, when the main component of the particles 2 is terbium oxide, a method is available in which a terbium alkoxide is added to the metal component-containing precursor liquid. Examples of terbium alkoxides include terbium-n-butoxide, terbium-t-butoxide, terbium-methoxypropoxide, terbium-2,4-pentanedionate, terbium-methoxyethoxide, terbium-2,4-pentanedionate, and terbium-2,2,6,6-tetramethyl-3,5-heptanedionate.

[0048] Examples of praseodymium alkoxides include praseodymium-n-butoxide, praseodymium-t-butoxide, praseodymium-methoxypropoxide, praseodymium-hexafluoropentanedionate, praseodymium-2,4-pentanedionate, praseodymium-2,2,6,6-tetramethyl-3,5-heptanedionate, and praseodymium(III)-6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate. The same applies to alkoxides of other metals.

[0049] Metal alkoxides and their solutions may be commercially available or may be synthesized by the method described in the claims and paragraph

[0003] of JP-A-9-157272. The composition containing each metal component can be prepared as a metal component-containing liquid by dissolving or dispersing it in an appropriate solvent. The solvent is appropriately selected from various known solvents taking into consideration dispersibility and coatability.

[0050] Examples of solvents used in preparing the metal component-containing solution include alcohol-based solvents such as methanol, ethanol, n-butanol, n-propanol, and isopropanol, ether-based solvents such as tetrahydrofuran and 1,4-dioxane, cellosolve-based solvents such as methyl cellosolve and ethyl cellosolve, amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, and nitrile-based solvents such as acetonitrile. When a metal alkoxide is used as the metal component, it is preferable to use an alcohol-based solvent.

[0051] There are no particular restrictions on the amount of solvent used to prepare the metal component-containing liquid, but adjusting the amount of solvent so that the metal solids concentration is approximately 5% by mass to 20% by mass is suitable for coating the surface of particle 1.

[0052] The method for covering the surface of particle 1 with the metal component-containing liquid is not particularly limited, but includes immersing particle 1 in the liquid, adding the liquid to particle 1, spraying the liquid onto particle 1, and the like.

[0053] (Feature 6) After the above step, a step of forming particles 2 on the surface of particles 1 by simultaneously heating particles 1 and the metal component-containing liquid attached to the surface of particles 1 is carried out.

[0054] This heating volatilizes the solvent in the metal component-containing liquid, further oxidizing and particulating the metal component, resulting in the deposition of particle 2 on the surface of particle 1. If the precursor composition is hydrolyzable, the hydrolysis reaction progresses, forming bonds between the metal and oxygen, resulting in the formation of fine metal oxide particles with a particle diameter of less than 1 μm. Furthermore, since particle 2 is formed by a chemical reaction, the bond with the base particle 1 is strong and the contact area is large. Therefore, the rate of heat transfer from particle 2 to particle 1 increases when irradiated with laser light.

[0055] The optimum heating temperature is selected depending on the type of material. For example, it is preferable to heat the material in stages, for example, at about 150 to 300°C to volatilize the solvent, and then at about 550 to 750°C to form particles.

[0056] The heating means is not limited, and a dryer, a hot plate, an electric furnace, an atmospheric furnace, etc. After heating, the obtained powder may be crushed again to make it into a fine powder, or may be sieved to make the particle size uniform.

[0057] (How to use) The method for producing a ceramic structure (shaped object) by using the ceramic shaping powder of the present invention as a raw material and irradiating it with a laser has the following features. (7) The method includes a step (i) of placing the ceramic shaping powder of the present invention in a laser irradiation area. (8) A step (ii) is included in which the ceramic forming powder placed in the laser irradiation section is selectively irradiated with laser light to sinter or melt the ceramic forming powder and then solidify the powder (including the case of sintering). (9) The method includes a step (iii) of producing a ceramic structure (shaped object) by repeating the steps (i) and (ii).

[0058] (Feature 7) The method for placing the ceramic modeling powder of the present invention in the laser irradiation unit is as described in Feature 1. For example, in the device shown in Figure 1, the ceramic modeling powder of the present invention filled in the powder container 11 can be placed on the modeling stage unit 12 by the recoater unit 13. Also, as described in Feature 1 using Figure 2, by ejecting the ceramic modeling powder at a predetermined location and irradiating that location with laser light, it is possible to form a model on a curved base.

