Method for generating silicon carbide layer on diamond surface at low temperature by molten salt method

Abstract

According to the method for generating the silicon carbide layer on the surface of the diamond at the low temperature through the molten salt method, Mg2Si serves as a silicon source, the uniform silicon carbide layer is generated in a molten salt system at the low temperature, and the problems that in the prior art, the reaction temperature is high, and the requirement for equipment is high are effectively solved. The silicon carbide layer generated by the method is uniform and compact, the interface bonding property of a composite material taking diamond as a reinforced phase is remarkably improved, and the method has important application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of diamond processing, and particularly relates to a method for generating a silicon carbide layer on the surface of diamond at low temperature by a molten salt method. Background Art

[0002] Diamond is one of the materials with the highest thermal conductivity in nature (the thermal conductivity is about 1000 - 2000 W / m·K), and has the advantages of good wear resistance, low expansion coefficient, high strength, high hardness and low density. With the continuous maturity of the preparation process of synthetic diamond and the reduction of production cost, it has been widely used in various materials such as cutting, grinding, polishing and thermal management.

[0003] However, in the preparation process of diamond - metal / ceramic matrix composites, the high chemical inertness of diamond leads to low interfacial bonding with the matrix. Therefore, during the cutting, grinding and polishing processes, diamond particles often fall off from the matrix, and the rapid wear of the tool results in a decline in processing quality. On the other hand, in thermal management materials, the interfacial bonding between diamond and the matrix plays a key role in high thermal conductivity, because the interfacial thermal resistance usually increases due to the weak bonding at the interface, leading to a sharp decline in thermal conductivity. In addition, diamond will oxidize in air during high - temperature applications and undergo a graphitization transformation under low pressure in a non - oxygen environment, which will seriously affect the performance of composites with diamond as the reinforcing phase.

[0004] Therefore, it is highly desirable to modify the surface of diamond, which is not only beneficial to preventing the oxidation and graphitization of diamond, but also helps to solve the problems of decline in mechanical and thermal properties caused by poor bonding between diamond and the matrix. Si is considered to be the most suitable element for surface modification of diamond, and the corresponding carbide silicon carbide not only has excellent oxidation resistance, high hardness and high thermal conductivity, but also has good physical compatibility and interfacial bonding with diamond.

[0005] However, there are still technical difficulties in generating a silicon carbide layer on the surface of diamond. Currently, the main method for generating a silicon carbide layer on the surface of diamond is in the form of reaction between liquid silicon or gaseous silicon and diamond, and the reaction temperature between Si and diamond is above the melting point of silicon (1410 °C). The high reaction temperature not only brings large thermal stress, but also causes the graphitization transformation of diamond. The silicon carbide layer can be generated on the surface of diamond at 1000 °C - 1150 °C by PVD or CVD methods, but the requirements for equipment are relatively high, which limits large - scale applications. Summary of the Invention

[0006] To solve the above problems, the present invention proposes a method for low-temperature formation of a silicon carbide layer on the surface of diamond by molten salt method. By using Mg2Si as the silicon source, Si atoms with high activity decomposed during the heating process of Mg2Si react with C atoms on the surface of diamond at low temperature to form silicon carbide. The sufficient contact between Si atoms and C atoms under the molten salt system is conducive to the formation of a uniform silicon carbide layer on the surface of diamond, improving the interfacial bonding of composites with diamond as the reinforcement phase during application. The single and uniform silicon carbide layer formed by this method is different from the form of silicon carbide layer + other layers formed by other low-temperature preparations. This method is simple in operation, low in cost, and high in repeatability, and can be applied to large-scale production. To achieve the above effects, on the one hand, the present invention provides a method for low-temperature formation of a silicon carbide layer on the surface of diamond by molten salt method, which is characterized by including the following steps: S1, successively clean the diamond with an acid solution and an alkali solution, dry it after washing to neutrality, and obtain pretreated diamond. S2, uniformly mix the pretreated diamond obtained in step S1 with Mg 2 Si in a certain proportion, then put it together with the chloride into an alumina crucible, heat and keep it warm for a certain time in a protective atmosphere, and form a coating on the surface of the diamond. S3, add the diamond with the coating obtained in step S2 to distilled water to dissolve the chloride salt, then soak it with sodium hydroxide solution, wash it with distilled water, dry it, and sieve it to obtain diamond with a silicon carbide layer formed on its surface. Further, in step S1, the acid can be one or several of hydrochloric acid, sulfuric acid, and nitric acid; the alkali can be one or several of sodium hydroxide, potassium hydroxide, and ammonia water.

