Particle compositions and related methods and uses to form sintered silicon

Abstract

The present invention relates to a feedstock composition comprising inorganic particles having a multi-modal particle size distribution and comprising: an irregular set of fine particles having a fine particle size distribution and an average fine particle diameter; and an irregular set of coarse particles having a coarse particle size distribution and an average coarse particle diameter in a range from 4 to 7 times the average fine particle diameter. The feedstock composition further includes a binder composition adapted to solidify to form a body including the inorganic particles and the solidified binder composition. In addition, the present composition provides a method of forming a molded body including inorganic particles dispersed in the binder composition and a method of forming a low porosity inorganic sintered body.

Description

Technical Field

[0001] The present disclosure describes multimodal particle compositions containing irregularly shaped particles having at least two different particle size modes, derived compositions such as raw material compositions, and methods of using the multimodal particle compositions and the raw material compositions to form shaped bodies, wherein the multimodal particle compositions contain irregularly shaped particles having at least two different particle size modes, the raw material compositions contain the particle compositions combined with an optional binder and are used to form shaped bodies. Background Art

[0002] Powder materials made from a collection of small solid particles of similar size and shape are used commercially in a range of processes to form shaped bodies made from the particles. The shaped bodies can be rigid, porous, non-porous, etc., and can have size and shape characteristics within very wide limits. The powders and shaped bodies can be made from many different types of materials, including organic (polymeric) particles and inorganic particles (such as ceramics or metals, including alloys).

[0003] By using certain common methods of powder materials, the powder composition can be melted to form a flowable liquid, and then molded or extruded to form a shaped body. With these methods, the particles are melted into a flowable liquid and the original size and shape characteristics of the particles are eliminated during molding. The original size and shape characteristics of the particles may have little effect on the properties of the shaped body.

[0004] Other methods do not require melting, flowing and molding or extruding the particles when forming a shaped body. Therefore, the original size and shape properties of the particles are important to the properties of the final shaped body. Generally speaking, some methods of forming a shaped body using a powder may include the steps of forming the particles into a shaped precursor having a desired size and shape and containing the particles in their original form. The shaped precursor is then heated to a temperature that causes the particles of the shaped precursor to combine, by melting and optionally fusing, to form a final shaped body that retains the shape and size of the shaped precursor.

[0005] With some such methods, exemplary steps include: forming the particles into a "feedstock" material containing particles optionally dispersed with one or more added ingredients (e.g., a "binder" or other additive); forming the feedstock into a shaped precursor (sometimes referred to as a "green body"), which comprises the particles still in the form of individual particles; and then heating (e.g., "sintering" the metal or ceramic particles) the shaped precursor so that the particles melt or fuse together at contact surfaces to form a finished shaped body.

[0006] When a shaped body (precursor or final shaped body) is formed by these methods, the size and shape properties of the particles of the powder component can affect the properties of the shaped body (shaped precursor or final shaped body or both). For example, some types of shaped bodies can be designed to include spacing between particles, such as to become a porous final shaped body. For these types of bodies, the particles can exhibit a relatively low packing density. Alternatively, if desired, the shaped body can be designed to include a reduced spacing or minimum spacing between particles, such as to form a final shaped body with a minimum porosity or low porosity. For these types of bodies, the particles desirably exhibit a relatively high packing density. Summary of the invention

[0007] Described below are multimodal particulate compositions containing irregularly shaped particles, wherein the particles have at least two different particle size distribution modes, and wherein the plurality of particle size distribution modes results in the multimodal particulate composition having an increased packing density.

[0008] The present description also relates to compositions (e.g., "feedstocks") and articles (e.g., various types of three-dimensional "shaped bodies") containing or formed from multimodal particulate compositions as described. The present description also describes examples of methods of using feedstock compositions to form shaped bodies, for example, by compaction methods or additive manufacturing methods.

[0009] When using a powder compaction method to form a shaped body using irregularly shaped particles, there is no suitable model or guide for selecting particle size and diameter ratios to achieve high packing density. The "McGeary model" can be used to combine coarse and fine powders to achieve a desired packing density for spherical particle powders, but this model is not applicable to irregular particles. To select the relative size and number of irregular particles to achieve high packing density, the number and size must be experimentally identified.

[0010] As described below, compositions and methods are described involving multimodal irregular particle compositions having relatively high packing density. The particle compositions (referred to as "multimodal particle compositions") can contain particles of any type (polymer, metal, ceramic) and size, and can be used to form any type of shaped body by any useful technique, including by molding techniques, compression techniques (e.g., in-line compression), or by any useful additive manufacturing technique.

[0011] In one aspect, the present disclosure relates to a powder composition having a multimodal particle size distribution. The composition contains: an irregular fine granular particle set having a fine particle size distribution and an average fine particle diameter (D50 value); and an irregular coarse granular particle set having a coarse particle size distribution and an average coarse particle diameter (D50 value) in the range of 4 to 7 times the average fine particle diameter (D50 value).

[0012] In another aspect, the present description relates to a raw material composition comprising inorganic particles and a binder composition. The raw material composition contains inorganic particles having a multimodal particle size distribution. The inorganic particles include: an irregular fine particle set having a fine particle size distribution and an average fine particle diameter; and an irregular coarse particle set having a coarse particle size distribution and an average coarse particle diameter in a range from 4 to 7 times the average fine particle diameter. The raw material composition also includes a binder composition suitable for solidification to form a body containing the inorganic particles and the solidified binder composition.

