Preparation Of Flexible Graphite Film And Its Thermal Conductivity Property Research

With the rapid development of information industry, the degree of integrationof microelectronic devices and power devices will become much higher while thesize become smaller which will result in high current and high heat flow density.Therefore, heat dissipation with higher requirements has become the techniquebottleneck of the development of electronic materials. Graphite film material hasexcellent electrical and thermal conduction performance with high thermalconductivity which can reach as high as2000W/m K in crystallite layer direction.In addition, graphite film exhibits low thermal expansion coefficient and density.Therefore, the shortage of metal thermal conductive materials and cooling problemsfor microelectronic devices and power devices can be easily resolved if graphitefilm can be widely used. In the dissertation, the heat conduction material of theflexible graphite film was prepared by chemical purification and graphitecalendering method and the influences of the process parameters on the thermalconductivity of graphite film were further investigated.Firstly, the preparation of expanded graphite with high purity and expandedvolume was investigated by chemical purification method and orthogonalexperimental design. The results showed that adopting flake graphite, perchloricacid and A to prepare the HClO4-graphite intercalation compounds, the factorsinfluenced the expanded graphite volume from high to low in turn were intercalatingreaction temperature, quality of A, intercalating reaction time, quality of perchloricacid. The volume and purity of the expanded graphite can reach387ml/g and98.65%respectively by optimizing process parameters×The chemical elements ofthe flake graphite, HClO4-GIC and expanded graphite and the formation andexpansion mechanism of the HClO4-GIC were further investigated by X-rayphotoelectron spectroscopy. The results showed that the process that the carbonatoms on the graphite surface or edge were oxidated by perchloric acid and formedthe compound caused the formation of the HClO4-GIC. Instant decomposition andsubsequent gases expansion of perchloric acid at high temperature which wouldcause quick opening in crystallite graphite layer resulted in the expansion ofHClO4-GIC.Secondly, the preparation of flexible graphite film with high thermalconductivity was researched by using hot pressing preforming combining withcalendering method. The results showed that the volume of expanded graphite, theparticle size of flake graphite, the carbon contents, the thickness and the density of graphite film had great inflences on the thermal conductivity of the flexible graphitefilm. The thermal conductivity of the graphite film in-plane direction can reach ashigh as486W/m K on the optimized calendering process conditions;Finally, the microstructure, crystallite orientation and the ordering of thesurface carbon atom of the expanded graphite and flexible graphite film wereinvestigated by SEM, XRD and Raman spectra. The results showed that expandedgraphite with low crystallization, crystallite orientation and the dgree of ordering ofthe surface carbon atom had a reticulate structure formed by microcrystallinegraphite slices×The microstucture of the flexible graphite film with highcrystallization and crystallite orientation exhibited high anisotropy and the degree ofthe ordering of the surface carbon atom was closly to that of the flake graphite,which reasonably explained that the thermal conductivity of the flexible graphitefilm with high heat conduction property had high anisotropy. The results of theelectrical resistivity, thermal resistivity and tensile strength mesurement showed thatthe flexible graphite film exhibited excellent characteristics of low electricalresistivity and thermal resistance, but weak tensile strength.