Cr2alc ceramic powder, preparation method and application thereof

Abstract

The application discloses a Cr2AlC ceramic powder and a preparation method and application thereof, and relates to the technical field of ceramic powder materials. The preparation method comprises the following steps: loading raw materials and a protective agent into a crucible to perform protective atmosphere sintering, wherein the protective agent covers the surface of the raw materials in the crucible; the raw materials comprise Cr3C2, Cr and Al with a molar ratio of 1:1:2; the protective agent comprises Al and graphite with a mass ratio of 1:(0.8-1.2), and the covering thickness of the protective agent is 15mm-20mm. The raw material surface is paved with a layer of protective agent to prevent the evaporation loss of aluminum, so that the component proportion of the raw materials is stable, and pure Cr2AlC ceramic powder can be formed after protective atmosphere sintering. Meanwhile, the method can be used for preparing large Cr2AlC ceramic powder, and high-yield and high-purity Cr2AlC ceramic powder can be obtained.

Description

Technical Field

[0001] This invention relates to the field of ceramic powder materials technology, and more specifically, to a Cr2AlC ceramic powder, its preparation method, and its applications. Background Technology

[0002] Cr2AlC is a ternary compound with a layered structure. It not only has the high hardness and high corrosion resistance of ceramic materials, but also the electrical and thermal conductivity of metals, making it a material with very broad development prospects.

[0003] Cr2AlC ceramic materials are typically prepared using methods such as spark plasma sintering. However, the materials produced by spark plasma sintering are relatively small in size, making mass production difficult. Additionally, there is a method for synthesizing Cr2AlC ceramic powder using molten salt. While this method can synthesize large quantities of Cr2AlC ceramic powder, it requires complex processes such as cleaning, and the resulting powder is relatively fine with low surface activity, which is detrimental to subsequent composite and sintering. Vacuum sintering is also a method for preparing Cr2AlC ceramic powder, but aluminum easily evaporates during vacuum sintering, making it difficult to control the chemical composition of the Cr2AlC ceramic powder.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a Cr2AlC ceramic powder, its preparation method, and its application, in order to solve the above-mentioned problems.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a method for preparing Cr2AlC ceramic powder, comprising loading raw materials and a protective agent into a crucible for sintering under a protective atmosphere, wherein the protective agent covers the surface of the raw materials in the crucible;

[0008] The raw materials include Cr3C2, Cr and Al in a molar ratio of 1:1:2; the protective agent includes Al and graphite in a mass ratio of 1:(0.8 to 1.2), and the protective agent has a coverage thickness of 15 mm to 20 mm.

[0009] Secondly, the present invention provides a Cr2AlC ceramic powder, which is prepared by any of the preparation methods described in the foregoing embodiments.

[0010] Thirdly, the present invention provides an application of the preparation method as described in any of the foregoing embodiments in reducing aluminum evaporation loss during the preparation of Cr2AlC ceramic powder.

[0011] The present invention has the following beneficial effects:

[0012] This invention provides a Cr2AlC ceramic powder, its preparation method, and its application. By laying a protective agent on the surface of the raw material, the evaporation loss of aluminum can be prevented, the proportion of each component in the raw material can be kept stable, and Cr2AlC ceramic powder can be sintered in a protective atmosphere. At the same time, this method can obtain a high yield of Cr2AlC ceramic powder. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a scanning electron microscope image of the fracture surface of the blocky Cr2AlC material prepared in Example 1 of the present invention;

[0015] Figure 2 The X-ray diffraction pattern of Cr2AlC ceramic powder prepared in Example 1 of this invention;

[0016] Figure 3 The X-ray diffraction pattern of the protective agent after sintering prepared in Example 1 of this invention;

[0017] Figure 4 This is a scanning electron microscope image of the fracture surface of the blocky Cr2AlC material prepared in Example 2 of the present invention;

[0018] Figure 5 The X-ray diffraction pattern of Cr2AlC ceramic powder prepared in Example 2 of this invention;

[0019] Figure 6 This is a scanning electron microscope image of the fracture surface of the blocky Cr2AlC material prepared in Comparative Example 1 of the present invention.

