Environment-friendly Ca²⁺/Cr³⁺ co-doping LaAlO₃ ceramics with excellent infrared radiation performance for energy-saving

Ca²⁺/Cr³⁺ co-doped LaAlO₃ infrared (IR) ceramics have been proven to be potential energy-saving materials for high-temperature industries because of their high emissivity and high-temperature stability. However, Cr⁶⁺ formation commonly occurs in materials and poses environmental and health risks, such as Cr⁶⁺ dissolution in water and CrO₃(g) volatilization. In this study, we combined high emissivity with in situ detoxification by introducing residual Al₂O₃ into Ca²⁺/Cr³⁺ co-doped LaAlO₃ ceramics. Compared with the undoped ceramics, the addition of 20 wt% residual Al₂O₃ resulted in a 78.5% reduction to 18.44 mg/kg (lower than the EU standard of 20 mg/kg) in Cr⁶⁺ dissolution and a decrease in 77.8% CrO₃(g) volatilization. This significant detoxification effect can be attributed to the formation of CaAl_12−xCr_xO₁₉. Additionally, as the residual Al₂O₃ content increased from 5 to 20 wt%, the ceramics maintained high emissivity, above 0.896 in the near-infrared band and 0.781 in the mid-infrared band. Furthermore, the IR coating effectively increased the surface temperature (from 767.1 to 790.7 °C/min) and the heat radiation of the heating source, increasing the heating rate from 31.7 to 34.6 °C/min during water heating. This work offers a promising approach for designing environmentally friendly IR ceramics with excellent IR performance for energy-saving applications in the high-temperature industry.