[0007] In step S1, clean the diamond with hydrochloric acid solution to remove surface metal impurities, wash it with distilled water to neutrality; then clean the diamond with sodium hydroxide solution to remove surface grease, and then wash it with distilled water to neutrality and dry it to obtain pretreated diamond.

[0008] Further, in step S1, the concentration of the hydrochloric acid solution is 10~15wt%, and the concentration of the sodium hydroxide solution is 5~15wt%.

[0009] Further, in step S2, the holding temperature is 950~1100°C; preferably 1000~1050°C.

[0010] Further, in step S2, the mass ratio of Mg 2 Si to diamond is 1:(4~35).

[0011] Further, in step S2, the particle size of Mg 2 Si is 1~5μm.

[0012] Further, in step S2, the chloride is CaCl 2 , NaCl, KCl or more.

[0013] Furthermore, in step S3, the concentration of the sodium hydroxide solution is 5-15wt%, and the soaking time is 6-15h.

[0014] Furthermore, in step S2, the protective atmosphere is one or more of argon and helium.

[0015] The present invention also provides a diamond prepared by the above method, characterized in that the surface of the diamond has a silicon carbide coating layer.

[0016] The beneficial effects of the present invention are: 1. The present invention provides a method for low-temperature formation of a silicon carbide layer on a diamond surface by a molten salt method, wherein Mg 2 Si is the silicon source, and then chloride salt is used as the medium to generate a uniform single silicon carbide layer on the diamond surface at low temperature; Mg 2 Si decomposes during the heat treatment process, which can provide a highly active silicon element, thereby reacting with carbon atoms on the surface of diamond at low temperature to form silicon carbide. The temperature is as low as below 1000°C, which effectively avoids the graphitization transformation of diamond caused by high temperature treatment. At the same time, the present invention uses chloride salt as a medium, which greatly promotes the 2 The active silicon element decomposed from Si is transferred to the diamond surface. The great convenience of the reaction is conducive to the formation of a more uniform and dense silicon carbide layer, which significantly improves the interface bonding of subsequent composite materials with diamond as the reinforcement phase, and has important application prospects.

[0017] 2. The silicon carbide layer generated by the present invention is a single SiC layer, which avoids the problem of coexistence of silicon carbide layers and other impurity layers commonly seen in other low-temperature preparation methods. This single silicon carbide layer not only has a uniform structure, but also has a tighter bond with the diamond matrix, significantly improving the mechanical and thermal properties of the composite material. This method generates a single uniform silicon carbide layer, which is different from the form of silicon carbide layer + other layers generated by other low-temperature preparations.

[0018] 3. The molten salt method adopted in the present invention has a simple process, is easy to operate, does not require complicated equipment or high-cost raw materials, and is suitable for large-scale industrial production. The process of the present invention is simple, effectively reduces the temperature of generating a silicon carbide layer on the diamond surface, reduces energy consumption, improves efficiency, is conducive to large-scale production, and has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings, and other implementation manners can also be obtained. In the accompanying drawings: Figure 1 It is a schematic diagram of a method for generating a silicon carbide layer on the surface of diamond at low temperature by the molten salt method; Figure 2 It is the XRD pattern and XRS pattern of the diamond prepared in Example 1; Figure 3 It is the SEM and EDS patterns of the diamond prepared in Example 1; Figure 4 It is the SEM and EDS patterns of the diamond prepared in Comparative Example 1; Figure 5 It is the SEM and EDS patterns of the diamond prepared in Comparative Example 2 Specific Embodiments The following will further describe in detail the specific embodiments of the present invention in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0020] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or groups.

