Particle compositions and methods of preparing and using particle compositions

Abstract

Described are nickel particle compositions that contain nickel particles that have a branch-like irregular morphogy, dispersant, and binder, and that are useful as a feedstock composition in additive manufacturing methods; methods for preparing the particle compositions; and methods of using the particle compositions as feedstock to form a porous shaped metal body by an additive manufacturing method.

Description

Attorney Docket No. JE0001020 WOPARTICLE COMPOSITIONS AND METHODS OF PREPARING AND USING PARTICLE COMPOSITIONSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to United States Provisional Application No. 63 / 713,151 filed on October 29, 2024, the contents of which are incorporated hereinFIELD

[0002] Described are nickel particle compositions that contain nickel particles that have a branch-like irregular morphogy, dispersant, and binder, and that are useful as a feedstock composition in additive manufacturing methods; methods for preparing the particle compositions; and methods of using the particle compositions as feedstock to form a porous shaped metal body by an additive manufacturing method.BACKGROUND

[0003] Additive manufacturing processes are known to be useful for forming shaped, three- dimensional bodies from polymeric or inorganic (e.g., metal) materials. As one example, additive manufacturing techniques have been studied for forming porous sintered metal bodies that are useful as filter membranes for filtering fluid materials used in the electronics and semiconductor manufacturing industries. Porous metal filter membranes may be used as in-line filters to remove particulate impurities from a fluid to prevent the particles from being introduced into a manufacturing process. The fluid may be a gas or a liquid.SUMMARY

[0004] Described as follows are nickel particle compositions (also referred to herein as “nickel powder compositions”) that contain aggregate nickel particles made of multiple, e.g., several or many, individual nickel particles of relatively small size (e.g., a nickel particle size of less than 20 or less than 10 microns). The nickel particle compositions contain the aggregate nickel particles in combination with dispersant, and binder, and are useful as feedstock compositions in additive manufacturing processes, particularly binder jet printing processes. As explained herein, the dispersant and binder can be included in a nickel particle composition to improve flow (e.g.,Attorney Docket No. JE0001020 WO rheology) and spreading properties of the nickel particle composition, which can allow the nickel particle composition to be used in binder jet printing processes.

[0005] Also described are processes for preparing the nickel particle compositions, processes of using the nickel particle compositions as feedstock for forming a porous metal (nickel) body by an additive manufacturing method such as binder jet printing techniques, and porous metal (nickel) bodies prepared by these processes.

[0006] Porous metal filters that are made from nickel provide advantages in various filtration applications because of their high corrosion resistance, high temperature tolerance, and high mechanical strength, and have proven to be an effective and practical alternative to other filtration and separation processes.

[0007] Additive manufacturing techniques are useful for preparing three-dimensional metal bodies and are capable of doing so in a generally rapid and efficient manner without the use of a mold or molding or injection equipment. One example of an additive manufacturing technique, known as “binder jet printing,” involves steps of sequentially forming thin, individual layers of a multi-layer three-dimensional body from powder feedstock that is held together by applying binder to the powder feedstock. Using multiple steps, individual layers of solidified feedstock are formed sequentially into a multi-layer composite, each layer being formed separately and in sequence. Steps of forming each individual layer involve forming a feedstock layer on a surface, adding liquid binder to a portion of the feedstock layer, and allowing or causing the liquid binder to solidify. The portion of the feedstock layer that includes the solidified binder becomes a layer of the final three-dimensional printed body.

[0008] Importantly, each individual feedstock layer must be formed as a thin layer of the feedstock that has a uniform thickness across the entire area of the layer, and a uniform distribution of particles across the area of the layer. A feedstock layer is formed on a flat surface by spreading (e.g.. rolling) an amount of feedstock composition over the surface. The feedstock composition must be capable of being evenly and smoothly spread over the surface to form each feedstock layer, without the feedstock layer containing inconsistent distribution of particles within the layer or having a non-uniform thickness across the layer. Furthermore, each individual feedstock layer must be compacted, layer-by-layer, for the binder to properly adhere where applied between feedstock layers, to ensure a three-dimensional printed body is produced without having cracks and with a smooth surface finish and acceptable strength. UniformAttorney Docket No. JE0001020 WO feedstock layers that contain evenly distributed and evenly-compacted particles, and are of a uniform thickness throughout the layer are needed to produce high quality three-dimensional printed bodies by binder jet printing processes.

[0009] Porous filter membranes include membranes of different porosities, including those referred to as “coarse” membranes and those referred to as “fine” membranes. Membranes referred to as “coarse” membranes can be prepared using relatively large individual metal particles (D50 > 20 microns) and may have a porosity up to about 50 or 55 percent. Membranes referred to as “fine” membranes have a higher porosity, e.g., from 55 to 70 percent and are prepared using individual metal particles having smaller individual metal particles. But certain challenges occur when using individual nickel particles having smaller individual nickel particle size, e.g., a mean (D50) diameter below 20 or 10 microns, in binder jet printing processes. Specifically, feedstock composition made with metal particles in this smaller size range can be difficult to apply to a bed of a binder jet printer as a uniform layer of feedstock and are said to have poor or deficient flow and spreading properties.

