A method for preparing a hot-pressed cubic boron nitride precursor

Abstract

The application relates to a preparation method of a hot-pressing cubic boron nitride precursor, which uses hexagonal boron nitride with appropriate particle size as raw material, and obtains the precursor through pretreatment such as drying, hot pressing, catalyst mixing and grinding. The precursor obtained by the method has high forming density, can inhibit pressure loss caused by volume collapse in the synthesis process of cubic boron nitride, is suitable for large-scale production, improves the conversion rate of h-BN to c-BN, and reduces the production cost.

Description

Technical Field

[0001] This invention belongs to the field of superhard material synthesis technology, and specifically relates to a method for preparing a synthetic cubic boron nitride precursor. Background Technology

[0002] As the second hardest natural mineral after diamond, cubic boron nitride (c-BN) has unparalleled advantages over diamond in terms of thermal stability and chemical inertness to ferrous metals. It has broad and irreplaceable application prospects, especially in the abrasive industry and high-precision metal processing.

[0003] In 1957, Wentolf of General Electric Company in the United States first synthesized c-BN single crystals using metallic Mg as a catalyst and a high-temperature, high-pressure method. Its excellent physicochemical properties attracted widespread research interest from scientists in various fields. Currently, the industrial synthesis of c-BN mainly employs the high-temperature, high-pressure catalytic method, using hexagonal boron nitride (h-BN) as raw material. A six-sided press is used, and under high temperature, high pressure, and the action of a catalyst, the transformation from h-BN to c-BN is achieved. h-BN is typically used as the raw material for c-BN synthesis, and its properties directly affect the grade and grain size of the synthesized c-BN. For example, the crystallinity, purity, and density of h-BN all influence the synthesis of c-BN. Therefore, during the high-pressure, high-temperature catalytic conversion of h-BN to c-BN, the particle size, compositional distribution, and forming density of the precursor are crucial for the nucleation of c-BN materials. Common precursor treatment methods include: removing impurities such as oxygen and water from the raw materials at high temperatures, or applying a certain pressure to the raw materials to improve their density. However, these treatments cannot significantly improve or reduce reaction conditions. Summary of the Invention

[0004] To address the problems in the prior art, the present invention aims to provide a method for preparing a precursor for the synthesis of cubic boron nitride. To achieve this objective, the technical solution adopted by the present invention is as follows:

[0005] (1) Select h-BN with an average particle size of 100nm as raw material, put it in a vacuum drying oven and dry it for 120mins at a temperature not exceeding 700℃.

[0006] (2) The dried sample was filled into a graphite tube heating body with a diameter of 10 mm, and then placed into a pyrophyllite assembly block. The whole assembly was placed into the cavity of a six-sided hydraulic press and held at a pressure of 5 GPa and a temperature of 1000℃ for 10-30 mins to form polymerized BN.

[0007] (3) Mix polymerized BN and catalyst uniformly at a mass ratio of 1:(1-1.5).

[0008] (4) After the mixture is pressed into shape by hydraulic press, it is put into a graphite tube heating body with a diameter of 4mm and then put into the pyrophyllite assembly block. The assembly block is heated and pressed at a pressure of 5GPa and a temperature of 500℃-700℃ for 20-30mins to obtain the precursor block material, which can be directly used to synthesize c-BN later.

[0009] This invention uses h-BN as raw material and obtains the precursor for synthesizing c-BN through processes such as drying, hot pressing, calcination, pulverization, mixing, and re-hot pressing. The precursor is obtained through two hot pressing processes under high temperature and high pressure, significantly increasing its density. The first hot pressing causes the h-BN raw material to form polymeric BN; the second hot pressing utilizes the excellent extensibility and fluidity of the metal catalyst to fully contact the polymeric BN, filling the gaps in the polymeric BN with the metal catalyst, ultimately obtaining a precursor with high molding density. This invention allows for the batch synthesis of high-density precursors, reducing pressure loss caused by volume collapse during the later c-BN synthesis process. The high-density precursor not only reduces the pressure and temperature required for c-BN synthesis but also improves the conversion rate from h-BN to c-BN, reducing production costs and increasing yield. Attached Figure Description

[0010] Figure 1 Scanning electron microscope (SEM) image of polymerized BN under pressure of 5 GPa, temperature of 1000℃, and pressure and heat treatment for 10 mins.

[0011] Figure 2 Comparison of X-ray diffraction (XRD) images of c-BN synthesized by mixing precursor and raw material h-BN with catalyst.

