A high-purity, dense, fine PtRh alloy spherical powder and its preparation method

Abstract

The present invention discloses a method for preparing high-purity, dense, and fine PtRh alloy spherical powder, comprising mixing sponge Pt and sponge Rh to obtain a premixture A; adding Na2B4O7 and SiO2 to the premixture A, and mixing thoroughly to obtain a ductile-brittle raw material system B; subjecting the ductile-brittle raw material system B to high-energy ball milling to obtain a composite powder C; subjecting the composite powder C to plasma in-situ melting and spheroidization treatment to obtain a composite spherical powder D; the composite spherical powder D is a core-shell structure in which a non-metallic slag phase is coated on the surface of the PtRh alloy; and removing the non-metallic slag phase from the composite spherical powder D using an alkaline solution to obtain a PtRh alloy spherical powder. The present invention also discloses a high-purity, dense, and fine PtRh alloy spherical powder, wherein the powder has a particle size of 1 to 5 μm, an average particle size of 2 to 4 μm, and a tap density of ≥7 g / cm 3 , sphericity ≥0.96, sphericity rate ≥98%, powder purity ≥99.9%.

Description

Technical Field

[0001] The invention relates to high-purity, dense, fine PtRh alloy spherical powder and a preparation method thereof, belonging to the technical field of precious metal powder preparation. Background Art

[0002] Due to their corrosion resistance, oxidation resistance, creep resistance, electrical and thermal conductivity, and strong catalytic activity, PtRh alloys are widely used in industrial fields such as glass fiber manufacturing, high-temperature measurement, and reaction catalysis. Since Rh has a higher melting point, hardness, and high-temperature strength than Pt, increasing the Rh content can significantly improve the physical and chemical properties of PtRh alloys. However, this also poses greater challenges to their processing.

[0003] Traditional methods for preparing PtRh alloy powders include mechanical pulverization, atomization, and electric spark discharge (EDD). Mechanical pulverization, which involves cutting, fracturing, and ball milling, produces fine PtRh powder. This process is time-consuming and energy-intensive, and the resulting powder has an irregular morphology, making it difficult to use in the near-net-shape production of PtRh components. Atomization, on the other hand, uses airflow or centrifugal rotation to atomize a PtRh alloy melt, producing spherical or quasi-spherical PtRh alloy powders. These products have a wide range of particle sizes, poor sphericity, and are prone to defects such as hollow cores and adhesion. Components produced using these materials for near-net-shape production generally exhibit poor mechanical properties. The EDD method involves continuous discharge between PtRh alloy electrodes, generating a high-temperature plasma that ablates the electrodes and produces the powder. Due to local overheating of the electrodes during the discharge, a large amount of metal vapor condenses and adheres to the powder surface in a flocculent form, reducing the powder's sphericity and causing powder agglomeration. Therefore, the PtRh alloys prepared by existing methods cannot meet the requirements of near-net-shape forming of PtRh alloys in terms of fluidity, dispersibility and filling properties.

[0004] In recent years, plasma spheroidization technology has been introduced into the field of PtRh alloy spherical powder preparation. This technology uses irregular PtRh alloy powder as raw material, uses the extremely high temperature of plasma to melt the powder, and the molten droplets condense into balls under the action of surface tension, and then rapidly cool to obtain PtRh alloy spherical powder with regular morphology. As the raw material for plasma spheroidization technology, irregular PtRh alloy powder needs to be obtained through alloy smelting, ingot casting, segmentation, crushing and other methods. However, PtRh alloys generally have composition segregation during the smelting and ingot casting process. Even if the ingot size is reduced and multiple remelting + composition homogenization heat treatments are performed, there are still differences in the elemental composition at different positions inside the ingot. This difference directly leads to a decrease in the compositional uniformity of the irregular PtRh powder obtained after crushing, and ultimately affects the PtRh spherical powder obtained by spheroidization through compositional heredity; in addition, the work hardening rate of the PtRh alloy increases sharply with the increase of the Rh content in the alloy, which makes the crushing of PtRh alloy ingots with high Rh content (≥30wt%) extremely difficult. Not only is the crushing process energy-consuming and time-consuming, but it is also very easy to introduce impurities; finally, although high-temperature plasma is conducive to the rapid melting of the raw material PtRh powder, the extremely high temperature will inevitably lead to the burning and gasification of alloy elements, especially irregular powders with a particle size of less than 10μm. The sharp positions on their surfaces will instantly vaporize and be carried away by the airflow when entering the high-temperature zone of the plasma. This phenomenon not only causes the final product composition to deviate from the original alloy design, but also leads to the loss of a large amount of precious metals. Therefore, although plasma spheroidization technology can achieve the preparation of PtRh alloy spherical powders, its existing problems cannot be ignored. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects and provide a high-purity, dense and fine PtRh alloy spherical powder and a preparation method thereof, which solves the technical problems of low composition uniformity, low purity and high precious metal loss rate of PtRh alloy spherical powder obtained by traditional preparation methods. The PtRh alloy spherical powder obtained by the present invention has a powder particle size of 1 to 5 μm, an average particle size of 2 to 4 μm, and a tap density of ≥7 g / cm 3 , sphericity ≥0.96, sphericity rate ≥98%, powder purity ≥99.9%.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for preparing high-purity, dense, fine PtRh alloy spherical powder, comprising:

