阅读说明：本技术 一种热喷涂用改性碳化硅的制备方法 (Preparation method of modified silicon carbide for thermal spraying ) 是由 黄新春 李朝雄 黄章峰 黄新谊 王卫泽 于 2020-11-26 设计创作，主要内容包括：本发明公开了一种热喷涂用改性碳化硅的制备方法。该方法包括碳化硅粉的预处理、铬盐溶液的配制,还原剂液的配制,将预处理的碳化硅粉、铬盐溶液、还原剂液抽入高压釜中,经加热反应以使铬盐还原成氢氧化铬沉积在碳化硅表面,再经过滤、洗涤、干燥、高温烧结,即得到氧化铬改性碳化硅。本发明方法制备的改性碳化硅可直接用于等离子喷涂,采用该法制备的碳化硅涂层沉积效率高,涂层致密,气孔率低,热稳定性好,导热性好,硬度高。同时该方法具有工艺简单、生产量大、经济可靠、可以工业推广等优点。(The invention discloses a preparation method of modified silicon carbide for thermal spraying. The method comprises the steps of pretreating silicon carbide powder, preparing a chromium salt solution and preparing a reducing agent solution, wherein pretreated silicon carbide powder, the chromium salt solution and the reducing agent solution are pumped into a high-pressure kettle, the mixture is heated and reacted to reduce chromium salt into chromium hydroxide to be deposited on the surface of silicon carbide, and the chromium hydroxide modified silicon carbide is obtained after filtering, washing, drying and high-temperature sintering. The modified silicon carbide prepared by the method can be directly used for plasma spraying, and the silicon carbide coating prepared by the method has the advantages of high deposition efficiency, compact coating, low porosity, good thermal stability, good thermal conductivity and high hardness. Meanwhile, the method has the advantages of simple process, large production capacity, economy, reliability, industrial popularization and the like.)

1. A preparation method of modified silicon carbide for thermal spraying is characterized by comprising the following steps: the method comprises the following steps:

s1, treating the silicon carbide with a boiled sodium hydroxide solution to remove an oxide film on the surface of the silicon carbide and coarsening the surface of the silicon carbide, wherein the concentration of the sodium hydroxide solution is 5-53%;

s2, preparing a chromium salt solution with the concentration of 15-250 g/l;

s3, preparing a reducing agent solution, wherein the reducing agent solution is as follows: 10-500g/l of reducing agent, 0.25-15g/l of surfactant and 0.1-50g/l of sodium hexametaphosphate;

s4, adding the silicon carbide powder prepared in the S1 into a chromium salt solution prepared in the S2, pumping the solution and excessive reducing agent solution into a high-pressure kettle under continuous stirring, heating the solution to 140-180 ℃ to react for 10-100min, so that chromium salt is reduced into chromium hydroxide which is uniformly deposited on the surface of the silicon carbide to form a chromium hydroxide layer coated on the surface of the silicon carbide;

and S5, after the reaction is finished, cooling to below 90 ℃, extracting the suspension, filtering, washing, drying, and sintering the dried powder at 800-1200 ℃ for 2-6 hours to obtain the chromium carbide modified silicon carbide powder for thermal spraying.

2. The method for preparing modified silicon carbide for thermal spraying according to claim 1, wherein: the granularity of the silicon carbide raw material in the S1 is 200 meshes to 1500 meshes.

3. The method for preparing modified silicon carbide for thermal spraying according to claim 1, wherein: the chromium salt in S2 may be one of sodium chromate, potassium chromate, sodium dichromate and potassium dichromate.

4. The method for preparing modified silicon carbide for thermal spraying according to claim 1, wherein: the reducing agent used in the S3 is any one of starch, glucose, sucrose, hydrazine hydrate and formaldehyde.

5. The method for preparing modified silicon carbide for thermal spraying according to claim 1, wherein: any one of the surfactants used in S3, polyethylene glycol, polyacrylic acid, carboxymethyl cellulose, and polyvinyl pyrrolidone.