[0059] (Feature 8) The method for selecting the laser light for melting and then solidifying the ceramic modeling powder is as described in Feature 1. As described above, in the present invention, sintering is also considered a form of melting and then solidifying operation. Strictly speaking, sintering refers to a reaction in which powder is bound in the solid phase (without melting) and grain growth occurs, while melting refers to a reaction in which the powder becomes liquid, but it also includes an intermediate state in which the solid and liquid phases are mixed. Prior to step (ii), it is preferable to spread the ceramic modeling powder placed in the laser irradiation section and then irradiate it with laser light, as this will result in a denser modeled object.

[0060] (Feature 9) By carrying out each of the steps (i) and (ii) once, a patterned ceramic object of one layer is obtained. By spreading new ceramic molding powder on top of this and repeating steps (i) and (ii) in different patterns, a ceramic object of the desired three-dimensional shape can be produced.

[0061] After molding, the molded object may be subjected to a heat treatment to increase its density and strength, or to reoxidize it. At this time, it is also possible to apply or impregnate it with an organic or inorganic compound as a glaze. There are no limitations on the heating method, and resistance heating, induction heating, infrared lamps, lasers, electron beams, and other methods can be used depending on the purpose.

[0062] [Example] The ceramic powder of the present invention, its manufacturing method, and its use will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0063] Example 1 The ceramic powder of the present invention was produced by the following procedure. The first particle group was a mixture of commercially available industrial Al2O3 powder (purity of 99% or more, average particle diameter of 20 μm) and Gd2O3 powder (purity of 99% or more, average particle diameter of 20 μm) in a mass ratio of 1:1.

[0064] A metal alkoxide solution of terbium, a hydrolyzable organometallic compound, was prepared as the metal component-containing liquid that would serve as the precursor of the particles that make up the second particle group. Specifically, terbium-2,4-pentanedionate, a commercially available general reagent, was dissolved in 1-methoxy-2-propanol as a solvent to prepare a metal oxide (Tb4O7) equivalent concentration of 10 mass%.

[0065] 97 g of the first particle group was weighed and placed in a high-purity alumina container, and 25 g of the metal component-containing liquid was added thereto and stirred thoroughly.

[0066] The container was placed in an electric furnace in an atmospheric air atmosphere, and a heat treatment was carried out by running a program that maintained a maximum temperature of 600°C for 3 hours. After the electric furnace was cooled to room temperature, the contents were removed from the alumina container and crushed to obtain the ceramic powder of the present invention.

[0067] Figure 4 shows a magnified image of a portion of the produced powder observed with an electron microscope. Figure 4 was observed at 5000x magnification to highlight the typical structure of the ceramic powder of Example 1, but other particles comprising the powder also had a similar structure. In Figure 4, the spherical particles with a diameter of approximately 20 μm that occupy the majority of the observation field were identified as aluminum oxide and particle 1, a member of the first particle group, by SEM-EDX analysis and X-ray diffraction measurement. The fine particles attached to the surface of particle 1 were identified as terbium oxide (Tb4O7) and a member of the second particle group by SEM-EDX analysis and X-ray diffraction measurement. The average particle diameter of the second particle group, calculated by image processing of the observed image, was estimated to be 0.3 μm at most. Because the second particle group also contains particles too fine to be recognized by image processing, the actual average particle diameter is likely even smaller. The coverage of particle 1 by particle 2, a member of the second particle group, calculated from the observed image was approximately 14% by area. Although not visible in the image in Figure 4, there is also an aggregate of gadolinium oxide particles (Particle 1) near this particle, with similarly fine particles (Particle 2) attached.

[0068] The ceramic powder of Example 1 was dissolved by heating in dilute sulfuric acid and analyzed for composition using ICP atomic emission spectroscopy. The mass ratios of Al2O3, Gd2O3, and Tb4O7 were 46.6:50.3:2.46. The content of other components was less than 0.1 mass% of the ceramic powder. Al2O3 and Gd2O3 constituted the first particle group, accounting for a total of 96.9 mass%.