[0008] Mixing sponge Pt and sponge Rh to obtain premix A;

[0009] Na2B4O7 and SiO2 are added to the premix A and mixed thoroughly to obtain a ductile-brittle raw material system B;

[0010] The ductile-brittle raw material system B is subjected to high-energy ball milling to obtain composite powder C;

[0011] Composite powder C is subjected to plasma in-situ melting and spheroidization treatment to obtain composite spherical powder D; composite spherical powder D has a core-shell structure in which a non-metallic slag phase is coated on the surface of a PtRh alloy;

[0012] The non-metallic slag phase in the composite spherical powder D is removed using an alkaline solution to obtain a PtRh alloy spherical powder.

[0013] Furthermore, the purity of the sponge Pt is ≥99.9 wt %, and the purity of the sponge Rh is ≥99.9 wt %;

[0014] In the premix A, the content of sponge Rh is 5 wt% to 50 wt%, and the rest is sponge Pt.

[0015] Further, Na2B4O7 and SiO2 are added to the premix A in a mass ratio of 1 to 4:1;

[0016] The total mass of Na2B4O7 and SiO2 is 4% to 10% of the mass of premix A.

[0017] Furthermore, the ductile-brittle raw material system B is subjected to high-energy ball milling using a planetary high-energy ball milling device, and the ball milling parameters include:

[0018] The ball-to-material ratio is 5-3:1, the filling ratio is 10%-50%, the ball mill speed is 250-600r / min, the transmission ratio of revolution and rotation is 1:2-4, the grinding ball diameter is 2-8mm, the ball milling time is 2-10h, and the grinding balls and the inner lining of the ball mill are made of SiO2.

[0019] Furthermore, the ductile-brittle raw material system B was subjected to high-energy ball milling without adding a process control agent.

[0020] Furthermore, the particle size of the composite powder C ranges from 1.5 to 7.5 μm.

[0021] Furthermore, the ductile-brittle raw material system B is subjected to high-energy ball milling to obtain the composite powder C as follows:

[0022] The powder obtained by high-energy ball milling of the ductile-brittle raw material system B is classified, and the powder within the desired particle size range is retained. The remaining powder is further subjected to high-energy ball milling. The above process is repeated until the particle size of all powders meets the desired particle size range, thereby obtaining composite powder C;

[0023] The classification method is mechanical screening or air flow classification.

[0024] Furthermore, the process parameters for plasma in-situ melting and spheroidization of the composite powder C are:

[0025] The power of the inductively coupled plasma torch is 20kW to 50kW; the working gas is oxygen, and the working gas flow rate is 20slpm to 40slpm; the side gas is oxygen, and the side gas flow rate is 100slpm to 400slpm; the carrier gas is oxygen, and the carrier gas flow rate is 1slpm to 10slpm; the system pressure of the inductively coupled plasma torch is 50kPa-98kPa;

[0026] The powder feeding rate of composite powder C is 10 g / min to 80 g / min.

[0027] Furthermore, the alkaline solution is an aqueous solution of NaOH, KOH, Na2CO3 or NaHCO3, and the pH value of the alkaline solution is ≥9; after removing the non-metallic slag phase in the composite spherical powder D using excess alkaline solution, the resulting product is repeatedly washed to neutrality and dried to obtain PtRh alloy spherical powder;

[0028] The recovery rate of PtRh alloy spherical powder is ≥98%. The recovery rate is the ratio of the total mass of the final platinum-rhodium alloy powder recovered to the total mass of the initially input sponge platinum and sponge rhodium, that is, the recovery ratio of precious metals.

[0029] A high-purity, dense, fine PtRh alloy spherical powder is obtained by the above-mentioned preparation method of a high-purity, dense, fine PtRh alloy spherical powder. The particle size range of the PtRh alloy spherical powder is 1 to 5 μm, the average particle size is 2 to 4 μm, and the tap density is ≥7 g / cm 3 , sphericity ≥ 0.96, sphericity ≥ 98%, purity ≥ 99.9%.