[0012] Figure 3 Scanning electron microscope (SEM) image of c-BN synthesized from precursor.

[0013] Figure 4 Scanning electron microscope (SEM) image of c-BN synthesized by mixing raw material h-BN with catalyst. Detailed Implementation

[0014] 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.

[0015] Example 1

[0016] h-BN with an average particle size of 100 nm was selected as the raw material and placed in a vacuum drying oven, where it was dried for 120 mins at a temperature not exceeding 700℃. The dried h-BN powder was then pressed into cylinders with a diameter of 10 mm using a hydraulic press. The pressed cylinders were then placed into graphite tube heating elements with a diameter of 10 mm, which were then fitted into pyrophyllite assembly blocks. The assembled pyrophyllite blocks were then placed into the cavity of a domestically produced six-sided hydraulic press and held at a pressure of 5 GPa and a temperature of 1000℃ for 10 mins to obtain polymerized BN. Figure 1 SEM images of polymerized BN at a pressure of 5 GPa, a temperature of 1000℃, and a holding time of 10 mins are presented. Figure 1 As can be seen, the lamellar h-BN in the raw material forms a new polymer under hot pressing, and the density of the polymerized BN increases significantly.

[0017] Example 2

[0018] Polymerized BN and a catalyst were thoroughly mixed at a mass ratio of 1:1.2 and pressed into cylinders with a diameter of 4 mm. These cylinders were then re-inserted into a heating device and placed inside a pyrophyllite assembly block. The assembly block was then hot-pressed at a pressure of 5 GPa and a temperature of 700 °C for 30 min. After hot pressing, a high-density precursor was obtained. To verify the effectiveness of the precursor, c-BN material was synthesized at a pressure of 5.5 GPa and a temperature of 2000 °C for 30 min. Figure 2 The XRD pattern of the final product is given. Figure 2 As can be seen in Figure a, the diffraction peaks of the synthesized sample correspond to the c-BN diffraction peaks of the standard card PDF#35-1365, indicating that h-BN can be effectively converted into c-BN under this temperature and pressure conditions. Figure 3 SEM images of the precursor synthesis of c-BN are given, from Figure 3 It can be clearly seen that the sample surface is a whole, with some bulk c-BN generated, and in some areas, the growth steps of exposed c-BN can be seen.

[0019] For comparison, experiments were conducted using a mixture of raw material h-BN and catalyst under the same high-temperature and high-pressure synthesis conditions for c-BN. Figure 2 As can be seen in b, there are no diffraction peaks of c-BN at all, only diffraction peaks of h-BN, indicating that c-BN material cannot be obtained by mixing under the same temperature and pressure conditions. Figure 4 SEM images of the synthesis of c-BN from the mixture of raw material h-BN and catalyst are presented. Figure 4 As can be seen, after being subjected to high temperature and high pressure conditions, the raw material layered h-BN and the metal catalyst do not cross-link with each other, the particles are distinct, the catalyst and h-BN do not undergo significant changes, and the synthesis of large-scale c-BN is not observed.

[0020] Comparative experiments have confirmed that using high-density precursors to synthesize c-BN can reduce pressure loss caused by volume collapse during synthesis, thereby reducing the pressure and temperature required for c-BN synthesis. It can also improve the conversion rate of h-BN to c-BN, reduce production costs, and increase yield.

[0021] 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 producing a hot-pressed cubic boron nitride precursor, characterized by, The average particle size of 100 nm hexagonal boron nitride h-BN is sequentially sleeved into a graphite tube heating body, a leaf wax stone assembly block, and a domestic six-face hydraulic machine cavity, and after heat pressing at a pressure of 5 GPa and a temperature of 1000 DEG C for 10-30 mins, a polymerized BN is formed; the polymerized BN is uniformly mixed with a catalyst at a mass ratio of 1:(1-1.5) and then reloaded into a high-temperature high-pressure device, and after heat pressing at a pressure of 5 GPa and a temperature of 500-700 DEG C for 20-30 mins, the metal catalyst and the polymerized BN are fully contacted, the polymerized BN gap is filled with the metal catalyst by using the excellent ductility and flowability of the metal, and after heat pressing, a precursor with high molding density is obtained.

2. The method of claim 1, wherein The average particle size of 100 nm h-BN is selected as a raw material, and is dried at a temperature of not more than 700 DEG C for 120 mins.

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