COMPOUND PARTICLES AND METHOD FOR THEIR PREPARATION

Abstract

A method for producing composite particles, wherein the method comprises mixing first particles that are positively charged in water and second particles that are positively charged in water and have a smaller average particle size than the first particles in an aqueous medium in the presence of ultrafine bubbles, whereby the second particles are deposited onto surfaces of the first particles to produce composite particles.

Description

TECHNICAL FIELD

[0001] The present invention relates to composite particles and a method for producing the composite particles.

[0002] This application claims priority to PCT / JP2022 / 019729, filed on May 9, 2022, the contents of which are hereby incorporated by reference. STATE OF THE ART

[0003] Metal particles with a particle size in the micrometer (µm) range are used as modeling materials for 3D printers. A 3D printer irradiates metal particles with a laser or electron beam, causing the metal particles to temporarily melt and solidify into the desired shape to create a model.

[0004] It is effective to modify the surface state of metal particles to improve the absorption efficiency of laser beams and electron beams, thus reducing the amount of energy required to melt metal particles in 3D printers. Examples of possible methods for modifying the surface state of metal particles include coating the surfaces of metal particles with inorganic fine particles having a particle size in the nanometer (nm) range to increase the surface area. Examples of possible uses of inorganic fine particles include oxide fine particles, which have a higher melting temperature than metal particles. However, metal particles are positively charged in water, and oxide fine particles are also positively charged in water. Therefore, when metal particles and oxide fine particles are mixed in water, both particles repel each other.Accordingly, it is difficult to evenly coat the surfaces of the metal particles in the water with the oxide fine particles.

[0005] Examples of known methods for producing composite particles with nanometer-sized (nm) fine particles deposited on the surface of micrometer-sized (µm) particles include a method in which, after adjusting the surface charges of parent particles (micrometer-sized (µm) particles) and daughter particles (nanometer-sized (nm) fine particles), the parent and daughter particles are mixed in a liquid, thereby combining both particles through electrostatic attraction to form a composite (Patent Document 1). As a method for adjusting the surface charges of the parent and daughter particles, Patent Document 1 describes a method in which the parent and daughter particles are caused to adsorb polyelectrolytes. REFERENCE LISTPATENT DOCUMENT

[0006] Patent document 1: WO 2017 / 099250 A SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0007] The particles to be used as modeling materials for 3D printers desirably do not generate any foreign matter when irradiated with laser beams or the like. Accordingly, it is desirable to use fewer chemical agents, such as polyelectrolytes, to adjust the surface charge when producing composite particles.

[0008] The present invention has been realized in view of the circumstances described above, and an object of the present invention is to provide a method for producing composite particles in which fine particles in the nanometer (nm) order can be deposited on the surfaces of particles in the micrometer (µm) order without using a surface charge adjusting agent such as a polyelectrolyte, and composite particles with less deposition of a surface charge adjusting agent. SOLUTION TO THE PROBLEM

[0009] The inventors have found that by mixing first particles that are positively charged in water and second particles that are positively charged in water and have a smaller average particle size than the first particles in an aqueous medium in the presence of ultrafine bubbles, the second particles can be deposited on the surfaces of the first particles without using an agent such as a polyelectrolyte for adjusting the surface charge, thus completing the present invention.

