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 500–1500°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 1100–1300°C. However, (Al,Cr)₂O₃ and cement phases react to form a ternary Cr(III) phase (Ca(Al,Cr)₁₂O₁₉) at 1500°C.