Preparation method of platinum, rhodium and palladium single crystal powder

Abstract

The invention discloses a preparation method of platinum, rhodium and palladium single crystal powder, which belongs to the field of metal powder material preparation and comprises the steps of carbon dissolution, slow cooling crystallization, single crystal powder preparation, carbon removal and the like. The operation method can be used for preparing micron-scale and submillimeter-scale single crystal powder of precious metals such as platinum, rhodium and palladium in batches.

Description

Technical Field

[0001] This application relates to the field of metal powder material preparation technology, and in particular to a method for preparing platinum, rhodium, and palladium single crystal powders. Background Technology

[0002] The preparation of single-crystal metal powders is a highly technical field. Single-crystal metal powders refer to materials in which each individual powder particle has a single crystal structure. Their typical characteristics include: the absence of grain boundaries within a single particle; all atoms within the particle sharing the same crystallographic orientation; and the existence of the material as independent particles at the nanometer, micrometer, or millimeter scale, rather than as bulk materials or thin films.

[0003] Current methods for preparing single-crystal metal powders mainly include: 1. Molten metal atomization method: molten metal streams are broken into fine droplets using high-pressure inert gas or centrifugal force, and single crystals are generated during the cooling and solidification process. 2. Chemical vapor deposition method: metal compounds decompose at high temperatures or react with reducing gases to deposit metal atoms on a substrate (usually requiring seed crystals), and the conditions are controlled to allow them to grow epitaxially into single-crystal particles. 3. Liquid-phase chemical reduction method: reducing agents (such as NaBH4, N2H4, ascorbic acid, polyols, etc.) are used in aqueous solutions or organic solvents to reduce salt metal ions. By controlling the reduction kinetics and adding surfactants or ligands, metal atoms are directionally grown into single-crystal particles on specific crystal planes. This method is also the most commonly used method for preparing noble metal single-crystal nanopowders. 4. Single-crystal crushing method: large high-purity metal single-crystal ingots are first prepared by zone melting or single-crystal pulling technology, and then crushed into powder by special mechanical crushing (such as low-temperature crushing, high-energy ball milling).

[0004] Platinum, rhodium, and palladium, the three platinum group metals, can dissolve a certain amount of carbon atoms in their molten state, but their solid solubility for carbon after solidification is extremely low. That is, the solid-phase carbon concentration (CS) is much lower than the liquid-phase carbon concentration (CL), with an equilibrium partition coefficient (k0 ≈ 0.1). This causes carbon to strongly segregate into the liquid phase at the solidification front, eventually precipitating at the grain boundaries. Simultaneously, since almost no stable carbides are formed in the platinum-carbon, rhodium-carbon, and palladium-carbon systems at low temperatures, the precipitated carbon is continuously distributed along the grain boundaries in the form of graphite sheets, inducing grain boundary embrittlement, reducing the ductility of the platinum group metals, causing intergranular fracture during processing, and making them easily fragmented into individual grains by physical crushing methods. This invention utilizes this characteristic to provide a novel method for preparing single-crystal metal powders. Summary of the Invention

[0005] This application provides a method for preparing single-crystal powders of platinum, rhodium, and palladium. Through steps such as carbon dissolution, slow cooling crystallization, single-crystal powder preparation, and carbon removal, micron- and sub-millimeter-sized single-crystal powders of precious metals such as platinum, rhodium, and palladium can be obtained in batches.

[0006] The technical solution adopted in this application is as follows:

[0007] A method for preparing platinum, rhodium, and palladium single crystal powder, the method comprising the following steps:

[0008] (1) Carbon dissolution: Platinum, rhodium or palladium and excess high-purity carbon powder are melted and kept warm in a high-purity graphite crucible under argon or vacuum atmosphere;

[0009] (2) Slow cooling crystallization: The melt is slowly cooled to crystallization, and then the temperature is continuously and slowly cooled to a certain temperature, with the cooling rate being lower than the critical value;

[0010] (3) Preparation of single crystal powder: The slowly cooled and crystallized ingot is crushed step by step until it is made into single crystal powder particles;

[0011] (4) Carbon removal: The carbon powder mixed with single crystal powder and the carbon coating on the surface of single crystal particles are removed by strong oxidizing acid treatment and high temperature oxidation.

