Cleaning Graphite Crucibles
Graphite crucibles are primarily used for heating and molding non-ferrous metals. Despite differences in specifications and materials used, all graphite crucibles require regular cleaning. New graphite crucibles are shiny inside and out, but prolonged exposure to high temperatures can dull their surfaces. Over time, this can lead to deeper penetration of contaminants and eventual cracking of the crucible. Therefore, it is essential to regularly clean the surface of the crucible. Here are specific methods for cleaning graphite crucibles:
- Initial Cleaning: First, remove any chemical substances from the crucible. The choice of cleaning agent depends on the residue inside the crucible. For inorganic residues, hydrochloric acid can be used as most of these residues are soluble.
- Stubborn Residues: For more difficult residues, boil the crucible in diluted hydrochloric acid or nitric acid. When using hydrochloric acid, ensure it does not contain nitric acid or nitrates. If diluted nitric acid is ineffective, you can use potassium metabisulfite, sodium carbonate, or borax melt for cleaning.
Due to their high density, high-temperature resistance, rapid heat transfer, and strong resistance to acids, bases, and oxidation, graphite crucibles are often used with corrosive substances. Despite their resistance to acids and bases, cleaning graphite crucibles after use with certain raw materials can be challenging.