[0010] Accordingly, the present invention has the following aspects. [1] A method for producing composite particles, the method including mixing first particles that are positively charged in water and second particles that are positively charged in water and have a smaller average particle size than the first particles in an aqueous medium in the presence of ultrafine bubbles, whereby the second particles are deposited on surfaces of the first particles to produce composite particles. [2] The method for producing composite particles according to [1], wherein a ratio of the average particle size of the second particles to the average particle size of the first particles is in a range of 1 / 10000 or more and 1 / 10 or less. [3] The method for producing composite particles according to [1] or [2], wherein the average particle size of the first particles is in a range of 1 µm or more and 1000 µm or less. [4] The method for producing composite particles according to [1] to [3], wherein the average particle size of the second particles is in a range of 1 nm or more and 500 nm or less. [5] Composite particles produced by the production process described in any one of [1] to [4], wherein the second particles are contained in an amount within a range of 0.2 mass% or more and 20 mass% or less based on the total mass of the composite particles, and the first particles have a circularity in a range of 0.8 or more to 0.99 or less. [6] The composite particles according to [5], wherein the second particles are contained in an amount within a range of 0.2 mass% or more and 10 mass% or less based on the total mass of the composite particles. [7] The composite particles according to [5] or [6], where the circularity of the first particles is in a range of 0.85 or more and 0.99 or less. [8] The composite particles according to [5], where the first particles are made of a titanium-aluminium-vanadium alloy and the second particles are made of aluminum oxide or zirconium oxide. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0011] The present invention can provide a method for producing composite particles in which fine particles in the nanometer (nm) range can be deposited on the surfaces of particles in the micrometer (µm) range without using a surface charge adjusting agent such as a polyelectrolyte, and composite particles with little deposition of a surface charge adjusting agent. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a conceptual diagram of a method for producing a composite particle according to an embodiment of the present invention. Fig. Figure 2 is an SEM image of a dry powder obtained in Example 1. Fig. Figure 3 is an SEM image of a dry powder obtained in Example 2. Fig. Figure 4 is an SEM image of a dry powder obtained in Example 3. Fig. Figure 5 is an SEM image of a Ti6Al4V powder used in Examples 1 to 3. Fig. Figure 6 is a STEM image of an L-PBF production part obtained using the composite particles obtained in Example 3. Fig. Figure 7 shows a close-up HRTEM image and a SAED pattern of an L-PBF production part obtained using the composite particles obtained in Example 3. Fig.Figure 8 shows the load versus penetration depth curves of an L-PBF production part obtained using the composite particles obtained in Example 3. Fig. Figure 9 shows the load versus penetration depth curves of an L-PBF production part obtained using a Ti6Al4V powder used in Examples 1 to 3. Fig. 10(a) is a plan view of a powder bed quality evaluation device for additive manufacturing used in an adhesion evaluation test in Example 5, and Fig. 10(b) is a cross-sectional view taken along line bb in Fig. 10(a). Fig. 11(a) is an SEM image of a zirconia / Ti6A14V composite particle before an adhesion evaluation test conducted in Example 5, and Fig. 11(b) is an enlarged SEM image thereof. Fig.12(a) is an SEM image of a zirconium oxide / Ti6Al4V composite particle after the adhesion evaluation test first conducted in Example 5, and Fig. 12(b) is an enlarged SEM image thereof. Fig. 13(a) is an SEM image of a zirconia / Ti6Al4V composite particle after the adhesion evaluation test conducted for the second time in Example 5, and Fig. 13(b) is an enlarged SEM image thereof. Fig. 14(a) is an SEM image of a zirconia / Ti6Al4V composite particle after the adhesion evaluation test conducted for the third time in Example 5, and Fig. 14(b) is an enlarged SEM image thereof. Fig. 15(a) is an SEM image of a zirconia / Ti6Al4V composite particle after the adhesion evaluation test conducted for the fourth time in Example 5, and Fig. 15(b) is an enlarged SEM image thereof. Fig.16(a) is an SEM image of a zirconia / Ti6Al4V composite particle after the adhesion evaluation test conducted for the fifth time in Example 5, and Fig. 16(b) is an enlarged SEM image thereof. Fig. Figure 17 is a graph of nominal stress vs. nominal strain obtained in a tensile test using the zirconia / Ti6Al4V composite particles obtained in Example 6.

[0012] Fig. Figure 18 is a graph of nominal stress vs. nominal strain obtained from a tensile test using free Ti6Al4V particles as a reference example. DESCRIPTION OF THE EMBODIMENT

[0013] Hereinafter, the present embodiments will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to better understand the features of the present invention, the specific parts are enlarged in some cases for convenience, and the dimensional ratios and the like of the components may differ from those of the actual components. Materials, dimensions, and the like exemplified in the following description are only an example, and the present invention is not limited thereto and can be modified and implemented accordingly without departing from the spirit of the present invention.

[0014] Fig. 1 is a conceptual diagram of a method for producing a composite particle according to an embodiment of the present invention.

[0015] As in Fig.1, in the method for producing composite particles of the present embodiment, first particles 1 and second particles 2 are mixed in an ultrafine bubble-containing dispersion liquid 4 containing ultrafine bubbles 3. The ultrafine bubble-containing dispersion liquid 4 can be produced, for example, by using a method of mixing a mixed aqueous dispersion liquid in which the first particles 1 and the second particles 2 are dispersed with water containing ultrafine bubbles 3, or a method of mixing a dispersion liquid of the first particles 1 containing the ultrafine bubbles 3 with a dispersion liquid of the second particles 2 containing the ultrafine bubbles 3.

[0016] The first particles 1 and the second particles 2 are each positively charged in water. In contrast, the ultrafine bubbles 3 are negatively charged in water. The first particles 1 and the second particles 2 dispersed in the dispersion liquid 4 containing ultrafine bubbles are electrically neutralized by the ultrafine bubbles 3. When the first particles 1 and the second particles 2 are electrically neutralized, the first particles 1 and the second particles 2 are attracted to each other by an intermolecular force. As a result, a large number of the second particles 2 are deposited on the surface of the first particle 1, forming a composite particle.

[0017] The first particles 1 have an average particle size, for example, in a range of 0.1 µm or more and 1000 µm or less. The lower limit of the average particle size of the first particles 1 is preferably 5 µm or more, and more preferably 10 µm or more. The upper limit of the average particle size of the first particles 1 is preferably 500 µm or less, and more preferably 100 µm or less. The second particles 2 have an average particle size, for example, in a range of 1 nm or more and 500 nm or less. The lower limit of the average particle size of the second particles 2 is preferably 5 nm or more, and more preferably 10 nm or more. The upper limit of the average particle size of the second particles 2 is preferably 300 nm or less, and more preferably 100 nm or less.The ratio of the average particle size of the second particles 2 to the average particle size of the first particles 1 is, for example, in a range of 1 / 10000 or more and 1 / 10 or less, preferably in a range of 1 / 5000 or more and 1 / 50 or less, and more preferably in a range of 1 / 2000 or more and 1 / 500 or less.

