Stabilizing Cr3+ in a mixture of solid solution phases for high-temperature applications

Abstract

The major drawback of Cr-containing materials is the generation of toxic Cr6+ compounds, especially at high temperatures in contact with oxygen, alkali or alkaline earth elements/oxides/salts. In this work, we compared the oxidation of two different Cr3+ species, (a) Cr2O3 and (b) a solid-solution mixture of Ca(Al,Cr)12O19 and (Al,Cr)2O3, upon reheating (500–1500 °C) in the presence of CaO, Al2O3, and SiO2 under air atmosphere. The mixture of Ca(Al,Cr)12O19 and (Al,Cr)2O3 was found to be more stable (7.5 mg/kg Cr6+) than Cr2O3 (5646 mg/kg Cr6+). Prolonged reheating (up to 24 h) of Cr3+ solid-solution phases at 900 °C reveals a slight increase in Cr6+ (3.0 to 4.8 mg/kg and 7.5 to 9.1 mg/kg for sample M2 and M2-S (with SiO2), respectively). However, the Cr3+ solid-solution phases in the presence of SiO2 reveal higher Cr-evaporation than undoped counterparts. Nonetheless, the mixture of (Al,Cr)2O3 and Ca(Al,Cr)12O19 hardly showed reoxidation and was more inert.