[0010] As described herein, nickel feedstock compositions are prepared and identified that contain individual nickel particles of a small size, e.g., having a mean (D50) diameter below 20 or 10 microns, and that have flowability and spreading properties that allow the nickel feedstock compositions to be used in a binder jet printing process. The nickel feedstock composition can be used in binder jet printing processes to form porous nickel bodies, including highly porous nickel bodies that have a porosity of at least 55 percent, e.g., a porosity in a range from 55 to 70 percent.

[0011] In one aspect, the disclosure relates to a method of preparing a nickel powder composition. The method includes: providing nickel powder ingredient comprising individual nickel particles having a mean (D50) particle size of less than 20 microns, the individual nickel particles being bonded together as aggregate nickel particles having irregular morphology and a mean aggregate nickel particle size; processing the nickel powder ingredient by milling to produce a milled nickel powder comprising aggregate nickel particles having irregular morphology and a reduced mean aggregate nickel particle size compared to the mean aggregate nickel particle size of the nickel powder ingredient; and combining the milled nickel powder with dispersant and binder to form the nickel powder composition.Attorney Docket No. JE0001020 WO

[0012] In another aspect, the disclosure relates to a feedstock composition useful in an additive manufacturing process. The feedstock composition includes aggregate nickel particles comprising individual nickel particles having a mean (D50) particle size of less than 20 microns, dispersant, and binder.

[0013] In yet another aspect, the disclosure relates to a method of forming a porous sintered body by additive manufacturing. The method includes: providing feedstock according to the present description; forming a layer of the feedstock on a surface; selectively applying liquid polymeric binder to areas of the layer of feedstock; solidifying the liquid polymeric binder to form solidified feedstock; forming a second layer of the feedstock over the layer that contains the solidified feedstock; selectively applying liquid polymeric binder to areas of the second layer of feedstock; and solidifying the liquid polymeric binder applied to the second layer to form solidified feedstock.

[0014] The preceding summary is provided to facilitate an understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole.BRIEF DESCRIPTION OF THE FIGURES

[0015] Figure 1 is a photograph made using a scanning electron microscope, showing examples of aggregate nickel particles that are part of a nickel powder ingredient before the nickel powder ingredient is processed as described herein to form a nickel feedstock composition.

[0016] Figures 2A (5,000 times magnification) and 2B (15,000 times magnification) are photographs made using a scanning electron microscope that show examples of aggregate nickel particles that are part of a nickel powder ingredient before the nickel powder ingredient is processed as described herein to form a nickel feedstock composition.

[0017] Figures 3A (5,000 times magnification) and 3B (15,000 times magnification) are photographs made using a scanning electron microscope that show example aggregate nickel particles of a nickel feedstock composition.Attorney Docket No. JE0001020 WODETAILED DESCRIPTION

[0018] Described as follows are nickel particle compositions (also referred to herein as “nickel powder compositions” or “nickel feedstock compositions”) that contain aggregate nickel particles, dispersant, and binder. The aggregate nickel particles are formed from multiple individual nickel particles that have a mean (D50) particle size that is below 20, 10, or 7 microns. The nickel particle compositions are adapted for use as nickel feedstock compositions for additive manufacturing processes such as binder jet printing.

[0019] The aggregate nickel particles are made from many (e.g., dozens or hundreds of) individual nickel particles of relatively small size. The individual nickel particles may have a mean particle size (D50) of less than 20, 10, or 7 microns. The relatively small, individual nickel particles form the aggregate nickel particles, which have sizes that are significantly larger than the relatively small individual nickel particles. The aggregate nickel particles have an irregular morphology that includes segments of branch-like or chain-like filamentary structures made from the multiple, connected individual nickel particles. This morphology is referred to herein as an “irregular branch-like morphogy.”

[0020] The nickel particle compositions contain the aggregate nickel particles in combination with dispersant and binder. The dispersant and binder are incorporated into the the nickel particle composition using processing steps that, together, improve flow and spreading properties of the nickel particle composition and produce a nickel particle composition that is useful in binder jet printing processes. The processing steps, e.g., milling, wet mixing, or both are effective, with the added dispersant and binder, to modify size and size distribution properties of the aggregate nickel particles in a way that improves flow properties and spreading properties of the nickel particle composition and facilitates the use of the nickel particle compositions in binder jet printing processes.

[0021] Binder jet printing techniques are effective to achieve rapid production of three- dimensional printed bodies without the need for molds. Additionally, binder jet printing techniques are capable of producing porous metal parts (bodies) that can be used in filtering applications, these parts sometimes referred to as “porous filter membranes,” “porous metal filter membranes,” or with a comparable term.

[0022] Porous filter membranes can be prepared to have different porosities. Membranes referred to as “coarse” membranes have a porosity up to about 50 or 55 percent and are normallyAttorney Docket No. JE0001020 WO made using relatively large individual metal particles (D50 > 20 microns). Membranes referred to as “fine” membranes have a higher porosity, e.g., from 55 to 70 percent and are typically made using finer particles, meaning particles having a smaller particle size.