[0018] The average particle sizes of the first particles 1 and the second particles 2 may be an average of particle sizes of 100 particles measured, for example, with an SEM (scanning electron microscope).

[0019] The material of the first particles and the material of the second particles are not particularly limited. The material of the first particles and the material of the second particles may be the same or different. As the materials of the first particles and the second particles, for example, metals, semimetals, oxides, hydroxides, carbonates, carbides, nitrides, and borides can be used. Examples of the metal include Mg, Ca, Sr, Ba, Sc, Y, La, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, W, Al, Zn, Ga, In, Sn, Pb, and Bi, and alloys of these metals.

[0020] Examples of semimetals include Si, Ge, and Sb. Examples of the oxide include magnesium oxide, calcium oxide, iron oxide, titanium oxide, zirconium oxide, zinc oxide, aluminum oxide, and silicon oxide. Examples of the hydroxide include magnesium hydroxide, calcium hydroxide, and aluminum hydroxide. Examples of the carbonate include lithium carbonate, magnesium carbonate, calcium carbonate, and barium carbonate. Examples of the carbide include calcium carbide, silicon carbide, and titanium carbide. Examples of the nitride include silicon nitride and titanium nitride. Examples of the boride include iron boride and titanium boride. As an example of a preferable combination of these materials, one material of the first particles 1 and the second particles 2 is an oxide (particularly magnesium oxide, aluminum oxide, zirconium oxide) and the other material of the first particles 1 and the second particles 2 is a metal (particularly Ti, Fe, Ni, Zr, Al).As an example, a combination may be mentioned in which the first particles 1 are made of a titanium-aluminium-vanadium alloy and the second particles are made of aluminium oxide or zirconium oxide.

[0021] The ultrafine bubbles 3 are also called nanobubbles and refer to fine bubbles with a volume-equivalent diameter of less than 1 µm, as defined in JIS B8741-1:2019 (Fine Bubble Technology - General Principles for Usage and Measurement of Fine Bubbles - Part 1: Terminology). Ultrafine bubble water is a liquid in which, when irradiated with a laser beam, diffuse reflection of the laser beam is observed by the ultrafine bubbles 3. Note that the dispersion liquid 4 containing ultrafine bubbles may contain fine bubbles (microbubbles).

[0022] For example, ultrafine bubble water is pure water in which ultrafine bubbles 3 are generated. Pure water is water without impurities or ultrapure water, even in which only very few impurities are present. Pure water can be used, for example, as pure water, with an electrical conductivity of 1 µS / cm or less. There are no particular restrictions on the type of gas that forms the ultrafine bubbles 3. Examples include air, oxygen, nitrogen, ozone, and carbon dioxide.

[0023] In the present embodiment, the first particles 1 and the second particles 2 are mixed in the ultrafine bubble-containing dispersion liquid 4 containing the ultrafine bubbles 3, whereby the second particles 2 can be deposited on the surfaces of the first particles 1 while suppressing the deformation of the first particles 1 compared to a case where the first particles 1 and the second particles 2 are merely mixed without using the ultrafine bubbles.

[0024] The ultrafine bubble-containing dispersion liquid 4 contains the first particles 1 in an amount, for example, in a range of 0.2 vol% or more to 1.5 vol% or less. The lower limit of the amount of the first particles 1 contained is preferably 0.3 vol% or more, more preferably 0.5 vol% or more. The upper limit of the amount of the first particles 1 contained is preferably 1.2 vol% or less, and more preferably 1.0 vol% or less. The ultrafine bubble-containing dispersion liquid 4 contains the second particles 2 in an amount, for example, in a range of 0.02 vol% or more and 0.3 vol% or less. The lower limit of the amount of the second particles 2 contained is preferably 0.02 vol% or more, and more preferably 0.05 vol% or more. The upper limit of the amount of the second particles 2 contained is preferably 0.20 vol% or less, and more preferably 0.15 vol% or less.The mass ratio of the amount of the second particles 2 contained to the amount of the first particles 1 contained (second particle content / first particle content) is, for example, in a range of 1 / 1000 or more and 1 / 10 or less, preferably in a range of 1 / 500 or more and 1 / 50 or less, and particularly preferably in a range of 1 / 400 or more and 1 / 100 or less.

[0025] The ultrafine bubble-containing dispersion liquid 4 has, for example, a pH value in a range of 6 or more to 8 or less. The ultrafine bubble-containing dispersion liquid 4 has, for example, a zeta potential in a range of -65 mV or higher and -10 mV or lower, and preferably in a range of -60 mV or higher and -10 mV or lower.

[0026] The composite particles generated in the dispersion liquid 4 containing ultrafine bubbles can be collected by a solid-liquid separation process such as decantation or filtration. The collected composite particles are typically subjected to a drying process. Vacuum drying, for example, can be used as the drying process.

[0027] Composite particles obtained by the method for producing composite particles of the present embodiment contain first particles 1 and a plurality of second particles 2 deposited on the surfaces of the first particles 1. The second particles 2 are contained in an amount in a range of 0.2 mass% or more and 20 mass% or less, preferably in a range of 0.2 mass% or more and 10 mass% or less, more preferably in a range of 0.2 mass% or more and 5 mass% or less, and even more preferably in a range of 0.3 mass% or more and 5 mass% or less, based on the total mass of the composite particle.