[0069] (Examples 2 and 3) The ceramic powder of the present invention was produced in the same manner as in Example 1, except that the raw material types and compounding ratios were changed according to Table 1. For the zirconium oxide (the first particle group), we used commercially available industrial ZrO powder (purity 99% or higher, average particle size 15 μm).For the praseodymium metal alkoxide, we used praseodymium-2,4-pentanedionate, a commercially available general reagent. The amount of the metal component-containing liquid added to the first particle group, which serves as a precursor of the second particle group, was appropriately changed.

[0070] (Examples 4 and 5) The ceramic powder of the present invention was produced in the same manner as in Examples 1 to 3, except that the raw material types and compounding ratios were changed according to Table 1. However, for the second particle group, commercially available Tb4O7 powder (average particle diameter 3 μm) and Pr6O 11 Powder (average particle size 4 μm) was used.

[0071] (Comparative Examples 1 to 3) Ceramic powders for comparison were produced in the same manner as in Example 1, according to the compounding ratios shown in Table 1. However, in Comparative Example 1, the ceramic powder was composed of only the first particle group without adding the second particle group. In Comparative Example 2, a powder with an average particle size of 40 μm, which was prepared by calcining commercially available Tb4O7 powder in an electric furnace at 700°C, and Pr6O were mixed without using a metal component-containing liquid that serves as a precursor for the second particle group. 11 Powders (average particle size 50 μm) were mixed to form powder for ceramic molding.

[0072] Table 1 TIFF2023168446000002.tif45170

[0073] (Use of ceramic molding powder) To clarify the differences in the molding speed of the ceramic powders in each Example and Comparative Example, each powder was spread evenly on a flat alumina substrate with a sufficient area to a thickness of approximately 50 μm, and then the surface was irradiated with a laser. The laser focal size was 100 μm and the output was 30 W. The laser light was scanned over a length of 4.5 mm, drawing two lines at a 50 μm pitch. Scanning speeds of 100 mm / s, 250 mm / s, 500 mm / s, and 1000 mm / s were used to compare the melting states. The powder in the laser irradiated area was observed using a microscope to see whether it had solidified and been formed into a ceramic shape after laser irradiation. The results are shown in Table 2.

[0074] When the ceramic powders of Examples 1, 2, and 3 were irradiated with laser light, ceramic-like objects could be obtained at any scanning speed. In particular, at scanning speeds of 250 to 1000 mm / s, the width of the boundary between the laser-irradiated and non-irradiated areas was 15 μm or less, and high molding accuracy was also achieved. In cases where a ceramic object with excellent molding accuracy was obtained, this was recorded as "a" in Table 2. On the other hand, at a scanning speed of 100 mm / s, there was fluctuation in the boundary line of the ceramic object, and the width was somewhat large at approximately 40 μm. In cases where the conditions were sufficient to obtain a ceramic object but there were some problems with molding accuracy, this was recorded as "b" in Table 2.

[0075] Thus, the powder for ceramic molding that satisfies the requirements of the present invention makes it possible to mold ceramics even at high scanning speeds, and can more than double the time required to obtain the desired molded object.

[0076] When the ceramic powder of Comparative Example 1 was irradiated with laser light, a ceramic object was obtained at a scanning speed of 100 mm / s, but the boundary was irregular and there were some areas where melting had not progressed. Furthermore, at scanning speeds of 250 mm / s or higher, melting did not progress and conversion from powder to a molded object was not observed. In cases where a ceramic object could not be obtained with sufficient precision, a "c" was recorded in Table 2.

[0077] When laser light was irradiated onto the ceramic powders of Comparative Examples 2 and 3, objects with excellent molding accuracy were obtained at scanning speeds of 100 to 250 mm / sec. However, at a scanning speed of 500 mm / sec, the objects contained small amounts of powder, and at a scanning speed of 1000 mm / sec, melting did not progress and no conversion from the powder to an object was observed.