[0013] In yet another aspect, the present description relates to a method of forming a shaped body containing inorganic particles dispersed in a binder composition. The method comprises using a raw material composition containing inorganic particles having a multimodal particle size distribution. The raw material composition contains: an irregular fine particle set having a fine particle size distribution and an average fine particle diameter; and an irregular coarse particle set having a coarse particle size distribution and an average coarse particle diameter in a range from 4 to 7 times the average fine particle diameter; and a binder composition. The method comprises forming the raw material composition into a shaped body containing the inorganic particles and a solidified binder composition.

[0014] Another aspect of the present description relates to a method for forming a low-porosity inorganic sintered body. The method includes using a raw material composition containing inorganic particles having a multimodal particle size distribution. The raw material composition contains: a powder composition having a multimodal particle size distribution, the powder composition comprising: an irregular fine particle set having a fine particle size distribution and an average fine particle diameter (D50 value); and an irregular coarse particle set having a coarse particle size distribution and an average coarse particle diameter (D50 value) in the range of 4 to 7 times the average fine particle diameter; and a binder composition. The raw material composition is formed into a molded precursor containing a solidified binder composition and the inorganic particles. The molded precursor is heated to a temperature causing the irregular fine particles to melt together with the irregular coarse particles to form the inorganic sintered body. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a SEM image of an example of an assembly of particles as described.

[0016] Figure 2 Example showing particle size distribution. DETAILED DESCRIPTION

[0017] The following relates to multimodal particulate compositions containing irregularly shaped particles, wherein the particles have at least two different particle size distribution modes, and wherein the plurality of particle size distribution modes results in the multimodal particulate composition having an increased packing density.

[0018] The multimodal particulate composition contains two different sets of irregularly shaped granular particles (i.e., herein "irregular granular particles" or "irregular particles"). The average particle size (diameter) of the two sets is each different from the average particle size of the other set. One particle set is a relatively small ("fine") particle set with a lower average particle size, and the second particle set is a relatively large ("coarse") particle set with a higher average particle size. In order to achieve a desirably high particle packing density in the multimodal particulate composition, the average particle size of the particles of the coarse particle set can be in the range of from 4 to 7 times the average particle size of the particles of the fine particle set.

[0019] Also preferably, the collection of fine particles and the collection of coarse particles may each have a relatively broad particle size distribution (see below) to further increase the packing density of the multimodal particle composition.

[0020] The present description also relates to compositions (e.g., "feedstocks") and articles (e.g., various types of three-dimensional "shaped bodies") containing or formed from multimodal particulate compositions as described. The present description also describes examples of methods of using feedstock compositions to form shaped precursors, e.g., by compaction methods or additive manufacturing methods, and further processing the shaped precursors by steps including heating the shaped precursors to form final shaped bodies.

[0021] An example of a composition containing a multimodal particle composition is a feedstock composition containing a multimodal particle composition combined with a binder composition that allows the feedstock to be formed into a desired three-dimensional form. The feedstock composition can be used to form a shaped precursor containing particles of the multimodal particle composition distributed within the binder composition, wherein the particles retain their original particle form. The shaped precursor can be further processed by a step comprising heating or sintering the shaped precursor to form a final shaped body in which the individual particles of the multimodal particle composition have been fused together, meaning that the particles will be partially melted, wherein the melting occurs at the particle surface to cause adjacent particles to be structurally fused together.

[0022] The multimodal particulate composition as described contains solid particles in the form of microparticles, granules, or small particles in the absence of a bulk liquid (i.e., considered dry and in "powder" form). The composition is substantially dry and flowable, wherein the particles are movable relative to each other and air spaces exist between particle surfaces. The multimodal particulate composition contains two distinct types of particles (e.g., two collections), wherein each collection has a characteristic particle size distribution mode that is different from the other collection.

[0023] As used herein, a "collection" of particles refers to a volume of individual solid particles having common shape and size characteristics (i.e., "irregular" and "granular"), including sizes (diameters) that fall within a particle size distribution that exhibits the shape of a curve (e.g., a bell curve). The particles in the form of a collection are substantially dry and flowable, wherein the particles can move relative to each other and there are air spaces between particle surfaces. Optionally and typically, the particles can be similar or identical in composition, for example, made of a single type of ceramic, polymer, or metallic material.

[0024] Examples of inorganic materials that can be particles of the multimodal particle composition include inorganic particles that are metals (including metal alloys) or ceramics. The metal particles may contain (include) one or more different metals (consist of one or more different metals, or consist essentially of one or more different metals), either as pure metals or as alloys. The term "metal" as used herein refers to any metallic or metalloid chemical element or an alloy of two or more of these elements. Exemplary metals include iron, refractory metals (e.g., tungsten, molybdenum, tantalum), titanium, and nickel. Examples of metal alloys include stainless steel, another iron or steel alloy, a nickel alloy, a titanium alloy, and the like.

[0025] Exemplary ceramics include metal oxides, such as zirconium oxide (ZrO 2 ), aluminum oxide (Al2O 3 ), silicon carbide, and the like. Certain more specific examples include ceramic powder materials that are prepared by mechanically processing larger pieces of ceramic material to form smaller pieces, which are sometimes referred to as "mechanically produced powders" prepared by a milling process. Other examples of useful ceramic materials are the types of silicon carbide powders known as "recrystallized silicon carbide" and "alpha" and "beta" silicon carbide materials.

[0026] The particles of each of the two different particle sets are considered to be "irregular" granular particles (or "granular particles") that do not have a high aspect ratio (length: width), and are not spherical. Exemplary particles in the set can be generally characterized as being irregular in shape, non-spherical, and having a range of relative roundness and aspect ratio values.

[0027] An exemplary measurement that can help identify granular particles as described is the aspect ratio, which is the ratio of the length of an individual particle to the width of the particle, which is suitable for irregularly shaped particles. The aspect ratio of individual granular particles of the present description can be at least 1.3 or at least 1.5 (length / width), for example, in the range of from 1.5 to 10.

