A method for eliminating oxide impurities in carbide ceramic blocks

Abstract

The present invention discloses a method for eliminating oxide impurities in carbide ceramic blocks, which belongs to the field of ultra-high temperature ceramic technology, and includes the following steps: S1, ultrasonically clean the initial carbide block sample and then dry it; S2, put the dried sample into a graphite can, and punch holes on the can cover to facilitate exhaust; S3, put the graphite can as a whole into a high-temperature carbon tube furnace, heat it to a certain temperature for sintering; S4, after the reaction is completed, cool it with the furnace to obtain a ceramic block without oxide impurities. The present invention adopts a multi-stage heat treatment process, and utilizes the chemical equilibrium principle of carbon thermal reduction reaction to expel gaseous reduction products outward along the grain boundary, so as to efficiently eliminate impurities in the sintered carbide block; the method is simple in process and high in efficiency, and can realize batch processing of samples, and has great application potential.

Description

Technical Field

[0001] The invention relates to the technical field of ultra-high temperature ceramics, and in particular to a method for eliminating oxide impurities in a carbide ceramic block. Background Art

[0002] As human exploration of space continues to deepen, the demand for high-performance hypersonic aerospace vehicles is becoming increasingly urgent, and the requirements for thermal protection materials are becoming more stringent. Ultra-high temperature ceramics (UHTCs) are a type of material with great application potential in the field of ultra-high temperature resistance in aerospace. Generally, UHTCs are defined as compounds with a melting point of more than 3000°C, mainly including three types: carbides, borides, and nitrides. Among them, carbides not only have extremely high melting points, but also have high hardness, elastic modulus, thermal stability, and good ablation resistance, so they have attracted widespread attention.

[0003] Since carbides have strong bond energy, the preparation of carbide bulk ceramics currently requires external high energy as a sintering driving force. Common methods include hot pressing (HP), hot isostatic pressing (HIP), spark plasma sintering (SPS), and flash sintering (ReaFSPS). The common feature of these methods is that they all need to be implemented in a high-temperature environment, and the sintering temperature is usually much higher than the starting oxidation temperature of carbide ceramics. Limited by the relatively easy oxidation characteristics of carbides and the size effect, whether it is carbide raw material powder or elemental powder raw material powder, there will inevitably be an oxide layer on the surface of the powder particles, that is, the raw material will carry oxygen impurities during the entire preparation process of carbide bulk ceramics. Therefore, under high-temperature sintering conditions, it is inevitable that carbide blocks will have oxidized impurities.

[0004] The grain boundaries of carbide ceramic blocks have many defects, so the local energy is high and oxidation occurs first. Therefore, the triple grain boundaries of sintered carbide grains are usually rich areas of oxide impurities. However, these triple grain boundaries are located inside the material matrix and are very diffusely distributed.

[0005] Based on the above content, a method for eliminating oxide impurities in carbide ceramic blocks is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a method for eliminating oxide impurities in carbide ceramic blocks. The method adopts a multi-stage heat treatment process and utilizes the chemical equilibrium principle of carbon thermal reduction reaction to expel gaseous reduction products outward along the grain boundaries, thereby efficiently eliminating impurities in the sintered carbide blocks. The method has simple process and high efficiency, can realize batch processing of samples, and has great application potential.

[0007] To achieve the above object, the present invention provides a method for eliminating oxide impurities in a carbide ceramic block, comprising the following steps:

[0008] S1. Ultrasonic cleaning of the initial carbide block sample to ensure that the surface oil, dust and other adsorbed impurities are cleaned and then dried;

[0009] S2. Place the dried sample into a graphite can and punch holes in the can cover to facilitate exhaust;

[0010] S3, placing the graphite can as a whole into a high-temperature carbon tube furnace, heating it to a certain temperature for sintering;

[0011] S4. After the reaction is completed, the furnace is cooled to obtain a ceramic block without oxide impurities.

[0012] Preferably, in S1, the duration of ultrasonic cleaning is greater than 10 minutes, and the cleaning medium is anhydrous ethanol or acetone.

[0013] Preferably, in S1, the apparatus used for the drying operation is an oven, the oven temperature is 40-50° C., and the drying time is ≥48 h.

[0014] Preferably, in S2, graphite paper for preventing the initial sample from directly contacting the can body is adhered to the inside of the graphite can, and the graphite can is dried before use.

[0015] Preferably, in S3, the mechanical pump switch is turned on to keep the high-temperature carbon tube furnace in a vacuum state, and the vacuum degree during the entire sintering process is lower than 10Pa.

[0016] Preferably, in S3, the heating rate of the high temperature carbon tube furnace is controlled to be 10° C. / min.

