How to Clean Crucibles

Keeping Your Crucibles Clean Is Good Practice
••• Dr. Charles Ward

Chemical and alloy experimentation often employs the use of crucibles in melting materials to change their properties. Any person who has used a crucible knows that not only are they an invaluable part of your laboratory gear, but they're expensive as well. Once you are done conducting your experiments, you need to know how to clean your crucibles effectively and without causing damage to the crucible surface so it can be used again. Cleaning chemicals from porcelain crucibles or alloy residue from platinum ones is relatively easy. You will only need a few basic chemicals and supplies.

    Gently scrape as much residue left from the materials used in your experiment from the crucible.

    Fill your porcelain or platinum crucible with fused potassium bicarbonate; this chemical will be in a solid form. You should have enough bicarbonate in the crucible to fill past the line of the remaining material from your experiments. If you need to fill the entire crucible, do so.

    Place the crucible on a burner. Heat the crucible until the fused bicarbonate melts. Heat it until a layer of red potassium salt appears on the surface. Using a mixing rod, stir the melt a few times. The entire melting procedure should take about one minute.

    Remove your crucible from the flame. Pour out the melt. If your crucible is made of porcelain, continue to step 5. If your crucible is platinum, submerge it in a boiling glass bath of hydrochloric acid (a 20% mix to water) for three minutes.

    Rinse the crucible in hot water. For porcelain crucibles, use a clean cloth to dry the surface. If your crucible is platinum, use alumina-impregnated nylon webbing to complete cleaning the surface. Let the crucible cool.

    Things You'll Need

    • Fused potassium bisulfate
    • Burner
    • Mixing rod
    • Hydrochrolic acid
    • Glass bath
    • Hot water
    • Clean cloth (for Porcelain Only)
    • Alumina-Impregnated nylon webbing (for platinum only)

    Tips

    • For light cleaning, use potassium bisulphate instead of the fused potassium bicarbonate.

    Warnings

    • Never "scrub" a crucible as you can remove the finish and render it useless for safely containing chemicals.

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