[0020] Figure 7 The X-ray diffraction pattern of the Cr2AlC ceramic powder prepared in Comparative Example 1 of this invention is shown below.

[0021] Figure 8 This is a scanning electron microscope image of the fracture surface of the blocky Cr2AlC material prepared in Comparative Example 2 of the present invention.

[0022] Figure 9 The X-ray diffraction pattern is shown for the Cr2AlC ceramic powder prepared in Comparative Example 2 of this invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0024] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0025] Currently, Cr2AlC ceramic powders prepared using vacuum sintering often contain impurity phases, such as Cr7C3 or Al2O3. The presence of these impurity phases affects the purity of the Cr2AlC ceramic powder and also increases raw material loss. The inventors' research revealed that the main reason for raw material loss and increased impurities is that aluminum easily evaporates and oxidizes during the sintering process. When aluminum evaporates, the chemical composition of the raw materials changes, leading to the formation of new impurities. Furthermore, the oxidation of aluminum directly results in the formation of Al2O3. To reduce aluminum evaporation and oxidation, the inventors propose the following solution.

[0026] In a first aspect, the present invention provides a method for preparing Cr2AlC ceramic powder, comprising loading raw materials and a protective agent into a crucible for sintering under a protective atmosphere, wherein the protective agent covers the surface of the raw materials in the crucible; the raw materials include Cr3C2, Cr and Al; the protective agent includes Al and graphite.

[0027] Protective atmosphere sintering refers to sintering performed under specific protective gas conditions within the furnace to prevent physical changes (such as sublimation) and chemical reactions (such as oxidation) that could damage the sample's properties. In the process of preparing Cr2AlC ceramic powder using protective atmosphere sintering, as the reaction temperature increases, the Al in the raw materials melts. The molten Al powder then impregnates the Cr and Cr3C2 powders, forming a concave liquid surface. This results in the aluminum vapor pressure in the space where the raw materials are located being lower than the equilibrium vapor pressure at the same temperature.

[0028] Because the surface of the raw material is covered with a protective agent composed of a mixture of Al and graphite, as the temperature of the reaction process increases, the Al in the protective agent melts. Since the aluminum liquid has poor wettability on the graphite powder, the aluminum liquid in the protective agent takes the form of droplets with a convex surface. Therefore, the vapor pressure of the aluminum in the protective agent is greater than the equilibrium vapor pressure at the same temperature.

[0029] Because the aluminum in the protective agent has a high vapor pressure, it will preferentially evaporate to form vapor during the aluminum melting stage, while the aluminum in the raw material will not evaporate or will evaporate very little, greatly reducing the loss of aluminum in the raw material.

[0030] During the continued heating process, the aluminum in the protective powder reacts with graphite to form Al4C3; in addition to reacting with chromium powder to form aluminum-chromium intermediates, the aluminum in the raw materials also reacts with Cr3C2 to form Cr2AlC and Al4C3. Since the aluminum-chromium intermediates and Cr2AlC are chemically more stable than Al4C3, the vapor pressure of aluminum in solid-gas equilibrium with the aluminum-chromium intermediates and Cr2AlC is lower than that with Al4C3. Therefore, in the presence of Al4C3, the aluminum in the aluminum-chromium intermediates and Cr2AlC will not sublimate, further preventing the loss of aluminum from the raw materials.

[0031] Because the raw materials are proportioned according to the required mass of Cr3C2, Cr, and Al to generate the target product Cr2AlC, the aluminum in the raw materials is used to react and generate Cr2AlC ceramic powder. Therefore, the amount of Al4C3 generated in the raw materials is small, or even non-existent. A protective agent is applied to the surface of the raw materials. This protective agent generates a large amount of Al4C3, and the sublimation of Al4C3 produces more aluminum vapor, thereby inhibiting the sublimation of Al in the raw materials and slowing down the loss of aluminum.

[0032] In an optional implementation, the raw material is loaded into a crucible and then a protective agent is applied to the surface of the raw material.

[0033] Preferably, the thickness of the protective agent is 15mm to 20mm. For example, the thickness of the protective agent can be 15mm, 16mm, 17mm, 18mm, 19mm or 20mm.