[0028] The amount of the second particles 2 contained can be calculated, for example, using the following equation. Content of second particle (mass−%) = [(Oxygen content (mass−%) in composite powder − Oxygen content (mass−%) in first particle) / (Atomic mass of oxygen × 2)] × Atomic mass of other particles

[0029] In the composite particles obtained by the method for producing composite particles of the present embodiment, the amount of the second particles 2 deposited on the first particles 1 can be adjusted, for example, so that a mass ratio of the amount of the second particles 2 contained to the amount of the first particles 1 (second particle content / first particle content) is in a range of 1 / 1200 or more and 1 / 12 or less, preferably in a range of 1 / 1100 or more and 1 / 13 or less, and more preferably in a range of 1 / 1000 or more and 1 / 14 or less.

[0030] In the composite particles obtained by the method for producing composite particles of the present embodiment, the first particles 1 have a circularity in a range of 0.8 or more and 0.99 or less, preferably in a range of 0.85 or more and 0.99 or less, more preferably in a range of 0.85 or more and 0.95 or less, and particularly preferably in a range of 0.9 or more and 0.95 or less.

[0031] The circularity of the first particles 1 can be calculated, for example, by determining an average value of the circularities calculated from the particle areas and circumferences determined by image analysis.

[0032] When the circularity of the first particles 1 before mixing is denoted by W1 and the circularity of the first particles 1 after mixing is denoted by W2, the absolute value of the difference between them (W1-W2) is preferably in a range of 0.1 or less, more preferably in a range of 0.05 or less, and even more preferably in a range of 0.03 or less. When the first particles 1 and the second particles 2 are merely mixed without using ultrafine bubbles, as in a known method, the surface of the first particle 1 is deformed to some extent, so that a depression is formed when the second particle 2 is deposited on the first particle 1 and the second particle 2 penetrates into the depression. Therefore, the circularity W2 of the first particles 1 after mixing is smaller than the circularity W1 of the first particles 1 before mixing.In contrast, when the first particles 1 and the second particles 2 are mixed using ultrafine bubbles as in the present embodiment, due to the intermolecular force between the first particle 1 and the second particle 2, the second particles are deposited on the surface of the first particle 1, while the surface of the first particle 1 remains almost undeformed. Accordingly, a decrease in the circularity W2 of the first particles 1 after mixing can be suppressed.

[0033] Composite particles with high purity can be obtained because no components other than the first particles 1, the second particles 2 and the ultrafine bubbles 3 are required in the ultrafine bubble-containing dispersion liquid 4 to be used for producing the composite particles.

[0034] According to the method for producing composite particles of the present embodiment configured as described above, the first particles 1 and the second particles 2 are mixed in the presence of the ultrafine bubbles 3, and thereby composite particles in which the second particles 2 are deposited on the surfaces of the first particles 1 can be obtained.

[0035] In the method for producing composite particles of the present embodiment, the second particles 2 can be more easily deposited uniformly on the surfaces of the first particles 1 when the ratio of the average particle size of the second particles 2 to the average particle size of the first particles 1 is in a range of 1 / 5000 or more and 1 / 10 or less.

[0036] When the average particle size of the first particles 1 is in a range of 1 µm or more and 1000 µm or less and the average particle size of the second particles 2 is in a range of 1 nm or more and 500 nm or less, the resulting composite particles can be used for various applications such as a modeling material for a laser 3D printer, a catalyst, and a ceramic raw material.

[0037] In the present embodiment, the composite particles are produced using the composite particle production method of the present embodiment, and therefore, the second particles 2 are uniformly deposited on the surface of the first particle, and the purity of the composite particles is high. Accordingly, the composite particles can be used for various applications, such as a modeling material for a laser 3D printer, a raw material for powder metallurgy, an optical device, a catalyst, and a ceramic raw material.

[0038] For example, in a composite particle to be used as a modeling material for a laser 3D printer, a metal particle to be used as a modeling material for a laser 3D printer is used as the first particle 1, and an oxide particle with high laser absorption efficiency is used as the second particle 2. This composite particle has unevenness compared to the free first particle 1, which is formed by the second particles 2 deposited on the surface of the first particle 1, and therefore melts and solidifies more easily upon irradiation with a laser beam compared to a single body of the first particle 1. As the first particle 1, examples include Ti6Al4V, MoTiAl, and NiAlCrMo. As the second particle 2, examples include alumina and zirconia.

[0039] For example, in a composite particle used as a catalyst, an inert and chemically stable particle is used as the first particle 1, and a particle with catalytic activity is used as the second particle 2. This composite particle exhibits a higher catalytic activity than the free second particle 2, since the second particles do not form an agglomerate but rather deposit on the surface of the first particle 1.

