Preparation And Properties Of Perovskite Type High Emissivity Infrared Radiation Materials

As materials strengthening the radiation heat transfer, infrared radiation materials show a promising future in high temperature applications for the purpose of energy-saving. Up to now, the research of infrared radiation energy-saving materials is mainly focused on the non-oxide and the oxide materials. The non-oxide materials which have high emissivity at wide band are hard to applied under the high temperature oxidation atmosphere, due to their poor oxidation resistance.Therefore, this papper is focus on oxide materials.By comparing the advantages and disadvantages of various kinds of infrared radiation materials, the perovskite type infrared radiation materials are studied in this paper. The infrared radiation property of doped perovskite ocide materials is researched in 0.76-2.5μm and 3-5μm. The physical mechanism of the high emissivity by doping is revealed. Subsequently, high emissivity coating is prepared via high temperature solid state sintering. The infrared radiation property and energy-saving effect are studied in this papper.1. The Ca2+-doped La FeO₃ ceramics are prepared by solid phase sintering. Effect of Ca2+-doping content on infrared performance of the samples is researched. It is found that the emissivity of Ca2+-doped LaFeO₃ based materials is significantly improved. The experimental result demonstrates that 10mol% Ca2+-doping La FeO₃, namely La0.9Ca0.1FeO₃, has an infrared emissivity as high as 0.88 and 0.90 in near-infrared and 3-5μm respectively. The introduction of Ca2+ broadens the infrared absorption spectrum of the samples from visible light region（0.59μm） to mid-infrared region（12.4μm）. Thus, the infrared radiation performance of the La1-xCaxFeO₃ samples is improved.2. The La1-xCaxCrO₃ samples are prepared via solid-state reaction. It is demonstrated that Ca2+-doped can effectively improve the emissivity of La CrO₃ based materials in the spectral region of 0.76-2.5μm and 3-5μm. The emissivity of La1-xCaxCrO₃ samples gets the maximum value 0.94 in 0.76-2.5μm and 3-5μm, when the x is 0.2. The doping of Ca2+ broadens the infrared absorption spectrum of the samples from visible light region（0.58μm） to near-infrared region（3.9μm）. Thus, the infrared radiation performance of the La1-x CaxCrO₃ samples is improved.3. The La0.8Ca0.2Al1-xCrxO₃ samples are prepared via solid state sintering. Effect of Cr3+-doping content on infrared performance of the samples is researched. The physical mechanism of the high emissivity by Cr3+-doping is revealed according to energy band calculation. The study shows that only a small amount of Ca-Cr Co-doped can significantly improve the infrared emissivity of the LaAlO₃ samples. The emissivity of La0.8Ca0.2Al1-xCrxO₃ samples gets the optimal value 0.91 in 0.76-2.5μm and 3-5μm, when the x is 0.1. The introduction of Cr element reduces the band gap of the sample material from 3.35 e V to 0.11 eV. This increases the concentration of free carrier and strengthens the infrared absorption of free carriers. Therefore, the emissivity of La0.8Ca0.2Al1-xCrxO₃ samples is improved.4. Perovskite type infrared radiation coating was prepared by using La0.8Ca0.2Al0.9Cr0.1O₃ as infrared radiation base material in this papper. It is demonstrated that the perovskite type infrared radiation coating has an infrared emissivity as high as 0.90 and 0.88 in near-infrared and 3-5μm respectively. The high temperature radiation performance is evaluated by the high temperature infrared radiation furnace. The result shows that the coating has the advantages of fast heating rate and high thermal equilibrium temperature at high temperature. The coating with high emissivity can effectively strengthen the radiation heat transfer, increase heat utilization efficiency, speed up the heating rate of water from 0.44℃/s to 0.76℃/s, shorten the heating time from 161 s to 104 s, and saved 35.4% of electric energy according to water-boiling experiment.The perovskite type infrared radiation materials used in this study have the advantages of high temperature resistance, oxidation resistance, high emissivity in the spectral region of near infrared and 3-5μm. The perovskite type materials are expected to be applied in the field of high temperature energy-saving, and making some contribution to our country’s high temperature and energy-saving.