[0034] The inventors discovered that by controlling the thickness of the protective agent within the aforementioned range, the loss of aluminum in the raw materials can be minimized during the sintering process of this application. The aforementioned range of protective agent thickness is merely a preferred embodiment and should not be construed as meaning that the thickness of the protective agent can only be within the aforementioned range. For example, a protective agent thickness of 14mm or 12mm can also reduce the loss of aluminum in the raw materials, but a thickness of 15mm to 20mm yields even better results.

[0035] In an optional embodiment, based on the reaction formula for preparing Cr2AlC from Cr3C2, Cr and Al, the molar ratio of Cr3C2, Cr and Al in the raw materials is calculated to be 1:1:2.

[0036] In an optional embodiment, in order to generate a sufficient amount of Al4C3 and reduce aluminum loss, the mass ratio of Al to graphite in the protective agent is 1:(0.8 to 1.2). For example, the mass ratio of Al to graphite in the protective agent is 1:1.

[0037] In an optional embodiment, the crucible is covered with a lid before sintering in a protective atmosphere. By covering the crucible surface with a lid, the aluminum vapor generated from the evaporation of aluminum in the protective agent and the aluminum vapor generated from the sublimation of Al4C3 escape from the crucible more slowly, which can greatly avoid the loss of aluminum in the raw materials, thereby ensuring that the Cr2AlC ceramic powder obtained after the protective atmosphere sintering reaction has the desired chemical composition.

[0038] In an optional embodiment, the sintering temperature for protective atmosphere sintering is 1180℃~1350℃, the holding time is 4h~6h, and the sintering atmosphere is a protective atmosphere.

[0039] For example, the sintering temperature can be 1180℃, 1200℃, 1250℃, 1260℃, 1270℃, 1280℃, 1290℃, 1300℃, 1310℃, 1320℃, 1330℃, 1340℃, or 1350℃. The holding time can be 4h, 5h, or 6h.

[0040] In an optional embodiment, the control of the sintering atmosphere includes first evacuating the vacuum sintering furnace, and then filling the vacuum sintering furnace with a protective gas. When a protective gas is added during the reaction process, a small amount of oxygen in the furnace will react with the protective agent on the surface first, thereby preventing the oxidation of aluminum in the raw materials.

[0041] In an optional embodiment, the vacuum degree inside the vacuum sintering furnace is evacuated to -0.090MPa to -0.095MPa. After the protective gas is filled, the gas pressure inside the vacuum sintering furnace is 0.008MPa to 0.012MPa. The protective gas includes either pure argon or pure nitrogen, and the purity of the gas is 99.99%.

[0042] Secondly, the present invention provides a Cr2AlC ceramic powder, which is prepared by any of the preparation methods described in the foregoing embodiments.

[0043] Thirdly, the present invention provides an application of the preparation method as described in any of the foregoing embodiments in reducing aluminum evaporation loss during the preparation of Cr2AlC ceramic powder.

[0044] Example 1

[0045] This embodiment provides a method for preparing Cr2AlC ceramic powder, including the following steps:

[0046] S01: Mix Cr3C2 powder, Cr powder and Al powder evenly in a molar ratio of 1:1:2 to obtain the raw material.

[0047] S02: Aluminum powder and graphite powder are mixed evenly in a mass ratio of 1:1 to obtain a protective agent.

[0048] S03: Add the raw material obtained in step S01 into the corundum crucible and level it; spread the protective agent from step S02 on the surface of the raw material, so that the protective agent completely covers the raw material and level it; the thickness of the protective agent in the corundum crucible is 20mm.

[0049] S04: After covering the corundum crucible from step S03 with a cover plate, place it in a vacuum sintering furnace. Evacuate the vacuum sintering furnace to -0.095MPa, then fill it with pure argon gas to raise the furnace pressure back to 0.01MPa. Maintain this pressure while heating the corundum crucible to 1200℃ with the furnace, hold it at this temperature for 6 hours, and then cool it to room temperature with the furnace.

