Method for synthesizing cubic boron nitride with composite catalyst

Abstract

The application relates to a method for synthesizing cubic boron nitride by using a composite catalyst. The method selects hexagonal boron nitride h-BN with a proper particle size as raw material, and a mixture of high-entropy alloy FeCoNiCrCu and elemental metal Al as a composite catalyst, fully mixes and presses into a sheet, and then synthesizes cubic boron nitride c-BN under the conditions of high temperature and high pressure. Yellow c-BN crystals can be obtained through acid and alkali purification. The composite catalyst is suitable for large-scale production, can effectively reduce the synthesis conditions of c-BN, and has a good application prospect in the synthesis of high-quality c-BN as a new catalyst.

Description

Technical Field

[0001] This invention belongs to the field of superhard material synthesis technology, and specifically relates to a method for synthesizing cubic boron nitride crystals using a composite catalyst. Background Technology

[0002] Cubic boron nitride (c-BN), along with diamond, SiC, and GaN, is known as a third-generation semiconductor material. It has a crystal structure similar to diamond, and its hardness is second only to diamond. It also has good chemical stability at high temperatures, corrosion resistance, oxidation resistance, ultra-wide bandgap, high thermal conductivity, and low dielectric constant. These properties make it superior to diamond in terms of thermal stability and chemical inertness to ferrous metals, and it is widely used in the cutting tool, abrasive industry, and high-precision metal processing fields.

[0003] In 1957, R.R. Wentoff of the United States first synthesized c-BN, and its excellent physicochemical properties attracted widespread attention from researchers. The synthesis of c-BN is mainly divided into high-pressure synthesis and low-pressure synthesis. Industrial-scale synthesis of c-BN primarily employs the high-temperature, high-pressure catalytic method, using hexagonal boron nitride (h-BN) as a raw material. The catalytic action of the catalyst lowers the reaction conditions, promoting the conversion of h-BN to c-BN and crystal growth under high temperature and pressure. This is another new high-tech product that emerged after the advent of synthetic diamond. The catalyst material not only reduces the temperature and pressure required for c-BN synthesis but also plays a dual role in dissolving h-BN and catalyzing its conversion to c-BN. Therefore, the type and quality of the catalyst material have a significant impact on the conversion rate, crystal form, impact strength, and particle size distribution of c-BN. Currently, alkali metals, alkaline earth metals, and their nitrides, borides, and nitrogen-borides are commonly used as catalyst materials. These catalyst materials are chemically active, easily oxidized, and difficult to store. They also have high environmental requirements in actual operation, which in turn affects the conversion rate of c-BN and the synthesis of high-quality c-BN.

[0004] Since catalysts have a significant impact on the synthesis of c-BN, researchers have been exploring novel catalyst materials to improve their chemical stability in order to ensure the acquisition of high-quality c-BN materials. Summary of the Invention

[0005] This invention provides a method for synthesizing cubic boron nitride using a high-entropy alloy FeCoNiCrCu and elemental metal Al as a composite catalyst. By preparing a specific ratio of high-entropy alloy FeCoNiCrCu mixed with elemental metal Al as a novel composite catalyst, and using it for the high-temperature and high-pressure synthesis of h-BN to c-BN, the shortcomings of existing technologies are overcome.

[0006] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0007] 1. High-entropy alloy FeCoNiCrCu was obtained by mechanical ball milling. Iron powder, cobalt powder, nickel powder, chromium powder and copper powder were weighed in an equimolar ratio and placed together in a ball mill jar. The mass ratio of grinding balls to the metal mixture powder was 25:1. The mixture was dry-milled at 800 rpm under an argon protective atmosphere. The milling cycle was repeated for 5 minutes in the forward direction followed by a 1-minute rest, then 5 minutes in the reverse direction followed by a 1-minute rest. The total milling time was 10 hours.

[0008] 2. High-entropy alloy FeCoNiCrCu and elemental metal Al are selected as composite catalysts, wherein the mass of metal Al accounts for 3% of the total mass of the composite catalyst.

[0009] 3. Select h-BN with suitable particle size as raw material and vacuum dry it for 120 mins at a temperature not exceeding 700℃.

[0010] 4. Weigh out h-BN and composite catalyst at a mass ratio of 1:1.3 and mix them thoroughly.

[0011] 5. Press the mixture into a cylindrical shape using a hydraulic press, insert a graphite heating device and then fit it into a pyrophyllite assembly block. Place the whole assembly into the chamber of a domestic six-sided hydraulic press and heat it at a pressure of 5-5.5 GPa and a temperature of 1500-2000℃ for 5-30 minutes.

[0012] 6. The synthesized sample was crushed and purified by acid and alkali to obtain c-BN crystals, which were amber to yellow in color and mostly irregular and sharp in shape.

[0013] This invention employs a high-entropy alloy FeCoNiCrCu and elemental metal Al as a composite catalyst, which exhibits good physicochemical stability and is easy to store. Compared to catalysts such as lithium nitride and calcium nitride, it is cheaper, reducing production costs. The production process of the composite catalyst is simple and convenient, providing a reliable guarantee for its application in c-BN synthesis. It overcomes the complexity, oxidizing properties, and inconvenience of existing alkali metal, alkaline earth metal, and their nitrides, borides, and nitrogen-borides catalysts. Therefore, this invention has positive and progressive effects and broad application prospects. Attached Figure Description

[0014] Figure 1 X-ray diffraction (XRD) pattern of the high-entropy alloy FeCoNiCrCu.

[0015] Figure 2 Scanning electron microscope (SEM) images and selected area electron spectroscopy (EDS) mapping diagrams of the high-entropy alloy FeCoNiCrCu.