[0012] Excessive high-purity toner refers to a toner mass fraction ≥0.1% for platinum and rhodium, and ≥1% for palladium.

[0013] Platinum, rhodium, or palladium are held in a graphite crucible at a temperature T ≤ Tm + 50℃, where Tm is the melting temperature, and the holding time is until the high-purity carbon powder dissolves to saturation.

[0014] Slowly cooling to a certain temperature means slowly cooling platinum to 1200℃, rhodium to 900℃, and palladium to 1100℃.

[0015] When preparing single-crystal powder of platinum, the critical value is 2℃ / min; when preparing single-crystal powder of rhodium, the critical value is 1℃ / min; and when preparing single-crystal powder of palladium, the critical value is 3℃ / min.

[0016] Strong oxidizing acid treatment refers to treating metal single crystal powder with concentrated sulfuric acid, a mixture of concentrated sulfuric acid and concentrated nitric acid, or perchloric acid at 80-120℃ for 2-4 hours.

[0017] High-temperature oxidation refers to heating the powder to 600-750℃ and holding it at that temperature for 1-3 hours in a flowing air or oxygen atmosphere.

[0018] The beneficial effects of this application are as follows:

[0019] This method utilizes the fact that the solid carbon concentration (CS) of metals such as platinum, rhodium, and palladium is much lower than the liquid carbon concentration (CL), and that graphite sheets continuously precipitate at the grain boundaries during slow solidification, leading to grain boundary embrittlement and easy intergranular fracture. Through steps such as carbon dissolution, slow cooling crystallization, single-crystal powder preparation, and carbon removal, micron- and sub-millimeter-sized single-crystal powders of precious metals such as platinum, rhodium, and palladium can be obtained in batches at low cost and high efficiency. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] Example 1

[0022] (1) Carbon dissolution: 2 kg of platinum and 4 g of high-purity carbon powder are melted in a high-purity graphite crucible under vacuum and kept at 1800 °C until the amount of carbon powder floating on the upper layer remains unchanged.

[0023] (2) Slow cooling crystallization: The platinum melt is slowly cooled to crystallization at a rate of 1.5℃ / min, and then slowly cooled to 1200℃ before being removed;

[0024] (3) Preparation of single crystal powder: The slowly cooled and crystallized platinum ingot is mechanically crushed step by step until it is made into single crystal powder particles;

[0025] (4) Carbon removal: The crushed platinum single crystal and graphite mixed powder are immersed in concentrated sulfuric acid, heated to 100°C and continuously stirred for 4 hours to oxidize and remove the graphite powder in the mixed powder. After sedimentation, the upper layer of concentrated sulfuric acid is removed. The remaining concentrated sulfuric acid is diluted with water, the platinum single crystal powder is filtered out, washed and dried, spread on a quartz boat and sent into a tube furnace. Flowing air is continuously introduced into the tube furnace, heated to 700°C and held for 3 hours to remove the carbon coating on the surface of the platinum single crystal particles and obtain pure platinum single crystal powder particles.

[0026] Example 2

[0027] (1) Carbon dissolution: 1 kg of rhodium and 2 g of high-purity carbon powder are melted in a high-purity graphite crucible under vacuum and kept at 2000℃ until the amount of carbon powder floating on the upper layer remains unchanged.

[0028] (2) Slow cooling crystallization: The rhodium melt is slowly cooled to crystallization at a rate of 1℃ / min, and then slowly cooled to 900℃ before being removed;

[0029] (3) Preparation of single crystal powder: The slowly cooled and crystallized rhodium ingot is mechanically crushed step by step until it is made into single crystal powder particles;

[0030] (4) Carbon removal: The crushed rhodium single crystal and graphite mixed powder are immersed in a mixture of 50% concentrated sulfuric acid and 50% concentrated nitric acid, heated to 100°C and continuously stirred for 2 hours to oxidize and remove the graphite powder in the mixed powder. After sedimentation, the upper layer of mixed concentrated acid is removed, the remaining mixed acid is diluted with water, the rhodium single crystal powder is filtered out, washed and dried, spread on a quartz boat and sent into a tube furnace. Flowing air is continuously introduced into the tube furnace, heated to 650°C and held for 2 hours to remove the carbon coating on the surface of the clean rhodium single crystal particles and obtain pure rhodium single crystal powder particles.

