Investigation of the role of impurities typical in secondary raw materials on the behaviour of high alumina castables - Part II: Influence on thermomechanical behaviour

The present work investigated the effect of relatively small additions of impurities originating in secondary raw materials on the thermomechanical properties of alumina castables bonded with active alumina. Castable compositions containing impurities for testing were selected on the basis of predictions from thermochemical calculations of their phase composition and the formation of large amounts of liquid phase at the temperature of 1600 °C. Viscosity of the emerging liquid phase was also calculated. The selected alumina castables with impurities from the systems: CaO–SiO2. Na2O–SiO2. Fe2O3–CaO. Fe2O3–CaO–SiO2 and TiO2–CaO–SiO2 were tested for thermomechanical properties by analysing the effect of impurities on refractoriness under load (RUL) creep in compression (CiC) and resonant frequencies and damping changes versus temperature (RFDA). Real composition of tested material via high temperature X-ray diffraction (HT-XRD) were verified. The obtained results indicate that impurities introduced into the refractory castables in a total amount of 0,18 wt% (2% in the fraction 0–45 μm) and in the most unfavourable ratio from the point of view of phase equilibria have an observable effect on the properties of the material at elevated temperature. The obtained results show that in the case of introducing impurities into the material with mutual proportions of shares limiting the formation of the liquid phase. It will be possible to maintain the thermomechanical properties of alumina castables at a satisfactory level (compared to the pure one) from the industrial process perspective in which it will be used. The obtained results shed new light on the possibilities of the conscious use of secondary raw materials in refractory monolithics technology