[0023] Feedstock compositions used to prepare coarse porous filter membranes from nickel particles by binder jet printing processes contain spherically-shaped individual nickel particles that have a mean particle size (D50) that is greater than 20 microns. Spherical nickel particles in this size range can be useful to prepare feedstock compositions that exhibit good flow, recoating, and spreading properties, as are required to form feedstock layers for binder jet printing processes, and are, therefore useful for forming coarse porous nickel membranes that have a porosity below 55 percent.

[0024] On the other hand, to prepare a fine porous nickel membrane having a higher porosity, e.g., a porosity of at least 55 percent, individual nickel particles having smaller particle sizes can be preferred, e.g., individual nickel particles having a mean (D50) particle size below 20 or 10 microns. Nickel powder ingredients used as raw materials for various industrial purposes, e.g.. manufacturing, are available in the form of nickel powders made from individual nickel particles having a mean (D50) diameter below 20 or 10 microns.

[0025] But, when these nickel powder ingredients are used (without additional processing or ingredients) as feedstock composition for binder jet printing processes, various challenges exist. When individual nickel particles of these small sizes are collected and formed into a nickel powder ingredient, the relatively small individual nickel particles become bonded together at their surfaces and form aggregate nickel particles. The aggregate nickel particles have an irregular branch-like morphology, a relatively high aggregate nickel particle size, e.g.. D50 > 100 or 150 microns, and a broad particle size distribution. These nickel powder ingredients contain (comprise, consist of, or consist essentially of) the individual nickel particles, including as individual nickel particles and as aggregate nickel particles of different sizes, in the absence of other types of metal particles or chemical materials, e.g., dispersants or polymeric materials such as polymeric binders.

[0026] Exemplary aggregate nickel particles of this type of nickel powder ingredient are shown in Figure 1. The illustrated aggregate nickel particles are formed from several, dozens, or hundreds of connected individual nickel particles that have diameters below 20 microns or below 10 microns, e.g., below 7 microns or 5 microns. The aggregate nickel particles shown in FigureAttorney Docket No. JE0001020 WO1 have an irregular branch-like morphology and include elongate segments that are made of “chains” or “filaments” formed as “strings” of multiple connected individual nickel particles. These segments have a relatively high aspect ratio, e.g., greater than 5 or 10. The aggregate nickel particles may have sizes (“aggregate nickel particle size” or “aggregate nickel particle size”) that well exceed tens or hundreds of microns, e.g., up to or exceeding 100 microns or 150 microns, and may have a mean (D50) aggregate nickel particle size that is greater than 100 or greater than 150 microns. Such nickel powder ingredients may also contain an amount of smaller aggregate nickel particles, e.g., aggregate nickel particles having a size less than 50, 20, 10, or 5 microns, as well as individual nickel particles having a particle size less than 1 micron, which are referred to as particle “fines.” The nickel powder ingredient, with this range of types and sizes of individual nickel particles and aggregate nickel particles, also has a broad particle size distribution.

[0027] Nickel powder ingredients such as these are not capable of being used directly as a nickel feedstock composition of a binder jet printing process. Nickel powder ingredients of this type do not have flow or spreading properties necessary to form the nickel powder ingredient into uniform feedstock layers. The large size and the irregularly-branched morphology of the aggregate nickel particles create significant challenges when attempting to form a feedstock layer from the nickel powder ingredient in original form, without added ingredients or processing to improve flow and spreading properties. The large size and irregular branch-like morphology of the aggregate nickel particles create a lack of smooth flow of the nickel powder ingredient when dispensing the nickel powder ingredient to a printing bed, and unevenness of a feedstock layer in the form of non-uniform thickness, clumping, and non-uniform distribution of the nickel powder ingredient when formed into a feedstock layer by spreading over a surface of the printing bed.

[0028] The present description involves methods of preparing nickel feedstock compositions that contain aggregate nickel particles formed from individual nickel particles that have a relatively low mean (D50) nickel particles size, e.g., a mean nickel particle size of below 20, 10 or 7 microns, e.g., in a range from 3 to 5 microns. The nickel feedstock composition can be formed by modifying a nickel powder ingredient as defined herein to adjust and refine the particle size and particle size distribution of aggregate nickel particles and to add dispersant and binder to the aggregate nickel particles. The combined effects of the adjusted size of the aggregate nickel particles and the presence of dispersant and binder produce a modified nickel powder ingredient,Attorney Docket No. JE0001020 WO i.e., a nickel feedstock composition, that has flow properties that allow the nickel feedstock composition to be used to form uniform feedstock layers when used in binder jet printing processes.

[0029] Thus, according to the present description, a nickel feedstock composition that contains individual nickel particles having a mean (D50) particles size below 20 microns, e.g., below 10, 7, or 5 microns, can be prepared to exhibit flow and spreading properties that allow the nickel feedstock composition to be used in a binder jet printing process. The nickel feedstock composition can be prepared by processing (modifying) a nickel powder ingredient that includes individual nickel particles having a mean (D50) particles size of greater than 20 microns that includes aggregate nickel particles made of the individual nickel particles and having relatively large aggregate nickel particle sizes (such as D50>100. or D50>150 microns), and that does not contain non-metal chemical additives. The nickel powder ingredient may comprise consist of, or consist essentially of the individual nickel particles, including in the form of aggregate nickel particles made up of the individual nickel particles connected by inter-particle forces. The individual nickel particles and the nickel powder ingredient may contain at least 90, 95, or 99 percent nickel.