[0030] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0031] (1) The present invention creatively proposes a method for preparing high-purity, dense, fine PtRh alloy spherical powder. When the raw materials are subjected to ball milling and composite granulation, a certain proportion of Na2B4O7 and SiO2 brittle phases are added to the ductile material system composed of sponge Pt and sponge Rh to form a "ductile-brittle" ball milling system. The addition of the brittle phase not only makes the grinding and crushing efficiency of sponge Pt and sponge Rh higher, but also can adhere to the surface of the ductile metal phase in the subsequent composite granulation process, reduce the surface energy of the powder, and achieve effective control of the composite powder particle size. At the same time, there is no need to introduce additional process control agents to control the composite powder particle size, thereby improving the product purity.

[0032] (2) The objects of the ball milling crushing of the present invention are ductile sponge Pt and sponge Rh elements, rather than PtRh alloys with higher mechanical properties, which greatly reduces the difficulty of ball milling crushing, especially for ball milling of PtRh alloys with high Rh content, the crushing difficulty is significantly reduced.

[0033] (3) The present invention classifies the composite powder obtained after ball milling and composite granulation in advance to limit the size of the composite powder, and controls the particle size of the composite powder sent to the plasma torch for alloying and spheroidization within a certain range, so that the plasma treatment process parameters are better matched with the particle size of the raw material powder, avoiding the situation where small-sized powder is severely burned and large-sized powder is not fully heated. At the same time, the product particle size is more concentrated, and the composite powder whose particle size does not meet the specifications after classification is returned to the ball milling step for further processing, which improves the utilization rate of the raw materials while the spheroidization rate and sphericity of the final product are also higher.

[0034] (4) The present invention directly feeds the composite powder C containing Pt and Rh elements into the plasma torch, so that the alloying and spheroidization of the composite powder are completed in one plasma treatment, shortening the processing flow, reducing costs and raw material losses, and achieving uniform product composition and a powder yield of ≥98%.

[0035] (5) The present invention introduces Na2B4O7 and SiO2 into the composite powder, so that the composite powder is heated more evenly in the plasma torch. The preferentially melted Na2B4O7 and SiO2 form a glassy melt to form a protective layer on the surface of the alloy melt, thereby avoiding the violent evaporation of Pt and Rh elements during the alloy smelting and spheroidization process, ensuring that the composition of the spherical alloy melt is stable and consistent during the smelting process, and reducing raw material loss.

[0036] (6) The present invention uses oxygen as the working medium in the plasma in-situ melting and spheroidization process. Oxygen is a diatomic gas, and its enthalpy value after excitation in the plasma torch is higher than that of monatomic gas. At the same time, its own strong oxidizing property is conducive to the oxidation and slagging of non-Pt and Rh impurity phases in the composite powder C, and dissolves in the glassy melt, thereby improving the purity of the final product.

[0037] (7) Due to the existence of the core-shell structure of the powder during the plasma treatment process, a small amount of vaporized powder material will condense on the surface of the non-metallic slag phase shell during the powder condensation process and be removed in the subsequent alkaline washing process, avoiding the formation of flocs on the surface of the PtRh alloy powder and improving the powder fluidity and sphericity. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the method for preparing spherical PtRh powder according to the present invention;

[0039] Figure 2This is a microscopic morphology of the high-purity, dense, fine PtRh25 alloy spherical powder obtained in Example 2 of the present invention;

[0040] Figure 3 This is a particle size distribution diagram of the PtRh25 alloy spherical powder of the present invention;

[0041] Figure 4 This is an electron microscope photograph of the composite powder C composed of the gray ductile phase (sponge Pt and sponge Rh) and the white brittle phase (Na2B4O7 and SiO2) of the present invention;

[0042] Figure 5 This is an electron microscope photograph of the core-shell structure "non-metallic slag phase-PtRh alloy" composite spherical powder of the present invention. DETAILED DESCRIPTION

[0043] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0044] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0045] The present invention provides a method for preparing high-purity, dense, fine PtRh alloy spherical powder, which is simple in process, energy-saving and efficient, and suitable for industrial production. The high-purity, dense, fine PtRh alloy spherical powder prepared by the method of the present invention has the advantages of high sphericity, good dispersibility, fine particle size, uniform and stable composition, and high yield.

[0046] like Figure 1 The preparation of high-purity, dense, fine PtRh alloy spherical powder of the present invention comprises the following steps:

[0047] Step 1: Batching and mixing: Using sponge Pt and sponge Rh as raw materials, batch sponge Pt and sponge Rh in the required proportion according to the composition of the prepared PtRh alloy to obtain a premixture A, add Na2B4O7 and SiO2 to the premixture A and mix thoroughly to form a "ductile-brittle" raw material system B.

