A method for preparing spherical micron metal particles

Abstract

The present invention provides a method for preparing spherical micron metal particles, which belongs to the field of metal 3D printing. The present invention mixes the oxide mixture of alloy elements in the micron metal particles to be prepared with carbon powder and a dispersion medium, and then sequentially performs carbon thermal reduction, decarburization under the action of ZnO, and then performs spheroidization treatment to prepare micron metal particles that meet the requirements of 3D printing. The results of the examples show that the preparation method provided by the present invention can obtain micron metal particles with a composition that meets the requirements, a small size, and good fluidity, wherein the particle size (D 90 ) is 51-76 μm, and the fluidity is 18-21 s / 50 g, which can meet the stringent requirements of 3D printing for the characteristics of micron metal particles.

Description

Technical Field

[0001] The present invention belongs to the field of metal 3D printing, and in particular relates to a method for preparing spherical micron metal particles. Background Art

[0002] 3D printing, also known as additive manufacturing, is a technology that uses digital model files as a foundation to construct objects layer by layer using bondable materials such as granular metal or plastic. 3D printing requires no molds, boasts short production cycles, and high raw material utilization. Hailed as the "third industrial revolution," 3D printing is widely used in industries such as aerospace, military, healthcare, and automotive. Currently, metal 3D printing technology has begun to progress from research and development to industrialization. However, the performance and price of micronized metal granule consumables remain a key bottleneck hindering the rapid and healthy development of the 3D printing industry.

[0003] Micron metal particles are a key material for 3D printing, and their performance largely determines the quality of the finished 3D-printed product. Spherical or near-spherical micron metal particles have excellent fluidity, are less likely to clog the powder supply system during printing, and can be laid down in thin layers, thereby improving the dimensional accuracy, surface quality, density, and structural uniformity of 3D-printed parts. The smaller the particle size and the greater the specific surface area, the more conducive it is to smooth sintering. Furthermore, the small gaps between tiny micron metal particles create a tight connection between adjacent powder layers, which helps improve sintering density and strength. Therefore, spherical, fine micron metal particles are the preferred raw material for metal 3D printing technology.

[0004] The performance of micron metal particles mainly depends on their preparation method. There are three methods for preparing micron metal particles: mechanical method, reduction method, electrolysis method, atomization method, etc. The micron metal particles prepared by mechanical method, reduction method, and electrolysis method have irregular morphology and basically cannot be used directly for 3D printing. At present, the micron metal particle consumables used in 3D printing are mainly prepared by aerosolization method, but the micron metal particles prepared by aerosolization also have a series of unavoidable problems, such as high production cost, low fine powder yield, the presence of hollow powder and satellite powder, etc. Among them, the yield of fine powder (less than 53μm) that meets the requirements of 3D printing is generally less than 30%. If you want to improve the fine powder yield, you need to significantly increase the atomization pressure, which will cause a sharp increase in production costs and seriously hinder the rapid development and application of metal 3D printing. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing spherical micron metal particles. The preparation method of the present invention is low-cost, and the prepared spherical metal particles have a spherical / near-spherical morphology and a small size, meeting the stringent requirements of 3D printing for the characteristics of micron metal particles.

[0006] The present invention provides a method for preparing spherical micron metal particles, comprising the following steps:

[0007] According to the elemental composition of the spherical micron metal particles to be prepared, oxides of the corresponding elements are mixed with carbon powder and a dispersion medium and then ground to obtain an oxide mixed powder; the oxides of the corresponding elements do not include carbon oxides; and the dispersion medium is an alkaline earth metal oxide mixture;

[0008] Carbothermal reduction of the oxide mixed powder to obtain a reduction product;

[0009] The reduction product is mixed with ZnO and then subjected to vacuum decarburization and spheroidization in sequence to obtain a slag-gold mixture; the slag-gold mixture comprises alkaline earth metal oxide mixture slag, spherical micron metal particles and residual ZnO; the spheroidization temperature is 5 to 300° C. higher than the solidus temperature of the micron metal particles; and the spheroidization time is 10 to 200 minutes;

[0010] performing slag-gold separation and acid leaching on the slag-gold mixture to remove the alkaline earth metal oxide mixture slag and residual ZnO in the slag-gold mixture to obtain the spherical micron metal particles;

[0011] The melting point of the alkaline earth metal oxide mixture is higher than the temperature of the carbothermal reduction, the temperature of the vacuum decarburization treatment, and the temperature of the spheroidization treatment.

[0012] Preferably, the mass of the carbon powder is (0.9-1.0)×M H ×(0.75w O +0.02), where M H is the total mass of all oxides of the corresponding elements, w O is the mass fraction of oxygen in the oxides of all corresponding elements.

[0013] Preferably, the mass of the alkaline earth metal oxide mixture is (1-5)×M H ×(1-w O ), where M H is the total mass of all oxides of the corresponding elements, w O is the mass fraction of oxygen in the oxides of all corresponding elements; in terms of mass percentage, the alkaline earth metal oxide mixture comprises 0-90% MgO and the balance CaO.

[0014] Preferably, the particle size of the oxide mixed powder is less than 10 μm.

[0015] Preferably, the carbothermal reduction includes a first carbothermal reduction and a second carbothermal reduction;

[0016] The temperature of the first carbon thermal reduction is 900-1095° C., and the holding time is 0-30 minutes; the temperature of the second carbon thermal reduction is 1100-1500° C., and the holding time is 20-60 minutes.

[0017] Preferably, the first carbothermal reduction is carried out in a reducing atmosphere; the second carbothermal reduction is carried out under vacuum conditions; and the gas phase pressure under the vacuum conditions is less than 100 Pa.

