The significance of raw material quality on thermo-mechanical properties

Within the scope of a larger project we characterized different refractory raw materials itself and – besides others – also investigated the thermo-mechanical properties of shaped and unshaped products based on these. The raw materials considered within this study were of different types of the system Al2O3 / SiO2 – e.g. andalusite, mullite and pure alumina. The investigation of the raw materials itself focused mainly on the chemical and mineralogical composition as well as on microstructural features. Bricks and castables were produced by standardized procedures and recipes in order to ensure the direct comparison of the results obtained. Several interesting effects could be observed by characterizing the refractoriness under load (RuL), creep in compression (CiC) and thermal shock behaviour of the bricks and castables. On different examples the causes and interdependencies of these effects on the raw materials properties will be displayed and discussed more deeply. The results show that the raw material quality is the decisive factor for the behaviour of the refractory products at high temperatures and thus determining their performance in demanding applications. Especially the impurity level is responsible for the temperature at which a first melting phase is formed but additionally determines their amount as well as viscosity and this, in turn, influences the course of RuL and CiC. Additionally some other characteristics like porosity and microstructural features have an impact too