[0048] Step 2: Ball milling and composite granulation: The "ductile-brittle" raw material system B is subjected to high-energy ball milling. During the ball milling process, the components in the raw material system B are fully crushed and then reaggregated and composited. Specifically, during the ball milling process, the ductile components sponge Pt and sponge Rh in the raw material system B are crushed and flaked, and the brittle components Na2B4O7 and SiO2 are directly crushed. After further ball milling, the flaky ductile components and the crushed brittle components are reaggregated and composited to obtain a spherical composite powder C containing four substances, such as Figure 4 As shown in the figure, the ductile flaky Pt and Rh elements in the composite powder C mechanically interlock with each other to form a layered structure, achieving the desired nominal composition of the PtRh alloy powder. The brittle Na2B4O7 and SiO2 are distributed in a mosaic form at the interface between the ductile Pt and Rh metal elements, preventing the abnormal growth of the ductile Pt and Rh flaky elements as the ball milling time increases.

[0049] Step 3: Classification: Classify the spherical composite powder C obtained by ball milling by mechanical screening or airflow classification, retain the composite powder C within the required particle size range, and return to step 2 to continue high-energy ball milling;

[0050] Step 4: Plasma in-situ melting and spheroidization: The spherical composite powder C obtained by classification is fed into an induction coupled plasma torch with oxygen as the working gas. In a very short period of time, the composite powder undergoes four stages: solid-phase heating, graded melting, alloy melting and spheroidization, and quenching and solidification, to obtain a "non-metallic slag phase-PtRh alloy" composite spherical powder with core-shell structure characteristics.

[0051] During the solid-phase heating stage, because composite powder C is spherical and possesses a layered composite structure formed by the mechanical interlocking of flaky Pt and Rh, compared to the dense powder obtained by crushing the ingot, the spherical composite powder C has a larger heating area and lacks sharp protrusions, resulting in a more rapid and uniform overall temperature rise. This avoids elemental burnout caused by localized rapid temperature increases (such as at sharp corners) during the solid-phase heating stage. The term "pellet" refers to the shape of the composite powder formed by ball milling the four raw materials: sponge Pt, sponge Rh, Na2B4O7, and SiO2. This spherical shape is determined by the basic principles of ball milling. The interior is not dense, but rather formed by the mechanical interlocking and embedding of the four raw materials.

[0052] During the graded melting stage, since the melting point of Na2B4O7 (melting point 878°C) is much lower than that of SiO2 (melting point 1723°C), Pt (melting point 1772°C) and Rh (melting point 1966°C), Na2B4O7 in the spherical composite powder C melts first after uniform heating. The molten Na2B4O7 has the function of fluxing SiO2. Therefore, the two brittle phases in the composite powder C form a glassy melt at a temperature much lower than the melting points of Pt and Rh, and penetrate into the layered gaps of the composite powder under the action of capillary force, thereby dissolving and adsorbing impurities introduced during the early powder ball milling and granulation processes, thereby improving the reaction activity of the subsequent Pt and Rh alloying process.

[0053] During the alloy smelting and spheroidization stage, as the powder continues to heat up to and above the melting points of Pt and Rh, all components of the powder are completely melted. The liquid phase Pt and Rh have infinite solid solution characteristics and spontaneously fuse into a spherical alloy melt under the action of surface tension. The composition of the alloy melt is homogenized under the combined action of diffusion and electromagnetic stirring. The density of the glassy melt formed by the molten Na2B4O7 and SiO2 is much lower than that of the PtRh alloy melt and it is immiscible with the alloy melt. Therefore, it spontaneously floats on the surface of the alloy melt to form a protective layer, avoiding the violent evaporation of Pt and Rh elements during the alloy smelting and spheroidization process, and ensuring the stability and consistency of the composition of the spherical alloy melt during the smelting process.

[0054] During the quenching and solidification stage, the high-temperature molten droplets separated from the plasma torch are quenched and solidified under a huge temperature gradient with the environment. The spherical alloy melt in the core of the molten droplet and the glassy melt wrapped around it solidify separately, and the following is obtained: Figure 5 The composite spherical powder of "non-metallic slag phase-PtRh alloy" with core-shell structural characteristics is shown. The non-metallic slag phase here contains a glassy melt of a mixture of Na2B4O7 and SiO2, and may also contain a small amount of metal and non-metallic impurities contained in the ball milling process and the raw materials. These impurities are oxidized in the oxidizing atmosphere of the plasma torch, and the formed oxides will also be mixed into the non-metallic slag phase.

[0055] Step 5: Alkali Washing, Water Washing, and Drying. The core-shell structured "non-metallic slag phase-PtRh alloy" composite spherical powder is placed in an excess of alkaline solution to remove the surface non-metallic slag phase. The filtered PtRh alloy spherical powder is then repeatedly washed with deionized water until neutral. After filtering and drying, high-purity, dense, and fine PtRh alloy spherical powder is obtained.