[0018] Preferably, the mass of the ZnO is (1-1.5)×6.75×M H ×(1-w O )×(w C1 -w C2 ), where M H is the total mass of all oxides of the corresponding elements, w O is the mass fraction of oxygen in the oxides of all corresponding elements; w C1 is the mass fraction of carbon in the micron metal particles contained in the reduction product, w C2 is the mass fraction of carbon element in the spherical micron metal particles to be prepared.

[0019] Preferably, the temperature of the vacuum decarburization treatment is 1100-1300° C., the pressure is less than 1 Pa, and the time is 20-180 min.

[0020] Preferably, the acid leaching solution used in the acid leaching is a nitric acid solution; the pH value of the acid leaching solution is 4-7.

[0021] Preferably, the slag-gold separation includes one or two of magnetic separation, flotation and heavy liquid separation.

[0022] The present invention provides a method for preparing spherical micron metal particles, comprising the following steps: according to the elemental composition of the spherical micron metal particles to be prepared, mixing oxides of corresponding elements with carbon powder and a dispersion medium, and then grinding the mixture to obtain an oxide mixed powder; the oxides of the corresponding elements do not include carbon oxides; the dispersion medium is an alkaline earth metal oxide mixture; performing carbothermal reduction on the oxide mixed powder to obtain a reduction product; mixing the reduction product with ZnO, and then performing vacuum decarburization and spheroidization in sequence to obtain a slag-metal mixture; the slag-metal mixture comprises alkaline earth metal oxide mixture slag, spherical micron metal particles and residual ZnO; the spheroidization temperature is 5 to 300° C. higher than the solidus temperature of the micron metal particles; the spheroidization time is 10 to 200 minutes; performing slag-metal separation on the slag-metal mixture and acid leaching to remove the alkaline earth metal oxide mixture slag and residual ZnO in the slag-metal mixture to obtain the spherical micron metal particles; the melting point of the alkaline earth metal oxide mixture is higher than the carbothermal reduction temperature, the vacuum decarburization temperature and the spheroidization temperature.

[0023] Liquid metal particles spontaneously spheroidize under the influence of surface tension, reducing surface area and, consequently, Gibbs free energy. The present invention utilizes carbothermal reduction of alloy oxides. During the reduction process, carbon diffuses into the resulting metal particles, significantly lowering their melting point and facilitating spheroidization. Furthermore, the melting point of the alkaline earth metal oxide mixture is higher than the temperature of the carbothermal reduction, the vacuum decarburization treatment, and the spheroidization treatment. This prevents the alkaline earth metal oxide mixture from melting during the reduction, decarburization, and spheroidization processes, preventing the liquid metal particles from flowing within the solid matrix. This inhibits rapid collision and growth, and simultaneously refines the micronized metal particles while spheroidizing them. During the decarburization stage, the present invention utilizes ZnO, resulting in a completely gaseous decarburization product, effectively preventing the generation of large quantities of irregular metal particles during the decarburization process. After decarburization, the present invention further spheroidizes the metal particles by adjusting the spheroidization temperature to liquefy them. The preparation method of the present invention is simple and safe to operate, enabling rapid, large-scale production of micronized metal particles at a low cost. The results of the examples show that the particle size of the metal particles prepared by the present invention (D 90 ) is 51-76 μm, and the fluidity is 18-21 s / 50 g.

[0024] Furthermore, the present invention further refines the metal particles by controlling the amount of alkaline earth metal oxide mixture added; the present invention can ensure that the alloy oxides are evenly distributed in the alkaline earth metal oxide mixture by controlling the particle size of the oxide mixed powder, which not only improves the composition uniformity of the micron metal particles to be prepared, but also further refines the metal particles.

[0025] Furthermore, the present invention employs a low-temperature reduction (i.e., the first carbothermal reduction) to prevent the alloying element oxides and the alkaline earth metal oxide mixture (e.g., CaO) from forming a liquid slag phase, thereby preventing the rapid collision and growth of the already formed metal particles. The subsequent high-temperature reduction (i.e., the second carbothermal reduction) ensures that the alloying element oxides are completely reduced.

[0026] Furthermore, the present invention sequentially performs carbothermal reduction in a reducing atmosphere and then a vacuum atmosphere to promote the reduction reaction. Controlling the volume fraction of H2 facilitates the production of low-oxygen micron-sized metal particles. During the purification phase, the present invention utilizes acid leaching, in addition to conventional slag-metal separation, to completely remove the alkaline earth metal oxide mixture, thereby producing ultra-low-oxygen micron-sized metal particles. Experimental results demonstrate that the metal particles produced by the present invention have an oxygen content of 0.031-0.052%.

[0027] The micron metal particles prepared by the present invention have a nearly spherical morphology, a small size, and low oxygen, phosphorus, and sulfur impurity contents, meeting the stringent requirements of 3D printing for the characteristics of micron metal particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a morphology picture of the 17-4PH stainless steel micron metal particles prepared in Example 1. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing spherical micron metal particles, comprising the following steps:

[0030] According to the elemental composition of the spherical micron metal particles to be prepared, oxides of the corresponding elements are mixed with carbon powder and a dispersion medium and then ground to obtain an oxide mixed powder; the oxides of the corresponding elements do not include carbon oxides; and the dispersion medium is an alkaline earth metal oxide mixture;

[0031] Carbothermal reduction of the oxide mixed powder to obtain a reduction product;

[0032] The reduction product is mixed with ZnO and then subjected to vacuum decarburization and spheroidization in sequence to obtain a slag-gold mixture; the slag-gold mixture comprises alkaline earth metal oxide mixture slag, spherical micron metal particles and residual ZnO; the spheroidization temperature is 5 to 300° C. higher than the solidus temperature of the micron metal particles; and the spheroidization time is 10 to 200 minutes;

[0033] performing slag-gold separation and acid leaching on the slag-gold mixture to remove the alkaline earth metal oxide mixture slag and residual ZnO in the slag-gold mixture to obtain the spherical micron metal particles;

[0034] The melting point of the alkaline earth metal oxide mixture is higher than the temperature of the carbothermal reduction, the temperature of the vacuum decarburization treatment, and the temperature of the spheroidization treatment.