[0040] For example, in a composite particle to be used as a ceramic raw material, a particle containing a first element as a constituent of a ceramic to be produced is used as the first particle 1, and a particle containing a second element as a constituent of the ceramic to be produced is used as the second particle 2. In this composite particle, the second particles 2 are uniformly deposited on the surfaces of the first particle 1, so that a ceramic produced using this composite particle has a uniform composition. Examples[Example 1]

[0041] To 95 mass parts of ion-exchanged water, 5 mass parts of alumina powder (with a purity of 99.9 mass% and an average particle size of 125 nm) were added, and the mixture was stirred with a stirrer for 1 hour while being cooled in an ice-water bath, followed by ultrasonic dispersion treatment to prepare an aqueous dispersion with an alumina particle concentration of 5 mass%. Similarly, 5 mass parts of Ti6Al4V powder (with a purity of 99.5 mass%, D10: 5.72 µm, D50: 14.06 µm, D90: 22.25 µm) were added to 95 mass parts of ion-exchanged water, and the mixture was stirred with a stirrer for 1 hour while being cooled in an ice-water bath, followed by ultrasonic dispersion treatment to prepare an aqueous dispersion with a Ti6Al4V particle concentration of 5 mass%.The Ti6Al4V powder used was spherical particles produced by an atomization process.

[0042] The aqueous dispersion of alumina particles and the dispersion of Ti6Al4V particles were mixed in a mass ratio of 1:9, and the mixture was stirred with a stirrer for 1 hour while cooling in an ice-water bath to obtain a mixed aqueous dispersion with a solid concentration of 5 mass%. The mixed aqueous dispersion contained 0.63 vol% of alumina and 0.56 vol% of Ti6Al4V. While stirring the resulting mixed aqueous dispersion with a stirrer, ultrafine bubble water (with a zeta potential of -20 mV, available from Nippon Tungsten Co., Ltd.) was added to the mixed aqueous dispersion using a separatory funnel. After the dropwise addition of the ultrafine bubble water was completed, the zeta potential of the mixed aqueous dispersion was -15 mV.It should be noted that the zeta potential of water with ultrafine bubbles was measured using a nanoparticle analyzer (SZ-100, available from HORIBA, Ltd.).

[0043] After the dropwise addition of ultrafine bubble water was completed, the stirrer was stopped, and the mixed aqueous dispersion was filtered to collect the solids. The collected solids were dried under vacuum at a temperature of 298 K to obtain a dry powder. [Example 2]

[0044] A dry powder was obtained in the same manner as in Example 1, except that the concentrations of the alumina particles in the aqueous dispersion and the concentrations of the Ti6Al4V particles in the aqueous dispersion were each changed to 10 mass%. The mixed aqueous dispersion contained the alumina in an amount of 1.2 vol% and Ti6Al4V in an amount of 1.1 vol%. [Example 3]

[0045] A dry powder was obtained in the same manner as in Example 1, except that a zirconia powder (with a purity of 99.9 mass% and an average particle size of 53 nm) was used instead of the alumina powder, and the concentrations of the zirconia particles in the aqueous dispersion and the concentrations of the Ti6Al4V particles in the aqueous dispersion were each changed to 10 mass%. The mixed aqueous dispersion contains 0.38 vol% of zirconia and 1.1 vol% of Ti6Al4V. [Evaluation](1) Surface shape of the particles

[0046] The particle surface of the dry powders obtained in Examples 1 to 3 was observed with a scanning electron microscope. Fig. Figure 2 shows an SEM image of the dry powder obtained in Example 1, Fig. Figure 3 shows an SEM image of the dry powder obtained in Example 2, Fig.Figure 4 shows an SEM image of the dry powder obtained in Example 3 and Fig. Figure 5 shows an SEM image of the Ti6A14V powder used in Examples 1 to 3.

[0047] By comparing the SEM images of Fig. 2 to 4 and the SEM image of Fig. 5, it was confirmed that in Examples 1 to 2, composite particles in which alumina particles are deposited on the surfaces of Ti6Al4V particles were prepared, and that in Example 3, composite particles in which zirconia particles are deposited on the surfaces of Ti6Al4V particles were prepared. (2) Formability by laser

[0048] The zirconia / Ti6Al4V composite particles obtained in Example 3 were melted and solidified by a laser powder bed fusion (L-PBF) process to obtain an L-PBF production part. A Yb:YAG fiber laser source (Wuhan, available from Raycus Fiber Laser Technologies, laser wavelength: 1070 nm, maximum power: 22 W) was used as the laser source. Laser irradiation was carried out in a high-purity argon gas atmosphere under conditions of laser power: 20.6 W and scanning speed: 10 mm s. -1 , a hatching distance of 100 µm and a layer thickness of 25 µm. The molten zirconium oxide / Ti6Al4V composite particles were condensed at a condensation rate of 10 3 up to 10 8 K / s. The L-PBF production part was a rectangular parallelepiped with a width of 4 mm, a length of 4 mm, and a height of 1.4 mm.

[0049] The STEM image of the resulting L-PBF production part is shown in Fig.6, and the HRTEM close-up image and SAED pattern are shown in Fig. 7. From the results of Fig. 6 and Fig. 7 it can be seen that the resulting L-PBF production part has a high solidification rate in the range of 10 3 up to 10 8 K / s has a fine martensite structure. Furthermore, the HRTEM close-up image in Fig. 7, no ceramic phase was detected. This suggests that zirconium oxide was decomposed by irradiation with high-energy lasers and dissolved into α'-Ti. From the element distribution in Fig. 6 shows that due to the thermally dynamic and non-equilibrium properties of L-PBF, zirconium is uniformly distributed throughout the structure without any significant segregation.