[0056] Preferably, in step 1, the purity of the raw material sponge Pt is ≥99.9wt%, the purity of the raw material sponge Rh is ≥99.9wt%, and in the premix A, the content of sponge Rh is 5wt% to 50wt%, and the rest is sponge Pt.

[0057] Preferably, in step 1, the total mass of Na2B4O7 and SiO2 is 4% to 10% of the mass of premix A, and the mass ratio of Na2B4O7 to SiO2 is 1 to 4:1. This ratio is firstly conducive to the sufficient crushing of the ductile powder during the ball milling process. Secondly, it is also conducive to the formation of the plasma slag phase, and finally it is conducive to the removal of the slag phase during the alkali washing process. More specifically, this ratio takes into account the solubility of SiO2 in Na2B4O7 at high temperatures. If the proportion of SiO2 is too high, it will not be fully dissolved in Na2B4O7, and a uniform melt cannot be formed. If the proportion of Na2B4O7 is too high, a ductile-brittle grinding system cannot be effectively formed, and SiO2 plays the role of sufficient grinding and controlling the powder particle size in the system.

[0058] Preferably, in step 2, no process control agent is added during the ball milling and composite granulation process.

[0059] Preferably, in step 2, the ball milling crushing and composite granulation method can adopt a planetary high-energy ball mill, a stirring high-energy ball mill or a vibration high-energy ball mill, preferably a planetary high-energy ball mill, and the preferred ball milling parameters are a ball-to-material ratio of 5 to 3:1, a filling ratio of 10% to 50%, a ball milling speed of 250 to 600 r / min, a transmission ratio of revolution to rotation of 1:2 to 4, a grinding ball diameter of 2 to 8 mm, a ball milling time of 2 to 10 h, and the grinding ball material and the ball mill lining material are SiO2.

[0060] Preferably, in step 4, the parameters of the plasma in-situ melting and spheroidization treatment process are: the power of the inductively coupled plasma torch is 20kW-50kW; the working gas is oxygen, and the flow rate is 20slpm-40slpm; the side gas is oxygen, and the flow rate is 100slpm-400slpm; the carrier gas is oxygen, and the carrier gas flow rate is 1slpm-10slpm; the system pressure of the inductively coupled plasma torch is 50kPa-98kPa; and the powder feeding rate of the composite powder C is 10g / min-80g / min.

[0061] Preferably, in step 5, the alkaline solution is an aqueous solution of NaOH, KOH, Na2CO3 or NaHCO3, and the pH value of the solution is ≥9; the high-purity, dense, fine PtRh alloy spherical powder has a powder particle size range of 1 to 5 μm, an average particle size of 2 to 4 μm, and a tap density of ≥7 g / cm 3 , sphericity ≥ 0.96, sphericity ≥ 98%, powder purity ≥ 99.9%, the particle size distribution of PtRh alloy spherical powder is as follows Figure 3 shown.

[0062] The preparation process of the present invention is simple, the production efficiency is high, and there is no pollution to the environment, and it is suitable for industrial production. The high-purity, dense, and fine PtRh alloy spherical powder prepared by the method of the present invention has the advantages of high sphericity, good dispersibility, and fine and uniform particle size, and can be used to manufacture devices such as high-temperature thermocouples, glass fiber industrial heat-resistant components, and catalytic electrodes.

[0063] Example 1: Preparation of PtRh10 alloy spherical powder

[0064] Step 1: Using 99.9wt% pure Pt sponge and 99.9wt% pure Rh sponge as raw materials, according to the composition of the prepared PtRh10 alloy, the Pt sponge and the Rh sponge are mixed in a weight ratio of 9:1 to obtain a premixture A, and 5% by weight of Na2B4O7 and SiO2 are added to the premixture A, with the mass ratio of Na2B4O7 and SiO2 being 2:1, and the mixture is thoroughly mixed to form a "ductile-brittle" raw material system B;

[0065] Step 2: Planetary high-energy ball milling was used to perform high-energy ball milling on the "ductile-brittle" raw material system B, with a ball-to-material ratio of 3:1, a filling ratio of 25%, a ball milling speed of 400 r / min, a transmission ratio of revolution to rotation of 1:2, a grinding ball diameter of 6 mm, a ball milling time of 7 h, and a grinding ball material and a ball mill lining material of SiO2. During the ball milling process, the ductile components of the raw material system B, the sponge Pt and the sponge Rh, were broken and flaked, and the brittle components Na2B4O7 and SiO2 were directly broken. After further ball milling, the flaked ductile components The ductile components and the broken brittle components are agglomerated and recombined to obtain a spherical composite powder C containing four raw materials. The ductile flaky Pt and Rh elements in the composite powder are mechanically interlocked to form a layered structure, achieving the desired nominal composition of the prepared PtRh10 alloy powder. The brittle Na2B4O7 and SiO2 are distributed in a mosaic form at the interface between the ductile Pt and Rh metal elements, preventing the ductile Pt and Rh flaky elements from growing abnormally with the extension of ball milling time. Therefore, no process control agent is added during the ball milling process.