[0035] According to the elemental composition of the spherical micron metal particles to be prepared, the oxides of the corresponding elements are mixed with carbon powder and a dispersion medium and then ground to obtain an oxide mixed powder. In the present invention, the oxides of the corresponding elements do not include carbon oxides.

[0036] In the present invention, the element composition of the spherical micron metal particles to be prepared preferably includes one or more of iron, chromium, nickel, molybdenum, tungsten, copper, manganese, niobium, cobalt, tantalum, vanadium, silver, boron, carbon and silicon.

[0037] In the present invention, the particle size of the oxide powder mixture is preferably less than 10 μm, more preferably less than 5 μm, and even more preferably less than 2 μm. By controlling the particle size of the oxide powder mixture within the above range, the present invention ensures uniform distribution of the alloy oxides in the alkaline earth metal oxide mixture. This not only improves the compositional uniformity of the micron metal particles to be prepared, but also facilitates the production of fine metal particles. The present invention does not specifically limit the grinding process; a method familiar to those skilled in the art can be employed to obtain an oxide powder mixture of the target particle size.

[0038] In the present invention, the mass of the carbon powder is preferably (0.9-1.0)×M H ×(0.75w O +0.02), more preferably (0.92 to 0.98)×M H ×(0.75w O +0.02), where M H is the total mass of all oxides of the corresponding elements, w O is the mass fraction of oxygen in the oxides of all corresponding elements. By controlling the amount of carbon powder added within the above range, the present invention not only ensures that the alloy oxides are completely reduced, but also ensures that the metal particles are liquid after the reduction due to the dissolution of an appropriate amount of carbon, which is conducive to obtaining spherical micron metal particles.

[0039] In the present invention, the mass of the alkaline earth metal oxide mixture is preferably (1-5)×M H ×(1-w O ), more preferably (2 to 3) × M H ×(1-w OIn the present invention, the melting point of the alkaline earth metal oxide mixture is higher than the temperature of the carbothermal reduction, the temperature of the vacuum decarburization treatment, and the temperature of the spheroidization treatment, so that the alkaline earth metal oxide mixture can remain in a solid state, thereby isolating the liquefied metal particles and inhibiting the rapid growth of the metal particles. The present invention facilitates obtaining fine-sized metal particles by controlling the amount of the alkaline earth metal oxide mixture added within the above range.

[0040] The alkaline earth metal oxide mixture of the present invention preferably comprises, by weight percentage, 0-90% MgO and the balance CaO. Furthermore, the MgO content is preferably 10-70%, more preferably 30-50%. By controlling the mass percentage of MgO in the mixture within this range, the present invention helps prevent severe sintering of the CaO and MgO mixture during high-temperature heating, providing sufficient free space for the spheroidization and deformation of the metal particles, thereby promoting spheroidization of the metal particles.

[0041] After obtaining the oxide mixed powder, the present invention performs carbon thermal reduction on the oxide mixed powder to obtain a reduction product.

[0042] In the present invention, the carbothermal reduction preferably includes sequentially performing a first carbothermal reduction and a second carbothermal reduction.

[0043] In the present invention, the temperature of the first carbothermal reduction is preferably 900-1095°C, more preferably 950-1050°C, and even more preferably 980-1020°C; the holding time is preferably 0-30 minutes, more preferably 8-15 minutes. In the present invention, when the spherical micron-shaped metal particles to be prepared do not contain iron, the time of the first carbothermal reduction can be 0; when they contain iron, the time of the first carbothermal reduction is not 0.

[0044] In the present invention, the first carbon thermal reduction is preferably carried out under a reducing atmosphere; the reducing atmosphere is preferably an Ar-H2 mixed gas; the volume fraction of H2 in the Ar-H2 mixed gas is preferably 0.1 to 50%, more preferably 1 to 20%, and even more preferably 2 to 10%. The first carbon thermal reduction of the present invention is carried out in a reducing atmosphere to promote the reduction reaction, and the present invention is conducive to obtaining micron metal particles with a low oxygen content by controlling the volume fraction of H2 within the above range. The present invention first adopts low-temperature reduction to avoid the formation of a liquid slag phase between the alloy element oxide and the alkaline earth metal oxide mixture (such as CaO), thereby avoiding the rapid collision and growth of the already formed liquid metal particles. High-temperature reduction is then used to ensure that the alloy element oxide is completely reduced.

[0045] In the present invention, the rate of heating from the first carbothermal reduction temperature to the second carbothermal reduction temperature is preferably greater than 5°C / min, more preferably greater than 10°C / min.

[0046] In the present invention, the temperature of the second carbothermic reduction is preferably 1100-1500°C, more preferably 1200-1400°C, and even more preferably 1300-1350°C; the holding time is preferably 20-60 minutes, more preferably 30-50 minutes, and even more preferably 40-45 minutes. By controlling the temperature and time of the second carbothermic reduction within the above ranges, the present invention can promote the carbothermic reduction, more thoroughly convert the alloy oxides into metal, improve the yield of alloying elements, and liquefy the metal particles, causing them to spontaneously spheroidize under the action of surface tension, thereby obtaining spherical micron-shaped metal particles.

