Description of high temperature sealant in vacuum system

Sealants are a class of adhesives used to join and seal various components in a vacuum system. It has good bonding strength, good vacuum sealing and pressure resistance, and is an indispensable material for the connection of various components of the vacuum system. With the wide application of vacuum technology in scientific research and production, the rapid development of electronic, radio, aerospace and aerospace industries has put forward more requirements for the sealing connection of vacuum components, and promoted the research of vacuum sealant. . Gas permeability indicates the ability of various gases to pass through the sealant in the presence of a pressure differential, and the gas permeability is generally used to indicate the gas permeability of the material. The amount of outgassing refers to the amount of gas released by the sealant itself at the operating temperature. High vacuum can only be achieved when both are low.

In a vacuum system, it is usually necessary to remove most of the gas adsorbed on the inner wall surface of the vacuum system by heating and exhausting (heating to 400-500 and other methods (ion or electron bombardment); some vacuum systems need to work at low temperatures. Therefore, the selected sealant should be able to adapt to the temperature change under vacuum conditions, both high temperature resistance and high temperature and low temperature alternating impact test.

There is a pressure difference between the vacuum system and the outside world (such as the atmosphere). The sealant must have the ability to withstand pressure differences and require a certain degree of toughness and sufficient mechanical strength.

The sealant should have good wettability to the adherend to facilitate sealing of the material and to obtain high bond strength.

Due to the special needs of vacuum system cleaning and leak detection, vacuum sealant is required to have certain anti-solvent properties, such as acetone resistance and absolute ethanol.

In the preparation of vacuum adhesives, these special requirements must be comprehensively considered to adjust the composition of the sealant and the molecular structure of the host resin to meet the requirements of use.

The main component of the commonly used organic vacuum sealant for the sealant is the organic polymer. This kind of adhesive has good adhesion and convenient operation. It can be connected with various materials, but its heat resistance is not good enough. Use at lower temperatures. It can be used at temperatures of 200~500*C or higher, and it still uses high temperature sealant which still has the original bonding performance. At present, it is mainly epoxy, modified phenolic, silicone, polyimide, Other nitrogen-containing heterocyclic and inorganic adhesives.

Epoxy resin is a vacuum adhesive commonly used in vacuum technology. Its chemical structure makes it do not emit any small molecular compounds during curing, so it has a very low vapor pressure, but its operating temperature is only *C long-term use. The maximum operating temperature can reach 315 ° 3. Silicone vacuum sealant has high heat resistance, but silicone polymer as a vacuum material also has its own shortcomings. Silicone resin releases small molecules of water during curing, heat Small molecules and cyclic compounds are also released during the cracking, which leads to the porosity of the rubber layer and reduces the airtightness. The use temperature is about 200-250 ° C. The epoxy-modified silicone vacuum adhesive The working temperature can reach 300 ° C. Polyimide (PI) vacuum sealant has excellent heat resistance and vacuum performance, small thermal expansion coefficient, good solvent resistance, and can work for a long time at 370~390*C. The short-time use temperature can exceed 5ro*C. The adhesive has good high temperature strength, stable electrothermal performance, excellent radiation and low temperature resistance, and excellent comprehensive performance. It is the most important type of high temperature resistant material/Ti2 (mass point). 1.5%) composite film baked at 400*C, weight loss after about 10h about 23.2 other properties of PAA/Ti2 sealant also have other excellent properties, as shown in Table 2: Table 2 other properties of sealant film The test results of the project are solvent-resistant acetone, 48h film intact, no bubbles, no peeling, no color change, anhydrous ethanol, 48h film intact, no bubbles, no peeling, no color change adhesion>2nd impact-resistant shear strength ceramic/ceramic Stainless steel/stainless steel vacuum performance and heat resistance can be heated and exhausted at 400C450C high temperature, 10 to 5 106Pa without air leakage. 3 Conclusion High temperature vacuum sealant is a special field in military, defense, aviation, aerospace, electronics, etc. The aspect is indispensable material. The PAA/Ti2 sealant prepared in this experiment has good storage stability. When the mass fraction of Ti2 is 1.5%, it can be stored at 10*C for 1 month. The higher imidized PI/Ti2 film has good thermal stability, and the thermal weight loss is 4.7% at 400C for 20h; the 1.51 film at 450° and 450° at 450° remains intact, without cracking and shedding; Solvent resistance , Vacuum performance and adhesive properties.