[0050] The mechanical strength of the L-PBF production part was measured by indentation testing. Fig.Figure 8 shows the load versus penetration depth curves of an L-PBF production part obtained using zirconia / Ti6Al4V composite particles, and Fig. Figure 9 shows the load versus penetration depth curves of an L-PBF production part obtained using Ti6Al4V particles.

[0051] From the results in Fig. 8 and Fig. 9, it can be seen that the L-PBF production part obtained using the zirconia / Ti6Al4V composite particles has a smaller indentation depth and a higher stiffness than the L-PBF production part obtained using the Ti6Al4V particles under the same load application.

[0052] The Vickers hardness of the L-PBF production part obtained using the zirconia / Ti6Al4V composite particles and the Vickers hardness of the L-PBF production part obtained using the Ti6Al4V particles were measured using a micro Vickers hardness tester (HM200, available from Mitutoyo Corporation). As a result, the Vickers hardness of the L-PBF production part obtained using the zirconia / Ti6Al4V composite particles was 714 HV, and the Vickers hardness was significantly improved compared to the Vickers hardness (519 HV) of the L-PBF production part obtained using the Ti6Al4V composite particles.

[0053] From the above results, it can be seen that the zirconium oxide / Ti6Al4V composite particles obtained in Example 3 are suitable as a modeling material for a laser 3D printer. [Example 4]

[0054] Ultrafine bubble water and pure water were mixed in the amounts shown in Table 1 below to prepare 500 ml of aqueous media Nos. 1 to 5. The ultrafine bubble water used had a zeta potential of -47.1 mV, which was prepared using pure water as the starting material and under conditions of a bubbling time of 10 hours. The Ti6Al4V powder and zirconium oxide powder used were the same as those used in Example 3.

[0055] To each of 500 ml of aqueous medium Nos. 1 to 5, 9 g of Ti6Al4V powder and 1 g of zirconium oxide powder were added. The mixture was then mixed with a stirrer for 20 minutes to prepare a mixed aqueous dispersion. After stirring, the mixed aqueous dispersion was filtered to collect the solid content. The collected solid content was dried under vacuum at a temperature of 298 K to obtain a composite powder. The oxygen content (mass %) of the resulting composite powder was measured using an oxygen / nitrogen / hydrogen elemental analyzer (ONH836, available from LECO Corporation). From the obtained oxygen content and the previously measured oxygen content (0.2334 mass %) of the Ti6Al4V powder, the content of zirconium oxide powder in the composite powder was calculated using the following equation. Zirconium oxide powder content (mass %) = [(Oxygen content (mass %) in the composite powder − Oxygen content (mass %) in the Ti6Al4V powder) / (Atomic mass of oxygen × 2)] × Atomic mass of ZrO2

[0056] Table 1 lists the oxygen content, the increased oxygen amount, and the zirconium oxide powder content of the composite powder. Note that the increased oxygen amount corresponds to the oxygen content obtained by subtracting the oxygen content in the Ti6Al4V powder from the oxygen content in the composite powder. [Table 1] Nr. Composition of the aqueous medium Composition of the composite powder Amount of water with ultrafine bubbles (ml) Amount of pure water (ml) Total amount (ml) Concentration (%) of water with ultrafine bubbles Oxygen content (mass%) Increased amount of oxygen (mass%) Zirconium oxide powder content (mass%) 1 100 400 500 20 2,0150 1,7816 6,8603 2 200 300 500 40 2,1300 1,8966 7,3031 3 300 200 500 60 2,3140 2,0806 8,0116 4 400 100 500 80 2,3498 2,1164 8,1495 5 500 0 500 100 2,3696 2,1362 8,2255

[0057] From the results in Table 1, it can be seen that a larger amount of water with ultrafine bubbles in the aqueous medium increases the zirconia powder content of the composite powder. This is because a larger amount of water with ultrafine bubbles increases the amount of nanometer-sized (nm) zirconia deposited on the surfaces of the micrometer-sized (µm) Ti6Al4V powder and decreases the amount of zirconia released to the outside when the mixed aqueous dispersion is filtered after stirring is completed. [Example 5]

[0058] Except for mixing the aqueous dispersion of zirconia particles and the aqueous dispersion of Ti6Al4V particles in a mass ratio of 5:95, the same procedure as in Example 3 was performed to prepare 100 g of zirconia / Ti6Al4V composite particles. An adhesion evaluation test between the zirconia particles and the Ti6Al4V composite particles in the resulting zirconia / Ti6Al4V composite particles was conducted using a powder bed quality evaluation device for additive manufacturing (PBQ-3, manufactured by TOEI SCIENTIFIC INDUSTRY CO., LTD.).

[0059] Fig. 10(a) is a plan view of a powder bed quality evaluation device for additive manufacturing used in an adhesion evaluation test, and Fig. 10(b) is a cross-sectional view taken along line bb of Fig.10(a). The powder bed quality evaluation device 10 for additive manufacturing includes a device main body 11, a particle supply platform 12, a build platform 13, an overflow particle collection container 14, and a wiper blade 15.

