Boron nitride is a kind of high temperature resistant crystal with good white lubricity, and its melting point is close to 3,000 degrees Celsius. Its insulating properties are particularly good. At high temperatures, its insulating properties exceed any high temperature resistant oxides, and at the same time, it has good thermal transmission properties and stable chemical properties, it is chemically inert to almost all molten metals, and corrosion resistant to inorganic acids and chemical reagents. Due to its high chemical stability, thermal stability, insulation and good conductor of heat, boron nitride is made into a crucible for melting many materials. However, after a long period of use, molten material can infiltrate the surface of the boron nitride crucible, making it difficult to clean with standard methods. As a result, a new boron nitride crucible is needed for each molten material that needs to maintain high purity. And boron nitride crucibles have always been expensive.
The following provides a method for repeated use of boron nitride crucibles. Specifically, it provides a simple, easy, and low-cost chemical method to thoroughly clean the used boron nitride crucibles without leaving any impurities. So that the same crucible can be used multiple times, melting different materials, reducing costs. The specific cleaning steps are as follows:
1. According to the original molten material remaining in the boron nitride crucible, select the corresponding chemical reagents to initially clean the boron nitride crucible;
2. Use a mixture of concentrated sulfuric acid, concentrated nitric acid, and hydrofluoric acid with a volume ratio of 1:1:1 to etch for more than 15 minutes, and then rinse with deionized water;
3. Boil with 60% caustic soda (NaOH) solution for more than 30 minutes, then rinse with deionized water, and then sonicate with deionized water twice, each for more than 10 minutes;
4. Use 1:3 concentrated nitric acid and concentrated hydrochloric acid mixed acid solution (aqua regia) to cook until the mixed acid solution turns from golden to red and then yellow, rinse with deionized water, and then use it. Lonized water ultrasonic treatment twice, each time for more than 10 minutes;
5. Boil the deionized water three times for more than 15 minutes each time, then dry it with an infrared lamp, and put it in a high-temperature diffusion furnace and bake it for more than 12 hours with oxygen.
After completing the above 5 steps, the boron nitride crucible can be thoroughly cleaned.
