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

Ca2+/Cr3+ co-doped LaAlO3 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 Cr6+ content in ceramics. In this work, Ca2+/Cr3+ co-doping LaAlO3 ceramics have been fabricated. By adjusting Ca2+/Cr3+ doped ratio (0 <= n(Ca2+)/n(Cr3+) <= 0.75), the "Cr3+->(Cr4+/Cr6+)" transformation ratio has been controlled. The results show that a higher concentration of Cr4+ in the material can significantly enhance the emissivity, while Cr6+ has no such effect. In addition, the Cr6+ content was measured by leaching method and high-temperature volatilization methods, respectively. This work can be used to guide the fabrication of environment-friendly Ca2+/Cr3+ co-doped LaAlO3-based ceramics with high emissivity in the field of energy-saving for thermal equipment.