A Study On Preparation And Heat-conducting Property Of High Thermal Conductivity Composites

With the rapid development of modern science and technology and industrialproduction, integration and power consumption of electronic products continue toimprove, heat dissipation has become one of the key factors affecting the reliability ofelectronic products. Meanwhile, the field of application of electronic productscontinues to expand, more higher requirements of high thermal conductivity material,such as high heat conductivity and excellent electrical insulation properties and shockresistance, good electromagnetic shielding performance. In this paper, high thermalconductivity insulation potting material and flexible graphite were studied for twodifferent applications, including preparation method and influence factor of thermalconductivity.1. The potting material was obtained from silicone rubber as matrix, the effects offillers type, content and particles morphology on the thermal conductivity, dielectricproperties were disscussed, meanwhile the effects of milling technology on aluminaflake and size distribution were studied.（1） Milling process affectes the morphology and particle size distribution of theAl₂O₃, when milling1h, speed200r/min, grinding ball diameter5mm, ball to powderratio20:1, Al₂O₃particle size distribution and flaking tends to improve thermalconductivity of the material;（2） The fillers morphology affectes the thermal conductivity of the composite,sheet Al₂O₃filled the composite material has the highest thermal conductivity.Spherical and irregular Al₂O₃mixed stuff is possible to improve the thermalconductivity of the composite material, thermal conductivity when the mixed ratio of9:1is increaed16.7%than spherical particles alone to fill.（3） By optimizing the morphology, particle size, the content of the filler particlesor the like, preparing an insulating potting material,thermal conductivity of which is2.1W/mK, the volume resistivity of about10¹⁴.cm, dielectric constant <6（10MHz^<sup>1G）.2. The flexible graphite was made of nature flake graphite, the impact of the intercalating agent/oxidant, the flake graphite size, heat treatment temperature on theexpansion ration, thermal conductivity and electrical conductivity,the relationshipbetween thermal conductivity and electrical conductivity,all of them were studied.（1） The stronger the oxidation of the oxidizing agent, the greater the expansionratio of graphite, but the electric conductivity and thermal conductivity will be reduced.AlCl₃+H₂SO₄as the intercalating agent is more propitious to improve the thermalconductivity than H₂SO₄; when flake graphite: concentrated H₂SO₄: KMnO4: AlCl₃is2g:6ml:0.1g:0.08g,（2） The transient temperature of the intercalation of graphite intercalation agentaffects gasification reaction rate, which affects the expansion ratio of graphite. Whenthe temperature is1000℃, the flexible graphite shaped well, and thermal conductivityof9.86W/m.K, electric resistivity of0.02/□;（3） Based on Solid State Physics and Whitman-Franz Theorem, heat carrier of theflexible graphite includes free electrons and phonons, the lattice vibrations of flexiblegraphite in the contribution of thermal conductivity is much larger than thecontribution of free electrons.