Abstract

In all discontinuous driven thermal processes refractory linings are exposed to thermo-mechanical stress that is often responsible for a premature wear. This is especially significant for monolithic refractory materials that are typically in green state prior to the first heat-up. Spinel has been identified as a valid countermeasure to overcome material damage caused by thermal stress a long time ago. Especially spinel forming high alumina refractory monolithics show a significant improvement. However 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 to lower 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. Thermo-mechanical induced spalling is typically initiated in this zone. The proposed presentation will demonstrate that a smart matrix design including the particle size distribution and the spinel precursor materials allows to adjust the formation velocity and the appearance of the spinel in dependence of the temperature. Distinct amounts of low temperature spinel enables a goal oriented strengthening of the described 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 and cement-free concretes. The influence on physical properties like CMoR, open porosity or the yield of spinel formed was measured. 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, the state of agglomeration, the particle size distribution and presence of impurities seems to play a decisive role in the spinel formation. By adding the spinel precursors to high alumina concretes the CMoR is influenced. In comparison to MgCO3, MgO seems to be more efficient to promote a spinel formation. Overall these information will provide very valuable information for an intelligent matrix design for an improved spinel formation adjusted to service conditions.