[0030] To prepare the nickel feedstock composition, the nickel powder ingredient can be processed by steps that refine (e.g., reduce or increase) the size of aggregate nickel particles of the nickel powder ingredient, reduce the size distribution of aggregate nickel particles of the nickel powder ingredient, and combine the nickel powder ingredient with dispersant and binder. The resultant nickel feedstock composition contains aggregate nickel particles derived from the nickel powder ingredient but that have reduced aggregate nickel particle size compared to that of the nickel powder ingredient. The nickel feedstock composition also has a reduced aggregate nickel particle size distribution, and also contains the binder and dispersant. Together, these modifications to the nickel particle ingredient improve flow and spreading properties and produce a resulting nickel feedstock composition that is useful in binder jet printing processes.

[0031] Exemplary steps of processing the nickel powder ingredient include a step of milling the nickel powder ingredient during which large aggregate nickel particles, or clusters of aggregate nickel particles, are broken down to smaller aggregate nickel particles. A milling step, e.g., “impact milling,” is a process of impacting the relatively large aggregate nickel particles of the nickel powder ingredient to crush or fracture the aggregate nickel particles to reduce the size ofAttorney Docket No. JE0001020 WO the aggregate nickel particles. A milling step may be a dry milling process (e.g., impact milling) or a wet milling process and may be performed using known milling techniques and equipment including milling equipment and methods referred to as mechnofusion, cyclomixing, impact milling, ball milling, jet milling, and the like. The effect of milling the nickel powder ingredient is to break down or fracture the aggregate nickel particles, for example by breaking or fracturing elongate segments of the aggregate nickel particles, to produce aggregate nickel particles of smaller aggregate nickel particle sizes. The nickel powder ingredient, after milling, which is referred to as a “milled nickel powder,” contains aggregate nickel particles having reduced aggregate nickel particle sizes compared to the aggregate nickel particles of the nickel powder ingredient. The mean aggregate nickel particle size of the milled nickel powder may be below 150 microns or below 100 microns. An additional effect of milling the nickel powder ingredient may be to reduce the amount of fine nickel particles, meaning nickel particles less than 1 micron in size, which also improves flowability of a resulting nickel feedstock powder.

[0032] The milled nickel powder is further processed to further refine the size and size distribution properties of aggregate nickel particles of the milled nickel powder, while adding dispersant and binder to the milled nickel powder. The dispersant and binder may be added to the milled nickel powder by any useful processing steps that are effective to thoroughly and uniformly combine the dispersant and binder with the aggregate nickel particles, for example by processes known as milling, wet mixing, or the like. The process (milling, wet mixing, or a comparable process) combines the milled nickel powder with liquid (which may be water, organic solvent, or a combination of these) to form a slurry. The slurry may contain approximately equal volumes of the milled nickel powder and the liquid. The slurry is processed in the presence of the dispersant, binder, or both, to uniformly distribute the dispersant, binder, or both throughout the slurry and among the aggregate nickel particles. The dispersant and binder may be combined with the milled nickel powder in a single step, such as by a single milling step. Alternately, dispersant and binder may be combined with the milled nickel powder using two or more separate steps, such as by a first milling or wet mixing step to add dispersant (but not binder) to the aggregate nickel particles, followed by a subsequent milling step to add the binder to the milled nickel powder and dispersant.

[0033] A useful dispersant can be effective to reduce the size of larger aggregate nickel particles and evenly distribute (i.e., “disperse”) the aggregate nickel particles throughout the slurry.Attorney Docket No. JE0001020 WOExemplary dispersants include known and commercially available dispersants that may be of an ionic type (e.g., Dolapix CE64 dispersant), a steric type such as polyvinylpyrrolidone (PVP), or various types of hydrophilic dispersants that are able to interact with liquid (e.g.. water) of the slurry and with a nickel surface of particles of the slurry to cause separation and even distribution of the particles in the slurry. An amount of dispersant added to a milled nickel powder may be any amount that is useful to evenly and uniformly disperse aggregate nickel particles within the slurry, while also causing larger aggregate nickel particles to separate into smaller aggregate nickel particles. Without limiting an amount of dispersant useful in a particular wet mixing or milling step, exemplary amounts of dispersant may be in a range from 0.5 to 1 weight percent dispersant based on total weight of the milled nickel powder.

