The Study Of Preparation And Properties Of Flexible Graphite Sealing Materials

With the rapid development of science and technology innovation,the application of graphite is becoming more and more extensive.The combination of graphite and new science and technology industry is more and more close,and the deep processing technology of graphite has higher requirements.At present,the purification of graphite,the preparation of expandable graphite and the production of flexible graphite sheet are in a decentralized state,and the poor integration among various industrial chains leads to the unreasonable utilization of resources.According to the properties of large scale graphite in Africa,the preparation technology and conditions of graphite purification and expandable graphite were determined.Based on this,the flexible graphite sheet in the flexible graphite sealing material was prepared.The influence of pressing technology and raw material properties on its properties was studied,and the preparation scheme of flexible graphite sheet was determined.This paper focuses on the research of purification,preparation of expandable graphite and comprehensive development and utilization of flexible graphite sheet,providing technical reference for the deep processing of this type of graphite resources.The optimum purification conditions of hydrofluoric acid method are as follows: graphite(g)? hydrochloric acid(mL)? hydrofluoric acid(mL)= 1?1.35?1.65,leaching temperature and time are 70 C and 4 h,respectively.The fixed carbon content of graphite can be increased from 93.20% to 99.41%.The optimum purification conditions of alkali-acid method are NaOH(g)? graphite(g)? hydrochloric acid(mL)? hydrofluoric acid = 0.5?1?1.6?0.8,calcination temperature and time 650 2 h,acid leaching temperature and time 70 1 h,and high purity graphite with 99.97% purity can be obtained.The comparison of the two methods shows that the alkali-acid method has better purification effect on this type of graphite.For purified flake graphite,sulfur-free expandable graphite was prepared by perchloric acid/potassium permanganate/acetic acid system.The maximum expansion volumes of +0.500 mm,-0.500+0.300 mm,-0.150 mm were 450 mL/g,410 mL/g and 305 mL/g,respectively.Sulfur-containing expandable graphite was prepared by concentrated sulfuric acid/hydrogen peroxide,and the maximum expansion volumes were 310 mL/g,255 mL/g and 210 mL/g,respectively.The comparison between the two methods shows that the expansibility of expanded graphite prepared by perchloric acid method is better than that prepared by perchloric acid method.For the preparation of flexible graphite sheet,flake graphite with fixed carbon content of 99.41%,+0.500 mm?-0.500+0.300 mm?-0.300 mm+0.150 mm gradation ratio of 1?1?2 was used as raw material;the tensile strength of sulfur-free flexible graphite sheet was 6.09 MPa,compression rate and resilience rate were 42.44% and 11.12%,chlorine content was 2089 ?g/g;and the tensile strength of sulfur-containing flexible graphite sheet was 5.84 MPa,compression rate and chlorine content were 2.The resilience was 42.71% and 10.24% respectively,and the sulfur content was 785 ?g/g.SEM was used to observe the surface and cross-section morphology of the flexible graphite sheet.The results show that the tensile strength of the flexible graphite sheet originates from the mechanical meshing and friction of the graphite sheet.The compression resilience is related to the micro-porous structure of the flexible graphite sheet.