Synthesis Of Mesophase Pitch-derived Carbon Foam And The Structural Change And Kinetic Analysis During Its Foaming Process

As a light functional material,mesophase pitch-derived carbon foam is now playing an ever-increasing role in special materials field,especially in heat exchange and electricity industry.Although researchers had studied the preparation process and properties of carbon foam a lot,there are still few literatures about the structural changes and kinetics analysis of mesophase pitch-derived carbon during foaming process.In this thesis,AR mesophase pitch was used as foaming precursor,the changes of foaming process were characterized by thermogravimetry(TG),mass spectrum(MS),infra-red spectrum(IR),scanning electron microscope(SEM)and X-ray Diffraction(XRD).The formation process of bubble structure in molten pitch was observed by polarizing microscope.The thermal weight loss of mesophase pitch during foaming process was simulated by TG analysis,and a simple mathematical model of foaming process at constant temperature has been established.On this basis,a series of carbon foams were prepared by self-bubbling method,and the influence of heating rate and foaming temperature on the properties of carbon foam was investigated.The main results were as follows:(1)The pyrolysis reaction during foaming process was mostly on aliphatic carbon chains,and gas like H2,CH4,H2O and CO were released,the molecular composition of molten pitch was changed and then the viscosity changed;(2)TG curves of mesophase pitch at different heating rate and foaming temperature were fitted,it was found that the thermal weight loss(Aw)of mesophase pitch at constant foaming temperature was proportional to a fractional exponential of holding time(t~b),the activation energy of pyrolysis reaction with different heating rate of 1,5,10?/min had 82.66,51.52 and 39.93 kJ/mol,respectively.The rate constant increased with the foaming temperature rises;(3)After raised to 320?,mosaic structures were formed as a result of the pyrolysis reaction in molten pitch,meanwhile,these mosaic structures were gathered by the gas produced and turn into bubble structures.Over 350?,all mosaic structures were transformed into bubble structures.(4)The bulk density of carbonized foam and graphitic foam decreased with the rise of heating rate;the compressive strength of carbonized foam was relatively high at heating rate of 5?/min;fewer microcracks were formed at higher foaming temperature,and thus enhanced the compressive strength of graphitic foam;(5)Bulk density is the main factor that influences thermal conductivity of graphitic foam ranging from 1-10?/min of heating rate and 420-480? of foaming temperature.