[0066] Step 3: Using an ultrasonic vibrating screen to classify the spherical composite powder C obtained by ball milling, the spherical composite powder C with a particle size range of 1.5 to 7.5 μm is retained, and the rest is returned to step 2 for high-energy ball milling;

[0067] Step 4: The composite powder C obtained by classification is fed into an inductively coupled plasma torch with oxygen as the working gas, and the power of the inductively coupled plasma torch is 40kW; the working gas is oxygen with a flow rate of 30slpm; the side gas is oxygen with a flow rate of 300slpm; the carrier gas is oxygen with a carrier gas flow rate of 8slpm; the system pressure of the inductively coupled plasma torch is 65kPa; the powder feeding rate of the spherical composite powder C of 1.5 to 7.5μm is 40g / min, and the composite powder C undergoes four stages of solid-phase heating, graded melting, alloy melting and spheroidization, and quenching and solidification in a very short time to obtain a composite spherical powder of "non-metallic slag phase-PtRh10 alloy" with core-shell structure characteristics.

[0068] Step 5: The composite spherical powder of "non-metallic slag phase-PtRh10 alloy" with core-shell structure characteristics obtained in step 4 is put into an excess NaOH solution with pH = 12 to remove the surface non-metallic slag phase, and then the filtered PtRh10 alloy spherical powder is repeatedly washed with deionized water until it is neutral, filtered out and dried to obtain high-purity, dense and fine PtRh10 alloy spherical powder with a powder particle size range of 1 to 5 μm, an average particle size of 2.8 μm, and a tap density of 7.2 g / cm 3 , sphericity 0.97, sphericity rate 98.5%, powder purity ≥99.93%.

[0069] Example 2: Preparation of PtRh25 alloy spherical powder

[0070] Step 1: Using 99.9wt% pure Pt sponge and 99.9wt% pure Rh sponge as raw materials, according to the composition of the prepared PtRh25 alloy, the Pt sponge and the Rh sponge are mixed in a weight ratio of 3:1 to obtain a premixture A, and 8% by weight of Na2B4O7 and SiO2 are added to the premixture A, with the mass ratio of Na2B4O7 and SiO2 being 5:2, and the mixture is thoroughly mixed to form a "ductile-brittle" raw material system B;

[0071] Step 2: Planetary high-energy ball milling was used to perform high-energy ball milling on the "ductile-brittle" raw material system B, with a ball-to-material ratio of 5:1, a filling ratio of 20%, a ball milling speed of 500 r / min, a transmission ratio of revolution to rotation of 1:3, a grinding ball diameter of 4 mm, a ball milling time of 5 h, and a grinding ball material and a ball mill lining material of SiO2. During the ball milling process, the ductile components sponge Pt and sponge Rh in the raw material system B were broken and flaked, and the brittle components Na2B4O7 and SiO2 were directly broken. After further ball milling, the flaked ductile components The ductile components and the broken brittle components are agglomerated and recombined to obtain a spherical composite powder C containing four raw materials. The ductile flaky Pt and Rh elements in the composite powder are mechanically interlocked to form a layered structure, achieving the desired nominal composition of the prepared PtRh25 alloy powder. The brittle Na2B4O7 and SiO2 are distributed in a mosaic form at the interface between the ductile Pt and Rh metal elements, preventing the ductile Pt and Rh flaky elements from growing abnormally with the extension of ball milling time. Therefore, no process control agent is added during the ball milling process.

[0072] Step 3: Using an ultrasonic vibrating screen to classify the spherical composite powder C obtained by ball milling, the spherical composite powder C with a particle size range of 1.8 to 4.8 μm is retained, and the rest is returned to step 2 for high-energy ball milling;

[0073] Step 4: The composite powder C obtained by classification is fed into an inductively coupled plasma torch with oxygen as the working gas, and the power of the inductively coupled plasma torch is 35kW; the working gas is oxygen with a flow rate of 25slpm; the side gas is oxygen with a flow rate of 180slpm; the carrier gas is oxygen with a carrier gas flow rate of 6slpm; the system pressure of the inductively coupled plasma torch is 90kPa; the powder feeding rate of the spherical composite powder C of 1.8 to 4.8μm is 50g / min, and the composite powder C undergoes four stages of solid-phase heating, graded melting, alloy melting and spheroidization, and quenching and solidification in a very short time to obtain a composite spherical powder of "non-metallic slag phase-PtRh25 alloy" with core-shell structure characteristics.

