Preparation And Performance Of High-temperature Resistant Organosilicone Adhesive

High-temperature resistant organosilicone adhesive was chosen as the research object, and a liquid preceramic polymer with vinyl groups, V-PMS, which possessed excellent high-temperature resistant and adhesive properties, was successfully synthesized via introducing cyclic silxone to the main chain of the low molecular polysilane rich of Si-H bonds. By adding single-phase or multiphase fillers to V-PMS, the mass loss and volume shrinkage of the adheisves during heat-treatment process were controlled, the densification of the bonding layer and join force at the interface were improved, and high performance organosilicone adhesives under both air and N2 atmosphere were prepared.Polymethylsilane(PMS) and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane(D4Vi) were chosen as raw materials, and a liquid preceramic polymer V-PMS, which could be used as a adhesive directly, was sucessfully synthesized by changing the proportion of the raw materials and controlling the degree of the polymerization. The optimal synthesis condition was found to perform at 120℃ for 3h with the mass ratio of PMS:D4Vi=1:1. The synthesis processes in this protocol are simple, cheap and easily controllable. The mass of the product V-PMS can be scaled easily to kilogram order, which is very promising for industry application.The as-synthesized V-PMS was characterized by elemental analysis, GPC, FTIR, NMR, TG and viscosity test. The results showed that the main chain of V-PMS was mostly made up of cyclotetrasiloxane, Si-C, Si-Si bonds, and the side chains were methyl, vinyl and Si-H bonds. The retained active Si-H and vinyl groups enable V-PMS cured easily to form network polymers with high crosslinking density, which can enhance the thermal stability and ceramic yield of V-PMS. The ceramic yields of V-PMS treated at 1200℃ under air and N2 were 90.8wt% and 81.0wt% respectively.V-PMS exhibited outstanding curing property. It could be cured at 100℃ for 18 h, or 150℃ for 8h, or 200℃ for 2h under air. The curing mechanism was based on both the addition reaction between Si-H and vinyl groups, and the oxidation crosslinking of Si-H bonds. V-PMS was used to join normal pressure sintered Si C ceramic, the shear strengths of the Si C joints treated at three curing conditions were 14.6MPa, 17.3MPa, 20.1MPa, respectively。The heat-resistant property of V-PMS was investigated. The results revealed that the room-temperature shear strengths of the joints treated at 400℃, 600℃, 800℃, 1000℃, 1200 ℃ under air were 19.6MPa, 3.5MPa, 7.6MPa, 30.9MPa, 14.8MPa, respectively. The room-temperature shear strengths of the joints treated at the same temperatures under N2 were 22.2MPa, 12.7MPa, 11.9MPa, 34.5MPa, 29.9MPa, respectively. During 400℃~800℃, V-PMS started to pyrolyze and released a lot of volatile. The volume shrinkage of bonding layer became obvious and a lot of cracks and pores appeared at the bonding layer, which made the strengths of the joints low at this range of temperature. Thus, it should be a key issue to elevate the densification of the bonding layer and improve the join force at the interface during 400℃~800℃.V-PMS+B4C(VP-B) was preparad by adding B4 C powder to V-PMS. It was found that the grain size and dosage of B4 C significant affected the properties of the adhesive. The smaller grain size of B4 C exhibited better modification on V-PMS. The preferable technics for preparing adhesive was performed under the mass ratio of V-PMS:B4C=100:40. The room-temperature shear strengths of the Si C joints bonded by VP-B treated at 200℃, 400℃, 600℃, 800℃, 1000℃, 1200℃ under air were 17.8MPa, 18.9MPa, 7.3MPa, 52.1MPa, 62.4MPa, 67.5MPa, respectively. B2O3 formed at high temperature by the oxidation reaction between B4 C and oxygen or oxygenic volatiles. The excellent fluidity of B2O3 melts enabled it repair the cracks and pores in the bonding layer effectively and enahnce the densification of the bonding layer. Moreover, the good chemical compatibility between B2O3 melts and ceramic materials remarkablely improved the join force at the interface. The high-temperature shear strengths of Si C joints bonded by VP-B tested at 200℃, 400℃, 600℃, 800℃, 1000℃ under air were 12.5MPa, 6.8MPa, 4.2MPa, 6.6MPa, 8.3MPa, respectively.B4C powder was regarded as an inert filler to reduce the volume shrinkage during heat-treatment process under N2 atmosphere. The room-temperature shear strengths of the Si C joints bonded by VP-B treated at 200℃, 400℃, 600℃, 800℃, 1000℃, 1200℃ under N2 were 17.8MPa, 15.7MPa, 16.0MPa, 12.9MPa, 18.9MPa, 22.8MPa, respectively.V-PMS+B4C+glass(VP-BG) was prepared by using low melting point glass powder as the second filler. The preferable technics for preparing adhesive was performed under the mass ratio of V-PMS:B4C:glass=100:40:30. The join property of the adhesive treated at 600℃~800℃ was successful improved by the introduction of the glass. However, the shear strengths of the adhesive tested at high temperatures were lowered. The high-temperature shear strengths of Si C joints bonded by VP-BG tested at 200℃、400℃、600℃、800℃、1000℃ under air were 8.9MPa, 7.9MPa, 6.7MPa, 11.3MPa, 5.7MPa, respectively.The modification of glass powder was much better under N2 atmosphere. The glass powder completely melted at high temperature and repaired the defect formed during heat treatment, enhanced the join strength at the interface. The room-temperature shear strengths of the Si C joints bonded by VP-BG treated at 200℃, 400℃, 600℃, 800℃, 1000℃, 1200℃ under N2 were 17.0MPa, 17.1MPa, 16.7MPa, 21.5MPa, 24.3MPa, 25.3MPa, respectively.V-PMS+B4C+Si O2(VP-BS) was prepared by selecting nano Si O2 as the second filler. The preferable technics for preparing adhesive was performed under the mass ratio of V-PMS:B4C:Si O2=100:40:10. The room-temperature shear strengths of the Si C joints bonded by VP-BS treated at 200℃, 400℃, 600℃, 800℃, 1000℃, 1200℃ under air were 18.1MPa, 19.2MPa, 15.2MPa, 48.8MPa, 55.7MPa, 61.5MPa, respectively. The nano Si O2 was more effective on the reduction of the volume shrinkage for the adhesive. Additionally, nano Si O2 could lower the oxidation temperature of B4 C and improve the property of the adhesive treated above 600℃. Moreover, nano Si O2 reacted with B2O3 to form borosilicate glasses, which could farther improve the high temperature property of the obtained adhesive. The high-temperature shear strengths of Si C joints bonded by VP-BS tested at 200℃, 400℃, 600℃, 800℃, 1000℃ under air were 7.6MPa, 10.1MPa, 8.7MPa, 7.7MPa, 8.4MPa, respectively.The high performance VP-BG and VP-BS adhesives were used to join alumina ceramic, Cf/Si C composites and thermal insulations materials. The results showed that the join of alumina ceramic and Cf/Si C composites was successfully achieved by using VP-BG and VP-BS under air. The obtained joints possessed outstanding shear strength, which exhibited a mixture failure model when treated above 800℃. However, under N2 atmosphere, the strengths of the treated joints were lower than that treated under air. In addition, the join of aerogel composite and titanic alloy, as well as thermal insulation materials was achieved by using VP-BG. The obtained join samples exhibited good adhesive property and heat-resistant property, which made the obtained adhesives promising candidates for joining thermal insulation materials in high-temperature applications.