Study on Reinforcing Properties of Woodceramics by Using Graphene Oxide
Author:Miao Zuo Zuo
Supervisor:liu yi xing
In order to improve the dimensional stability of woodceramics during sintering,reinforce the function,make woodceramics more applied value,in this study woodceramics were prepared from wood powder,epoxy resin and self-made graphene oxide(GO)through the processing of impregnation,prepressing,hot pressing and then sintered under argon gas protecting at a high temperature using a tube sintering furnace.The carbon yield and volume change rate were obtained by measuring the mass change and the size change of samples respectively before and after sintering.Bending strength of woodceramics was tested by three-point bending method.The electromagnetic shielding performance,thermal conductivity and electrical conductivity of the samples were respectively tested by coaxial method,transient hot-wire method and four-probe method.The degree of graphitization of woodceramics was characterized by XRD and Raman spectroscopy,the microscopic morphology of woodceramics was observed by SEM.The main contents and results can be summarized as follows:(1)Woodceramics were prepared by changing the amount of GO and epoxy resin to discuss the effects of raw material ratio on GO reinforced woodceramics.When GO addition amount varied from 0 to 5%of the wood powder quality,with the increase of GO content,the carbon yield of woodceramics gradually increased,the size shrinkage decreased,the microstructure became compact from loose,the bending strength increased and then slightly decreased,and the degree of graphitization and thermal conductivity were improved.With the decrease of epoxy resin content,the carbon yield of GO reinforced woodceramics was almost unchanged,the size shrinkage gradually increased,the structure became loose,and the bending strength decreased.(2)Woodceramics were prepared by changing sintering parameters to discuss the effects of sintering temperature,sintering rate and holding time at the highest temperature on GO reinforced woodceramics.With the increase of sintering temperature(800～1600℃),the carbon yield of GO reinforced woodceramics gradually decreased,size shrinkage rate increased slightly,bending strength increased significantly,degree of graphitization and thermal conductivity increased.With the increase of sintering rate(2.5～10℃/min),the carbon yield of GO reinforced woodceramics decreased,size shrinkage rate increased gradually,bending strength decreased sharply,the degree of graphitization decreased.When holding time at the highest temperature extended from 0.5h to 1h and 2h,the carbon yield of GO reinforced woodceramics decreased slightly,size shrinkage rate increased but limited,degree of graphitization and bending strength increased.(3)In the range of 2～18 GHz,electromagnetic shielding efficiency of GO reinforced woodceramics was tested by coaxial method using a network vector analyzer.In the case of the same sintering parameters,the addition of GO was conducive to improving the electromagnetic shielding efficiency of woodceramics,which was dominated by the absorption efficiency.However,due to the comprehensive influence of factors such as electrical conductivity and pore structure,there was no regularity between the electromagnetic shielding efficiency of GO reinforced woodceramics and the addition amount of GO.In the test range of this study,when the sintering temperature was 1200 ℃,sintering rate was 5 ℃/min,holding time was 1 h,the electromagnetic shielding efficiency of all test samples was able to satisfy the requirement of general commercial applied.When addition amount of GO was 0.5%in woodceramics,electromagnetic shielding efficiency of the woodceramics was the highest,up to 46.5～80 dB.In the test range of this study,the electromagnetic shielding efficiency of GO reinforced woodceramics was greatly affected by sintering process parameters.With the increase of sintering temperature or the decrease of sintering rate,also or the extension of holding time,the electromagnetic shielding efficiency of GO reinforced woodceramics could be improved.When the sintering temperature was 1600℃,or sintering rate was 2.5℃/min,or holding time was 3 h,in a certain frequency range,the highest electromagnetic shielding efficiency of GO reinforced woodceramics was up to 80 dB.(4)The microwave absorbtion materials were prepared by woodceramics of GO addition rate of 0.5%and paraffin substrate at the mass ratio of 3:7,4:6,5:5,then tested the microwave absorption performance in the frequency range of 2～18 GHz.When the mass ratio was 3:7 and the thickness of materials was 4.5～5.5 mm,in high frequency range(>14 GHz)the reflection loss of the prepared materials was less than-10 dB which was able to meet the commercial applied requirement.When the mass ratio was 5:5 and the thickness of materials was 1.5～5.5 mm,in all test frequency range the reflection loss of the prepared microwave absorbtion materials was more than-10 dB.When the mass ratio was 4:6 and the thickness of materials was 1.5～5.5 mm,in a specific frequency range corresponding to each thickness,the reflection loss of the prepared microwave absorbtion materials was less than the commercial applied efficiency of-10dB.For the mass ratio of 4:6,with the increase of thickness,the peak value of reflection loss decreased gradually and moved to the lower frequency range,and the effective bandwidth decreased gradually.When the thickness of material was 1.5 mm,the peak value of reflection loss was-17.41 dB and the effective bandwidth was 3.68 GHz(12.48-16.16 GHz).When the thickness of material was 2.0 mm,the peak value of reflection loss was-17.33 dB,the effective bandwidth of 3.68 GHz(12.48-16.16 GHz)was in the X-band,which meeted the requirements of "thin,light,wide and strong" for microwave absorbtion materials.