[0074] Step 5: The composite spherical powder of "non-metallic slag phase-PtRh25 alloy" with core-shell structure characteristics obtained in step 4 is put into an excess KOH solution with pH = 13 to remove the surface non-metallic slag phase, and then the filtered PtRh25 alloy spherical powder is repeatedly washed with deionized water until it is neutral, filtered out and dried to obtain high-purity, dense and fine PtRh25 alloy spherical powder with a powder particle size of 1.2 to 4.1 μm, an average particle size of 3.1 μm, and a tap density of 7.1 g / cm 3 , sphericity 0.97, sphericity 98.8%, powder purity 99.92%, such as Figure 2 shown.

[0075] Example 3: Preparation of PtRh48 alloy spherical powder

[0076] Step 1: Using 99.9wt% pure Pt sponge and 99.9wt% pure Rh sponge as raw materials, according to the composition of the prepared PtRh48 alloy, the Pt sponge and Rh sponge are mixed in a weight ratio of 13:12 to obtain a premixture A, and 8% by weight of Na2B4O7 and SiO2 are added to the premixture A, with the mass ratio of Na2B4O7 and SiO2 being 3:1, and the mixture is thoroughly mixed to form a "ductile-brittle" raw material system B;

[0077] Step 2: Planetary high-energy ball milling was used to perform high-energy ball milling on the "ductile-brittle" raw material system B, with a ball-to-material ratio of 5:1, a filling ratio of 30%, a ball milling speed of 500 r / min, a transmission ratio of revolution to rotation of 1:4, a grinding ball diameter of 8 mm, a ball milling time of 9 h, and a grinding ball material and a ball mill lining material of SiO2. During the ball milling process, the ductile components sponge Pt and sponge Rh in the raw material system B were broken and flaked, and the brittle components Na2B4O7 and SiO2 were directly broken. After further ball milling, the flaked ductile components The ductile components and the broken brittle components are agglomerated and recombined to obtain a spherical composite powder C containing four raw materials. The ductile flaky Pt and Rh elements in the composite powder are mechanically interlocked to form a layered structure, achieving the desired nominal composition of the prepared PtRh48 alloy powder. The brittle Na2B4O7 and SiO2 are distributed in a mosaic form at the interface between the ductile Pt and Rh metal elements, preventing the ductile Pt and Rh flaky elements from growing abnormally with the extension of ball milling time. Therefore, no process control agent is added during the ball milling process.

[0078] Step 3: Use an ultrasonic vibrating screen to classify the spherical composite powder C obtained by ball milling. The spherical composite powder C with a particle size range of 2 to 6 μm is retained, and the rest is returned to step 2 for high-energy ball milling.

[0079] Step 4: The composite powder C obtained by classification is fed into an inductively coupled plasma torch with oxygen as the working gas, and the power of the inductively coupled plasma torch is 50kW; the working gas is oxygen with a flow rate of 40slpm; the side gas is oxygen with a flow rate of 400slpm; the carrier gas is oxygen with a carrier gas flow rate of 10slpm; the system pressure of the inductively coupled plasma torch is 80kPa; the powder feeding rate of the spherical composite powder C of 2 to 6μm is 75g / min, and the composite powder C undergoes four stages of solid-phase heating, graded melting, alloy melting and spheroidization, and quenching and solidification in a very short time to obtain a composite spherical powder of "non-metallic slag phase-PtRh48 alloy" with core-shell structure characteristics.

[0080] Step 5: The composite spherical powder of "non-metallic slag phase-PtRh48 alloy" with core-shell structure characteristics obtained in step 4 is put into an excess Na2CO3 solution with a pH of 13 to remove the surface non-metallic slag phase, and then the filtered PtRh48 alloy spherical powder is repeatedly washed with deionized water until it is neutral, filtered out and dried to obtain high-purity, dense and fine PtRh48 alloy spherical powder with a powder particle size of 1.8 to 4.9 μm, an average particle size of 3.2 μm, and a tap density of 7.15 g / cm 3 , sphericity 0.98, sphericity rate 98.3%, powder purity ≥99.92%.

[0081] Comparative Example 1:

[0082] The remaining steps were the same as in Example 1, except that the amount of SiO2 added to Na2B4O7 was changed to 2% of the premixture A. During the plasma treatment of the composite powder C, the glassy melt formed could not fully encapsulate the Pt and Rh metals, and the non-metallic slag phase formed could not fully cover the metallic Pt and Rh phases, resulting in a large amount of gasification loss of platinum and rhodium elements and a reduced yield of precious metals.