[0078] [Table 1]

[0079] Example 4 The ceramic molding powders of Examples 1 to 3 were loaded into the SLS device shown in Figure 1, and the additive manufacturing process was repeated multiple times with the laser light scanning speed set to 1000 mm / sec to obtain a three-dimensional ceramic object of the desired shape. (Industrial Applicability)

[0080] By using the ceramic shaping powder of the present invention, it is possible to obtain fine ceramic shaped objects by three-dimensional shaping, and the powder can be used in the field of ceramic parts that require complex shapes. [Explanation of symbols]

[0081] 1 Particles included in the first particle group 2, 3 Particles included in the second particle group 11 powder powder 12 Modeling stage 13 Recoater section 14 Scanner unit 15 Laser 20 Base 21 Cladding Nozzle 22 Powder supply hole 23 Laser

Claims

1. A step of arranging ceramic powder, A step of irradiating the ceramic powder with laser light, A method for manufacturing a ceramic structure in which the above steps are repeated to form a shaped object, The ceramic powder includes composite particles composed of first particles containing a first inorganic compound and second particles having a smaller particle diameter than the first particles and adhering to the surface of the first particles and containing a second inorganic compound, By the irradiation, the second particles absorb the laser light and generate heat, The manufacturing method is characterized in that the shaped object has a eutectic structure.

2. The first inorganic compound is an oxide, nitride, oxynitride, carbide or boride, The second inorganic compound is an oxide, nitride, oxynitride or boride, The manufacturing method according to claim 1, characterized in that.

3. The first inorganic compound is aluminum oxide, The manufacturing method according to claim 2, characterized in that.

4. The first inorganic compound is silicon dioxide or zirconium oxide, The manufacturing method according to claim 1 or 2, characterized in that.

5. The first inorganic compound is a nitride, oxynitride, carbide or boride, The second inorganic compound is an oxide, nitride, oxynitride, carbide or boride, The manufacturing method according to claim 1, characterized in that.

6. By the irradiation, the portion of the powder irradiated with the laser light becomes liquid, The manufacturing method according to any one of claims 1 to 5, characterized in that.

7. By the irradiation, the second inorganic compound undergoes a composition change and the absorption rate of the laser light decreases, The manufacturing method according to any one of claims 1 to 6, characterized in that.

8. The second inorganic compound is an oxide, The decrease in the absorption rate is due to a change in the valence of an element other than oxygen constituting the second inorganic compound, The manufacturing method according to claim 7, characterized in that.

9. The second inorganic compound is an oxide of a metal element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta, W, In, Sn, Bi, Ce, Pr, Sm, Eu, Tb, Yb, The manufacturing method according to any one of claims 1 to 8, characterized in that.

10. The first particles contain two or more kinds of inorganic compounds that are compounded, The manufacturing method according to any one of claims 1 to 9, characterized in that.

11. The ceramic powder contains third particles containing a third inorganic compound, The manufacturing method according to any one of claims 1 to 10, characterized in that.

12. The third inorganic compound is an oxide, nitride, oxynitride, carbide or boride, The manufacturing method according to claim 11, characterized in that.

13. The third inorganic compound is a rare earth metal oxide, The manufacturing method according to claim 11, characterized in that.

14. In the ceramic powder, the mass of the second inorganic compound relative to the mass of the first inorganic compound is 2% or more and 20% or less, The manufacturing method according to any one of claims 1 to 13, characterized in that.

15. In the ceramic powder, the total of the mass of the first inorganic compound and the mass of the second inorganic compound is 80% or more of the mass of the ceramic powder, The manufacturing method according to any one of claims 1 to 14, characterized in that.

16. In the ceramic powder, the mass of the first inorganic compound is 70% or more of the mass of the ceramic powder, The manufacturing method according to any one of claims 1 to 15, characterized in that.

17. In the ceramic powder, the average particle diameter of the first particle group composed of particles containing the first inorganic compound is 10 μm or more and 100 μm or less, The manufacturing method according to any one of claims 1 to 16, characterized in that.

18. In the ceramic powder, the average particle diameter of the second particle group composed of particles containing the second inorganic compound is 0.05 μm or more and less than 10 μm, The manufacturing method according to any one of claims 1 to 17, characterized in that.

19. The laser light is an Nd:YAG laser or a Yb fiber laser, The manufacturing method according to any one of claims 1 to 18, characterized in that.

20. The shaped object is formed by a powder lamination method, The manufacturing method according to any one of claims 1 to 19, characterized in that.

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