[0028] Another measurement that can help identify granular particles as described is a measurement of "relative roundness". Relative roundness is a measurement of how close the shape of an object is to the shape of a mathematically perfect circle, and can be measured using an optical camera. Spherical or nearly spherical particles will have a relative roundness value of at least 0.8 or 0.9 and less than 1.0 (which is a sphere). Individual irregular granular particles, as well as the average of all granular particles of different particle collections as described herein, may have a relative roundness below 0.7 (e.g., in the range of from 0.2 to 0.7).

[0029] Based on these shape characteristics, particles that are considered irregular granular particles are not spherical particles, and the particles have a mostly or entirely rounded surface with an aspect ratio in the range of from 1.2:1 to 1:1.2. Irregular granular particles are also not high aspect ratio particles, which means that irregular granular particles do not have an aspect ratio greater than 10.

[0030] The described granular particles are also not of the type that would be considered "dendritic". Dendritic particles are described in U.S. Pat. No. 5,814,272. As presented in said text, the term "dendritic" refers to a highly anisotropic, irregular morphology characterized by particles having one or more fibrils, having an irregular surface, and individually having one dimension substantially larger than the other two dimensions of the fibrils. The fibrils may be straight or curved, and may also be branched or unbranched. Dendritic particles are also characterized by low packing efficiency compared to particles of more regular morphology, and therefore, dendritic particles form powders having lower apparent (overall) density than those powders formed from particles of more regular morphology. Dendritic particles are still characterized as being formed by a process comprising the steps of: (1) heating a powder comprising non-dendritic metal particles under conditions suitable for forming a lightly sintered material; and (2) causing the lightly sintered material to break up to form a powder comprising dendritic metal particles.

[0031] Examples of particles that may be considered "irregular granular particles" include particles having one or more of the characteristics of relative roundness and aspect ratio presented above. These particles may be further characterized as having multiple corners that are acute or slightly angled or rounded, and the surfaces between the corners may be significantly flat or slightly curved. The edges of the particles may be relatively sharp (e.g., jagged), and the surfaces may be substantially flat (i.e., flat) or slightly rounded or curved to produce a collection of particles that is visually similar to the granular, faceted, angular or slightly rounded particles that make up sand, abrasive granules, roofing granules, and the like.

[0032] Figure 1 A single non-limiting example of an irregular granular collection of particles that can be used as particles in a multimodal particulate composition is shown.

[0033] Each of the multimodal particle compositions and first ("fine particles") and second ("coarse particles") collections of particles as described comprises (includes) a significant portion of (or consists essentially of) the total particles of the multimodal composition or collection that are irregular granular particles as described. Examples of multimodal particle compositions and fine or coarse particle collections as described may contain (based on the total amount of particles in the multimodal particle composition or collection) at least 80%, 90%, 95%, or 99% of particles that exhibit these characteristics of irregular granular particles.

[0034] As described, a collection of particles can be described as having a statistical distribution of different particle sizes (e.g., based on the diameter of the particles). The sizes of the particles within the collection are often represented as a frequency distribution curve, which is a graph of the frequency (percentage, on the y-axis) of particles within a sample of particles having particles of a particular size (diameter, such as microns) on a logarithmic x-axis.

[0035] The particle collection of the present description (e.g., irregular fine granular particle collection, irregular coarse granular particle collection, or both, respectively) may have a unimodal particle size distribution characterized in that the particle size (diameter) distribution is in the form of a continuous curve that is bell-shaped or approximately bell-shaped (e.g., Gaussian), so that there is a minimum particle size at one end of the curve, a maximum particle size at the second end of the curve, a single peak (maximum) between the first end and the second end, a continuous and gradually rising curve between the first end and the single peak, and a continuous and gradually falling curve between the single peak and the second end. The curve may also be characterized by a standard deviation value that defines the "width" or "narrowness" of the curve.

[0036] Figure 2An exemplary particle size distribution of a useful collection of unimodal irregular granular particles is shown at . The particle size distribution of the irregular granular particles is exemplary, and particles used according to the present description may have a particle size distribution of Figure 2 The samples were compared with different particle size distributions.

[0037] Figure 2 Two particle size distribution curves are shown. Each curve is a unimodal bell-shaped curve that plots the frequency (percentage, y-axis) of particles within a collection of particles versus the size (diameter) range of the particles (x-axis, on a logarithmic scale). Each of the two frequency curves has a minimum particle size at one end of the curve, a maximum particle size at the second end of the curve, a single peak (maximum) between the first and second ends of the curve, a continuous and gradually rising curve between the first end and the single peak, and a continuous and gradually falling curve between the single peak and the second end.

[0038] By common terminology, a particle size data point on the x-axis of a particle size distribution curve may be identified based on the amount (as a percentage) of particles in the measured sample having a size (e.g., diameter) greater than the particle size data point at the x-axis. For example, Figure 2 Identify the positions on the particle size distribution curve labeled D10, D50, and D90. These positions represent the particle size (diameter) value on the x-axis corresponding to being larger than 10% of all particles in the measured sample (D10), or the particle size (diameter) value on the x-axis corresponding to being larger than 50% of all particles in the measured sample (D50), or the particle size (diameter) value on the x-axis corresponding to being larger than 90% of all particles in the measured sample (D90).

[0039] Also refer to Figure 2 , showing two different curves, each with a different "width". The width of a particle size distribution curve refers to the relative distance between the low end of the curve and the high end of the curve. Figure 2 Here, one curve has a relatively narrow particle size distribution and the second curve has a relatively broad particle size distribution.

