The Studies On Preparation Of Expandable Graphite And Process Characteristic

Because of its unique network-like pore structure and excellent characteristics of physical and chemical,expanded graphite,deep processing product of flake graphite,is widely used in many fields,including environmental production,seal,electronic cooling,bio-medical,military,etc.Expansion temperature of expanded graphite prepared by traditional methods is usually high,high expansion volume can only be gotten when temperature exceeds 600?,even reaches 900¹000?,so its application is greatly limited in low temperature cryogenic fire,and it is important to prepare expandable graphite with high expansion volume at low temperature.The natural flake graphite in Inner Mongolia province is used as raw material,carbon content is 98.86%,and its size is 50 mesh.Expandable graphite is prepared by chemical oxidization method with potassium permanganate,perchloric acid and ammonium nitrate.Effects of reaction condition researched,such as quality of regents,stirring method,stirring intensity,reaction temperature and reaction time.Besides,the influence of auxiliary procedures to expanded volume is also studied,including washing temperature,washing degree,drying temperature,drying time,expansion temperature,etc.According to the experiments,the optimum preparation conditions are obtained,the best proportion of flake graphite:KMnO₄:HClO₄:NH₄NO₃?mass ratio?is 1:0.45:8:0.12,continuous stirring for 15mins,and stirring intensity is200r/min,washing temperature is 0²0?,pH value of expandable graphite after washing is 6.17,drying at 70?for 4 h.The initial expansion temperature of expandable graphite is 150?,and its expansion volume is up to 430 mL/g at 400?,meanwhile,it can reach 480 mL/g at 900?.In addition,the flake graphite,expandable graphite and expanded graphite are analyzed by XRD,FTIR,Raman,SEM.The interlayer structure,functional groups and micro-morphology are researched.The characterization and analysis of graphite in different stages show that the interlayer structure,functional groups and surface morphology have changed in the whole process.After oxidation and intercalation,oxygen-containing groups grafted onto graphite,interlayer spacing is increased,perchlorate ion and nitrate ion interpolate between slices and graphite intercalation compounds is formed,crystal quality of graphite and lamination of graphite crystallite is decreased,disorder increased,however,the structure of inner layer changes just a little.Heated and expanding to expanded graphite,the macro-structure and micro-structure are totally different.Acid radical ion escape from the graphite as gas at low temperature,and layers of graphite are distracted,a kind of unique pore structure of worm-like expanded graphite is formed.The crystal structure is destroyed,crystal quality is decreased,and lamination of graphite crystallite still exists.