[0050] After removing the remaining protective agent from the upper part of the corundum crucible, the bulk material at the bottom of the crucible is obtained, which is the blocky Cr2AlC material prepared by the reaction. The fracture surface of the blocky Cr2AlC material is observed under a scanning electron microscope, and the results are as follows. Figure 1 The results are shown. (From...) Figure 1 It can be seen that the blocky Cr2AlC material synthesized in this embodiment is a loose blocky material with distinct particles, which is crushed to obtain Cr2AlC ceramic powder.

[0051] X-ray diffraction analysis was performed on Cr2AlC ceramic powder to obtain the following results: Figure 2 The results shown are from Figure 2 It can be seen that no other impurities were detected in the Cr2AlC ceramic powder prepared by the method of this embodiment, and the product has high purity.

[0052] Furthermore, the remaining protective agent in the upper part of the corundum crucible was subjected to X-ray diffraction analysis to obtain the following results: Figure 3 The results shown are from Figure 3 It can be seen that the protective agents in this embodiment all react to form Al4C3 after sintering in a protective atmosphere, which confirms the effect of Al4C3 in reducing aluminum loss as analyzed above.

[0053] Example 2

[0054] This embodiment provides a method for preparing Cr2AlC ceramic powder, including the following steps:

[0055] S01: Mix Cr3C2 powder, Cr powder and Al powder evenly in a molar ratio of 1:1:2 to obtain the raw material.

[0056] S02: Aluminum powder and graphite powder are mixed evenly in a mass ratio of 1:1.2 to obtain a protective agent.

[0057] S03: Add the raw material obtained in step S01 into the corundum crucible and level it; spread the protective agent from step S02 on the surface of the raw material, so that the protective agent completely covers the raw material and level it; the thickness of the protective agent in the corundum crucible is 15mm.

[0058] S04: After covering the corundum crucible from step S03 with a cover plate, place it in a vacuum sintering furnace. Evacuate the vacuum sintering furnace to -0.095MPa, then fill it with pure nitrogen to raise the furnace pressure back to 0.01MPa. Maintain this pressure while heating the corundum crucible to 1200℃ with the furnace, hold it at this temperature for 4 hours, and then cool it to room temperature with the furnace.

[0059] After removing the remaining protective agent from the upper part of the corundum crucible, the bulk material at the bottom of the crucible is obtained, which is the blocky Cr2AlC material prepared by the reaction. The fracture surface of the blocky Cr2AlC material is observed under a scanning electron microscope, and the results are as follows. Figure 4 The results are shown. (From...) Figure 4 It can be seen that the blocky Cr2AlC material synthesized in this embodiment is a loose blocky material with distinct particles. It is pulverized to obtain Cr2AlC ceramic powder. X-ray diffraction analysis of the Cr2AlC ceramic powder yields the following results: Figure 5 The results shown are from Figure 5 It can be seen that no other impurities were detected in the Cr2AlC ceramic powder prepared by the method of this embodiment, and the product has high purity.

[0060] Comparative Example 1

[0061] This comparative example provides a vacuum sintering preparation method for Cr2AlC ceramic powder, including the following steps:

[0062] S01: Mix Cr3C2 powder, Cr powder and Al powder evenly in a molar ratio of 1:1:2 to obtain the raw material.

[0063] S02: Add the raw material obtained in step S01 to the corundum crucible, level it, then cover it with a cover plate and place it in a vacuum sintering furnace. Evacuate the vacuum sintering furnace to -0.095MPa and maintain this pressure while heating the corundum crucible to 1200℃ with the furnace. Hold it at this temperature for 4 hours and then cool it to room temperature with the furnace.

[0064] The loose layer at the top of the corundum crucible is removed to obtain the bulk material at the bottom, which is the blocky Cr2AlC material obtained from the reaction. The fracture surface of the blocky Cr2AlC material is observed under a scanning electron microscope to obtain the following... Figure 6 The results are shown. (From...) Figure 6 It can be seen that the blocky Cr2AlC material synthesized in this comparative example is a loosely packed block, but with fluffy, non-conductive fine particles (white particles in the figure) formed between the particles. These particles were pulverized to obtain Cr2AlC ceramic powder. X-ray diffraction analysis of the Cr2AlC ceramic powder yielded the following results: Figure 7 The results shown are from Figure 7It can be seen that Cr7C3 and Al2O3 impurities were detected in the Cr2AlC ceramic powder prepared by the method of this comparative example. Obviously, the non-conductive fine particles are Al2O3. The purity of the product is significantly lower than that of Example 1 and Example 2, and there is a loss of aluminum in the raw materials. Among them, Al2O3 is formed by the direct oxidation of aluminum, which is an oxidation loss. As can be seen from the Al-Cr-C ternary phase diagram, the presence of detectable Cr7C3 in the synthesized product is due to insufficient aluminum. However, the raw materials were prepared according to the chemical ratio in the process, which indicates that there was a significant aluminum loss during the sintering process.

