Preparation Of High-temperature Coating By Silicone Ceramic And Improvement Of Its Adhesion

It has been known that the inorganic oxide coating is easily to peel off due to its mismatch of the thermal expansion coefficient with resin matrix composites,and the heat resistance of the organic coating can not reach the requirements at the medium and high temperature(400~800 ?).Herein,for these defects of the insulation protective coatings used on the resin matrix composites,a kind of organic/inorganic hybrid coating was designed.The adhesion of the resin matrix composites substrate was modified by the phthalazinone-silicone copolymer as base coating,and the organic silicone coating was prepared as the surface coating.The heat resistance performance of the coating was improved because of the ceramic transition of the silicone resin at higher temperature environment.In the second chapter,the silicone ceramic precursor was prepared by sol-gel method,and the corresponding curing agent was also prepared.The curing kinetics of silicone ceramic precursor was studied by the non-isothermal DSC.Combined with the specific experimental results,the cure process was determined as :80?/2h +100?/2h +120?/2h +150?/2h +180?/2h+200?/2h.In the third chapter,the thermal stability and ceramic mechanism of the silicone resin coating was studied by the non-isothermal TGA.The results showed that the thermal decomposition mechanism of the silicone resin could roughly be divided into two stages: the first stage focused on 300~390 ?,mainly involving thermal decomposition of non cross-linked small molecules;the second stage focused on 390~800?,mainly involving the ceramic transition.Besides,the ceramic transition was divided into three steps: in the 390~450?,Si-OH had a nucleophilic reaction to the Si atoms on the main chain,and the linear and cyclic oligomers were obtained by the thermal decomposition;In the 450~650?,the Si-C and C-C bonds breaked down,releasing small molecular hydrocarbons;In the 650~800?,the active silicon atoms generated by the Si-C bond breaking reacted with oxygen to form silicon dioxide.In addition,by adding boron carbide and vermiculite with the ration of 1: 1,the ceramic yield was increased to 90% and the line shrinkage was reduced to 3%.In the fourth chapter,the composite coating was prepared by using the phthalazinone-silicone copolymer as the base layer and the silicone as the surface.The results showed that the adhesion of the composite coating was improved.Thermal insulation of ceramic coatings with different thickness were tested.The results showed that in the period of 80~180s,the temperature of the coated sample was obviously lower than that of the uncoated metal matrix and it will decrease with the increase of the thickness of the coating.