A clay graphite crucible is made of a mixture of clay and graphite which is then fired and it is bound together by silica in the clay part of the mixture. A graphite crucible usually described as a pure graphite crucible is close to 100% graphite and typically they are a lot smaller. This is a critical distinction as a discovered to my chagrin. If you have a material that will dissolve silica and you fire it in a clay graphite crucible it will eat through the crucible. I did this with a glass formulation where I bought a clay graphite crucible (several in fact) then fired my batch in it and it melted down through the crucible to the shelf underneath. I found that pure graphite crucible don’t melt and I can fire my glass formulation safely in those.
Ceramic crucibles for sale are commonly used in manufacturing, particularly metallurgy, analysis and quality control. They are also common tools in research environments in fields such as material science, Earth science, and engineering. Crucibles can also be found in use in the arts, either for work with metals or pigments.
Second, there is a difference in color. The color of pure graphite crucible is black and has metallic luster. Because graphite is processed, graphite crucible has all the characteristics of graphite; the color of clay crucible is gray-brown, without metallic luster and rough surface.
Quartz crucible is coated with high purity quartz sand to form a compact layer on the surface of crucible dissolved in ordinary quartz sand. The compact layer can prevent the reaction between silicon and quartz crucible during high temperature drawing of monocrystalline silicon and improve the crystallization rate. It differs from ceramic crucibles in the following aspects:
- Quartz crucible and ceramic crucible have different high temperature resistance and acid and alkali resistance.
- Quartz crucible can be divided into opalescent and transparent. The opalescent crucible is used below 1200 degrees and the transparent crucible is used below 1400 degrees. Ceramic crucibles are used at 1400-1600 degrees.
- Quartz crucible is acid and alkali resistant, but it can not be used for hydrofluoric acid.
- Quartz crucible is more alkali resistant than ceramic crucible.
Regardless of application, a variety of characteristics should be considered when selecting a ceramic crucible. Chemical composition is usually the most significant characteristic, since it most directly impacts the temperatures and pressures at which the crucible will be useful. Other relevant characteristics include total capacity, overall shape, and wall and bottom thickness.