Preparation Of Wave-Transmitting Coating Material With Low Expansion

In order to obtain a kind of radome coating material that can integrate the core well and have a stated transmission rate, we used Li2O-Al2O3-SiO2(LAS) ceramic material as the origination in this study, and we doped La to improve the dielectric properties of the LAS ceramic and CaSiO3 to down the sintered temperature and wide the sintered temperature range. As to produce the coating material in a low cost and a wide dimension, we used the gel-sol method and glazing technology together. In this research, the effect of the parameters during the sol-gel process on the gel time and gel quality, doping (La and CaSiO3) and heat treatment on the microstructure and properties of LAS ceramic coating are studied. The results indicated that:1 The type and amount of catalyst, the amount of ethanol and water and reaction temperature all have influence on gel time and gel quality. By research we determined the optimum parameters are as follows:The pH of the solution approximately 1.54, ethanol/ester= 4.2, water/ester= 4.2 and reaction at 80℃. After the reaction, there had no paste or clarify liquid left, we can obtain a transparent and crisp gel;2 It can influence the crystal phase of the LAS ceramic as the La doped, the rate of theβ-quartz and theβ-spodumene changed followed the change of the amount of the LaCb·6H2O so that brought the change of the properties of the samples. La did not enter the network of the ceramic, but to be the modifier of the network of the ceramic. Because of this the viscosity, the sintered temperature of the LAS ceramic decreased. the LAS ceramic with 5wt% LaCl3·6H2O have a lowest sintered temperature(1280℃), and the main crystal phase of this LAS ceramic isβ-spodumene, and it have a lowest thermal expansion, a=0.32×10-6/K, as the SiO2 enter the network ofβ-spodumene; this sample have a biggest bending strength,σ=57.2MPa too. After heat treated at 1280℃, the LAS ceramic with 5wt% LaC3·6H2O have the highest dielectric constant,ε=4.8, and smallest dielectric wastage tgδ=0.98×10-3.3 As the CaSiO3 doped, the sintered temperature of the LAS ceramic which have 5wt% LaCb·6H2O changed, the sintered temperature of the LAS ceramics which have 2.5wt% or 5wt% CaSiO3 rise, but the sintered temperature of the LAS ceramics which have 7.5wt% CaSiO3 is near the 1280℃, and the sintered temperature range be wider, the ceramics with 7.5wt% CaSiO3 have a similar density which heat treated at 1260℃,1280℃,1300℃and 1320℃. The CaSiO3 can encourage the bending strength of the LAS ceramic which have 5wt% LaCl3·6H2O, the sample with 7.5wt% CaSiO3 and 5wt% LaCl3·6H2O have a bending strength 63.1MPa, when sintered at 1280℃, and a appropriateα(=0.67×10-6/K) which can satisfy the requies.