[0021] To make the drawings concise, only the parts related to the present invention are schematically shown in each drawing, and they do not represent the actual structure of the product. In addition, to make the drawings concise and easy to understand, in some drawings, components with the same structure or function are only schematically shown one of them, or only one of them is marked. In this article, "one" not only means "only this one", but also means "more than one" situation.

[0022] It should also be further understood that the term "and / or" used in the specification and appended claims of this application refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0023] In the embodiments shown in the drawings, the indication of directions (such as up, down, left, right, front and back) is used to explain that the structures and movements of various components of the present invention are not absolute but relative. When these components are in the positions shown in the drawings, these descriptions are appropriate. If the descriptions of the positions of these components change, the indication of these directions also changes accordingly.

[0024] In addition, in the description of the present application, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0025] Embodiment 1 A method for generating a silicon carbide layer on the surface of diamond at low temperature by a molten salt method, comprising the following steps: S1. Clean the diamond successively with a 10 wt% hydrochloric acid solution and a 10 wt% sodium hydroxide solution, then wash with distilled water until neutral and dry to obtain pretreated diamond; S2. Uniformly mix the pretreated diamond obtained in step S1 with Mg 2 Si in a mass ratio of 4:1, and then put it together with sodium chloride into an alumina crucible, heat and keep warm for a certain time in an argon atmosphere, the heating temperature is 1000 °C, and a coating is formed on the surface of the diamond.

[0026] S3. Add distilled water to the diamond with the coating obtained in step S2 to dissolve sodium chloride, soak it with a 10 wt% sodium hydroxide solution, wash with distilled water, dry and screen to obtain diamond with a silicon carbide layer formed on the surface.

[0027] Embodiment 2 A method for generating a silicon carbide layer on the surface of diamond at low temperature by a molten salt method, comprising the following steps: S1. Clean the diamond successively with a 10 wt% hydrochloric acid solution and a 10 wt% sodium hydroxide solution, then wash with distilled water until neutral and dry to obtain pretreated diamond; S2. Uniformly mix the pretreated diamond obtained in step S1 with Mg 2 Si in a mass ratio of 10:1, and then put it together with sodium chloride into an alumina crucible, heat and keep warm for a certain time in an argon atmosphere, the heating temperature is 1000 °C, and a coating is formed on the surface of the diamond.

[0028] S3. Add distilled water to the diamond with the coating obtained in step S2 to dissolve sodium chloride, soak it with a 10 wt% sodium hydroxide solution, wash with distilled water, dry and screen to obtain diamond with a silicon carbide layer formed on the surface.

[0029] Embodiment 3 A method for generating a silicon carbide layer on the surface of diamond at low temperature by a molten salt method, comprising the following steps: S1. Clean the diamond successively with 10wt% hydrochloric acid solution and 10wt% sodium hydroxide solution, then wash it with distilled water until neutral and dry to obtain the pretreated diamond; S2. Mix the pretreated diamond obtained in step S1 with Mg 2 Si in a mass ratio of 35:1 uniformly, then put it together with sodium chloride into an alumina crucible, heat and keep warm for a certain time in an argon atmosphere, the heating temperature is 1000 °C, and a coating is formed on the diamond surface.

[0030] S3. Add distilled water to the diamond with the coating obtained in step S2 to dissolve sodium chloride, soak it with 10wt% sodium hydroxide solution, wash it with distilled water, dry it and screen it to obtain the diamond with a silicon carbide layer formed on the surface.

[0031] Comparative Example 1 A method for low-temperature forming a silicon carbide layer on the diamond surface by the molten salt method, comprising the following steps: S1. Clean the diamond successively with 10wt% hydrochloric acid solution and 10wt% sodium hydroxide solution, then wash it with distilled water until neutral and dry to obtain the pretreated diamond; S2. Mix the pretreated diamond obtained in step S1 with Mg 2 Si in a mass ratio of 40:1 uniformly, then put it together with sodium chloride into an alumina crucible, heat and keep warm for a certain time in an argon atmosphere, the heating temperature is 1000 °C, and a coating is formed on the diamond surface.