[0034] Useful binders include organic compounds that are able to effect bonding or attachment between smaller aggregate nickel particles of the slurry to form larger aggregate nickel particles. Preferably, a binder is effective to cause smaller aggregate nickel particles of a slurry to become attached together after the initial milling step to form larger aggregate nickel particles. This effect reduces the amount of aggregate nickel particles of smaller size ranges, which effectively improves flowability properties of the composition. Examples of useful binders include aqueous binders available under the trade name ExOne®, as well as polymeric binders that include polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), and similarly effective polymers. An amount of binder added to a milled nickel powder may be any amount that is useful to produce aggregate nickel particles of a desired size and size distribution within a milled nickel powder. Without limiting an amount of binder useful in a particular wet mixing or wet milling step, exemplary amounts of binder may be in a range from 3 to 13 weight percent dispersant based on total weight of the milled nickel powder.

[0035] According to an exemplary series of steps, the milled nickel powder may be dried if needed, and the dried milled nickel powder may be formed into a slurry (e.g., an aqueous slurry) that also contains the dispersant without the binder for a wet mixing step. The milled nickel powder and the dispersant are mixed by agitation, stirring, or the like (wet mixing), with or without the need for mixing media (mixing balls) in the slurry. Ceramic or non-ceramic mixing balls may be useful mixing media, with nickel-based alloy mixing balls being useful to limit contamination of the milled nickel powder. The effect of the wet mixing step is that the dispersant will cause further separation of larger aggregate nickel particles, forming smallerAttorney Docket No. JE0001020 WO aggregate nickel particles from the larger aggregate nickel particles by separation caused by the dispersant. The slurry will contain relatively smaller aggregate nickel particles, which will be more uniform in size and will have lower aggregate nickel particle size distribution.

[0036] In this exemplary series of steps, the slurry that contains the milled nickel powder with dispersant produced in the wet mixing step can be further processed by another milling step, e.g., a wet milling (e.g., ball milling) step. The slurry produced by the wet mixing step and that contains the dispersant may be dried and a new slurry may be formed by combining the particles of the dried slurry, including dispersant, with liquid that contains the binder. The slurry produced by the wet mixing step may include aggregate nickel particles having a range of aggregate nickel particle sizes, including relatively smaller aggregate nickel particles and relatively larger aggregate nickel particles. By a subsequent wet milling step that adds the binder to the milled nickel powder and dispersant of the wet mixing step, the binder can be effective to cause some of the smaller aggregate nickel particles to be bonded together to form relatively larger aggregate nickel particles to increase mean aggregate nickel particle size.

[0037] Alternately, as opposed to performing a wet mixing step to add dispersant to the milled nickel powder, followed by a wet milling (e.g., ball milling) step to add the binder, a single wet milling step may be performed by combining the milled nickel powder with liquid to form a slurry, adding both the dispersant and the binder to the slurry, and milling (e.g., wet milling, particularly ball milling) the slurry. The effect can be the combined effects of the two separate wet mixing and wet milling (e.g., ball milling) steps, e.g., to modify the size of the aggregate nickel particle, reduce the particle size distribution of the aggregate nickel particles, and disperse the aggregate nickel particles having the adjusted aggregate nickel particle size and aggregate nickel particle size distribution.

[0038] The resultant particles produced by these steps may then be dried by exposure to heat (e.g., a temperature of 150 degrees Celsius) for at least 18 or 24 hours to form a dried powder composition. This dried powder composition may be further processed by a milling step (e.g., ball milling) to reduce the size of the particles of the dried powder. The dried powder after milling may optionally be further processed by a sieving step to remove larger aggregate nickel particles from the milled dried powder. For example, the milled dried powder may be passed through a sieve (e.g., a 140 micron sieve, or another size sieve) to remove larger-sized aggregate nickel particles. The result is to further reduce the size distribution of aggregate nickel particles.Attorney Docket No. JE0001020 WOThe milled dried powder, after sieving, may be processed by an additional drying step to remove a final amount of moisture from the milled dried powder.

[0039] These steps are effective to prepare a nickel feedstock composition (or “nickel powder composition”) that contains aggregate nickel particles that have an irregular branch-like morphology, and that are made of individual nickel particles that have a relatively low mean particle size, e.g., a mean nickel particle size of below 20, 10, 7. or 5 microns, e.g., having a mean (D50) individual nickel particles size in a range from 3 to 5 microns. The nickel feedstock composition may also, preferably, have a mean aggregate nickel particle size that is less than 150 microns, e.g., less than 100 microns.

[0040] Figures 2 A (5,000 times magnification) and 2B (15,000 times magnification) are photographs made using a scanning electron microscope that show examples of aggregate nickel particles that are part of a nickel powder ingredient before the nickel powder ingredient is processed as described herein to form a nickel feedstock composition.

[0041] Figures 3A (5,000 times magnification) and 3B (15,000 times magnification) are photographs made using a scanning electron microscope that show example aggregate nickel particles of a nickel feedstock composition as described, formed by processing a nickel powder ingredient as described herein.

[0042] The nickel feedstock composition has flow properties that allow the nickel feedstock composition to be used in a binder jet printing process. The nickel feedstock compositions have flow and spreading properties that allow the nickel feedstock composition to be smoothly delivered onto a surface of a binder jet printing apparatus, and thereafter spread over the surface to form a feedstock layer having a uniform distribution of the nickel feedstock composition, including uniform thickness.

