Crucibles are used to contain chemical compounds when heated to high temperatures, often to encourage phase transformations or chemical reactions. Crucibles come in a wide variety of sizes and materials. It is critically important to ensure chemical compatibility when selecting a crucible, with inert materials like alumina or platinum finding common use. A comprehensive list of crucible compatibility can be found at https://luxel.com/wp-content/uploads/2017/08/Crucible-Selection-Guide-Rev.08-2017.pdf.
Solid samples are placed into the crucible, and then transferred into a furnace for firing.
Crucibles are often cleaned by sonicating, soaking or boiling the sample in a compatible acid or solvent. A rough clean of an alumina can be obtained by an overnight soak in a 20% hydrochloric acid solution, followed by an overnight soak in water. For optimal results, crucibles should be fired at an elevated temperature using a furnace or butane torch before reuse. More detailed instructions can be found https://www.netzsch-thermal-academy.com/en/e-learning/tips-tricks/not-just-clean-but-ultra-clean/
Crucibles can be purchased at many general lab supply stores. Alumina crucibles can be fabricated in-house via sintering alumina powder in a mold. Metallic crucibles can be fabricated by machining a cavity into the desired metal.