[0016] Figure 3X-ray diffraction (XRD) pattern of c-BN under pressure of 5.5 GPa, temperature of 1800℃, and pressure and heat treatment for 30 mins.

[0017] Figure 4 The optical microscope image of c-BN crystal was obtained after acid-base purification treatment.

[0018] Figure 5 X-ray diffraction (XRD) pattern of c-BN under pressure of 5 GPa, temperature of 1500℃, and pressure and heat preservation for 30 mins. Detailed Implementation

[0019] To make the essential features of the present invention easier to understand, the embodiments are further described in detail with reference to the accompanying drawings and descriptions. However, the following descriptions and explanations of the embodiments do not constitute any limitation on the scope of protection of the present invention.

[0020] Example 1: Preparation of high-entropy alloys FeCoNiCrCu

[0021] This invention uses a high-entropy alloy FeCoNiCrCu and elemental metal Al as a composite catalyst. The elements in the high-entropy alloy FeCoNiCrCu are weighed in an equimolar ratio and placed together in a ball mill jar for mechanical ball milling. The mass ratio of balls to high-entropy alloy is 25:1. The ball mill is operated at 800 rpm under an argon protective atmosphere for dry milling. The milling cycle is repeated for 5 minutes in the forward direction followed by a 1-minute rest, then 5 minutes in the reverse direction followed by a 1-minute rest, for a total of 10 hours. Figure 1 The XRD patterns of the high-entropy alloy FeCoNiCrCu synthesized by ball milling are presented. Figure 1 As can be seen from the data, the synthesized sample is a high-entropy alloy with a face-centered cubic phase structure, and the sample is pure and free of impurities. Figure 2 The images show scanning electron microscope (SEM) images and selected area electron spectroscopy (EDS) mappings of the high-entropy alloy FeCoNiCrCu. Figure 2 As can be seen, the elements are evenly distributed with no obvious segregation, and... Figure 1 The XRD results were consistent, confirming that the sample synthesized after ball milling was a high-entropy alloy FeCoNiCrCu with a single-phase face-centered cubic structure.

[0022] Example 2: Synthesis of c-BN using composite catalyst

[0023] The synthesis experiment of this invention was carried out on a domestically produced six-sided top press. h-BN with a suitable particle size was selected as the raw material and vacuum dried for 120 minutes at a temperature not exceeding 700°C. A high-entropy alloy FeCoNiCrCu and elemental metal Al were used as the composite catalyst, with Al accounting for 3% of the total mass of the composite catalyst. The raw material h-BN and the composite catalyst were weighed and thoroughly mixed at a mass ratio of 1:1.3. The mixture was then pressed into a cylindrical shape using a hydraulic press, placed inside a graphite heating device, and fitted with a pyrophyllite assembly block. The entire assembly was then placed in the chamber of a domestically produced six-sided top hydraulic press and held at a pressure of 5.5 GPa and a temperature of 1800°C for 30 minutes. Figure 3 The XRD patterns of samples synthesized under heating at 5.5 GPa and 1800℃ for 30 mins are presented. Figure 3 As can be seen, the XRD peaks of the synthesized sample correspond to the c-BN peaks in the standard card PDF#35-1365, confirming that h-BN has completed the phase transition to c-BN, thus obtaining the c-BN material. Figure 4 Optical microscope image of c-BN crystal obtained after crushing and acid-base purification treatment, from Figure 4 As can be clearly seen, the synthesized c-BN is amber to yellow in color, with mostly irregular and sharp crystal morphologies, and a particle size distribution of 50-500 μm. For comparison, Figure 5 The XRD patterns of samples synthesized under a pressure of 5 GPa and a temperature of 1500 °C for 30 mins are presented. Figure 5 As can be seen, the XRD peaks of the synthesized sample correspond to those of the standard card PDF#35-1365, indicating that c-BN materials can be obtained even under reduced high-temperature and high-pressure synthesis conditions. This demonstrates that the composite catalyst of the novel high-entropy alloy FeCoNiCrCu and elemental metal Al can effectively reduce the synthesis conditions of c-BN.

[0024] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, all modifications and improvements made by those skilled in the art to the technical solutions within the scope of the present invention or equivalent to the scope of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for synthesizing cubic boron nitride using a composite catalyst, comprising: selecting hexagonal boron nitride with suitable particle size as raw material, and vacuum drying at a temperature not exceeding 700℃ for 120 mins; using high-entropy alloy FeCoNiCrCu and elemental metal Al as composite catalyst, weighing and thoroughly mixing them according to a mass ratio of h-BN:(FeCoNiCrCu+Al)=1:1.3; hydraulically pressing the mixture into a cylindrical shape, loading it into a heating device and fitting it into a pyrophyllite assembly block, and placing the whole assembly into the chamber of a domestic six-sided hydraulic press, maintaining the pressure at a pressure of 5-5.5 GPa and a temperature of 1500-2000℃ for 5-30 mins; and obtaining cubic boron nitride crystals after acid-base purification treatment.

2. The method for synthesizing cubic boron nitride using a composite catalyst according to claim 1, characterized in that: The high-entropy alloy FeCoNiCrCu used has elements in equimolar ratios, and the mass of elemental metal Al accounts for 3% of the total mass of the composite catalyst.

3. The method for synthesizing cubic boron nitride using a composite catalyst according to claim 1, characterized in that: The high-entropy alloy FeCoNiCrCu was obtained by mechanical ball milling, with a ball-to-raw material mass ratio of 25:

1. The ball milling was carried out at 800 rpm in an argon atmosphere, with a 5-minute clockwise rotation followed by a 1-minute rest, then a 5-minute counterclockwise rotation followed by a 1-minute rest, and this cycle was repeated for a total of 10 hours.

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