[0043] The flowability of the nickel feedstock composition is reflected in measured properties of a feedstock composition referred to “total energy” or “basic flow energy” (BFE) of the nickel feedstock composition, and flow rate index (FRI). These properties are well-understood objective properties of powders and can be measured using equipment such as an FT4 Powder Rheometer® available commercially from Freeman Technology, Ltd., UK.

[0044] Examples of useful nickel feedstock compositions that contain aggregate nickel particles as described can have a basic flow energy and a flow rate index that are comparable to typical flowing powders, including powders used as feedstock compositions for binder jet printingAttorney Docket No. JE0001020 WO processes. Exemplary nickel feedstock compositions may have a basic flow energy of 180 + / - 11.4 mJ. Exemplary nickel feedstock compositions may also have a positive flow rate index, e.g.. a flow rate index of 1.9 + / - 0.12.

[0045] A nickel feedstock composition as described can be used in additive manufacturing processes (i.e., “three-dimensional printing” methods) to form a shaped body that can be further processed to form a porous sintered body, such as a porous sintered nickel membrane that is useful as a nickel filter membrane. Useful additive manufacturing methods involve multiple steps that sequentially form individual layers of solidified feedstock composition (“solidified feedstock”) that contain aggregate nickel particles. Using a series of additive steps, multiple layers of solidified feedstock are formed into a multi-layer composite, each layer being formed separately and in sequence.

[0046] The multi-layer composite contains aggregate nickel particles dispersed and held in place together by polymeric binder, which is selectively applied to the feedstock and thereafter solidified. Polymeric binder may be a thermoplastic polymer that may be reversibly heated to form a liquid and then cooled to form a solid (e.g., may be reversibly melted and solidified). Alternately or additionally, a polymeric binder may be chemically curable, for example by exposure to elevated temperature (thermosetting) or by exposure to electromagnetic radiation such as from a laser, e.g., a UV laser.

[0047] In exemplary methods, the nickel feedstock composition may be used in binder jet printing processes. The technique referred to as binder jet printing (also known as “Powder bed and inkjet” printing, “binder jet 3D printing,” and “Drop-On-Powder printing,” and the like), like other additive manufacturing techniques, is a method for making three-dimensional objects described by digital data such as a CAD (computer-aided design) file. Also like other additive manufacturing processes, the three-dimensional body is sequentially built up by a series of individual steps that combine to produce a shaped body in the form of a multi-layer composite made of many thin cross sectional layers. A print head (or other liquid dispensing mechanism) moves across a layer of feedstock, which according to the present description contains aggregate nickel particles. The print head selectively deposits liquid polymer (“binder,” herein) at portions of the top surface of the feedstock layer. The liquid polymer flows into the feedstock layer and is cooled, dried, or otherwise solidified to form solidified feedstock at those portions of the layer. The solidified feedstock contains the aggregate nickel particles and solidifies polymeric binder.Attorney Docket No. JE0001020 WOMultiple feedstock layers are deposited, successively, one over each completed layer, to form the multi-layer composite.

[0048] As needed, the multi-layer composite can be further processed to remove polymeric materials and also to cause the nickel particles to become bonded together to form a porous sintered nickel body. The polymeric materials may be removed by solvent or by heat. The nickel particles can become bonded together by heat, e.g., by sintering.

[0049] The term “sintering” as used herein has a meaning that is consistent with the meaning that this term is given when used in the arts of porous sintered metal bodies, such as porous sintered metal membranes of the type that may be used as a metal filter membrane. Consistent therewith, the term “sintering” can be used to refer to processes of bonding (e.g., “solid state welding” or “fusing”) together a collection of small, sinterable particles of one or more different types (sizes, compositions, shapes, etc.) by applying heat to the particles in a non-oxidizing environment so that surfaces of the particles reach a temperature that causes the particle surfaces to become fused together by a physical (mechanical) bond between the particle surfaces, but that does not cause the particles to melt (i.e., none of the metal materials reaches its melting temperature).

[0050] A sintering step can be performed at a temperature that is above the sintering point of metal particles but below the melting temperature of the metal particles. As used herein, a “sintering point” of a particle is a temperature at which the material of the particle is capable of being sintered, i.e., a temperature at which the particles begin adhering to other particles of the body being sintered, and can be fused to another particle, e.g., at a particular pressure such as at atmospheric pressure. A sintering point of a metal particle is normally below a melting temperature of the metal particle, meaning the temperature at which the metal particle becomes liquid.

[0051] Useful temperatures for performing a sintering step can depend on the composition of the metal particles and the sintering point of the metal particles, as well as the size of the metal particles being sintered, e.g., whether the particles are “coarse” (larger) or fine (smaller). For nickel particles, a sintering step may be performed at a temperature in a range from 550 to 800 degrees Celsius. The sintering step can be performed in a furnace or oven and in a non-oxidizing atmosphere that will not react with or otherwise detrimentally affect the metal particles beingAttorney Docket No. JE0001020 WO sintered, e.g., 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.