[0040] According to the exemplary unimodal particle collections used to prepare multimodal particle compositions as described, the use of unimodal particle collections having a relatively broad particle size distribution is preferred for preparing multimodal particle compositions having a relatively high packing density. In turn, the multimodal particle compositions are preferred for preparing feedstock compositions that also have densely packed particles, shaped precursors having densely packed particles, and finished shaped bodies having low porosity.

[0041] The multimodal particle composition of the present description contains two unimodal irregular particle assemblies, and each assembly has a different statistical distribution of particle sizes. The characteristic of the particle assembly is the median diameter (D50) of the particles in the assembly, which is the diameter at which 50% of the particles in the assembly have a larger diameter and 50% of the particles in the assembly have a smaller diameter.

[0042] A different characteristic is the relative distribution width or narrowness, which means the distance between the largest particle size and the smallest particle size in the set. The width or narrowness can be expressed by the standard deviation value of the particle size distribution curve. Examples of useful or preferred standard deviations for a set of irregular fine granular particles can range from 1 to 5. Examples of useful or preferred standard deviations for a set of irregular coarse granular particles can range from 1 to 5.

[0043] As a related measure, a desirable broad particle size distribution for a collection of fine or coarse particles can be measured by a "span value." The span value relates to the standard deviation relative to the mean particle size value, and is calculated as the ratio (D90-D10) / D50. Broader particle size distributions will have larger values. Examples of useful or preferred span values ​​for an irregular collection of fine particles can range from 1 to 5. Examples of useful or preferred span values ​​for an irregular collection of coarse particles can range from 1 to 5.

[0044] As described herein, a multimodal particle composition contains two unimodal particle collections, wherein one of the collections (referred to as the "irregular fine granular particles" or "fine particles" collection) has a relatively small average particle size (D50) and the second collection (referred to as the "irregular coarse granular particles" or "coarse particles" collection) has a relatively high average particle size (D50).

[0045] The average particle size (D50) of particles in the collection of fine particles can be the average particle size used in the multimodal particle composition as described. An exemplary average particle size of the collection of fine particles can be, for example, from 1 micron to 30 microns.

[0046] The average particle size (D50) of the particles in the coarse particle collection can be the average particle size used in the multimodal particle composition as described. An example average particle size of the coarse particle collection can be, for example, from 30 microns to 200 microns.

[0047] Also according to useful or preferred examples of multimodal particle compositions, the average diameter (D50) of the larger (coarse) particle set is in the range of from 4 to 7 times the average diameter (D50) of the smaller (fine) particle set. This ratio has been identified as a ratio that will provide a desirably useful and desirably high packing density of the modal multimodal particle composition.

[0048] The multimodal particle composition may contain any relative amount of the fine particle assembly and the coarse particle assembly. According to a useful or preferred example, the multimodal particle composition may contain a majority of the irregular coarse particle assembly by weight and a lower amount of irregular fine particles by weight. Useful or preferred multimodal particle compositions may contain from 10 wt % to 50 wt % of the irregular fine particle assembly and from 50 wt % to 90 wt % of the irregular coarse particle assembly, for example, from 20 wt % to 40 wt % of the irregular fine particle assembly and from 60 wt % to 80 wt % of the irregular coarse particle assembly, based on the total weight of the composition or based on the total weight of the irregular fine particle assembly and the irregular coarse particle assembly.

[0049] Multimodal particulate compositions as described can have a relatively high packing density and correspondingly low interstitial spacing. Multimodal particulate compositions contain particles in a volume ("bulk volume") containing particles with open spaces (e.g., containing air) between the surfaces of the particles (sometimes referred to as "interstitial spacing"). In this form, the "packing density" of a particulate composition refers to the fraction (percentage) of the bulk volume occupied by the particles - that is, the volume of the particles making up the collection divided by the "bulk volume" defined as the particles and the spacing between the particles.

[0050] A measure of the packing density with respect to the volume of a particle (bulk volume) is the "void fraction" of the particle, which is sometimes referred to as "porosity". Porosity or "void fraction" refers to the relative amount of void spaces (i.e., "air spaces") in the bulk volume of the particle as a percentage of the total bulk volume (particle plus void spaces). Void spaces are calculated as the fraction of the bulk volume of open space divided by the total bulk volume of the body. Alternatively, void spaces (percent) are units (1.00) minus the packing density. A composition having zero percent void spaces (zero percent porosity) is completely solid.

[0051] The multimodal particulate compositions as described may have a desirably high bulk density, which may be a bulk density of at least 55%, 60%, or 62%.

[0052] The multimodal particle composition as described can be used to form a shaped body, including a shaped precursor and a final shaped body formed from the shaped precursor. According to a general method, particles of the multimodal particle composition in powder form can be combined with an optional binder and formed into a shaped precursor by any of a variety of methods, which can include compaction methods, additive manufacturing methods, molding methods, and the like.

[0053] According to the compaction method, a composition containing particles and optionally a binder composition or other additives is placed under pressure to form a shaped precursor. A specific type of compaction method is called "in-line" compression, by which a "raw material" composition containing the particles is formed into a shaped precursor using molding and high pressure. The shaped precursor can then be processed (including by heating) to form a finished shaped body.

[0054] According to various examples, the multimodal particle composition as described (optionally in combination with a binder composition) can be formed into a shaped precursor by any of a variety of different known types of additive manufacturing techniques. Generally speaking, in these methods, the particles are placed in a raw material composition that is formed into a multilayer precursor having a desired shape and containing particles of the multimodal particle composition still in the form of individual particles. The shaped precursor can be further processed in a manner that causes the particles to fuse or melt together to form a finished shaped body, preferably, the finished shaped body has a low porosity as described.

