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.

It is important to develop high emissivity infrared radiation materials for energy saving in high-temperature furnaces. In this work, Ni²⁺-doped MgCr₂O₄ materials were prepared by a high-temperature solid-phase reaction process. The effect of Ni²⁺ doping content on the infrared radiation properties of MgCr₂O₄ materials was investigated, and the mechanism of emissivity enhancement of MgCr₂O₄ materials was explored. The results show that Ni²⁺ ions can be doped into the lattice of MgCr₂O₄ materials, and the prepared Mg_1–xNi_xCr₂O₄ (0.1≤x≤0.5) materials produce the lattice distortion and a small amount of Ni²⁺ valence state transformation. Also, the concentration of oxygen vacancies increases,the forbidden band width decreases with the increase of Ni²⁺ doping, thus improving the emissivity of the prepared materials in the near–mid-infrared band. The material with x of 0.5 (Mg_0.5Ni_0.5Cr₂O₄) has an average emissivity of 0.88 in the near infrared ref bands (i.e.,0.8–2.5 μm), which is 167% greater than that of the undoped specimens. Ni²⁺ ions doping enhances the lattice vibration absorption, free carrier absorption and impurity energy level absorption, and improves the infrared emissivity of MgCr₂O₄ materials in the near–mid-infrared band.

n(Ca²⁺)/n(Co²⁺)(n is mole) co-doped LaAlO₃ ceramics were synthesized by a solid-phase reaction technique. The effect of n(Ca²⁺)/nCo²⁺ doping ratio on the infrared radiation performance of LaAlO₃ ceramics (La_1–xCa_xAl_0.8Co_0.2O₃, 0.25≤n(Ca²⁺)/n(Co²⁺)≤2.00) was investigated, and the mechanism for improving infrared radiation property was analyzed. The result reveals that n(Ca²⁺)/n(Co²⁺) co-doped LaAlO₃ ceramics have a perovskite crystal structure. Increasing the doping ratio (0.25≤n(Ca²⁺)/n(Co²⁺)≤1.00) improves the emissivity in the wavelength range of 0.76–2.50 μm. The ceramic specimen with n(Ca²⁺)/n(Co²⁺) of 1.00 (La_0.8Ca_0.2Al_0.8Co_0.2O₃) has the maximum average emissivity (0.87). In the 2.50–14.0 μm band, the average emissivity of all n(Ca²⁺)/n(Co²⁺) co-doped LaAlO₃ ceramics is generally greater than 0.94. The improvement of emissivity can be attributed to the enhancement of free carrier absorption, impurity absorption and lattice vibration absorption. This novel infrared ceramic with a high emissivity has promising prospects for energy-saving applications of thermal equipment.