[0060] The particle supply platform 12 and the build platform 13 are arranged side by side on the surface of the device main body 11. The overflow particle collection container 14 is arranged at a position opposite the build platform 13 to the particle supply platform 12.

[0061] The particle feed platform 12 and the build platform 13 each have a quadrangular shape in plan view. The particle feed platform 12 and the build platform 13 are configured to be movable in the vertical direction. The build platform 13 is a flat plate made of nickel-plated steel (surface roughness Ra: 3.87 µm). The wiper blade 15 is configured to be movable along the surface of the device main body 11 from the particle feed platform 12 to the overflow particle collection container 14. The wiper blade 15 is a wiper blade for a laser additive manufacturing device (available from Concept Laser GmbH, Y-shaped lip 120 mm).

[0062] The liability assessment test is carried out as follows. (1) The particle supply platform 12 is moved downward to create a gap 12a between the particle supply platform 12 and the device main body 11. (2) A sample 20 (zirconium oxide / Ti6A14V composite particles) is filled into the gap 12a of the particle feeding platform 12 to smooth the surface. (3) The particle supply platform 12 is moved upward by 60 μm, causing the sample 20 to protrude from the device main body 11 at a height of 60 μm above the device main body 11. The build platform 13 is moved downward by 25 μm to create a gap 13a between the build platform 13 and the device main body 11. (4) The wiper blade 15 is moved from the end of the particle supply platform 12 on the opposite side to the build platform 13 toward the overflow particle collection container 14 at a speed of 75 mm / s. As a result, the sample 20 protruding from the device main body 11 is scraped off, the scraped sample 20 is moved onto the build platform 13, a portion of the sample 20 is spread over the gap 13a of the build platform 13 (reapplied thereto), and the remaining sample 20 is moved into the overflow particle collection container 14. The overflow particle collection container 14 collects the remaining sample 20 that has not been spread over the gap 13a of the build platform 13. (5) The position of the wiper blade 15 is returned to the end of the particle supply platform 12 on the opposite side of the build platform 13. (6) The above-described operations (3) to (5) are continued until the sample 20 filled into the gap 12a of the particle supply platform 12 is used up. (7) A one-gram sample is taken from the sample 20 distributed over the gap 13a of the build platform 13 and the taken sample 20 is examined by SEM.

[0063] The adhesion evaluation test is repeated five times. In the second and subsequent evaluation tests, the particles collected by the overflow particle collection container 14 in the respective previous evaluation test are used as sample 20.

[0064] Fig. 11(a) is an SEM image of the zirconia / Ti6Al4V composite particles before the adhesion evaluation test and Fig. 11(b) is an enlarged SEM image thereof. Fig. 12 to 16(a) are SEM images of the zirconium oxide / Ti6Al4V composite particles after the adhesion evaluation test and Fig. 12 to 16(b) are enlarged SEM images thereof. Fig. 12, Fig. 13, Fig. 14, Fig. 15 and Fig. 16 are SEM images after the first, second, third, fourth and fifth adhesion evaluation tests, respectively.

[0065] From the comparison between the SEM image of Fig. 11 and the SEM images of Fig. 12 to 16, no significant changes in the surface state of the zirconia / Ti6Al4V composite particles were observed before and after the adhesion evaluation test. These results confirmed that the zirconia / Ti6Al4V composite particles produced by the method according to the present invention exhibited high adhesion between the zirconia particles and the Ti6Al4V particles, and that the zirconia particles were less likely to fall off when recoated with the wiper blade 15 (wiper blade for a laser additive manufacturing device). [Example 6]

[0066] Except that the concentrations of the zirconia particles in the aqueous dispersion and the concentrations of the Ti6Al4V particles in the aqueous dispersion were each changed to 1 mass%, the same procedure as in Example 3 was carried out to prepare 100 g of zirconia / Ti6Al4V composite particles. [Example 7]

[0067] Except that the concentrations of the zirconia particles in the aqueous dispersion and the concentrations of the Ti6Al4V particles in the aqueous dispersion were each changed to 5 mass%, the same procedure as in Example 3 was carried out to prepare 100 g of zirconia / Ti6Al4V composite particles. (Measurement of circularity)

[0068] The circularity of the Ti6Al4V particles in the resulting zirconia / Ti6Al4V composite particles was measured. An optical microscope (BX51, available from OLYMPUS Inc.) and analysis software (WinROOF V6.5, available from MITANI SANGYO Co., Ltd.) were used for the circularity measurement. The circularity C of each particle was calculated according to the international standard ISO 9276-6 using the following equation. C=4πA / P2

[0069] Where A is the area of ​​the particle (the number of pixels) and P is the circumference.

[0070] The circularity is an average value of the circularities C calculated from 200 freely chosen particles.