[0065] Comparative Example 2

[0066] This comparative example provides a method for preparing Cr2AlC ceramic powder under a protective atmosphere, including the following steps:

[0067] S01: Mix Cr3C2 powder, Cr powder and Al powder evenly in a molar ratio of 1:1:2 to obtain the raw material.

[0068] S02: Add the raw material obtained in step S01 to the corundum crucible, level it, then cover it with a lid and place it in a vacuum sintering furnace. Evacuate the vacuum sintering furnace to -0.095MPa, then fill it with pure nitrogen to raise the furnace pressure back to 0.01MPa. Maintain this pressure while heating the corundum crucible to 1200℃ with the furnace, hold it at this temperature for 4 hours, and then cool it to room temperature with the furnace.

[0069] The loose layer at the top of the corundum crucible is removed to obtain the bulk material at the bottom, which is the blocky Cr2AlC material obtained from the reaction. The fracture surface of the blocky Cr2AlC material is observed under a scanning electron microscope to obtain the following... Figure 8 The results are shown. (From...) Figure 8 It can be seen that the blocky Cr2AlC material synthesized in this comparative example is a loosely packed block with non-conductive fine particles (white particles in the figure) between the particles, but the number is less than that of comparative example 1. This material was pulverized to obtain Cr2AlC ceramic powder. X-ray diffraction analysis of the Cr2AlC ceramic powder yielded the following results: Figure 9 The results shown are from Figure 9 It can be seen that Cr7C3 impurities were detected in the Cr2AlC ceramic powder prepared by the method of this comparative example, but no Al2O3 impurities were detected. Although no Al2O3 impurities were detected, compared with Comparative Example 1, it can still be inferred that the non-conductive fine particles are Al2O3. Obviously, the purity of the product in this comparative example is significantly lower than that of Example 1 and Example 2, and there is a loss of aluminum in the raw materials: compared with Comparative Example 1, although there is no significant loss of aluminum oxidation, the presence of Cr7C3 still indicates that there is a significant loss of aluminum, which is obviously the loss of aluminum evaporation.

[0070] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing Cr2AlC ceramic powder, characterized in that, The process includes loading raw materials and a protective agent into a crucible for sintering under a protective atmosphere, wherein the protective agent covers the surface of the raw materials in the crucible; The raw materials include Cr3C2, Cr and Al in a molar ratio of 1:1:2; the protective agent includes Al and graphite in a mass ratio of 1:(0.8~1.2); the protective agent has a coverage thickness of 15mm~20mm.

2. The preparation method according to claim 1, characterized in that, This includes sintering the crucible under a protective atmosphere after covering it with a lid.

3. The preparation method according to claim 1, characterized in that, The sintering temperature for the protective atmosphere sintering is 1180℃~1350℃, and the holding time is 4h~6h.

4. The preparation method according to claim 3, characterized in that, The atmosphere control during the protective atmosphere sintering process includes first evacuating the vacuum sintering furnace, and then filling the vacuum sintering furnace with a protective atmosphere.

5. The preparation method according to claim 4, characterized in that, The vacuum degree inside the vacuum sintering furnace is evacuated to -0.090MPa to -0.095MPa. After the protective atmosphere is introduced, the gas pressure inside the vacuum sintering furnace is 0.008MPa to 0.012MPa. The protective atmosphere includes either pure argon or pure nitrogen.

6. The application of the preparation method according to any one of claims 1 to 5 in reducing aluminum evaporation loss during the preparation of Cr2AlC ceramic powder.

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