MATRIX DESIGN FOR IMPROVED SPINEL FORMATION IN HIGH ALUMINA REFRACTORY MONOLITHICS THAT IS ADJUSTED TO THE SERVICE CONDITIONS

摘要

In service, monolithic linings are exposed to a temperature gradient that only forms a sintered layer at the hot face. In deeper zones the monolithic lining remains in an unfinished state due tolower temperatures that are dependent on the thermal conductivity of the material. Here the material suffers of an unfinished ceramic structure. Especially the zone beneath the sintered zone is critical because here the thermo-mechanical impact is still high. A smart matrix design including the particle size distribution and the spinelprecursor materials allows to adjust the formation velocity and theappearance of the spinel in dependence of the temperature. Distinct amounts of low temperature spinel enable a goal oriented strengthening of the weak zone in the lining. In matrix formulations Mg-delivering precursors were chosen due to their ability to form spinel and their workability in the mixture. The choice was taken for a dead burned magnesia (MgO) and a raw magnesite (MgCO3).The precursors were implemented in different amounts into cement-containing concretes. The influence on physical propertieslike CMoR, open porosity or the yield of spinel formed wasmeasured. Investigations of the spinel formation kinetics confirm, that generally the higher the firing temperature and the finer the particles, the more efficient is the spinel formation. However, thestate of agglomeration and the particle size distribution seem to play a decisive role in the spinel formation. By adding the spinelprecursors to high alumina concretes the CMoR is influenced. In comparison to MgCO3, MgO seems to be more efficient to promote a spinel formation. But the grain size of spinel and its distribution is essential, too. This is proved by electronic microscopy examinations. Overall these results will provide very valuableinformation for an intelligent matrix design for an improved spinelformation adjusted to service conditions.