[0047] In the present invention, the second carbon thermal reduction is preferably carried out under vacuum conditions. In the present invention, the gas phase pressure in the vacuum conditions is preferably less than 100 Pa, more preferably less than 10 Pa. By carrying out the reduction under vacuum conditions and controlling the gas phase pressure within the above-mentioned range, the present invention can promote the progress of carbon thermal reduction, especially for difficult-to-reduce oxides, more thoroughly converting the alloy element oxides into metals, improving the yield of the alloy elements, and thus more accurately controlling the composition of the micron metal particles. The present invention carries out the reduction under vacuum conditions, and the reduction rates of alloy oxides such as iron, chromium, nickel, molybdenum, tungsten, copper, manganese, niobium, cobalt, tantalum, vanadium, silver, boron, and silicon are very high, all greater than 98%.

[0048] The present invention first employs low-temperature reduction (i.e., first carbothermal reduction) to prevent the formation of a liquid slag phase between the alloying element oxides and the alkaline earth metal oxide mixture (e.g., CaO), thereby preventing the rapid collision and growth of the already formed metal particles. Subsequently, high-temperature reduction (i.e., second carbothermal reduction) is employed to ensure complete reduction of the alloying element oxides.

[0049] After the reduction reaction, the product is preferably cooled to room temperature and then crushed and ground to obtain a reduced product. In the present invention, the particle size of the alkaline earth metal oxide mixture in the reduced product is preferably less than 20 μm, more preferably less than 10 μm. The crushing and grinding are not particularly limited in the present invention; methods familiar to those skilled in the art may be employed to obtain the desired alkaline earth metal oxide mixture particle size. The reduced product comprises carbon-containing micron metal particles and an alkaline earth metal oxide mixture.

[0050] After obtaining the reduction product, the present invention mixes the reduction product with ZnO and then sequentially performs vacuum decarburization and spheroidization to obtain a slag-gold mixture. In the present invention, the particle size of the ZnO is preferably less than 10 μm, more preferably less than 2 μm. By controlling the particle size of the decarburizer within the above range, the reduction product and the decarburizer can be uniformly mixed, thereby increasing the decarburization rate. In the present invention, the mass of the ZnO is preferably (1 to 1.5) × 6.75 × MH ×(1-w O )×(w C1 -w C2 ), more preferably (1.05-1.3)×6.75×M H ×(1-w O )×(w C1 -w C2 ), where w C1 is the mass fraction of carbon in the micron metal particles contained in the reduction product, w C2 is the mass fraction of carbon in the spherical micron metal particles to be prepared. In the present invention, the temperature of the vacuum decarburization treatment is preferably 1100-1300°C, more preferably 1150-1250°C; the pressure is preferably less than 1 Pa, more preferably less than 0.1 Pa; the time is preferably 20-180 min, more preferably 40-150 min, and further preferably 60-120 min. The present invention uses ZnO for decarburization, and its decarburization chemical reaction formula is: C+ZnO=Zn↑+CO↑. The decarburization products are all gaseous substances, which can effectively avoid the generation of a large number of irregular metal particles during the decarburization process. By selecting ZnO as a decarburizing agent and controlling the addition amount within the above range, the present invention can avoid the generation of irregular metal particles and obtain micron metal particles with a carbon content that meets the requirements.

[0051] In the present invention, the spheroidization temperature is 5 to 300°C, preferably 30 to 150°C, higher than the solidus temperature of the alloy particles; the duration is 10 to 200 minutes, preferably 20 to 100 minutes, and more preferably 30 to 60 minutes. In the present invention, the heating rate from the vacuum decarburization temperature to the spheroidization temperature is preferably greater than 5°C / min, more preferably greater than 10°C / min. During the vacuum decarburization process, the morphology of the spheroidized micronized metal particles deteriorates to a certain extent. The present invention improves the morphology of micronized metal particles through spheroidization. By employing spheroidization and controlling the spheroidization time and temperature within the above-mentioned ranges, the sphericity of the micronized metal particles can be significantly improved. In the present invention, the spheroidization is preferably performed under a reducing atmosphere; the reducing atmosphere is preferably an Ar-H2 mixed gas; the volume fraction of H2 in the Ar-H2 mixed gas is preferably 0.1 to 50%, more preferably 1 to 20%, and even more preferably 2 to 10%. A reducing atmosphere can promote the reduction reaction and prevent oxidation of the metal particles during the spheroidization process. The present invention facilitates obtaining micronized metal particles with a low oxygen content by adopting a reducing atmosphere and controlling the volume ratio of H2 within the above range.

[0052] In the present invention, the slag-metal mixture comprises alkaline earth metal oxide mixture slag, spherical micron metal particles and residual ZnO.

[0053] After obtaining the slag-gold mixture, the present invention performs slag-gold separation and acid leaching on the slag-gold mixture to remove the alkaline earth metal oxide mixture slag and residual ZnO in the slag-gold mixture, thereby obtaining the spherical micron metal particles.

[0054] Prior to the primary slag-metal separation, the present invention preferably grinds the slag-metal mixture to produce a ground material. In the present invention, the grinding is preferably performed using mechanical ball milling in an inert atmosphere; the inert atmosphere preferably contains argon. After grinding, the particle size of the alkaline earth metal oxide mixture slag and residual ZnO in the ground material is preferably less than 20 μm, more preferably less than 10 μm. The present invention does not specify the grinding time or speed; protocols familiar to those skilled in the art can be used to obtain an alkaline earth metal oxide mixture of the desired particle size.

