Study On Charging Effects Of Polyimide Under Combined Environments Of Electron Irradiations And Temperature

The charge and discharge effects of space orbital plasmas and high-energy electrons are one of the difficulties in evaluating spacecraft anomalies and failures.Spacecraft dielectric materials are the main medium for generating charge and discharge problems.This article uses polyimide materials as the research object,using in-situ telemetering and surface potential measurement devices,electronic paramagnetic resonance spectrometers and scanning electron microscopes and other equipment and analytical techniques to study the combined effects of electron irradiation/temperature.The evolutionary behaviors of the radiative conductivity,the delayed conductivity and the surface potential of the polyimide were established.The corresponding physical model was established and the risk of charge and discharge of the material under the space-large elliptical orbit was evaluated.The results show that the radioconductivity of the polyimide firstly rises and then reaches the steady state under the condition of room temperature electron irradiation,and has a bipolar conduction model of electron/hole conduction.In the monotonous ascending phase,the radiative conductivity is proportional to the ionization dose rate,which is a power function of the irradiation time,and the exponent is the dispersion parameter ?,which is 0.34.In the steady state stage,the radiative conductivity is a power function of the ionization dose rate,with a power index ? of 0.75.After the electron irradiation stopped at room temperature,the delayed conductivity of the polyimide first decayed inversely proportional to the time and then declined exponentially.This was due to the thermodynamic compound effect of the free radicals induced by electron irradiation.Under low temperature electron irradiation conditions,the radiative conductivity of polyimide first rises after reaching the peak,then falls and then reaches the steady state.It has the characteristic of electronically conductive unipolar conduction model.The low-temperature steady-state radiative conductivity is one order of magnitude lower than room temperature.At low temperatures,the change in conduction mode is due to the combination of low temperature and carrier detraction,and the slow interaction of holes at low temperatures.After the irradiation of low-temperature electrons is stopped,the decay of the delayed conductivity of polyimide is the same as room temperature.The low-temperature delay conductivity is lower than the room-temperature delay conductivity,and the low-temperature delay conductivity decay time constant is lower than the room temperature by 1-2 orders of magnitude.Under the conditions of room temperature and electron irradiation,the surfacepotential of polyimide was negative,and it first decreased with the irradiation time and then reached a steady state.When the irradiation electron range is smaller than the sample thickness,the surface potential drops rapidly and does not reach the steady state,and the internal electric field strength can reach the breakdown field strength and discharge occurs.When the irradiation electron range is greater than the sample thickness,the surface potential of the material is higher than-200 V and the discharge risk is reduced.Under the conditions of low temperature and electron irradiation,the decrease of surface potential of polyimide is similar to that of room temperature,but the potential is lower and discharge is more likely to occur.Tests have found that there is a risk of flashover discharges along the surface of the sample in the gaps or shaped areas.The large-ellipse orbital electron spectrum irradiation of polyimide,the thicker the thickness,the lower the surface potential,the greater the maximum electric field intensity,the easier it is to discharge.The lower the temperature,the lower the surface potential,the greater the maximum electric field strength,and the easier it is to discharge.