Technical Field

The invention belongs to the field of thermal spraying technology and material processing, and particularly relates to a preparation method of modified silicon carbide for thermal spraying.

Background

The silicon carbide has stable chemical properties, high heat conductivity coefficient, small thermal expansion coefficient and good wear resistance, and has other purposes besides being used as an abrasive, for example, the silicon carbide powder is coated on the inner wall of a water turbine impeller or a cylinder body by a special process, so that the wear resistance of the silicon carbide powder can be improved, and the service life of the silicon carbide powder is prolonged by 1-2 times; the high-grade refractory material has the advantages of thermal shock resistance, small volume, light weight, high strength and good energy-saving effect. The low-grade silicon carbide (containing SiC about 85%) is an excellent deoxidizer, and can be used for speeding up steel-making, easily controlling chemical composition and raising steel quality. In addition, silicon carbide is also used in great quantity to make silicon carbide rod for electric heating element.

Because of stable chemical properties, the silicon carbide does not react with chlorine, oxygen, sulfur and strong acid at high temperature, has high heat conductivity coefficient, small thermal expansion coefficient and good wear resistance, has the price of only 1/10-1/30 of hard alloys such as tungsten carbide, chromium carbide and the like, and is an ideal hard-surface coating material. However, when the plasma spraying process is adopted to prepare the silicon carbide coating, the temperature of plasma flame flow is up to 15000 ℃, silicon carbide is sublimated at the temperature of more than 1800 ℃, and the powder is partially decomposed into vapor containing carbon and silicon at high temperature, so that the coating is difficult to form. At present, no silicon carbide powder suitable for plasma spraying exists in the market. How to fully utilize the physicochemical properties of silicon carbide to prepare a hard-surface coating is one of the research hotspots in the field of thermal spraying materials at present.

Disclosure of Invention

The invention aims to provide a preparation method of modified silicon carbide spraying powder, which has the advantages of simple process, easy control of the process, high deposition efficiency when plasma spraying is adopted and no sublimation.

The technical scheme of the invention is that a chromium oxide protective layer is deposited on the surface of silicon carbide by a liquid phase reduction-high temperature sintering process, so as to realize the surface coating chromium oxide modification of silicon carbide powder. Since chromium oxide has physical properties similar to silicon carbide, it is also a commonly used hard-facing material. The chromium oxide coated silicon carbide powder firstly forms a liquefied protective film when the chromium oxide on the surface layer is sprayed by plasma, so that the decomposition of silicon carbide is effectively avoided. Meanwhile, the liquefied chromium oxide serves as a binding phase, and deposition of a silicon carbide coating is facilitated.

In order to achieve the purpose, the invention provides the following technical scheme: a preparation method of modified silicon carbide for thermal spraying comprises the following steps:

s1, treating the silicon carbide with a boiled sodium hydroxide solution to remove an oxide film on the surface of the silicon carbide and coarsening the surface of the silicon carbide, wherein the concentration of the sodium hydroxide solution is 5-53%;

s2, preparing a chromium salt solution with the concentration of 15-250 g/l;

s3, preparing a reducing agent solution, wherein the reducing agent solution is as follows: 10-500g/l of reducing agent, 0.25-15g/l of surfactant and 0.1-50g/l of sodium hexametaphosphate;

s4, adding the silicon carbide powder prepared in the S1 into a chromium salt solution prepared in the S2, pumping the solution and excessive reducing agent solution into a high-pressure kettle under continuous stirring, heating the solution to 140-180 ℃ to react for 10-100min, so that chromium salt is reduced into chromium hydroxide which is uniformly deposited on the surface of the silicon carbide to form a chromium hydroxide layer coated on the surface of the silicon carbide;

and S5, after the reaction is finished, cooling to below 90 ℃, extracting the suspension, filtering, washing, drying, and sintering the dried powder at 800-1200 ℃ for 2-6 hours to obtain the chromium carbide modified silicon carbide powder for thermal spraying.

