Effect of Ca2+/Cr3+doping ratio on the infrared radiation performance and Cr6+ formation in LaAlO3 ceramics

Ca 2+ /Cr 3+ co-doped LaAlO 3 has been considered as important ceramic to achieve energy-savings in thermal equipment due to excellent infrared radiation (IR) performance. However, following problems restricted its industrial applications: one is the correlation between emissivity and the valence state of Cr which is not clear, then there is no quantitative evaluation of Cr 6+ content in ceramics. In this work, Ca 2+ /Cr 3+ co-doping LaAlO 3 ceramics have been fabricated. By adjusting Ca 2+ /Cr 3+ doped ratio (0 ≤  n (Ca 2+ )/ n (Cr 3+ ) ≤ 0.75), the “Cr 3+ →(Cr 4+ /Cr 6+ )” transformation ratio has been controlled. The results show that a higher concentration of Cr 4+ in the material can significantly enhance the emissivity, while Cr 6+ has no such effect. In addition, the Cr 6+ content was measured by leaching method and high-temperature volatilization methods, respectively. This work can be used to guide the fabrication of environment-friendly Ca 2+ /Cr 3+ co-doped LaAlO 3 -based ceramics with high emissivity in the field of energy-saving for thermal equipment.