Elements containing graphite and silicon carbide

Graphite, an allotropic form of carbon, is very often used in foundries and iron and steel works because of its high resistance to extreme temperatures and its good electrical conductivity. It is used particularly for the construction of crucibles and for industrial-scale electrodes in electric steel-making plants. Graphite is not only used in its pure form, but also in mixtures containing other refractory materials like corundum or magnesium oxide.

Silicon carbide is also used for particularly demanding refractory applications, as well as being employed in the manufacture of high-performance brake discs for sports cars and aircraft.

Oxidation protection

To avoid premature material failure, refractory elements containing graphite or silicon carbide must be protected against oxidation.

Both substances are susceptible to oxidation with airborne oxygen and other oxidants at high temperatures. The burning of carbon, such as during the manufacturing of a graphite crucible, would reduce its structural stability, and, in turn, would cause it to lose its favourable thermal and electrical properties.

The oxidation of crucibles or the too-rapid erosive burning of extremely expensive graphite electrodes can be avoided by vacuum impregnation with phosphates from Budenheim. In cases where impregnation is not possible, the suspension is applied directly to the surface of the components. In both cases, the result is a high-viscosity coating that does not run, even at high temperatures, and offers outstanding protection against oxidation.