The effect of the addition of fine andalusite particles in refractory bricks on gaseous corrosion

In the past, the mechanisms of corrosion in refractory materials used in the flue wall of anode baking furnaces have been poorly understood. To better understand the processes of degradation, a study of corroded refractories from anode baking furnaces was conducted. This study found that all refractory bricks contain fine andalusite particles in the matrix and fireclay as aggregates. The first stage of corrosion is the penetration of gaseous sodium, coming from recycled anodes, through the porosity of materials. Then, at high temperature, sodium becomes oxidized and is included in the liquid phase. The sodium-rich liquid phase corrodes the refractory material, in particular mullite networks. To understand why the andalusite mineral is used in the refractory materials, a corrosion test able to simulate the gaseous corrosion of materials at laboratory scale was developed. Several recipes, composed of andalusite or fireclay, were submitted to the corrosion test. The microstructural observations showed that the matrix is more sensitive to corrosion. Thus, the use of a raw material such as andalusite in the matrix is advised in order to reduce the gaseous sodium corrosion of fireclay based bricks.