[0052] A porous sintered body prepared as described, using aggregate nickel particles, may highly porous, e.g., have a porosity in a range from 55 to 70 percent.Example and Comparative Feedstock Compositions

[0053] Highly cohesive powders, such as powders with small particle sizes in the range of 3pm to 5pm, tend to have high inter-particulate forces compared to the gravitational force on each particle. This causes the powder to agglomerate easily, with large amount of air trapped within the powder bulk. Hence, the powder with branch-like morphology has to be broken up and modified to suitable for BJP process.

[0054] Several powder preparation methods were explored to improve the powder flow. It was observed that an initial crushing process improves flowability in comparison to raw nickel powder ingredient. Impact milling (crushing) was performed using the Netzsch Condux® 60 impact mill at a frequency of 400 Hz. The purpose of the crushing was to break the long branches of filamentary Ni powder into smaller pieces / chains / filaments, essentially reducing the irregular branch-like morphology of the powder. In addition, the crushing process was observed to reduce fine Ni particles typically in less than 1pm range, presumably filtered away during the process. Both these factors contributed positively to improve the flow of the feedstock.Table 1. Example Nickel Powder FeedstocksAttorney Docket No. JE0001020 WO* Dolapix CE64 is polymeric additive to provide dispersion and stabilization of solid particles in water-based suspensions.

[0055] With impact milling alone (Feedstock B in Table 1), the feedstock was able to be dispensed and subsequently spread on a powder bed. However, the high interlocking forces between the powder particles resulted in the cracking of the powder bed, indicating inadequate particle separation. To overcome this challenge, a wet mixing process was introduced, where the milled feedstock was mixed with a Dolapix CE64 dispersant (and water) and then dried (Feedstock C in Table 1). The aim of this process was to break the agglomerated particles, promote an even distribution of the feedstock, and improve mixing homogeneity. This step improved the flowability and quality of the feedstock.

[0056] For further enhancement, aqueous binder was added into the feedstock preparation to serve two purposes. Firstly, the binder functioned to agglomerate the dispersed powder particles into larger clusters, thereby enhancing the flowability of the feedstock. Secondly, the binder also acted as a space holder within the feedstock, resulting in a slight increase in the open porosity of sintered parts prepared from the feedstock (Feedstock D in Table 1). However, the loose powder is difficult to remove during the depowdering stage when 13% binder is added, as the loose powder particles around the printed parts also became hardened during a curing stage. An alternate feedstock preparation included a reduced amount of aqueous binder added into the feedstock to 5% (Feedstock E in Table 1). Feedstock E was used to fabricate highly porous diskshaped and cup-shaped nickel membranes. Feedstock E, with improved flowability, provided aAttorney Docket No. JE0001020 WO good quality powder bed allowing the printing of complex designs and subsequently good surface finishing to the printed parts.ASPECTS

[0057] In a first aspect, the disclosure provides a method of preparing a nickel powder composition, the method comprising: providing a nickel powder ingredient comprising individual nickel particles having a mean (D50) particle size of less than 20 microns, the individual nickel particles being bonded together as aggregate nickel particles having an irregular morphology and a mean aggregate nickel particle size; processing the nickel powder ingredient by milling to produce a milled nickel powder comprising aggregate nickel particles having an irregular morphology and a reduced mean aggregate nickel particle size compared to the mean aggregate nickel particle size of the nickel powder ingredient; and combining the milled nickel powder with a dispersant and a binder to form the nickel powder composition.

[0058] In a second aspect, the method of the first aspect further comprises forming a slurry that comprises the milled nickel powder, dispersant, and binder, and wet milling the slurry.

[0059] In a third aspect, according to the second aspect, the slurry comprises from 0.5 to 1 weight percent dispersant and from 3 to 13 weight percent binder, based on the total weight of the milled nickel powder.

[0060] In a fourth aspect, the method of the third aspect comprises wet milling the slurry to increase a mean (D50) aggregate nickel particle size in the slurry to a mean aggregate nickel particle size in a range from 20 to 100 microns.

[0061] In a fifth aspect, according to any of the preceding aspects, the dispersant comprises an ionic dispersant, a steric dispersant, or a hydrophilic dispersant.

[0062] In a sixth aspect, according to any of the preceding aspects, the binder comprises polyethylene glycol or polyvinylpyrrolidone.

[0063] In a seventh aspect, the method of the fourth aspect further comprises, after wet milling, drying the slurry to form a dried powder composition, milling the dried powder composition, and passing the milled dried powder composition through a sieve.

[0064] In an eighth aspect, according to the seventh aspect, the resulting nickel composition has a basic flow energy of 180.0 ± 11.4 mJ and a flow rate index that is a positive value in a range of 1.90 + 0.12.Attorney Docket No. JE0001020 WO

[0065] In a ninth aspect, the disclosure provides a feedstock composition useful in an additive manufacturing process, the feedstock composition comprising: aggregate nickel particles comprising individual nickel particles having a mean (D50) particle size of less than 20 microns; a dispersant; and a binder.

[0066] In a tenth aspect, according to the ninth aspect, the aggregate nickel particles have a mean (D50) aggregate nickel particle size in a range from 20 to 100 microns.