[0055] The multimodal particle compositions as described can be used to form shaped (three-dimensional) precursors by using various known additive manufacturing methods, including methods often referred to as "3-D printing" techniques. Various different additive manufacturing techniques are known. Specific examples are those additive manufacturing methods often referred to as "powder bed", which include various "binder jet printing" techniques. Other examples include stereolithography (SLS) and "feedstock dispenser method" (FDM).

[0056] By using additive manufacturing techniques, a feedstock composition containing a multimodal particle composition can be processed to individually and sequentially form multiple solidified feedstock composition layers (e.g., "paths") containing a multimodal particle composition dispersed in a solidified binder composition. The solidified binder composition acts as a structure that holds the particles of the multimodal particle composition together within the solidified feedstock composition. Using a series of additive manufacturing steps, multiple solidified feedstock layers are sequentially formed into a multilayer composite made of the solidified feedstock layers, and the multilayer composite is an example of a molding precursor.

[0057] In more detail, the additive manufacturing process for forming a shaped precursor in the form of a multilayer composite containing a multimodal particle composition may involve a raw material composition containing a multimodal particle composition and one or more components that are combined to form a binder composition. The binder composition can be combined with the particles as a raw material, and the binder composition can be solidified (hardened, cured, etc.) during the additive manufacturing step to produce a solidified raw material composition, which contains a solidified binder composition that serves as a physical support structure (substrate) for the particles. The relative amount of particles and the binder composition in the raw material composition can be any useful amount, for example, based on the total weight of the raw material or based on the total weight of the particles and the binder in the raw material composition, from 60% by weight to 95% by weight or from 70% by weight to 90% by weight of the particles, and from 5% by weight to 40% by weight or from 10% by weight to 30% by weight of the binder.

[0058] The steps of combining the particles with the binder composition and causing the binder composition to solidify into a layer of the composite may vary according to different types of additive manufacturing techniques, for example, the steps of combining the particles with the binder composition may be different for powder bed techniques and different versions of powder bed techniques compared to stereolithography and feedstock dispersion methods. The ingredients of the binder composition may also be different for different types of additive manufacturing techniques.

[0059] In general, the binder composition may include any material that can solidify as part of the raw material composition or by being added to the raw material layer to selectively form a solidified raw material at a portion of the raw material layer. In general, examples include organic materials such as polymers (e.g., synthetic polymers or natural polymers, one of which may optionally be chemically curable) and inorganic materials such as clay and other inorganic particles, fugitive materials, etc.

[0060] Examples of materials useful as binder compositions or components thereof include polymeric materials that may be thermoplastic or may be irreversibly chemically cured, and non-polymeric inorganic particles (eg, clays) that may be suspended in a liquid and dried to form a solid material by removal of the liquid.

[0061] The polymeric binder may be a thermoplastic polymer that can be reversibly heated to form a liquid and then cooled to form a solid (e.g., can reversibly melt and solidify). Alternatively or in addition, the polymeric binder material may be chemically curable, for example, by exposure to elevated temperatures (thermosetting) or by exposure to electromagnetic radiation, for example, from a laser (e.g., a UV laser).

[0062] Advantageously, a feedstock composition containing a multimodal particle composition as described and added ingredients such as a binder can exhibit a relatively high particle density for a multimodal particle composition because the particles exhibit a high packing density. The high packing density of the multimodal particle composition can efficiently prepare a feedstock composition containing particles and a binder that also has a high concentration of particles, which is referred to as the volume percent of particles in the feedstock. The "volume percent" of particles in a feedstock composition refers to the number (percentage) of the volume of particles in the volume of the feedstock based on the total volume of the feedstock. The same measurement of volume percent can also be applied to shaped precursors formed using the feedstock.

[0063] Exemplary feedstock compositions and shaped precursors made from the feedstock compositions may contain an amount of particles as a percentage by volume of the bulk that is at least 55%, 60%, or 62% based on the total volume of the feedstock composition or shaped precursor.

[0064] The shaped precursor may be further processed by steps ("post-processing") including one or more of a step to remove the binder composition from the body (sometimes referred to as a "debinding" step) and a step to fuse the particles of the precursor together (i.e., a heating or "sintering step"). Optionally, if the feedstock is of a type containing a chemically curable polymer binder, another step may be performed to further harden or "cure" the solidified feedstock by further causing additional curing of the curable polymer binder.

[0065] The debinding step and the sintering step may be performed in a single device (e.g., an oven or furnace), or may be performed in a sequence in which the debinding step is performed in a first device and the subsequent sintering step is performed in a second (different) device. The temperature for the debinding step is lower than the temperature for the sintering step. The temperature for the thermal debinding step may depend on the type of polymer of the binder composition, with examples being in the range of less than 600°C, such as in the range of from 100°C to 550°C or 600°C. The temperature for sintering may be substantially higher than the temperature for the debinding step, such as greater than 550°C or 600°C.

[0066] A useful or preferred degumming step will remove the components of the adhesive composition from the shaped precursor, leaving only the particles. An exemplary degumming step (referred to as a "thermal degumming" step) exposes the shaped precursor to a high temperature sufficient to remove the components of the adhesive composition from the shaped precursor. Alternatively or additionally, depending on the type of adhesive composition, the degumming step may expose the shaped precursor to a chemical solvent that removes the components of the adhesive composition from the multilayer composite, which is referred to as a "chemical degumming" step.

[0067] After the debinding step, the particles of the shaped precursor remain as a substantially residual porous body comprising substantially only the particles. After the debinding step, without a heating or sintering step, the body may be in the form of particles in an unmelted, unsintered state, but self-supporting.