[0055] After obtaining the ground material, the present invention preferably performs a primary slag-metal separation on the ground material to obtain a primary slag-metal separation. The primary slag-metal separation mainly comprises micron metal particles.

[0056] In the present invention, the primary slag-gold separation method includes one or two of magnetic separation, flotation, and heavy liquid separation. In the present invention, for magnetic metal particles, the present invention preferably uses magnetic separation for slag-gold separation; for non-magnetic metal particles, the present invention preferably uses flotation for slag-gold separation. The present invention does not specifically limit the specific operations of the magnetic separation, flotation, and heavy liquid separation, and schemes familiar to those skilled in the art can be used. Specifically, in an embodiment of the present invention, the primary slag-gold separation is to mix the slag-gold mixture with pure alcohol and then use a magnetic separation column, a flotation column, or a heavy liquid to separate the slag-gold.

[0057] After the primary slag-gold separation, the present invention preferably performs acid leaching on the obtained primary slag-gold separation to obtain an acid leaching product.

[0058] Prior to acid leaching, the present invention preferably dries the primary slag-gold separation. In the present invention, the acid leaching solution used in the acid leaching is preferably a nitric acid solution; the pH of the acid leaching solution is preferably 4-7, more preferably 5-6. In the present invention, the acid leaching solution is preferably obtained by mixing water and dilute nitric acid. In the present invention, the acid leaching preferably comprises mixing the primary slag-gold separation with water and then adding dilute nitric acid. In the present invention, the concentration of the dilute nitric acid is preferably 1-5 mol / L, more preferably 1-3 mol / L. The amounts of water and nitric acid used are not particularly limited; they can be adjusted to the pH of the acid leaching solution. By using dilute nitric acid and controlling the pH and concentration of the added nitric acid within the above ranges, the present invention facilitates precise control of the pH of the acid leaching solution, thereby facilitating the complete dissolution and removal of the alkaline earth metal oxide mixture slag and residual ZnO, while effectively inhibiting the erosion of micronized metal particles. In the present invention, the acid leaching temperature is preferably 2-50°C, more preferably 10-20°C. The present invention helps to inhibit the corrosion of micron metal particles by controlling the operating temperature of the acid leaching within the above range.

[0059] In the present invention, the acid leaching is preferably concluded when the pH of the aqueous solution increases by less than 0.2 over 30 minutes, more preferably by less than 0.1. During the acid leaching process, the pH of the aqueous solution increases due to the dissolution of the alkaline-earth metal oxide mixture slag and residual ZnO. By controlling the pH increase over 30 minutes within the above range, the present invention accurately determines whether the alkaline-earth metal oxide mixture and residual ZnO are completely dissolved, thereby minimizing the erosion of the micronized metal particles. After the acid leaching is completed, the present invention preferably filters the acid leaching system to obtain the acid leaching product.

[0060] After obtaining the acid leaching product, the present invention preferably performs a secondary slag-metal separation on the acid leaching product to obtain a secondary slag-metal separate. The present invention does not particularly limit the specific operation of the secondary slag-metal separation; a method well known to those skilled in the art can be used to remove trace amounts of acid-insoluble oxides. The method for the secondary slag-metal separation is similar to that for the primary slag-metal separation and will not be further described here.

[0061] After obtaining the secondary slag-gold separation, the present invention preferably washes and dries the secondary slag-gold separation to obtain spheroidized micron metal particles. In the present invention, the washing is preferably performed 1 to 5 times with ultrapure water, more preferably 2 to 4 times with ultrapure water.

[0062] In the present invention, the drying is preferably performed under low-temperature vacuum conditions; the temperature of the low-temperature vacuum is preferably 0 to 50°C, more preferably 10 to 20°C; and the vacuum degree of the low-temperature vacuum is preferably below 300 Pa, more preferably below 200 Pa. The present invention reduces the degree of oxidation of the micronized metal particles by using low-temperature vacuum treatment.

[0063] To further illustrate the present invention, the preparation method of the spherical micron metal particles provided by the present invention is described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0064] In the embodiment of the present invention, the target weight of the prepared micron metal particles is 10 kg; the equipment used for magnetic separation is a magnetic separation column; the equipment used for flotation is a flotation column; the heavy liquid separation adopts a density of more than 3.6 g / cm 3 In the embodiment of the present invention, the purity of all raw materials is greater than 99%.

[0065] Example 1

[0066] Preparation of 17-4PH stainless steel micron metal particles, the steps are:

[0067] (1) Weigh 0.065 kg MnO, 0.043 kg SiO2, 2.338 kg Cr2O3, 0.509 kg NiO, 0.501 kg CuO, 0.036 kg Nb2O5, 10.711 kg Fe2O3, 3.161 kg carbon powder and 30 kg CaO and MgO mixture (MgO mass proportion is 20%), mix and grind in a high-energy ball mill to obtain an oxide mixed powder with a particle size of less than 2 μm.

[0068] (2) Using a multifunctional atmosphere protection / vacuum muffle furnace, the oxide powder mixture in step (1) is first subjected to low-temperature reduction in an Ar-2% H2 reducing atmosphere at a temperature of 950°C for 15 minutes. Thereafter, the furnace temperature is raised to 1350°C at a rate of 15°C / min for high-temperature reduction for 40 minutes. The high-temperature reduction is performed under vacuum conditions with a gas phase pressure of less than 2 Pa. After the reduction is completed, the mixture is cooled to room temperature and the reduced product is ground using a ball mill to ensure that the particle size of CaO and MgO in the reduced product is less than 10 μm.

[0069] (3) Using an electron probe microanalyzer, the carbon content of the metal particles in the reduction product was measured to be 1.84% to calculate the amount of ZnO decarburizer to be added.