[0031] Example 3

[0032] (1) Carbon dissolution: 2 kg of palladium and 25 g of high-purity carbon powder are melted in a high-purity graphite crucible under vacuum and kept at 1580 °C until the amount of carbon powder floating on the upper layer remains unchanged.

[0033] (2) Slow cooling crystallization: The palladium melt is slowly cooled to crystallization at a rate of 3℃ / min, and then slowly cooled to 1100℃ before being removed;

[0034] (3) Preparation of single crystal powder: The palladium ingot that has been slowly cooled and crystallized is crushed step by step by mechanical means until it is made into single crystal powder particles;

[0035] (4) Carbon removal: The crushed palladium single crystal and graphite mixed powder are immersed in perchloric acid, heated to 80°C and continuously stirred for 4 hours to oxidize and remove the graphite powder in the mixed powder. After sedimentation, the upper layer of concentrated acid is removed. The remaining perchloric acid is diluted with water, the palladium single crystal powder is filtered out, washed and dried, spread on a quartz boat and sent into a tube furnace. Flowing oxygen is continuously introduced into the tube furnace, heated to 750°C and held for 3 hours to remove the carbon coating on the surface of the palladium single crystal particles, and obtain pure palladium single crystal powder particles.

[0036] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A method for producing a platinum, rhodium, palladium single crystal powder, characterized by, The preparation method comprises the following steps: (1) carbon dissolving: melting and holding platinum, rhodium or palladium with excess high-purity carbon powder in a high-purity graphite crucible under an argon or vacuum atmosphere; (2) slow cooling crystallization: slowly cooling the melt to crystallize, and continuously slowly cooling to a certain temperature at a cooling rate lower than a critical value; (3) single crystal powder preparation: step-by-step crushing the slowly cooled and crystallized ingot until single crystal powder particles are prepared; (4) carbon removal: removing the carbon powder mixed with the single crystal powder and the carbon coated on the surface of the single crystal particles by using strong oxidizing acid treatment and high-temperature oxidation.

2. The production method according to claim 1, characterized by: The excess high-purity carbon powder refers to a mass fraction of carbon powder ≥0.1% for platinum and rhodium.

3. The production method according to claim 1, wherein: The excess high-purity carbon powder refers to a mass fraction of carbon powder ≥1% for palladium.

4. The production method according to claim 1, wherein: The holding temperature of platinum, rhodium or palladium in the graphite crucible is T≤Tm+50℃, Tm is the melting temperature, and the holding time is until the high-purity carbon powder is dissolved to reach a saturated state.

5. The production method according to claim 1, wherein: The slowly cooling to a certain temperature refers to slowly cooling platinum to 1200℃, slowly cooling rhodium to 900℃, and slowly cooling palladium to 1100℃.

6. The production method according to claim 1, wherein: The critical value for preparing platinum single crystal powder is 2℃ / min.

7. The production method according to claim 1, wherein: The critical value for preparing rhodium single crystal powder is 1℃ / min.

8. The production method according to claim 1, wherein: The critical value for preparing palladium single crystal powder is 3℃ / min.

9. The production method according to claim 1, wherein: The strong oxidizing acid treatment refers to stirring the metal single crystal powder at 80-120℃ for 2-4 hours by using concentrated sulfuric acid, a mixture of concentrated sulfuric acid and concentrated nitric acid or perchloric acid.

10. The production method according to claim 1, wherein: The high-temperature oxidation method refers to heating the powder to 600-750℃ and holding the treatment for 1-3 hours in a flowing air or oxygen atmosphere.