Enhanced infrared emission property of NiCr spinel coating doped with MnO2 and rare-earth oxides

In order to enhance the infrared emission property, a NiCr spinel coating was synthesized via the air plasma spraying method, and doped with MnO2 and rare-earth oxides (CeO2, Pr6O11, and Tb4O7). The obtained coating had a thickness of approximately 150-200 mu m with a typical laminated structure. The deposited coating was composed of mainly a mixture of NiCr2O4 and NiCrMnO4. Compared with the non-doped NiCr spinel coating, doping MnO2 and rare-earth oxides could effectively improve the infrared emissivity in the wavelength ranges of 2.5-8 mu m and 15-25 mu m, owing to the charge transfer transitions in NiCrMnO4 spinel and the lower symmetry of lattice vibration. The prepared infrared radiation coating showed a considerably high total emissivity of 0.917 in the wavelength range of 2.5-25 mu m at 1000 degrees C. Further, good thermal shock resistance was confirmed, as microcracks only appeared in the coating after 37 thermal cycles with air-cooling from 1000 degrees C to 25 degrees C.