[0068] When the particles of the multimodal particle composition are inorganic (e.g., ceramic or metal), the shaped precursor can be treated by a heating step (e.g., a sintering step). The meaning of the term "sintering" as used herein is consistent with the meaning given to this term in the field of forming sintered bodies. Consistent with this term, the term "sintering" can be used to refer to a process of joining (e.g., "solid state welding" or "melting") a collection of one or more small sinterable particles of different types (size, composition, shape, etc.) together, the process being applied to the particles (i.e., the precursor) in a non-oxidizing environment. Heat is applied so that the particle surfaces reach a temperature that causes the particle surfaces to be fused together by physical (mechanical) bonding between the particle surfaces but does not cause the particles to melt (i.e., the metal material does not reach its melting temperature).

[0069] The sintering step is performed at a temperature that is higher than the sintering point of the inorganic particles of the body but lower than the melting temperature of the particles. As used herein, the "sintering point" of a particle is the temperature of the material that is capable of sintering the particle, i.e., the temperature at which particles of the body adhere to other particles of the body and adjacent particles can melt together. The sintering point of a material (e.g., a metal) is normally lower than the melting temperature of the material, which means the temperature at which the particles become liquid.

[0070] Useful temperatures for performing the sintering step may depend on factors such as the size, shape, and composition of the inorganic particles. Particles of different types, sizes, and shapes may have different sintering points and may require longer sintering cycles or shorter sintering cycles (periods of time maintained at sintering temperatures). Metal particles made of nickel, nickel alloys, stainless steel, and the like may typically have sintering temperatures in the range of from about 550°C to about 1300°C. Ceramic particles made of alumina or zirconium oxide, and the like may typically have sintering temperatures in the range of from about 1600°C to about 2000°C. Particles made of refractory metals or silicon carbide may typically have sintering temperatures in the range of from about 1600°C to about 2100°C.

[0071] Typical sintering cycles may range from 5 minutes to 60 minutes, depending on the particle material, particle size, and particle shape.

[0072] The sintering step can be performed in a furnace or oven and in a non-oxidizing atmosphere that will not react with or otherwise adversely affect the particles of the sintered body (for example, in a vacuum or in an atmosphere of concentrated or pure hydrogen, concentrated or pure inert gas, or a combination of concentrated or pure hydrogen and inert gas).

[0073] For a body made of silicon carbide particles, the additional step may be treating the body to form reaction bonded silicon carbide. Methods of forming reaction bonded silicon carbide are known, an example of which is described in US Patent 8,142,845.

[0074] After post-processing of the shaped precursor has been completed, the body is considered a "finished shaped body." Because the useful multimodal particulate compositions described herein can preferably have a high packing density, the finished shaped bodies prepared from the multimodal particulate compositions as described can have low porosity and high relative apparent density.

[0075] Examples of finished shaped bodies prepared using the multimodal particulate compositions as described can have desirably low porosity, for example, less than 15%, 12%, or 10% porosity.

[0076] "Relative density" is the density of a body compared to the "theoretical" density of a body having zero porosity, i.e., the density of a body divided by the density of the material from which the body is formed. Examples of shaped finished bodies prepared using the multimodal particulate compositions as described may have a relative apparent density of at least 75%, 80%, or 85%.

[0077] The final shaped body prepared as described can be a body having specific characteristics of shape, size, and physical and mechanical properties. Useful examples of shaped final bodies can be bodies that advantageously exhibit low porosity, have physical properties of strength, wear resistance, temperature resistance, and chemical inertness.

[0078] The specific properties of the final shaped body will depend on the material of the body. According to a useful or preferred example, a shaped final body made of silicon carbide can be used as a part requiring high strength, high wear resistance, high temperature resistance, high chemical inertness, good thermal stability and low thermal conductivity.

[0079] Silicon carbide has a wide and varied range of uses because it has a highly useful combination of physical properties. Articles made from silicon carbide are known to exhibit: high hardness (close to the hardness of diamond), low density (similar to the density of aluminum), high melting point, high wear and corrosion resistance, excellent oxidation resistance, strength and stability at high temperatures, stability in varying chemical environments, and good thermal conductivity with low thermal expansion. With a highly useful combination of physical properties, silicon carbide is used to make many articles that require high strength, chemical resistance, wear resistance, and stability at high temperatures. Examples include: high temperature bearings, composite armor (such as bulletproof plates, scanning mirrors, glass, nozzles, high temperature corrosion resistant parts, and electronic equipment parts.

[0080] Exemplary Compositions and Methods

[0081] Aspect 1. A powder composition having a multimodal particle size distribution, the composition comprising: an irregular fine granular particle collection having a fine particle size distribution and an average fine particle diameter (D50 value); and an irregular coarse granular particle collection having a coarse particle size distribution and an average coarse particle diameter (D50 value) in the range from 4 times to 7 times the average fine particle diameter (D50 value).

[0082] Aspect 2. The composition according to aspect 1, wherein: the fine particle size distribution has a standard deviation in the range from 1 to 5; and the coarse particle size distribution has a standard deviation in the range from 1 to 5.

[0083] Aspect 3. The powder composition according to aspect 1 or 2, which has a bulk density of at least 60%.

[0084] Aspect 4. A composition according to any one of Aspects 1 to 3, wherein: the irregular fine particles have an average fine particle diameter (D50 value) in the range of from 1 micron to 30 microns, and the irregular coarse particles have an average coarse particle diameter (D50) in the range of from 30 microns to 200 microns.

[0085] Aspect 5. The composition according to any one of aspects 1 to 4, comprising: from 10 wt% to 50 wt% of irregular fine particles; and from 50 wt% to 90 wt% of irregular coarse particles, based on the total weight of the composition.

[0086] Aspect 6. The composition according to any one of aspects 1 to 5, wherein: the irregular fine particles are selected from metal particles and ceramic particles; and the irregular coarse particles are selected from metal particles and ceramic particles.

