Preparation And Infrared Radiation Performance Of Lanthanum Aluminate Based High Emissivity Coating Materials

The infrared radiation material has a high emissivity,and coating the lining substrate of the kiln can strengthen the radiant heat transfer of the kiln,thereby achieving the energy saving effect.lanthanum aluminate has a high melting point?2180°C?,good high temperature stability,typical indirect transition energy band structure,and also has a high degree of chemical composition and thermal expansion coefficient with the furnace lining material?aluminum-silicon refractory?compatibility,so in this experiment,the lanthanum aluminate was used as the matrix,and the pure LaAlO₃ and doped LaAlO₃ were prepared by high temperature solid phase reaction at1600°C to study the near-infrared radiation properties of the material.The main results are as follows:?1?The infrared radiation materials after Cr-Fe co-doping were all perovskite structure compounds.The radiation performance of Cr³⁺-Fe³⁺co-doped samples in near-infrared were greatly improved compared with undoped LaAlO₃.At a fixed doping ratio of Cr?mol?:Fe?mol?=1:1,the infrared emissivity of the lanthanum aluminate material increased with the increase of the B-site doping concentration.When the doping amount of Cr³⁺and Fe³⁺were both 25 mol%,the average emissivity was 0.83 in the region of 0.76².5?m.?2?When preparing Ca-Fe co-doped lanthanum aluminate,when the doping amount of the A and B sites were x=y=0.1,0.2,La_0.9Ca_0.1Al_0.9Fe_0.1O₃ and La_0.8Ca_0.2Al_0.8Fe_0.2O₃ are both perovskite structural compounds;when the doping amount of A site is x=0.2,and the doping amount of B site were y=0.3,0.4,0.5,?CaLa?Al₃O₇ and Ca₂Fe₂O₅ low melting phase appeared in the system;The infrared radiation performance of the sample after Ca-Fe co-doping was significantly higher than that of pure LaAlO₃.When 20 mol%Ca²⁺and 20 mol%Fe³⁺were doped,the average emissivity in the region of 0.76².5?m was 0.917,which was higher than that of pure LaAlO3??=0.236?about 289%.?3?When investigating the effect of ZrO₂ introduction on the infrared radiation performance of Ca-Cr co-doped lanthanum aluminate coating materials,La_1-xCa_xAl_0.8Cr_0.2O₃?0?x?0.2?and CaZrO₃ oxides were orthorhombic perovskite structure,when the molar ratio of the theoretical amount of CaZrO₃ and La_1-xCa_xAl_0.8Cr_0.2O₃ is 0.20,a La₂Zr₂O₇ phase having a fluorite structure appears.When the molar ratio of the theoretical yield of CaZrO₃ and La_1-xCa_xAl_0.8Cr_0.2O₃ were less than 0.20,the emissivity of the composite ceramics in the region of 0.76².5?m were further improved than that of La_0.8Ca_0.2Al_0.8Cr_0.2O₃;when the molar ratio of the theoretical amount of CaZrO₃ and La_1-xCa_xAl_0.8Cr_0.2O₃ was 0.04,the emissivity was optimally 0.95,and the refractoriness was?29?1800?.?4?The thermal conductivity of LaAlO₃ material were Ca-Cr doping effectively reduced by Ca-Cr co-doping.The thermal conductivity of La_0.8Ca_0.2Al_0.8Cr_0.2O₃ at1200°C was 2.602 W·m^-1·K^-1,which was lower than that of pure LaAlO₃(4.20W·m^-1·K^-1)38%;the thermal conductivity of the composite ceramic material was further lower than that of La_0.8Ca_0.2Al_0.8Cr_0.2O₃,when the molar ratio of the theoretical amount of CaZrO₃ and La_1-xCa_xAl_0.8Cr_0.2O₃ was 0.04,the thermal conductivity of the composite ceramic material at 1200?was 2.005 W·m^-1·K^-1.