[0070] The reduced product from step (2) was uniformly mixed with 1.563 kg of a ZnO decarburizer having a particle size of less than 1 μm, and then subjected to vacuum decarburization treatment for 120 minutes at 1250° C. and a pressure of less than 0.1 Pa in a multifunctional atmosphere-protected vacuum muffle furnace. The furnace temperature was then raised to 1456° C. (50° C. above the solidus temperature) at a rate of 8° C. / min for 30 minutes of spheroidization treatment in an Ar-10% H2 reducing atmosphere. After spheroidization, the mixture was cooled to room temperature and ground using a ball mill to ensure that the particle sizes of CaO, MgO, and residual ZnO in the mixture were less than 7 μm.

[0071] (4) After the slag-gold mixture is mixed with pure alcohol, a magnetic separation column is used to perform a first slag-gold separation to obtain a primary slag-gold separated product.

[0072] The resulting primary slag-gold separation is then dried and mixed with high-purity water. The pH of the aqueous solution is monitored online in real time using a pH meter. By adding 3 mol / L dilute nitric acid, the pH is controlled between 5 and 6 to promote the dissolution of the residual CaO and MgO mixture. The sample temperature is maintained at 10°C in a water bath throughout the acid leaching process. The acid leaching process is concluded when the pH of the aqueous solution increases by less than 0.2 over 30 minutes.

[0073] After the acid leaching is complete, the leaching solution is filtered, pure alcohol is added, and a second slag-metal separation is performed using a magnetic separation column to remove trace amounts of acid-insoluble oxides. The alcohol is filtered out, and the micron-sized metal particles are rinsed twice with high-purity water. They are then vacuum-dried at 10°C and a vacuum of less than 200 Pa. After drying, the finished micron-sized metal particles are obtained.

[0074] Example 2

[0075] Preparation of H13 steel micron metal particles, the steps are:

[0076] (1) Weigh 0.039 kg MnO, 0.193 kg SiO2, 0.731 kg Cr2O3, 0.187 kg MoO2, 0.161 kg V2O5, 13.014 kg Fe2O3, 3.459 kg carbon powder and 25 kg CaO and MgO mixture (MgO mass proportion is 30%), mix and grind using a high-energy ball mill to obtain an oxide mixed powder with a particle size of less than 1.5 μm.

[0077] (2) Using a multifunctional atmosphere protection / vacuum muffle furnace, the oxide powder mixture in step (1) is first subjected to low-temperature reduction in an Ar-10% H2 reducing atmosphere at a temperature of 1050°C for 15 minutes. Subsequently, the furnace temperature is raised to 1400°C at a rate of 16°C / min for high-temperature reduction for 50 minutes. The high-temperature reduction is performed under vacuum conditions with a gas phase pressure of less than 1 Pa. After the reduction is completed, the mixture is cooled to room temperature and the reduced product is ground using a ball mill to ensure that the particle size of CaO and MgO in the reduced product is less than 8 μm.

[0078] (3) Using an electron probe microanalyzer, the carbon content of the metal particles in the reduction product was measured to be 3.64% to calculate the amount of ZnO decarburizer to be added. After the reduction product in step (2) was evenly mixed with 2.302 kg of ZnO decarburizer with a particle size of less than 2 μm, a vacuum decarburization treatment was performed in an atmosphere protection / vacuum multifunctional muffle furnace at 1150°C and a pressure of less than 0.5 Pa for 30 minutes. Thereafter, the furnace temperature was raised to 1455°C (10°C higher than the solidus temperature) at a rate of 12°C / min for spheroidization treatment for 120 minutes. The spheroidization treatment was performed in an Ar-20% H2 reducing atmosphere. After the spheroidization was completed, the mixture was cooled to room temperature and ground using a ball mill to ensure that the particle size of CaO, MgO and residual ZnO in the mixture was less than 9 μm.

[0079] (4) After the slag-gold mixture is mixed with pure alcohol, a magnetic separation column is used to perform a first slag-gold separation to obtain a primary slag-gold separation.

[0080] The resulting primary slag-gold separation is then dried and mixed with high-purity water. The pH of the aqueous solution is monitored online in real time using a pH meter. The pH is controlled between 5 and 6 by adding 1 mol / L dilute nitric acid to promote the dissolution of the residual CaO and MgO mixture. The sample temperature is maintained at 2°C in a water bath throughout the acid leaching process. The acid leaching process is concluded when the pH of the aqueous solution increases by less than 0.2 over 30 minutes.

[0081] After the acid leaching is complete, the leaching solution is filtered, pure alcohol is added, and a second slag-metal separation is performed using a magnetic separation column to remove trace amounts of acid-insoluble oxides. The alcohol is filtered out, and the micron-sized metal particles are rinsed three times with high-purity water. They are then vacuum-dried at 5°C and a vacuum of less than 200 Pa. After drying, the finished micron-sized metal particles are obtained.

[0082] Example 3

[0083] Preparation of pure Ni micron metal particles, the steps are:

[0084] (1) 12.726 kg of NiO, 2.184 kg of carbon powder, and 20 kg of a mixture of CaO and MgO (MgO accounts for 40% by mass) were weighed, mixed, and ground using a high-energy ball mill to obtain an oxide mixed powder with a particle size of less than 1 μm.

[0085] (2) The oxide mixed powder in step (1) is subjected to high-temperature reduction at 1380° C. for 30 minutes in a multifunctional atmosphere protection / vacuum muffle furnace. The high-temperature reduction is performed under vacuum conditions with a gas phase pressure of less than 50 Pa. After the reduction is completed, the mixture is cooled to room temperature and the reduced product is ground using a ball mill to ensure that the particle size of CaO and MgO in the reduced product is less than 12 μm.

