Effect of temperature on hexavalent chromium formation in (Al,Cr)2O3 with calcium aluminate cement in air

Abstract

Cr2O3 containing refractories castables are widely used as linings of various furnaces because of its remarkable corrosion resistance. However, Cr2O3 can be oxidized to toxic Cr(VI) by calcium aluminate cement phases (CA and CA2) which are used as hydraulic binder in castables. In the present research, one of the most stable Cr(III) phase viz., (Al,Cr)2O3 solid solution was synthesized and then reacted with cement phases in order to check the formation of Cr(VI). The (Al, Cr)2O3 solid solution and calcium aluminate cement (70% Al2O3) were mixed in the ratio 1:1 (mass%) and heated in the temperature range of 500-1 500°C in air. The phase compositions and formation/leachability of Cr(VI) were investigated using XRD, XPS and the leaching tests. The (Al,Cr)2O3 solid solution didn't react with calcium aluminate cement at 500-900°C, while it partially converted to a Cr(VI)-containing phase at 1 100-1 300°C. However, (Al,Cr)2O3 and cement phases react to form a ternary Cr(III) phase (Ca(Al,Cr)12O19) at 1 500°C.