Preparation And Thermal And Mechanical Properties Of Rare Earth Silicate Low Thermal Conductivity Ceramics

The application of thermal barrier coatings in the field of aeronautics,traffic,thermal power generation,which need to put higherrequire for the use of thermal barrier coatings in high temperature,in oeder to settle the problem that the low thermal conductivity and poor phase stability,in this work,we use the yttrium tantalate and lanthanum rare earth tantalate as the new candidate material to reduce the thermal conductivity and obtain better high temperature mechanical properties.Lanthanum rare earth tantalate block ceramics were synthesized by solid-state reaction method.the grain diameter and porosity of samples is 2?14?m and 4%?9%,respenctively.NdTaO4,EuTaO4,DyTaO4,GdTaO4 and ErTaO4 is m phase,YbTaO4 and LuTaO4 is m' phase.Specific heat capacity at constant volume of block ceramics lower than 7-8YSZ due to the effect of volumetric expansion and phonon excitations.Thermal diffusion coefficient(0.38mm2/s to 1.3mm2/s)and therlal conductivity(0.3J/k·mol to 0.46W·m-1·k-1)decreases with increasing temperature at low temperature.because of the effect of thermal radiation,the heat-transfer mechanism of photons have a significant influence on the thermal conductivity of ceramics,which decreases gradually and tends to the lowest value at high temperature.The lowest thermal conductivity is 1.38W·m-1·K-1 at 800? for DyTaO4.The thermal conductivities of NdTaO4 with 1.41 W m-1·K-1 at 800? were close to DyTaO4.Meanwhile,the thermal diffusivity and thermal conductivity of rare earth tantalate block ceramics decrease with increasing porosity.Due to m phase has the lowest energy,it is a low temperature stable structure at low temperature.When the temperature is above 1430 C,t phase has the lowest energy,which is high temperature stable structure.YTaO4 powder with high chemical stability and thermal stability is sprayed on the 45 steel substrate,The YTaO4 thermal barrier coatings with a thickness of about 1.2mm were prepared by plasma spraying technolog.After rising to 700 ?,the thermal diffusivity and the thermal conductivity of the coating increase due to the heat transfer mechanism of photons and the decrease and condensation of pores.The Vickers hardness of coating YTaO4 is 498HV,which is lower than that of block YTaO4.Particle spacing and porosity of YTaO4 coating is larger than that of block YTa04,on the other hand,the surface of coating YTaO4 is rough.