[0017] Preferably, in S3, during the sintering process, the temperature is first raised to 200-400° C. and kept at that temperature for 15-25 min, and then raised to 1900-2000° C. and kept at that temperature for 40-60 min.

[0018] Therefore, the present invention provides a method for eliminating oxide impurities in carbide ceramic blocks. The method adopts the chemical equilibrium principle of carbon thermal reduction reaction and utilizes the reducing property of carbon. Under high temperature and vacuum conditions, the oxide impurities in the initial carbide can be effectively reduced, and the gaseous reduction products are expelled outward along the grain boundaries to obtain a pure, single-phase target sample. The method has a simple process and high efficiency, and can realize batch processing of samples, greatly improve the purity of hot-sintered carbide ceramic blocks, realize the preparation of high-performance carbide ceramics, and is expected to be expanded to other ceramic preparation fields, with great application potential.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The XRD results of the ceramic block before and after heat treatment of Example 1 of the present invention are shown;

[0021] Figure 2 This is a microscopic morphology of a ceramic block according to Example 1 of the present invention;

[0022] Figure 3 The XRD results of the ceramic block before and after heat treatment of Example 2 of the present invention are shown;

[0023] Figure 4 This is a microscopic morphology of the ceramic block of Example 2 of the present invention;

[0024] Figure 5 This is a microscopic morphology of the ceramic block of Example 3 of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0026] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0027] Example 1

[0028] The impurity treatment is carried out using the initial HfC bulk containing oxide impurities as raw material:

[0029] S1. The initial HfC bulk sample containing oxide impurities was ultrasonically cleaned twice with anhydrous ethanol, each cleaning time was 10 minutes, to ensure that the surface oil, dust and other adsorbed impurities were cleaned; then it was placed in an oven for drying at a temperature of 40°C for 48 hours;

[0030] S2. Place the graphite can in a 40°C oven and dry for 12 hours, and adhere graphite paper to the inner cavity of the graphite can to prevent the HfC sample from directly contacting the can body;

[0031] S3, placing the dried HfC sample into a graphite tank and punching holes in the tank cover to facilitate exhaust;

[0032] S4. Place the graphite tank containing the HfC sample into the high-temperature carbon tube furnace, turn on the mechanical pump switch, and keep the inside of the furnace chamber in a vacuum state throughout the whole process, with a vacuum degree lower than 10Pa;

[0033] S5, set the temperature rising program, raise the temperature to 200°C at a rate of 10°C / min, and keep it at that temperature for 20 minutes; then raise the temperature to 1900°C at a rate of 10°C / min, and keep it at that temperature for 60 minutes;

[0034] S6. After cooling in the furnace, a ceramic block free of oxide impurities is obtained.

[0035] The initial sample and the obtained product in Example 1 were tested and their microscopic morphology was observed. Figure 1 As shown in the figure, there are two groups of XRD diffraction peaks in the initial HfC ceramic block before heat treatment, one group is the main diffraction peak of the face-centered cubic HfC matrix, and the other group is the diffraction peak of the monoclinic HfO2 oxide impurity. After deoxidation treatment at 1900℃, the diffraction peak of the HfO2 oxide impurity disappears, leaving only the main peak of the carbide matrix, indicating that a pure sample without impurities is obtained; Figure 2 As shown, there are diffusely distributed dark contrast oxide impurities in the initial HfC ceramic block before heat treatment; after purification, the oxide impurities disappear and the sample composition is uniform.

[0036] Example 2

[0037] The impurity treatment is carried out using the initial ZrC block containing oxide impurities as raw material:

[0038] S1. The initial ZrC block sample containing oxide impurities was ultrasonically cleaned twice with acetone, each cleaning time was 10 minutes, to ensure that the surface oil, dust and other adsorbed impurities were cleaned; then it was placed in an oven for drying at a temperature of 50°C for 48 hours;

[0039] S2. Place the graphite can in a 50°C oven and dry for 12 hours, and adhere graphite paper to the inner cavity of the graphite can to prevent the ZrC sample from directly contacting the can body;

[0040] S3, putting the dried ZrC sample into a graphite can and punching holes in the can cover to facilitate exhaust;

[0041] S4. Place the graphite mold loaded with the ZrC sample into a high-temperature carbon tube furnace, turn on the mechanical pump switch, and keep the inside of the furnace chamber in a vacuum state throughout the process, with a vacuum degree lower than 10Pa;

[0042] S5, set the temperature rising program, raise the temperature to 200°C at a rate of 10°C / min, and keep it at that temperature for 20 minutes; then raise the temperature to 2000°C at a rate of 10°C / min, and keep it at that temperature for 60 minutes;

[0043] S6. After cooling in the furnace, a ceramic block free of oxide impurities is obtained.

