A graphite crucible is a container made of graphite and clay, used for melting non-ferrous metals. It is resistant to high temperatures and low reactivity with molten metals. Proper conditioning and storage are important for its use. It should not be used for iron-containing metals and should be handled with care.
A graphite crucible is a container typically used for melting non-ferrous or non-ferrous metals such as gold, silver, aluminum or brass. Graphite, a form of carbon, is often used for crucibles due to its resistance to high temperatures and low reactivity with molten metals. A graphite crucible is typically made of graphite and clay which is molded and fired at very high temperatures to form a solid container.
The purpose of a graphite crucible is to provide a non-reactive vessel that will survive the high temperatures required for melting and working metals. Crucibles provide a stable container that does not react with metals or materials that are burned at high temperatures. Graphite is carbon that may look like flakes or sheets. When mixed with clay, graphite can be molded into heat-resistant and durable vessels or containers. Like many ceramic vessels, graphite crucibles can be fragile and must be handled with care.
There are several types of crucibles which vary mainly in shape. Common shapes include the “bilge,” which is barrel-shaped; and “A”, which are cup-shaped. “A” crucibles may be less expensive because the open cup shape is easier to produce than the barrel shape.
Proper use of a graphite crucible includes conditioning and storage. It is important that a new graphite crucible is conditioned before being used. The crucible should be placed in an oven at 500 degrees Fahrenheit (260 degrees Celsius) for two hours and then allowed to cool slowly in a dry place. This pushes moisture out of the crucible and prevents cracking. Crucibles should be stored away from moisture and should be reconditioned if they become wet.
A graphite crucible must be thoroughly cleaned after use. Do not let the metal cool in the crucible. Residual metal can expand and crack the crucible when heated. You must use crucible tongs that match the shape of the crucible. To avoid breakage, the tongs should hold the crucible without putting pressure on the sides.
Graphite crucibles can be damaged by improper use or handling. They should not be used for iron-containing metals, because the iron will directly react with the carbon in the crucible and change the composition of the metal or destroy the crucible. Solid metals should be loosely packed in a crucible before being heated. Metals may expand, and a tightly packed crucible can crack or break. Water or wet metals should never be added to molten metal in a crucible, as this could cause a steam explosion or cause the crucible to fail.
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