High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement

Al(2)O(3)-CaO-Cr(2)O(3) castables are used in various furnaces due to excellent corrosion resistance and sufficient early strength, but toxic Cr(VI) generation during service remains a concern. Here, we investigated the relative reactivity of analogous Cr(III) phases such as Cr(2)O(3), (Al(1−x)Cr(x))(2)O(3) and in situ Cr(III) solid solution with the calcium aluminate cement under an oxidizing atmosphere at various temperatures. The aim is to comprehend the relative Cr(VI) generation in the low-cement castables (Al(2)O(3)-CaO-Cr(2)O(3)-O(2) system) and achieve an environment-friendly application. The solid-state reactions and Cr(VI) formation were investigated using powder XRD, SEM, and leaching tests. Compared to Cr(2)O(3), the stability of (Al(1−x)Cr(x))(2)O(3) against CAC was much higher, which improved gradually with the concentration of Al(2)O(3) in (Al(1−x)Cr(x))(2)O(3). The substitution of Cr(2)O(3) with (Al(1−x)Cr(x))(2)O(3) in the Al(2)O(3)-CaO-Cr(2)O(3) castables could completely inhibit the formation of Cr(VI) compound CaCrO(4) at 500–1100 °C and could drastically suppress Ca(4)Al(6)CrO(16) generation at 900 to 1300 °C. The Cr(VI) reduction amounting up to 98.1% could be achieved by replacing Cr(2)O(3) with (Al(1−x)Cr(x))(2)O(3) solid solution. However, in situ stabilized Cr(III) phases as a mixture of (Al(1−x)Cr(x))(2)O(3) and Ca(Al(12−x)Cr(x))O(19) solid solution hardly reveal any reoxidation. Moreover, the CA(6) was much more stable than CA and CA(2), and it did not participate in any chemical reaction with (Al(1−x)Cr(x))(2)O(3) solid solution.