[0044] The initial sample and the obtained product in Example 2 were tested and the microscopic morphology was observed. Figure 3 As shown in the figure, there are two groups of XRD diffraction peaks in the initial HfC ceramic block before heat treatment, one group is the main diffraction peak of the face-centered cubic ZrC matrix, and the other group is the diffraction peak of the monoclinic ZrO2 oxide impurity. After deoxidation treatment at 2000℃, the diffraction peak of the ZrO2 oxide impurity disappears, leaving only the main peak of the ZrC carbide matrix, indicating that a pure sample without impurities is obtained.

[0045] like Figure 4 As shown, the initial HfC ceramic block also has diffusely distributed dark contrast oxide impurities before heat treatment; after purification, the oxide impurities disappear and the sample composition is uniform.

[0046] Example 3

[0047] The impurity treatment is carried out using the initial (Hf, Ti)C block containing oxide impurities as raw material:

[0048] S1. The initial (Hf, Ti)C bulk sample containing oxide impurities was ultrasonically cleaned twice with anhydrous ethanol, each cleaning time was 15 minutes, to ensure that the surface oil, dust and other adsorbed impurities were cleaned; then it was placed in an oven for drying at a temperature of 40°C for 48 hours;

[0049] S2. Place the graphite can in a 40°C oven and dry for 12 hours, and adhere graphite paper to the inner cavity of the graphite can to prevent the (Hf, Ti)C sample from directly contacting the can body;

[0050] S3, placing the dried (Hf, Ti)C sample into a graphite can and punching holes in the can cover to facilitate exhaust;

[0051] S4, placing the graphite mold loaded with the initial (Hf, Ti)C sample into a high-temperature carbon tube furnace; turning on the mechanical pump switch to keep the inside of the furnace chamber in a vacuum state throughout the process, with a vacuum degree lower than 10Pa;

[0052] S5, set the temperature rising program, raise the temperature to 200°C at a rate of 10°C / min, and keep it at that temperature for 20 minutes; then raise the temperature to 1700°C at a rate of 10°C / min, and keep it at that temperature for 60 minutes;

[0053] S6. After cooling in the furnace, a ceramic block still containing oxide impurities is obtained.

[0054] The microscopic morphology of the initial sample and the obtained product in Example 3 was observed respectively. Figure 5 As shown, the initial (Hf, Ti)C ceramic block also has diffusely distributed dark contrast oxide impurities; after purification treatment at 1700°C, the oxide impurity content is reduced, but because the temperature does not reach a reasonable value, the reaction is not sufficient and the oxide impurities still remain.

[0055] Therefore, the present invention provides a method for eliminating oxide impurities in carbide ceramic blocks, which adopts a multi-stage heat treatment process and utilizes the chemical equilibrium principle of carbon thermal reduction reaction to expel gaseous reduction products outward along the grain boundaries, thereby efficiently eliminating impurities in the sintered carbide blocks; the method has a simple process and high efficiency, can realize batch processing of samples, and has great application potential.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for eliminating oxide impurities in a carbide ceramic block, characterized in that: The following steps are involved: S1, ultrasonically cleaning the initial carbide block sample and then drying it; S2. Place the dried sample into a graphite can and punch holes in the can cover to facilitate exhaust; S3, putting the graphite can as a whole into a high-temperature carbon tube furnace, heating it to a certain temperature for sintering; during the sintering process, the temperature is first raised to 200-400°C, kept warm for 15-25 minutes, and then raised to 1900-2000°C, kept warm for 40-60 minutes; S4. After the reaction is completed, the furnace is cooled to obtain a ceramic block without oxide impurities.

2. A method for eliminating oxide impurities in a carbide ceramic block according to claim 1, characterized in that: In S1, the duration of ultrasonic cleaning is greater than 10 minutes, and the cleaning medium is anhydrous ethanol or acetone.

3. A method for eliminating oxide impurities in a carbide ceramic block according to claim 2, characterized in that: In S1, the drying operation is performed using an oven, the oven temperature is 40-50°C, and the drying time is ≥48h.

4. A method for eliminating oxide impurities in a carbide ceramic block according to claim 3, characterized in that: In S2, graphite paper is adhered inside the graphite can to prevent the initial sample from directly contacting the can body, and the graphite can is dried before use.

5. A method for eliminating oxide impurities in a carbide ceramic block according to claim 4, characterized in that: In S3, the high temperature carbon tube furnace is in a vacuum state, and the vacuum degree during the entire sintering process is less than 10Pa.

6. A method for eliminating oxide impurities in a carbide ceramic block according to claim 5, characterized in that: In S3, the heating rate of the high temperature carbon tube furnace is controlled to be 10° C. / min.

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