The substances that can be used as bonding agents for magnesia carbon bricks are summarized as follows: coal tar, asphalt, petroleum asphalt. Traditional asphalt bonded magnesia carbon brick is cheap, reliable, high carbon residue rate, and petroleum asphalt has a strong affinity for magnesium oxide. However, due to the elastic after-effect of graphite after molding and heat treatment, the volume of magnesia carbon brick expands, and the brick body is not dense. Later, thermosetting phenolic resin is used to obtain good body strength, oxidation resistance and thermal shock performance are improved.
Phenolic resin eventually forms polymer-linked glass carbon in the heat treatment process. The solid phase carbonization structure of phenolic resin generally presents an optical isotropic glassy structure. The liquid carbonized carbon of asphalt and tar, due to its high liquid viscosity, cannot flow and has a Mosaic structure. The resin is cured before liquid phase lamination at high temperature, forming isodirectional carbon. Compared with hetero-directional carbon, the former shrinks by 90% and the latter by 5%, resulting in the formation of high-strength dense carbon.
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