[0067] In an eleventh aspect, according to either of the ninth or tenth aspects, the dispersant comprises an ionic dispersant, a steric dispersant, or a hydrophilic dispersant.

[0068] In a twelfth aspect, according to any of the ninth through eleventh aspects, the binder comprises polyethylene glycol or polyvinylpyrrolidone.

[0069] In a thirteenth aspect, according to any of the ninth through twelfth aspects, the feedstock composition has a basic flow energy of 180.0 ± 11.4 mJ and a flow rate index that is a positive value in a range of 1.90 ± 0.12.

[0070] In a fourteenth aspect, the disclosure provides a method of forming a porous sintered body by additive manufacturing, the method comprising: providing a feedstock according to any of the ninth through thirteenth aspects; forming a layer of the feedstock on a surface; selectively applying a liquid polymeric binder to areas of the layer of feedstock; solidifying the liquid polymeric binder to form solidified feedstock; forming a second layer of the feedstock over the layer that contains the solidified feedstock; selectively applying liquid polymeric binder to areas of the second layer of feedstock; and solidifying the liquid polymeric binder applied to the second layer to form solidified feedstock.

[0071] In a fifteenth aspect, the method of the fourteenth aspect comprises forming a multi-layer composite comprising the solidified feedstock.

[0072] In a sixteenth aspect, the method of the fifteenth aspect further comprises sintering the multi-layer composite to form a porous sintered body.

[0073] In a seventeenth aspect, according to the sixteenth aspect, the porous sintered body has a porosity in a range from 55 to 70 percent.

[0074] Having thus described several illustrative embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the disclosure covered by this document have been set forth in the foregoing description. It will be understood, however, thatAttorney Docket No. JE0001020 WO this disclosure is, in many respect, only illustrative. The disclosure’s scope is, of course, defined in the language in which the appended claims are expressed.

Claims

Attorney Docket No. JE0001020 WOClaims:

1. A method of preparing a nickel powder composition, the method comprising: obtaining a nickel powder ingredient comprising individual nickel particles having a mean (D50) particle size of less than 20 microns, the individual nickel particles being bonded together as aggregate nickel particles having irregular morphology and a mean aggregate nickel particle size, processing the nickel powder ingredient by milling to produce a milled nickel powder comprising aggregate nickel particles having an irregular morphology and a reduced mean aggregate nickel particle size compared to the mean aggregate nickel particle size of the nickel powder ingredient, and combining the milled nickel powder with dispersant and binder to form the nickel powder composition.

2. The method of claim 1, comprising forming a slurry that comprises the milled nickel powder, dispersant, and binder, and wet milling the slurry.

3. The method of claim 2, wherein the slurry comprises: from 0.5 to 1 weight percent dispersant, and from 3 to 13 weight percent binder, based on total weight milled nickel powder.

4. The method of claim 3, comprising wet milling the slurry to effect a mean (D50) aggregate nickel particle size in the slurry to a mean aggregate nickel particle size in a range from 20 to 100 microns.

5. The method of claim 1, wherein the dispersant comprises an ionic dispersant, a steric dispersant, or a hydrophilic dispersant.

6. The method of claim 1, wherein the binder comprises polyethylene glycol or polyvinylpyrrolidone.Attorney Docket No. JE0001020 WO7. The method of claim 4, comprising, after wet milling, drying the slurry to form a dried powder composition, milling the dried powder composition, and passing the milled dried powder composition through a sieve.

8. The method of claim 7, the nickel composition having a basic flow energy of 180.0 ± 11.4 mJ and a flow rate index that is a positive value in range of 1.90 ± 0.12.

9. A feedstock composition useful in an additive manufacturing process, the feedstock composition comprising: aggregate nickel particles comprising individual nickel particles having a mean (D50) particle size of less than 20 microns, dispersant, and binder.

10. The feedstock of claim 9, the aggregate nickel particles having a mean (D50) aggregate nickel particle size in a range from 20 to 100 microns.

11. The feedstock of claim 9, wherein the dispersant comprises an ionic dispersant, a steric dispersant, or a hydrophilic dispersant.

12. The feedstock of claim 9, wherein the binder comprises polyethylene glycol or polyvinylpyrrolidone.

13. The feedstock of claim 9. having a basic flow energy of 180.0 ± 11.4 mJ and a flow rate index that is a positive value in range of 1.90 + 0.12.

14. A method of forming a porous sintered body by additive manufacturing, the method comprising: providing feedstock according to claim 9, forming a layer of the feedstock on a surface;Attorney Docket No. JE0001020 WO selectively applying liquid polymeric binder to areas of the layer of feedstock, solidifying the liquid polymeric binder to form solidified feedstock, forming a second layer of the feedstock over the layer that contains the solidified feedstock, selectively applying liquid polymeric binder to areas of the second layer of feedstock, and solidifying the liquid polymeric binder applied to the second layer to form solidified feedstock.

15. The method of claim 14, comprising forming a multi-layer composite comprising the solidified feedstock.

16. The method of claim 15, comprising sintering the multi-layer composite to form a porous sintered body.

17. The method of claim 16, wherein the porous sintered body has a porosity in a range from 55 to 70 percent.

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