Study Of Thearmal Conduction Mechanism Of Epoxy Based Composites

Alumina particles with different shape and sizes were used as fillers toprepareAl₂O₃/EPcompositesbyblendingandhotmoldingprocessinthisthesis. The results show that alumina platelets have large contributions tothethermalconductivityofcompositesatlowerfillingcontents.However,the flowability of the composites decreases due to the large resistance oftheirregular shapes. Thus, the composites with high thermal conductivitycannot be achieved due to the low filling contents when the platelets areused.Epoxy resin matrix composites were prepared by blending methodusing aluminum and diamand powders with different particle sizes asfillers. The thermal conductivity of composites was measured by thestable method. SEM and DSC were used to achieve the phasecompositions, morphologies and the thermal change respectively. Thechange of composite thermal conductivities was studied with the increaseof filler volume fractions. The results show that the thermalconductivities of the composites filled with aluminum particles with thesizes of 2?m and 5?m suddenly increase when the volume fractions ofaluminumpowdersincreasetosomedegree.However,thesuddenchange of thermal conductivity is not obvious in the system containing finediamond particles with the sizes of 100nm and 200nm. The possiblecrystallization mechanism bringing the sudden change of the thermalconductivity in the epoxy resin was excluded according to the measuringresults by SEM and DTA methods. The thermal conduction throughmolecular chains begins to become the key factor when the filler volumefraction increases and the thickness of the epoxy resin layer between thefillersdecreases.Thesinglemolecularchainlengthofepoxyresinandthedistancebetweenthefillerparticleswerecalculatedtoexplainthethermalconduction through the polymer layer. The mechanism was described asfollowing: the sudden increase of thermal conductivity appears when thefiller volume fraction is so large that the polymer layer becomes thinenough and the thermal conduction occurs through one single EPmolecular chain between two particles. The thermal resistance on theinterface is important when the fillers are small to near the nanometerdegree though fine particles benefit forming the joint of single molecularchain. As the results, the large particles contribute the high thermalconductivityat the high volume contents. On the contrary, small particleshavetheobviouseffectsatthelowfillingcontents.