[0071] Note that the circularity of the Ti6Al4V particles in the alumina / Ti6Al4V composite particles obtained in Example 1, the circularity of the Ti6Al4V particles in the zirconia / Ti6Al4V composite particles obtained in Example 3, and the circularity of the free Ti6Al4V particles as a reference example were each calculated using the same method as in Examples 6 and 7. The results are shown in Table 2. [Table 2] Composite particles Concentration of ZrO2 particles in aqueous dispersion (mass%) Concentration of Al2O3 particles in aqueous dispersion (mass%) Concentration of Ti6Al4V particles in aqueous dispersion (mass%) ZrO2 powder content (mass%) Al2O3 powder content (mass%) Circularity of Ti6Al4V particles (-) Example 1 Al2O 3 / Ti-6Al-4V - 5 5 - 4,9 0,92 (± 0,04) Example 6 ZrO 2 / Ti-6Al-4V 1 - 1 0,96 - 0,91 (± 0,05) Example 7 ZrO 2 / Ti-6Al-4V 5 - 5 4,9 - 0,94 (± 0,04) Example 3 ZrO2 / Ti-6Al-4V 10 - 10 8,22 - 0,92 (± 0,04) Reference example Ti-6A1-4V single body - - 0,93 (± 0,04)

[0072] From the results in Table 2, it can be seen that in Example 1, the alumina / Ti6Al4V composite particles have a circularity in the range of 0.88 to 0.96, the difference from the circularity (0.89 to 0.97) of the free Ti6Al4V particles is small, and a decrease in circularity can be suppressed. Similarly, it was confirmed that in Examples 3, 6, and 7, the circularity of the zirconia / Ti6Al4V composite particles is in the range of 0.86 to 0.98, the difference from the circularity of the free Ti6Al4V particles is small, and a decrease in circularity can be suppressed. (Measurement of mechanical strength)

[0073] The zirconium oxide / Ti6Al4V composite particles obtained in Example 6 were used to manufacture an additively manufactured part using a laser 3D powder additive manufacturing (L-PBF) process. An additive manufacturing system (MlabR, available from Concept Laser) equipped with a Yb fiber laser with a wavelength of 1070 nm was used for the production. The manufacturing conditions were a laser power of 95 W and a scanning speed of 800 mm s. -1 , a hatching width of 90 µm, and a lamination thickness of 25 µm. The L-PBF production part was a rectangular parallelepiped with a width of 6 mm, a length of 30 mm, and a height of 6 mm. The L-PBF process was carried out in an argon (Ar) gas atmosphere, and the oxygen concentration was maintained at 0.1 mass percent or less.

[0074] The mechanical strength of the resulting L-PBF production part was measured by a tensile test. A dumbbell-shaped test piece was cut from the L-PBF production part, and this test piece was used to construct a stress-strain diagram. As a reference example, free Ti6Al4V particles were melted and solidified by a laser powder bed fusion process (L-PBF) to obtain an L-PBF production part, and a test piece cut using the same method as described above was used to construct a nominal stress-strain diagram. These results are shown in Fig. 17 and Fig. 18 shown.

[0075] From the results in Fig. 17 showed that when using the zirconia / Ti6Al4V composite particles, the tensile strength was 1210 MPa (±16 MPa), the yield strength was 1397 MPa (±3 MPa), and the elongation was 8.1% (±0.7%). On the other hand, the results of Fig.18 shows that using the individual Ti6Al4V particles, the tensile strength was 1167 MPa (±2 MPa), the yield strength was 1312 MPa (±9 MPa), and the elongation was 6.4% (±0.8%). This confirmed that a compact formed using the zirconia / Ti6Al4V composite particles exhibited excellent values ​​in terms of tensile strength, yield strength, and elongation compared to a compact formed using the free Ti6Al4V particles. List of reference symbols 1 First particles 2 Second particles 3 Ultrafine bubbles 4 Ultrafine bubble-containing dispersion liquid 10 Powder bed quality assessment device for additive manufacturing 11 Main body of the facility 12 Particle feed platform 12a gap 13 Construction platform 13a gap 14 overflow particle collection containers 15 wiper blade 20 samples QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2022 / 019729

[0002] WO 2017 / 099250 A

[0006]

Claims

[1] A method for producing composite particles, the method comprising mixing first particles which are positively charged in water and second particles which are positively charged in water and have a smaller average particle size than the first particles in an aqueous medium in the presence of ultrafine bubbles, whereby the second particles are deposited on surfaces of the first particles to produce composite particles. [2] The method for producing composite particles according to claim 1, wherein a ratio of the average particle size of the second particles to the average particle size of the first particles is in a range of 1 / 10000 or more and 1 / 10 or less. [3] The method for producing composite particles according to claim 1 or 2, wherein the average particle size of the first particles is in a range of 1 µm or more and 1000 µm or less. [4] The method for producing composite particles according to claim 1 or 2, wherein the average particle size of the second particles is in a range of 1 nm or more and 500 nm or less. [5] Composite particles produced by the production method described in claim 1, wherein the second particles are contained in an amount within a range of 0.2 mass% or more and 20 mass% or less based on the total mass of the composite particles, and the first particles have a circularity in a range of 0.8 or more to 0.99 or less. [6] The composite particles according to claim 5, wherein the second particles are contained in an amount within a range of 0.2 mass% or more and 10 mass% or less based on the total mass of the composite particles. [7] Composite particles according to claim 5 or 6, wherein the circularity of the first particles is in a range of 0.85 or more and 0.99 or less. [8] Composite particles according to claim 5, wherein the first particles are made of a titanium-aluminium-vanadium alloy and the second particles are made of aluminum oxide or zirconium oxide.

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