Preferably, the grain size of the silicon carbide raw material in the S1 is 200 meshes to 1500 meshes.

Preferably, the chromium salt in S2 may be one of sodium chromate, potassium chromate, sodium dichromate and potassium dichromate.

Preferably, the reducing agent used in S3 is any one of starch, glucose, sucrose, hydrazine hydrate, and formaldehyde.

Preferably, the surfactant used in S3 is any one of polyethylene glycol, polyacrylic acid, carboxymethyl cellulose, and polyvinyl pyrrolidone.

The invention has the technical effects and advantages that:

(1) the chromium oxide is uniformly coated, so that the deposition of the silicon carbide coating is facilitated;

(2) the coating modification process is novel, and can be applied to the preparation of other chromium oxide coated powder materials;

(3) the modified silicon carbide powder has high deposition efficiency and excellent coating performance;

in conclusion, the modified silicon carbide powder for thermal spraying prepared by the method has the advantages of uniform coating and high deposition efficiency, and a coating formed by spraying the modified silicon carbide powder prepared by the method is compact, high in hardness and good in corrosion resistance; meanwhile, the preparation method has the advantages of simple process, easy operation, low production cost, good product quality, large production capacity, economy, reliability, industrial popularization and the like.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

A preparation method of modified silicon carbide for thermal spraying;

the method comprises the following steps:

s1, treating the silicon carbide with a boiled sodium hydroxide solution to remove an oxide film on the surface of the silicon carbide and coarsening the surface of the silicon carbide, wherein the concentration of the sodium hydroxide solution is 5-53%, and the granularity of the silicon carbide raw material is 200-1500 meshes;

s2, preparing a chromium salt solution with the concentration of 15-250 g/l, wherein the chromium salt can be one of sodium chromate, potassium chromate, sodium dichromate and potassium dichromate;

s3, preparing a reducing agent solution, wherein the reducing agent solution is as follows: 10-500g/l of reducing agent, 0.25-15g/l of surfactant and 0.1-50g/l of sodium hexametaphosphate, wherein the reducing agent is any one of starch, glucose, sucrose, hydrazine hydrate and formaldehyde, and the surfactant is any one of polyethylene glycol, polyacrylic acid, carboxymethyl cellulose and polyvinylpyrrolidone;

s4, adding the silicon carbide powder prepared in the S1 into a chromium salt solution prepared in the S2, pumping the solution and excessive reducing agent solution into a high-pressure kettle under continuous stirring, heating the solution to 140-180 ℃ to react for 10-100min, so that chromium salt is reduced into chromium hydroxide which is uniformly deposited on the surface of the silicon carbide to form a chromium hydroxide layer coated on the surface of the silicon carbide;

and S5, after the reaction is finished, cooling to below 90 ℃, extracting the suspension, filtering, washing, drying, and sintering the dried powder at 800-1200 ℃ for 2-6 hours to obtain the chromium carbide modified silicon carbide powder for thermal spraying.

Example 1:

1) preparing 1000 ml of 35 g/L sodium hydroxide solution, adding 200 g of 200-325-mesh silicon carbide into the sodium hydroxide solution, boiling for 10 minutes, pouring out supernatant, and washing silicon carbide powder with deionized water until tail liquid is neutral;

2) 500 ml of sodium chromate solution with the concentration of 200 g/l is prepared;

3) 500 ml of reducing agent liquid is prepared, wherein the reducing agent liquid contains 200 g of glucose, 2g of polyvinylpyrrolidone and 0.5 g of sodium hexametaphosphate;

4) adding the treated silicon carbide powder into a reducing agent liquid, sucking the reducing agent liquid and a sodium chromate liquid into a 2-liter high-pressure kettle under the condition of continuous stirring, heating to 150 ℃, and reacting for 30min to ensure that chromium oxide is completely reduced and uniformly deposited on the surface of the core powder to form a chromium hydroxide layer coated on the surface of the silicon carbide powder;

5) after the reaction is finished, cooling to 80 ℃, extracting suspended clear liquid under continuous stirring, filtering, washing with deionized water until tail liquid is neutral, and drying at 120 ℃.