[0087] Aspect 7. The composition according to any one of aspects 1 to 6, wherein: the irregular fine particles are composed of silicon carbide particles; and the irregular coarse particles are composed of silicon carbide particles.

[0088] Aspect 8. The composition according to any one of aspects 1 to 7, which consists essentially of the irregular fine particles and the irregular coarse particles.

[0089] Aspect 9. The composition according to any one of aspects 1 to 7, which consists of the irregular fine particles and the irregular coarse particles.

[0090] Aspect 10. The composition according to any one of aspects 1 to 9, wherein the irregular fine particles and the irregular coarse particles are silicon carbide.

[0091] Aspect 11. A method of forming the composition of any one of aspects 1 to 10, the method comprising combining an irregular collection of fine particles with an irregular collection of coarse particles.

[0092] Aspect 12. A raw material composition comprising inorganic particles and a binder composition, the raw material composition comprising:

[0093] Inorganic particles having a multimodal particle size distribution, the inorganic particles comprising:

[0094] an irregular collection of fine particles having a fine particle size distribution and an average fine particle diameter, and

[0095] an irregular coarse particle assembly having a coarse particle size distribution and an average coarse particle diameter in the range from 4 to 7 times the average fine particle diameter; and

[0096] A binder composition is suitable for solidification to form a body including the inorganic particles and the solidified binder composition.

[0097] Aspect 13. The composition of aspect 12, wherein: the fine particle size distribution has a standard deviation in the range from 1 to 5; and the coarse particle size distribution has a standard deviation in the range from 1 to 5.

[0098] Aspect 14. The composition of aspect 12, wherein the inorganic particles have a bulk density of at least 60%.

[0099] Aspect 15. A composition according to any one of Aspects 12 to 14, wherein: the irregular fine particles have an average fine particle diameter (D50 value) in the range of from 1 micron to 30 microns, and the irregular coarse particles have an average coarse particle diameter (D50) in the range of from 30 microns to 200 microns.

[0100] Aspect 16. The composition according to any one of aspects 12 to 15, comprising: from 10 wt% to 50 wt% of irregular fine particles; and from 50 wt% to 90 wt% of irregular coarse particles, based on the total weight of the composition.

[0101] Aspect 17. The composition according to any one of aspects 12 to 16, wherein: the irregular fine particles are selected from metal particles and ceramic particles; and the irregular coarse particles are selected from metal particles and ceramic particles.

[0102] Aspect 18. The composition according to any one of aspects 12 to 16, wherein: the irregular fine particles are composed of silicon carbide particles; and the irregular coarse particles are composed of silicon carbide particles.

[0103] Aspect 19. A composition according to any one of Aspects 12 to 18, comprising: from 10 wt % to 30 wt % of inorganic particles having a multimodal particle size distribution, based on the total weight of the raw material composition; and from 70 wt % to 90 wt % of a binder composition.

[0104] Aspect 20. A method of forming the feedstock composition according to any one of aspects 12 to 19, the method comprising combining: the irregular fine particle assembly; the irregular coarse particle assembly; and the binder composition.

[0105] Aspect 21. A method of forming a shaped body comprising inorganic particles dispersed in a binder composition, the method comprising:

[0106] Using a feedstock composition comprising inorganic particles having a multimodal particle size distribution, the feedstock composition comprising:

[0107] an irregular collection of fine particles having a fine particle size distribution and an average fine particle diameter, and

[0108] an irregular coarse particle assembly having a coarse particle size distribution and an average coarse particle diameter in the range from 4 to 7 times the average fine particle diameter; and

[0109] an adhesive composition; and

[0110] The raw material composition is formed into a molded body including the inorganic particles and the solidified binder composition.

[0111] Aspect 22. The method according to aspect 21, comprising forming the raw material composition into a shaped precursor by an additive manufacturing step.

[0112] Aspect 23. The method according to aspect 21 or 22, wherein the inorganic particles have a bulk density of at least 60%.

[0113] Aspect 24. A method according to any one of Aspects 21 to 23, wherein: the irregular fine particles have an average fine particle diameter (D50 value) in the range of from 1 micron to 30 microns; and the irregular coarse particles have an average coarse particle diameter (D50) in the range of from 30 microns to 200 microns.

[0114] Aspect 25. The method according to any one of aspects 21 to 24, comprising: from 10 wt% to 50 wt% of irregular fine particles; and from 50 wt% to 90 wt% of irregular coarse particles, based on the total weight of the composition.

[0115] Aspect 26. The method according to any one of Aspects 21 to 25, wherein: the irregular fine particles are composed of silicon carbide particles; and the irregular coarse particles are composed of silicon carbide particles.

[0116] Aspect 27. A method according to any one of Aspects 21 to 26, wherein the raw material composition comprises: from 10 wt % to 30 wt % of inorganic particles having a multimodal particle size distribution, based on the total weight of the raw material composition; and from 70 wt % to 90 wt % of a binder composition.

[0117] Aspect 28. A method for forming a low-porosity inorganic sintered body, the method comprising:

[0118] Using a feedstock composition comprising inorganic particles having a multimodal particle size distribution, the feedstock composition comprising:

[0119] A powder composition having a multimodal particle size distribution, the powder composition comprising:

[0120] An irregular fine particle collection having a fine particle size distribution and an average fine particle diameter (D50 value); and

[0121] an irregular coarse particle assembly having a coarse particle size distribution and an average coarse particle diameter (D50 value) in the range from 4 to 7 times the average fine particle diameter, and

[0122] Adhesive composition;

[0123] forming the raw material composition into a shaped precursor including a solidified binder composition and the inorganic particles;

[0124] The molded precursor is heated to a temperature that causes the irregular fine particles and the irregular coarse particles to fuse together to form the inorganic sintered body.