[0086] (3) Using an electron probe microanalyzer, the carbon content of the metal particles in the reduction product was measured to be 3.06%, so as to calculate the amount of ZnO decarburizer to be added. After the reduction product in step (2) was evenly mixed with 2.457 kg of ZnO decarburizer with a particle size of less than 3 μm, a vacuum decarburization treatment was performed in an atmosphere protection / vacuum multifunctional muffle furnace at 1200°C and a pressure of less than 0.1 Pa for 90 minutes. Thereafter, the furnace temperature was raised to 1485°C (30°C higher than the solidus temperature) at a rate of 9°C / min for spheroidization treatment for 60 minutes. The spheroidization treatment was performed in an Ar-5% H2 reducing atmosphere. After the spheroidization was completed, the mixture was cooled to room temperature and ground using a ball mill to ensure that the particle size of CaO, MgO and residual ZnO in the mixture was less than 5 μm.

[0087] (4) After the slag-gold mixture is mixed with pure alcohol, a magnetic separation column is used to perform a first slag-gold separation to obtain a primary slag-gold separated product.

[0088] The resulting primary slag-gold separation is then dried and mixed with high-purity water. The pH of the aqueous solution is monitored online in real time using a pH meter. The pH is controlled between 5 and 6 by adding 2 mol / L dilute nitric acid to promote the dissolution of the residual CaO and MgO mixture. The sample temperature is maintained at 20°C in a water bath throughout the acid leaching process. The acid leaching process is concluded when the pH of the aqueous solution increases by less than 0.2 over 30 minutes.

[0089] After the acid leaching is complete, the leaching solution is filtered and a heavy liquid is added for a second slag-metal separation to remove trace amounts of acid-insoluble oxides. The heavy liquid is filtered and the micron-sized metal particles are rinsed three times with high-purity water. They are then vacuum-dried at 20°C and a vacuum level of less than 200 Pa. After drying, the finished micron-sized metal particles are obtained.

[0090] Example 4

[0091] Preparation of pure Cu micron metal particles, the steps are:

[0092] (1) Weigh 12.520 kg of CuO, 1.926 kg of carbon powder, and 40 kg of a mixture of CaO and MgO (MgO accounts for 50% by mass) and grind them in a high-energy ball mill to obtain an oxide mixed powder with a particle size of less than 3 μm.

[0093] (2) The oxide mixed powder in step (1) is subjected to high-temperature reduction at 1135° C. for 25 minutes using a multifunctional atmosphere protection / vacuum muffle furnace. The high-temperature reduction is performed under vacuum conditions with a gas phase pressure of less than 100 Pa. After the reduction is completed, the mixture is cooled to room temperature and the reduced product is ground using a ball mill to ensure that the particle size of CaO and MgO in the reduced product is less than 6 μm.

[0094] (3) Using an electron probe microanalyzer, the carbon content of the metal particles in the reduction product was measured to be 0.68%, so as to calculate the amount of ZnO decarburizer to be added.

[0095] The reduced product from step (2) was mixed uniformly with 0.675 kg of a ZnO decarburizer having a particle size of less than 4 μm, and then subjected to vacuum decarburization treatment for 60 minutes at 1100° C. and a pressure of less than 0.1 Pa in a multifunctional atmosphere protection / vacuum muffle furnace. The furnace temperature was then raised to 1235° C. (150° C. above the solidus temperature) at a rate of 20° C. / min for spheroidization treatment for 20 minutes in an Ar-2% H2 reducing atmosphere. After spheroidization, the mixture was cooled to room temperature and ground using a ball mill to ensure that the particle sizes of CaO, MgO, and residual ZnO in the mixture were less than 4 μm.

[0096] (4) After the slag-gold mixture is mixed with pure alcohol, a flotation column is used to perform a first slag-gold separation to obtain a primary slag-gold separated product.

[0097] The resulting primary slag-gold separation is then dried and mixed with high-purity water. The pH of the aqueous solution is monitored online in real time using a pH meter. The pH is controlled between 5 and 6 by adding 4 mol / L dilute nitric acid to promote the dissolution of the residual CaO and MgO mixture. The sample temperature is maintained at 50°C in a water bath throughout the acid leaching process. The acid leaching process is concluded when the pH of the aqueous solution increases by less than 0.2 over 30 minutes.

[0098] After the acid leaching is complete, the leaching solution is filtered and a heavy liquid is added for a second slag-metal separation to remove trace amounts of acid-insoluble oxides. The heavy liquid is filtered, and the micron-sized metal particles are rinsed four times with high-purity water. They are then vacuum-dried at 50°C and a vacuum of less than 200 Pa. After drying, the finished micron-sized metal particles are obtained.

[0099] Comparative Example 1

[0100] The only difference from Example 1 is that pure Al2O3 oxide is used in place of CaO and MgO oxides in step (1).

[0101] Comparative Example 2

[0102] The only difference from Example 1 is that the temperature of the high-temperature spheroidization treatment in step (3) is 1409° C. (3° C. higher than the solidus temperature of 17-4PH stainless steel).

[0103] Comparative Example 3

[0104] The only difference from Example 1 is that the time for high-temperature spheroidization treatment in step (3) is 5 minutes.

[0105] Comparative Example 4

[0106] The only difference from Example 1 is that the decarburizing agent in step (3) is 1.049 kg Fe2O3 (which carries the same amount of oxygen as 1.563 kg ZnO).

[0107] Comparative Example 5

[0108] The only difference from Example 1 is that there is no acid leaching step in step (4).