6) And sintering the dried powder at the high temperature of 1100 ℃ for 2 hours to obtain the modified silicon carbide powder for thermal spraying.

The physical properties of the finished product were as follows: the bulk density was 1.61g/cm3, and the flow rate was 47.6s/50 g. The deposition efficiency of the coating prepared by adopting the plasma spraying process is 42 percent.

Example 2:

1) preparing 1000 ml of 35 g/L sodium hydroxide solution, adding 200 g of 325-600-mesh silicon carbide into the sodium hydroxide solution, boiling for 10 minutes, pouring out supernatant, and washing silicon carbide powder with deionized water until tail liquid is neutral;

2) 500 ml of sodium dichromate solution with the concentration of 100 g/l is prepared;

3) 500 ml of reducing agent liquid is prepared, wherein the reducing agent liquid contains 200 g of potato starch, 0.5 g of carboxymethyl cellulose and 0.5 g of sodium hexametaphosphate;

4) adding the treated silicon carbide powder into a reducing agent liquid, sucking the reducing agent liquid and a sodium dichromate liquid into a 2-liter high-pressure kettle under the condition of continuous stirring, heating to 140 ℃, and reacting for 30min to ensure that chromium oxide is completely reduced and uniformly deposited on the surface of the core powder to form a chromium hydroxide layer coated on the surface of the silicon carbide powder;

5) after the reaction is finished, cooling to 80 ℃, extracting suspended clear liquid under continuous stirring, filtering, washing with deionized water until tail liquid is neutral, and drying at 120 ℃.

6) And sintering the dried powder at 1000 ℃ for 2 hours to obtain the modified silicon carbide powder for thermal spraying.

The physical properties of the finished product were as follows: the bulk density was 1.57g/cm3, and the flow rate was 61.6s/50 g. The deposition efficiency of the coating prepared by adopting the plasma spraying process is 52 percent.

Example 3:

1) preparing 1000 ml of 35 g/L sodium hydroxide solution, adding 200 g of 500-1500 mesh silicon carbide into the sodium hydroxide solution, boiling for 10 minutes, pouring out supernatant, and washing silicon carbide powder with deionized water until tail liquid is neutral;

2) 500 ml of potassium chromate solution with the concentration of 200 g/l is prepared;

3) 500 ml of reducing agent liquid is prepared, wherein the reducing agent liquid contains 200 g of formaldehyde, 0.4 g of polyacrylic acid and 0.5 g of sodium hexametaphosphate;

4) adding the treated silicon carbide powder into a reducing agent liquid, sucking the reducing agent liquid and a potassium chromate liquid into a 2-liter high-pressure kettle under the condition of continuous stirring, heating to 180 ℃, and reacting for 60min to ensure that chromium oxide is completely reduced and uniformly deposited on the surface of the core powder to form a chromium hydroxide layer coated on the surface of the silicon carbide powder;

5) after the reaction is finished, cooling to 80 ℃, extracting suspended clear liquid under continuous stirring, filtering, washing with deionized water until tail liquid is neutral, and drying at 120 ℃.

6) And sintering the dried powder at the high temperature of 1100 ℃ for 2 hours to obtain the modified silicon carbide powder for thermal spraying.

The physical properties of the finished product were as follows: the bulk density was 1.42g/cm3, and the flow rate was 83.4s/50 g. The deposition efficiency of the coating prepared by adopting the plasma spraying process is 38 percent.

In summary, the following steps: the modified silicon carbide powder for thermal spraying prepared by the method has the advantages of uniform coating and high deposition efficiency, and a coating formed by spraying the modified silicon carbide powder prepared by the method is compact, high in hardness and good in corrosion resistance; meanwhile, the preparation method has the advantages of simple process, easy operation, low production cost, good product quality, large production capacity, economy, reliability, industrial popularization and the like.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments or portions thereof without departing from the spirit and scope of the invention.