Research On Property Degradation And Mechanism Of Potting Materials For High Voltage Power Supply Under Alternating Thermal Cycle

Rigid potting materials represented by epoxy resin and elastic potting materials represented by silicone rubber are widely used in aerospace and military fields,with excellent processing properties,excellent electrical insulation,chemical resistance and dimensional stability and many other advantages.The traveling wave tube amplifier in the spacecraft are used for a long time at a higher temperature,and the voltage of several thousand to 10,000 volts is transmitted to the traveling wave tube,which can be regarded as a working environment in which a weak thermal field and a weak electric field work together.In order to ensure the normal operation of spacecraft,the typical aging mechanism of high-pressure power potting materials under space flight conditions is studied,which is crucial for the selection,modification and reliability analysis of space potting materials in space flight.The subject is based on bisphenol A epoxy resin and RTV560 silicone rubber.The epoxy resin,silicone rubber,wire-epoxy resin,and ceramic-silicone rubber are respectively studied under the conditions of alternating thermal cycle and vacuum gassing space.The surface morphology was characterized by scanning electron microscopy and atomic force microscopy.The mass loss rate was measured by high-precision electronic balance.The hardness change was measured by Shore hardness test.Scanning calorimetry and thermogravimetric analysis were used to characterize its thermal properties.Broadband dielectric spectra and breakdown voltages were used to characterize their electrical properties.Infrared spectra and X-ray photoelectron spectroscopy were used to characterize their molecular structures.The results show that with the increase of the number of alternating thermal cycles,the surface of bisphenol A epoxy resin gradually appears small pores and eventually enlarges to form large-area damage,the material quality loss increases,and the thermal stability can increase first and then decrease.The macroscopic surface change of RTV560 silicone rubber is not obvious,but the micro surface roughness and mass loss rate increase,the hardness and thermal stability of the material increase first and decrease.The dielectric properties of the two materials change obviously.The electric constant decrease,the insulation performance becomes stronger,the late dielectric constant becomes larger,the electrical conductivity increases,and the insulation performance deteriorates.The vacuum gassing experiment shows that the main precipitation of bisphenol A type epoxy gassing effect is Water molecules adsorbed on the surface,and a very small amount of condensable volatiles are precipitated.RTV560 silicone rubber is mainly based on the loss of organic volatiles,and the precipitation of water vapor is secondary.The damage mechanism of bisphenol A epoxy resin and RTV560 silicone rubber is obtained through the change of chemical properties.The damage mechanism of bisphenol A epoxy resin: the ether and ester chain in the main chain may form ketone,ester or ether after chain scission.Or the secondary chain of the main chain may form an aldehyde,an aliphatic hydrocarbon or the like after being broken.RTV560 silicone rubber damage mechanism: The methyl group mainly formed after the substitution of the methyl group on the side chain continues to react with the adjacent methyl group to cause the chain transfer reaction and form the Si-O-Si network structure to further crosslink.