Preparation And Performance Study Of High Temperature Resistant Silicate Adhesives

When the ceramic fiber rigid heat insulation tile and ceramic fiber flexible heat insulation mat are attached to the surface of supersonic vehicle,in order to eliminate the problem of thermal expansion of the vehicle surface,gaps will be kept between each other,and in order to avoid the hazards caused by the transfer of high temperature heat flow from the surface to the inside,heat-resistant adhesives are required.At present,heat-resistant adhesives generally have problems such as high curing temperature and low adhesive strength.Therefore,it is of great practical importance to develop an adhesive that can be cured at a lower temperature and has high bond strength.In this paper,a silicate adhesive was prepared using silicate resin as the base resin（A）and alumina,silica,whisker,metal powder and boron-based powder as fillers（B）.The effects of the amount of each filler,resin density,and curing process on the bond strength were investigated.The results showed that when alumina,silica,whisker,metal powder and boron system powder were 40,40,6,6 and 10 parts,respectively,and A:B=1:1（mass ratio）was applied,it had the best bond strength of 14.98 MPa for 6 h curing at 80℃,and each filler was well dispersed and no agglomeration occurred.In order to understand the curing and bonding mode of silicate adhesives,the curing kinetics and bonding mechanism of the adhesives were analyzed.The results showed that the curing of silicate adhesives was the result of a combination of chemical and physical reactions of non-integer order,with apparent activation energy Ea=11.789 k J/mol and exponential prefactor A=0.57310.The active Si O₂ colloids diffused to the surface of the bonded material and preferentially reacted with the more reactive sites on the surface of the bonded material to form new chemical bonds such as Si-O-X,while waiting for other independent Si O₂ colloids or agglomerated Si O₂ colloids to continue their collide reactions with them.Meanwhile,it waited for other independent Si O₂ colloids or agglomerated Si O₂ colloids to continue the collision reaction with it.To investigate the practical performance of the prepared silicate adhesives,the bonding strength of silicate adhesives to different metallic materials and their durability in different media and environments were investigated using the optimal formulation and curing process in this paper.The results showed that among the three metals examined,the silicate adhesive had the best effect on the bonding of titanium alloy,followed by alloy steel and the worst of aviation aluminum,and the bonding strength could be maintained at about 50-70%in the high temperature range of 400-600℃;The bonding effect was greatest in alkaline conditions,next in acidic conditions and least in organic solutions;Prolonged exposure to air had essentially no effect on bond strength;The adhesive had good thermal stability,boron powder A oxidation expansion at about 400℃and had a molten state can make up for the pores in the adhesive,metal powder A oxidation expansion at about 800℃could make up for the pores in the adhesive;Poor water resistance,with water immersion time,the bonding strength showed an almost linear decline;No significant changed in the bonding strength of heat aging for 24 h and heat aging for 96 h.It could be used in a high temperature environment at 600℃for a long time;For titanium alloy bonding at 600℃air-cooled shock 5 times,the bonding strength became 5.88MPa,air-cooled shock 20 times,the bonding strength became 2.46 MPa;The adhesive strength became 3.29 MPa when water-cooled shock at 600℃for 1 time,and the adhesive failed when water-cooled shock for 4 times.