[0032] S3. Add distilled water to the diamond with the coating obtained in step S2 to dissolve sodium chloride, soak it with 10wt% sodium hydroxide solution, wash it with distilled water, dry it and screen it to obtain the diamond with a silicon carbide layer formed on the surface.

[0033] Comparative Example 2 A method for low-temperature forming a silicon carbide layer on the diamond surface by the molten salt method, comprising the following steps: S1. Clean the diamond successively with 10wt% hydrochloric acid solution and 10wt% sodium hydroxide solution, then wash it with distilled water until neutral and dry to obtain the pretreated diamond; S2. Mix the pretreated diamond obtained in step S1 with Mg 2 Si in a mass ratio of 1:1 uniformly, then put it together with sodium chloride into an alumina crucible, heat and keep warm for a certain time in an argon atmosphere, the heating temperature is 1000 °C, and a coating is formed on the diamond surface.

[0034] S3. Add distilled water to the diamond with the coating obtained in step S2 to dissolve sodium chloride, soak it with 10wt% sodium hydroxide solution, wash it with distilled water, dry it and screen it to obtain the diamond with a silicon carbide layer formed on the surface.

[0035] Figure 1 It is a schematic diagram of a method for generating a silicon carbide layer on the surface of diamond at low temperature by the molten salt method, using Mg 2 Si will decompose at a certain temperature, decomposing into Si atoms with higher activity, which will then react with C atoms on the diamond surface to form SiC. The temperature at which SiC is generated by this method is effectively reduced, and a single SiC layer is formed. Also, the graphitization problem of diamond under high-temperature treatment is avoided.

[0036] Figure 2 It is the XRD and XPS tests on the diamond with a Si coating after holding at 1000 °C for 4 h with a mass ratio of diamond to Mg 2 Si of 1:35 (where b is the full XPS spectrum, and c and d are the Si2p and C1s graphs respectively). The XRD test results show that the coating on the diamond surface is SiC. XPS shows that: as can be seen in Fig. (b), the main components of the modified layer are Si, C, and O, and the O element may come from oxygen in the atmosphere. The high-resolution results of C1s and Si2p are shown in Figs. (c) and (d). It can be seen that C1s mainly exists in the form of C-C bonds and C-Si bonds, and Si2p exists in the form of Si-C bonds and Si-O bonds. The peaks at 283.0 eV for C1s and 100.9 eV for Si2p conform to the characteristics of the SiC phase, indicating that SiC is formed on the diamond surface, which is consistent with the XRD test results. All the evidence proves that a SiC modified layer is formed on the diamond surface. It should be noted that no Si-Si bonds are detected on the diamond surface, indicating that Si is not deposited on the diamond surface.

[0037] Figure 3 It is the surface morphology and energy spectrum stratification image obtained in Example 1. The particles on the diamond surface after holding for 4 h are evenly and densely packed, and the Si element is evenly distributed. It is proved by the above method that a SiC layer is formed on the diamond surface. Figure 4 and Figure 5 are the surface morphology and energy spectrum stratification images obtained in Comparative Example 1 and Comparative Example 2. By comparing Examples 1-3 and Comparative Examples 1-2, it can be concluded that the experimental results show that when the mass ratio of Mg 2 Si to diamond is in the range of 1:4 to 1:35, a uniform and stable silicon carbide (SiC) coating layer can be formed on the diamond surface. The mass ratio within this range ensures sufficient contact between the silicon source (Mg 2 Si) and the carbon atoms on the diamond surface, thus enabling an efficient reaction in the molten salt medium to form a dense and uniform SiC layer. The experimental results show that within these ranges, the SiC layer is evenly distributed on the diamond surface, and the coating layer structure is dense and tightly bonded to the diamond matrix. This indicates that within this mass ratio range, Mg 2The active silicon element decomposed from Si can fully react with the carbon atoms on the diamond surface to form a high-quality SiC layer.

