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A modern crucible used in the production of silicon ingots via the Czochralski process Smaller clay graphite crucibles for copper alloy melting. A crucible is a container in which metals or other substances may be melted or subjected to very high temperatures.
To manufacture synthetic graphite items, carbon powder and silica are mixed with a binder, such as tar, and baked after being pressed into shape such as that of electrodes or crucibles. [ 8 ] [ 9 ] They are then surrounded with granulated carbon acting as a resistive element that heats them.
The metal is first melted in contact with a carbon source, possibly a graphite crucible inside which the melt is carried out or graphite powder/chunks that are placed in the melt. Keeping the melt in contact with the carbon at a specific temperature dissolves the carbon atoms, saturating the melt based on the metal–carbon binary phase diagram ...
When silicon is grown by the Czochralski method, the melt is contained in a silica crucible. During growth, the walls of the crucible dissolve into the melt and Czochralski silicon therefore contains oxygen at a typical concentration of 10 18 cm −3. Oxygen impurities can have beneficial or detrimental effects.
The silicon carbide near the outer walls of the crucible sublimes and is deposited on a graphite rod near the center of the crucible, which is at a lower temperature. [2] Several modified versions of the Lely process exist, most commonly the silicon carbide is heated from the bottom end rather than the walls of the crucible, and deposited on ...
The expanded graphite can be used to make graphite foil or used directly as a "hot top" compound to insulate molten metal in a ladle or red-hot steel ingots and decrease heat loss, or as firestops fitted around a fire door or in sheet metal collars surrounding plastic pipe (during a fire, the graphite expands and chars to resist fire ...
The crucible process existed in India at the same time that the west- facing technology was operating in Sri Lanka. [38] Excavations of the Yodhawewa (near Mannar) site (in 2018) have uncovered a lower half of a bottom spherical furnace and crucible fragments used to make crucible steel in Sri Lanka during the 7th-8th centuries AD.
Graphitization can be observed in various contexts. For example, it occurs naturally during the formation of certain types of coal or graphite in the Earth's crust.It can also be artificially induced during the manufacture of specific carbon materials, such as graphite electrodes used in fuel cells, nuclear reactors or metallurgical applications.