[0125] Aspect 29. The method according to aspect 28, comprising forming the raw material composition into a shaped precursor by an additive manufacturing step.

[0126] Aspect 30. The method according to aspect 28 or 29, wherein the inorganic sintered body has a porosity of less than 5%.

[0127] Aspect 31. The method according to any one of aspects 28 to 30, wherein the inorganic sintered body comprises at least 97 wt % silicon carbide.

[0128] Aspect 32. The method according to any one of aspects 28 to 31, wherein the inorganic sintered body comprises: a chemical mechanical polishing pad conditioner, a cutting tool, a wear-resistant surface, or a heat-resistant surface.

[0129] Aspect 33. The method of any one of aspects 28 to 32, comprising reaction bonding silicon carbide.

[0130] Aspect 34. The method according to any one of aspects 28 to 33, wherein the particulate composition has a bulk density of at least 60%.

[0131] Aspect 35. A method according to any one of Aspects 28 to 34, wherein the raw material composition comprises: from 10 wt % to 30 wt % of inorganic particles having a multimodal particle size distribution, based on the total weight of the raw material composition; and from 70 wt % to 90 wt % of a binder composition.

Claims

1. A raw material composition comprising inorganic particles and a binder composition, wherein the raw material composition include: Inorganic particles having a multimodal particle size distribution, the inorganic particles comprising: an irregular collection of fine particles having a fine particle size distribution and an average fine particle diameter, and an irregular coarse particle assembly having a coarse particle size distribution and an average coarse particle diameter in the range from 4 to 7 times the average fine particle diameter; and The binder composition is suitable for solidification to form a body including the inorganic particles and the solidified binder composition.

2. The composition according to claim 1, in: The fine particle size distribution has a standard deviation in the range from 1 to 5, and The coarse particle size distribution has a standard deviation in the range from 1 to 5.

3. The composition of claim 1, wherein the inorganic particles have a bulk density of at least 60%.

4. The composition according to claim 1, wherein The irregular fine particles have an average fine particle diameter (D50 value) in the range from 1 micrometer to 30 micrometers, and The irregular coarse particles have an average coarse particle diameter (D50) in the range from 30 μm to 200 μm.

5. The composition according to claim 1, include: Based on the total weight of the composition, from 10% to 50% by weight of irregular fine particles, and From 50% to 90% by weight of irregular coarse particles.

6. The composition according to claim 1, wherein The irregular fine particles consist of silicon carbide particles, and The irregular coarse particles consist of silicon carbide particles.

7. The composition according to claim 1, include: Based on the total weight of the raw material composition, from 10 to 30 weight percent inorganic particles having a multimodal particle size distribution, and From 70% to 90% by weight of the adhesive composition.

8. A method for forming a molded body comprising inorganic particles dispersed in a binder composition, the method include: Using a feedstock composition comprising inorganic particles having a multimodal particle size distribution, the feedstock composition comprising: an irregular collection of fine particles having a fine particle size distribution and an average fine particle diameter, and an irregular coarse particle assembly having a coarse particle size distribution and an average coarse particle diameter in the range from 4 to 7 times the average fine particle diameter; and an adhesive composition; and The raw material composition is formed into a molded body including the inorganic particles and the solidified binder composition.

9. The method of claim 8, comprising forming the feedstock composition into a shaped precursor by an additive manufacturing step.

10. The method of claim 8, wherein the inorganic particles have a bulk density of at least 60%.

11. The method according to claim 8, wherein The irregular fine particles have an average fine particle diameter (D50 value) in the range from 1 micrometer to 30 micrometers, and The irregular coarse particles have an average coarse particle diameter (D50) in the range from 30 μm to 200 μm.

12. The method according to claim 8, wherein include: Based on the total weight of the composition, from 10% to 50% by weight of irregular fine particles, and From 50% to 90% by weight of irregular coarse particles.

13. The method according to claim 8, wherein The irregular fine particles consist of silicon carbide particles, and The irregular coarse particles consist of silicon carbide particles.

14. The method according to claim 8, wherein the raw material composition include: Based on the total weight of the raw material composition, from 10 wt % to 30 wt % of inorganic particles having a multimodal particle size distribution, and From 70% to 90% by weight of the adhesive composition.

15. A method for forming a low-porosity inorganic sintered body, the method include: Using a feedstock composition comprising inorganic particles having a multimodal particle size distribution, the feedstock composition comprising: A powder composition having a multimodal particle size distribution, the powder composition comprising: An irregular fine particle collection having a fine particle size distribution and an average fine particle diameter (D50 value); and an irregular coarse particle assembly having a coarse particle size distribution and an average coarse particle diameter (D50 value) in the range from 4 to 7 times the average fine particle diameter, and Adhesive composition; forming the raw material composition into a shaped precursor including a solidified binder composition and the inorganic particles; The molded precursor is heated to a temperature that causes the irregular fine particles and the irregular coarse particles to fuse together to form the inorganic sintered body.

16. The method of claim 15, comprising forming the feedstock composition into a shaped precursor by an additive manufacturing step.

17. The method according to claim 15, wherein the inorganic sintered body has a porosity of less than 5%.

18. The method of any one of claims 15, wherein the inorganic sintered body comprises at least 97 wt% silicon carbide.

19. The method of claim 15, wherein the particulate composition has a bulk density of at least 60%.

20. The method according to claim 15, wherein the raw material composition include: Based on the total weight of the raw material composition, from 10 wt % to 30 wt % of inorganic particles having a multimodal particle size distribution, and From 70% to 90% by weight of the adhesive composition.

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