[0038] When the mass ratio of Mg 2 Si to diamond is lower than 1:4 (such as 1:1), the silicon source is relatively excessive, resulting in that the silicon element cannot fully combine with the carbon atoms on the diamond surface during the reaction. Part of the silicon element forms a free state in the molten salt, and finally an uneven SiC layer is formed on the diamond surface, and even the residue of the silicon element appears, which affects the uniformity and stability of the coating layer. When Mg 2 Si to diamond is higher than 1:35 (such as 1:40), the silicon source is relatively insufficient, resulting in that the carbon atoms on the diamond surface cannot react with enough silicon element, and the formed SiC layer is thin and discontinuous, and a complete coating layer cannot be formed, which affects the stability and functionality of the SiC layer. By optimizing the mass ratio of Mg 2 Si to diamond, the present invention can not only form a uniform and stable SiC layer on the diamond surface, but also provide reliable technical support for the preparation of diamond-based composites. This high-quality SiC coating layer can significantly improve the interfacial bonding property, thermal conductivity and antioxidant property of the composites, and has broad application prospects in the fields of cutting tools, thermal management materials, electronic devices, etc.

[0039] The embodiments described above are some embodiments of the present invention, rather than all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for low-temperature formation of a silicon carbide layer on a diamond surface using a molten salt method, characterized in that: The steps include: S1, washing the diamond with an acid solution and an alkali solution in sequence, washing until it becomes neutral and then drying to obtain a pretreated diamond; S2, uniformly mixing the pretreated diamond obtained in step S1 with Mg2Si in a certain proportion, and then putting it into an alumina crucible together with chloride, heating and keeping it warm for a certain period of time in a protective atmosphere to form a coating on the surface of the diamond; S3, adding distilled water to dissolve chloride salt in the diamond with coating obtained in step S2, then soaking it in sodium hydroxide solution, washing it with distilled water, drying it, and sieving it to obtain diamond with silicon carbide layer formed on its surface.

2. The method for low-temperature formation of a silicon carbide layer on a diamond surface by a molten salt method according to claim 1, characterized in that: In step S1, the acid may be one or more of hydrochloric acid, sulfuric acid, and nitric acid; the alkali may be one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

3. The method for low-temperature formation of a silicon carbide layer on a diamond surface by a molten salt method according to claim 1, characterized in that: In step S1, the concentration of the hydrochloric acid solution is 10-15wt%, and the concentration of the sodium hydroxide solution is 5-15wt%.

4. The method for low-temperature formation of a silicon carbide layer on a diamond surface by a molten salt method according to claim 1, characterized in that: In step S2, the insulation temperature is 950-1100°C, preferably 1000-1050°C.

5. The method for low-temperature formation of a silicon carbide layer on a diamond surface by a molten salt method according to claim 1, characterized in that: In step S2, the mass ratio of Mg2Si to diamond is 1:(4-35).

6. The method for low-temperature formation of a silicon carbide layer on a diamond surface by a molten salt method according to claim 1, characterized in that: In the step S2, the particle size of Mg2Si is 1-5 μm.

7. The method for low-temperature formation of a silicon carbide layer on a diamond surface by a molten salt method according to claim 1, wherein in step S2, the chloride is one or more of CaCl2, NaCl, and KCl.

8. The method for generating a silicon carbide layer on a diamond surface at low temperature by a molten salt method according to claim 1, wherein in step S3, the concentration of the sodium hydroxide solution is 5-15wt%, and the immersion time is 6-15h.

9. The method for low-temperature generation of a silicon carbide layer on a diamond surface by a molten salt method according to claim 1, wherein in step S2, the protective atmosphere is one or more of argon and helium.

10. A diamond prepared by the method according to any one of claims 1 to 9, characterized in that: The diamond surface has a silicon carbide coating layer.

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