[0083] Comparative Example 2:

[0084] The remaining steps are the same as those in Example 1, except that the amount of SiO2 added to Na2B4O7 is changed to 15% of the premixture A. The addition of a large amount of low-melting-point brittle phase in the composite powder C causes a large amount of energy to be consumed by the evaporation and melting of the non-metallic phase during the plasma treatment of the composite powder. The metal Pt and Rh cannot be fully heated and cannot melt to form a spherical shape. Some non-metallic phases fail to fully float to the surface to form a core-shell structure. Ultimately, the morphology of the PtRh alloy powder does not change, and the interior contains non-metallic impurities that cannot be melted.

[0085] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

[0086] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for preparing high-purity, dense, fine PtRh alloy spherical powder, characterized in that: include: Mixing sponge Pt and sponge Rh to obtain premix A; Na2B4O7 and SiO2 are added to the premix A and mixed thoroughly to obtain a ductile-brittle raw material system B; The ductile-brittle raw material system B is subjected to high-energy ball milling to obtain composite powder C; Composite powder C is subjected to plasma in-situ melting and spheroidization treatment to obtain composite spherical powder D; composite spherical powder D has a core-shell structure in which a non-metallic slag phase is coated on the surface of a PtRh alloy; Using an alkaline solution to remove the non-metallic slag phase in the composite spherical powder D, a PtRh alloy spherical powder is obtained; Add Na2B4O7 and SiO2 to premix A in a mass ratio of 1 to 4:1; The total mass of Na2B4O7 and SiO2 is 4% to 10% of the mass of premix A.

2. The method for preparing high-purity, dense, fine PtRh alloy spherical powder according to claim 1, characterized in that: The purity of the sponge Pt is ≥99.9wt%, and the purity of the sponge Rh is ≥99.9wt%; In the premix A, the content of sponge Rh is 5 wt% to 50 wt%, and the rest is sponge Pt.

3. The method for preparing high-purity, dense, fine PtRh alloy spherical powder according to claim 1, characterized in that: The ductile-brittle raw material system B was subjected to high-energy ball milling using a planetary high-energy ball mill. The ball milling parameters included: The ball-to-material ratio is 5-3:1, the filling ratio is 10%-50%, the ball mill speed is 250-600r / min, the transmission ratio of revolution and rotation is 1:2-4, the grinding ball diameter is 2-8mm, the ball milling time is 2-10h, and the grinding balls and the inner lining of the ball mill are made of SiO2.

4. The method for preparing high-purity, dense, fine PtRh alloy spherical powder according to claim 1, characterized in that: The ductile-brittle raw material system B was subjected to high-energy ball milling without adding process control agents.

5. The method for preparing high-purity, dense, fine PtRh alloy spherical powder according to claim 1, characterized in that: The particle size range of the composite powder C is 1.5 to 7.5 μm.

6. The method for preparing high-purity, dense, fine PtRh alloy spherical powder according to claim 1, characterized in that: The method for obtaining composite powder C by high-energy ball milling the ductile-brittle raw material system B is as follows: The powder obtained by high-energy ball milling of the ductile-brittle raw material system B is classified, and the powder within the desired particle size range is retained. The remaining powder is further subjected to high-energy ball milling. The above process is repeated until the particle size of all powders meets the desired particle size range, thereby obtaining composite powder C; The classification method is mechanical screening or air flow classification.

7. The method for preparing high-purity, dense, fine PtRh alloy spherical powder according to claim 1, characterized in that: The process parameters for plasma in-situ melting and spheroidization of composite powder C are: The power of the inductively coupled plasma torch is 20kW to 50kW; the working gas is oxygen, and the working gas flow rate is 20slpm to 40slpm; the side gas is oxygen, and the side gas flow rate is 100slpm to 400slpm; the carrier gas is oxygen, and the carrier gas flow rate is 1slpm to 10slpm; the system pressure of the inductively coupled plasma torch is 50kPa-98kPa; The powder feeding rate of composite powder C is 10 g / min to 80 g / min.

8. The method for preparing high-purity, dense, fine PtRh alloy spherical powder according to claim 1, characterized in that: The alkaline solution is an aqueous solution of NaOH, KOH, Na2CO3 or NaHCO3, and the pH value of the alkaline solution is ≥9; after removing the non-metallic slag phase in the composite spherical powder D using excess alkaline solution, the resulting product is repeatedly washed to neutrality and dried to obtain PtRh alloy spherical powder; The yield of PtRh alloy spherical powder is ≥98%.

9. A high-purity, dense, fine PtRh alloy spherical powder, characterized in that: The method for preparing a high-purity, dense, fine PtRh alloy spherical powder according to any one of claims 1 to 8 is used to obtain the PtRh alloy spherical powder, wherein the particle size range of the PtRh alloy spherical powder is 1 to 5 μm, the average particle size is 2 to 4 μm, and the tap density is ≥7 g / cm 3 , sphericity ≥ 0.96, sphericity ≥ 98%, purity ≥ 99.9%.

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