REACTION PROCESSES IN THE INTERIOR OF AN MGO-CARBON BRICK WITH BORON-CARBIDE ADDITIVE

This paper deals with oxidation protection afforded to carbon-containing refractory materials by boron carbide. Following the previous tests on the stability of B4C at high temperatures and on the microstructural characteristics of a fired MgO-C brick, now the reactions, which are to be expected in the interior of the brick, in a neutral atmosphere are discussed. The results of the theoretical consideration and the experiments carried out provide evidence that MgO is unstable in the presence of boron carbide as from approx. 1300-degrees-C. Similar instability is shown by magnesium borate, which is reduced by carbon as from about 1300-degrees-C. In both reactions, reactive gases occur (Mg vapour and B2O2), which prevent its ingress and hence oxidation of the carbon by binding the oxygen. As well as the dense layer of borate melt on the brick surface, this phenomenon is obviously responsible for the high efficiency of the boron carbide as an antioxidant for MgO-C materials.