Study On Electromagnetic Shielding Performance Of SiC Modified Activated Carbon Fiber Felt

In order to prepare a high temperature resistant,oxidation resistant and lightweight electromagnetic shielding material,the effect of heat treatment temperature on the microstructure and electromagnetic shielding properties of ACF under argon atmosphere was studied by using activated carbon fiber felt(ACF,5.5×10^-2g/cm³)as raw material.Secondly,the ACF was modified by silicon evaporating reaction deposition method.The effects of Fe catalyst on the microstructure of ACF at different temperatures were discussed.Finally,the effect of high temperature oxidation on the electromagnetic shielding performance of Si C modified ACF was investigated.The results suggest that as the heat treatment temperature(1200°C?1600°C)increases,the ordered degree offree carbon in ACF increases,but when the temperature exceeds 1400°C,the value of I_D/I_G increases,the ordered degree of carbon decreases;the total electromagnetic shielding efficiency(SE_T)increases first and then decreases with the heat treatment temperature increasing,reaching a maximum at 1400°C,which is during 38.0 d B?39.0 d B.The Si C modified ACF was deposited by the catalyst-free Si evaporation reaction,and the ACF weight gain value was increased from 0.5 wt%at 1200°C to 9.2 wt%at1500°C,indicating an increase in the amount of generated Si C.However,the SE_T of ACF decreases from 27.0 d B?28.0 d B to 22.0 d B?22.7 d B with temperature increasing.The reason is that the conductivity of Si C generated by ACF reaction is much lower than that of carbon,resulting in a slight decrease in electromagnetic shielding performance.The reaction rate of ACF and the electromagnetic shielding performance increases and decreases with the increase of temperature respectively.Adding 0.25 wt%Fe catalyst to the silica powder,the ACF weight gain value increased from 1.2 wt%at1200°C to 23.8 wt%at 1500°C.The SE_T of ACF increased first and then decreased with increasing temperature.At 1400°C,the SE_T reached its maximum.The value is28.0 d B?29.0 d B.At 1500°C,the amount of Si C generated by the reaction of ACF increases significantly,and the electromagnetic shielding performance is seriously reduced reaching only 11.0 d B?12.0 d B.The effect of oxidation at 800°C on the electromagnetic shielding performance of catalyst-free Si C modified ACF(1500°C)was studied.It was found that the SET decreased from 22.0 d B?22.6 d B to 8.0 d B?10.6 d B.The oxidation time(1h,2h,3h)had little effect on the variation of electromagnetic shielding performance at 800?.The effect of different oxidation time on the electromagnetic shielding performance of Si C modified ACF(1500°C,0.25 wt%Fe)at 800°C was studied.After 1h,the SE_Tincreased to 15.0 d B?17.0 d B,and decreased to 9.1 d B?11.6 d B after 2h and 3h.The effect of oxidation temperature(700°C,800°C,900°C,3h)on the electromagnetic shielding performance of Si C modified ACF(1500°C,0.25 wt%Fe)was investigated,which reduced to 6.7 d B?8.2 d B at 700°C,indicating Si C modified ACF has poor oxidation resistance at 700°C.The reason is that Si C failed to form a dense Si O₂ layer to protect ACF.At 800°C and 900°C,the electromagnetic shielding performance remained at 10.2 d B?11.6 d B and 9.1 d B?10.9 d B respectively,because the surface Si C is oxidized to form a dense Si O₂ layer and the ACF is under protection from oxygen.