[0109] The chemical composition of the finished micron metal particles in Examples 1 to 4 and Comparative Examples 1 to 5 was measured, and the results are shown in Table 1. The oxygen content was measured using a nitrogen and oxygen analyzer, the carbon content was measured using a carbon and sulfur analyzer, and the contents of other elements were measured using direct reading spectroscopy.

[0110] Table 1 Chemical composition (wt.%) of the finished micron metal particles in Examples 1 to 4 and Comparative Examples 1 to 5

[0111]

[0112]

[0113] The particle size and fluidity of the finished micron metal particles in Examples 1 to 4 and Comparative Examples 1 to 5 were measured, and the results are shown in Table 2. The particle size was measured using a laser particle size analyzer, and the fluidity was measured using a standard funnel method.

[0114] Table 2 Particle size and fluidity of finished micron metal particles in Examples 1 to 4 and Comparative Examples 1 to 5

[0115]

[0116] The morphology of the finished product 17-4PH stainless steel micron metal particles in Example 1 was observed using a metallographic microscope. The results are as follows: Figure 1 shown.

[0117] Combined with Tables 1 to 2 and Figure 1 It can be seen that the preparation method provided by the present invention can obtain micron metal particles with the required composition, low oxygen content, small size and good fluidity, wherein the oxygen content is as low as 0.031-0.052%, and the particle size (D 90 ) is 51-76 μm, and the fluidity is 18-21 s / 50 g. In Comparative Example 1, when Al2O3 is used as the dispersion medium, the oxygen content increases to 1.724%; in Comparative Example 2, when the high-temperature spheroidization temperature is reduced, the fluidity increases to 22 s / 50 g, significantly deteriorating the fluidity; in Comparative Example 3, when the high-temperature spheroidization time is reduced, the fluidity increases to 21 s / 50 g, significantly deteriorating the fluidity; in Comparative Example 4, when Fe2O3 is used as the decarburizing agent, the fluidity increases to 24 s / 50 g, significantly deteriorating the fluidity; in Comparative Example 5, when the acid leaching treatment is omitted, the oxygen content increases to 0.614%.

[0118] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing spherical micron metal particles, characterized in that: The following steps are involved: According to the elemental composition of the spherical micron metal particles to be prepared, oxides of the corresponding elements are mixed with carbon powder and a dispersion medium, and then ground to obtain an oxide mixed powder; the oxides of the corresponding elements do not include carbon oxides; the dispersion medium is an alkaline earth metal oxide mixture, and the alkaline earth metal oxide mixture is a mixture of calcium oxide and magnesium oxide; Carbothermal reduction of the oxide mixed powder to obtain a reduction product; The reduction product is mixed with ZnO and then subjected to vacuum decarburization and spheroidization in sequence to obtain a slag-gold mixture; the slag-gold mixture comprises alkaline earth metal oxide mixture slag, spherical micron metal particles and residual ZnO; the spheroidization temperature is 10-300° C. higher than the solidus temperature of the micron metal particles; and the spheroidization time is 20-200 minutes; performing slag-gold separation and acid leaching on the slag-gold mixture to remove the alkaline earth metal oxide mixture slag and residual ZnO in the slag-gold mixture to obtain the spherical micron metal particles; The melting point of the alkaline earth metal oxide mixture is higher than the temperature of the carbothermal reduction, the temperature of the vacuum decarburization treatment, and the temperature of the spheroidization treatment.

2. The preparation method according to claim 1, characterized in that The mass of the carbon powder is (0.9~1.0)×M H ×(0.75w O +0.02), where M H is the total mass of all oxides of the corresponding elements, w O is the mass fraction of oxygen in the oxides of all corresponding elements.

3. The preparation method according to claim 1, characterized in that The mass of the alkaline earth metal oxide mixture is (1-5)×M H ×(1-w O ), where M H is the total mass of all oxides of the corresponding elements, w O is the mass fraction of oxygen in the oxides of all corresponding elements; in terms of mass percentage, the alkaline earth metal oxide mixture comprises 0-90% MgO and the balance CaO.

4. The preparation method according to claim 1, characterized in that The particle size of the oxide mixed powder is less than 10 μm.

5. The preparation method according to claim 1, characterized in that The carbothermal reduction includes a first carbothermal reduction and a second carbothermal reduction; The temperature of the first carbothermal reduction is 900-1095° C., and the holding time is 0-30 min; the temperature of the second carbothermal reduction is 1100-1500° C., and the holding time is 20-60 min.

6. The preparation method according to claim 5, characterized in that The first carbothermal reduction is performed in a reducing atmosphere; the second carbothermal reduction is performed under vacuum conditions; and the gas phase pressure under the vacuum conditions is less than 100 Pa.

7. The preparation method according to claim 1, characterized in that The mass of the ZnO is (1~1.5)×6.75×M H ×(1-w O )×(w C1 -w C2 ), where M H is the total mass of all oxides of the corresponding elements, w O is the mass fraction of oxygen in the oxides of all corresponding elements; w C1 is the mass fraction of carbon in the micron metal particles contained in the reduction product, w C2 is the mass fraction of carbon element in the spherical micron metal particles to be prepared.

8. The preparation method according to claim 1, characterized in that The vacuum decarburization treatment is performed at a temperature of 1100-1300° C., a pressure of less than 1 Pa, and a time of 20-180 min.

9. The preparation method according to claim 1, characterized in that The acid leaching solution used in the acid leaching is a nitric acid solution; the pH value of the acid leaching solution is 4-7.

10. The preparation method according to claim 1, characterized in that The slag-gold separation includes one or two of magnetic separation, flotation and heavy liquid separation.

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