Study On Epoxy Resin Adhesive Modified By Nano- Sio₂ And Technical And Adhesion Principle Of SiC Ceramic

SiC ceramic is widely used in industries of aerospace, mechanical and electron due to the properties of high-specific stiffness, low-thermal expansion property, especially excellent heat shock-resisting. However, large size part of SiC ceramic is hardly made because of the poor manufacturing technology. Brazing and diffusion bonding are also fail to join SiC ceramic because of high residual stress and strain from high temperature to room temperature. So, we selected adhesion to bond SiC ceramic due to low temperature and low cost. The adhesive was selected optimally and modified by nano-SiO₂, and the modifying and adhesion principals were studied. The resistance to aging and thermal decomposition of adhesive was analyzed and the equation of thermal decomposition was created.J-101 epoxy resin adhesive was preferred from phenolic resin modified by organ-silicone, J-228 epoxy resin adhesive, J-101 epoxy resin adhesive and J-27H epoxy resin adhesive, because it had higher bonding strength and better quality of joint. Through experiments, when J-101 was cured at 90℃for 2.5h without pressure and contained 20%-23% curing agent, the adhesion joint of SiC ceramic could get the higher shear strength and much better quality.Nano-SiO₂ was used to modify J-101 epoxy resin adhesive because the cured of epoxy resin adhesive was brittle and thermal stability was not satisfied. When the content of nano-SiO₂ was 3%, the shear strength of adhesive joint of SiC ceramic reached 43.33MPa, which was more 25.6% than the joint of J-101 epoxy resin adhesive. After modifying with nano-SiO₂, the fracture of J-101 epoxy resin adhesive was uneven, which showed that the fracture was more ductile fracture than brittle fracture and the toughness of J-101 epoxy resin adhesive was improved. Silane coupling agent KH-550 was added to improve the adhesion strength of the SiC ceramic joint. When the content of KH-550 was 2%, the shear strength of adhesive joint of SiC ceramic reached 48.45MPa, which was more 40.5% than the joint of J-101 epoxy resin adhesive.The adhesion principal of SiC ceramic joint revealed that mechanical bond and adsorption were mainly source of the adhesion strength. There were many rugged grooves and pores on the surface of SiC ceramic, and in the process of curing epoxy resin adhesive filled these grooves and pores by diffusion firstly, which made mechanical combination, as the distance of molecules between the surface of SiC ceramic and epoxy adhesive was below to 10?, there would be adsorption.By using the method of thermal accelerated aging, we studied the effect rule of aging temperature on the adhesion properties of epoxy adhesive. In different aging temperatures, with the increasing aging time, the shear strength of the SiC ceramic joint increased first and then decreased. Analysis of the mechanism of aging showed that oxygen was the most important elements of aging. After aging, the contents of C-C and C-H reduced but C-O increased, then C-O was oxidized into O = C-O, therefore, the final oxidations were C-O and O = C-O. Through determining the mechanism function and solving the kinetic parameters of thermal decomposition reaction kinetics of epoxy adhesive, the pyrolysis kinetics equation was created.