Al2O3 and MgO Rich Spinel and Influence of Cr2O3 for Refractory Application

Abstract

With the increasing demand of high-quality refractories in iron and steel, glass, cement and other industries where the very high temperature is required, it is important to develop refractories with good physical, chemical, thermal, mechanical and thermomechanical properties. The aim of this study was to determine how the behaviour of magnesium aluminate spinel-based refractories changes with chromium oxide (Cr2O3) and how chromium oxide (Cr2O3) affects the mineralogical composition and the chemistry of existing phases. The addition of chromium oxide (Cr2O3) to magnesium aluminate spinel (MgAl2O4) refractories results in the formation of a solid solution with spinel phase and increases the degree of densification, thus improving the strength and resistance to corrosion and thermal shock of the material. In this research work, chromium oxide was added in three different compositions i.e. 0, 5 and 10 wt.%. The variable compositions of alumina and magnesia were used as 92 to 42 wt.% and 8 to 48 wt.% respectively. Specimens were pressed at a load of 4 ton and sintered at 16500C with a holding time of 2 hrs. Among all compositions, alumina rich specimen (S2) having 87 wt.% Al2O3, 8 wt.% MgO and 5 wt.% Cr2O3 and magnesia-rich specimen (S14) having 47 wt.% Al2O3, 48 wt.% MgO and 5 wt.% Cr2O3 were found to have better properties compare to stoichiometric composition i.e. 72 wt.% Al2O3 and 28 wt.% MgO (S7). For alumina rich specimen S2, maximum density ~93% of theoretical density, linear shrinkage ~15%, compressive strength ~459 MPa, diametral tensile strength ~76 MPa were obtained. And for magnesia-rich specimen S14, maximum density ~94% of theoretical density, linear shrinkage ~20%, compressive strength ~589 MPa, diametral tensile strength ~77 MPa were obtained. Alumina rich specimen S2 was found to have higher thermal shock resistance, low wear depth (~25-122 microns) and low coefficient of friction (µ = 0.07-0.11) compared to magnesiarich specimen S14 against steel tribocouple. Whereas the slag penetration resistance was found more for this magnesia-rich specimen S14 compare to alumina rich specimen S2 and stoichiometric composition. In this context, one can conclude that the Cr2O3 has significant influence in order to enhance the high temperature properties of secondary phase enriched spinel, and can be used for refractory applications.