In-situ Growth Of AlN/C Hybrid Fillers And The Application In The Paraffin Based Phase Change Heat Storage Materials

With the rapid development of microelectronic technology,electronic devices are gradually developing towards high integration,which requires higher heat dissipation performance of packaging materials.Phase change heat storage technology uses the characteristics of phase change materials to absorb and release high density energy in the solid-liquid phase transition process to store and release heat energy,to cushion the electronic devices from the thermal shock,thereby ensuring the safety and stability of electronic devices.The low thermal conductivity affects the heat transfer properties of paraffin-based phase change heat storage materials.AlN is the first choice for thermal conductive fillers because of its high intrinsic thermal conductivity.In this thesis,AlN powder was synthesized by a wet chemical method using urea as a nitrogen source,AlCl3·6H2O as an aluminum source,and anhydrous methanol as an organic solvent.The composites of AlN and carbon related materials were synthesized by making effective use of the graphitization of carbon and carbide intermediate phase and adding catalyst.Finally,the AlN/graphite and the AlN/carbon tube were used as fillers in paraffin phase change heat storage materials,and the thermal conductivity and phase change heat storage properties of the composites were characterized.The conclusions are as below:(1)The effects of urea to AlCl3·6H2O molar ratio(R)and calcination temperature on the morphology and structure of the synthesized powder were studied.Calcinated at 1000 ?,the products are dispersed AlN and Al2O3 nano-powder when the R ratio is less than 5.The spherical pure AlN can be synthesized when the R ratio is greater than 5.The spherical aggregation AlN shows petal-like morphology when the R ratio is greater than 7.A network morphology appears when the R ratio is greater than 8,and the spherical AlN is embedded in suchmorphology.In addition,the pure AlN can be synthesized when the calcination temperature is over 950 ? for the sample of R12,and the network morphology became obvious with the increase of temperature,but the network morphology disappeared when the calcination temperature is above 1200 ?.The analysis shows that the network morphology is amorphous carbon,and the increase of temperature can promote the graphitization transformation.Finally,the AlN and graphite composites were obtained.(2)For the sample of 12,nickel acetylacetonate was added as a catalyst,and the AlN/carbon tube was in-situ grown by adjusting the content of catalyst and calcination temperature.It is found that the content of nickel acetylacetonate has a great effect on morphology.When the mass ratio of nickel acetylacetonate is 1%,2%,and 3%,the carbon tube morphology with a wide size distribution can be obtained.When the content of nickel acetylacetonate is 10%,the content of the carbon tube decreases obviously,which is presumed to be related to the preparation process.When the mass of nickel acetylacetonate is 2%,an amorphous carbon tube with a diameter of 20?1000 nm and the nano-AlN nanoparticles with good crystallinity which were embedded in the carbon nanotubes were obtained.The crystallinity of the carbon tube increased with the increase of calcination temperature,and the diameter of the tube became smaller and the surface became smoother.(3)Self-made AlN/ graphite(R12)powder,AlN(R12)/ carbon tube composite powder,and three commercial AlN powders(the particle size is 2 ?m,5 ?m,20 ?m,respectively)were filled into paraffin wax as thermally conductive fillers.The effect of different fillers on the thermal conductivity of phase change materials was studied.The thermal conductivity of paraffin composite phase change materials filled with different thermal conductive fillers with different content was detected,and the thermal conductivity order with the filler content of 20% was R12/carbon tube > R12/graphite > 2 ?m > 5 ?m > 20 ?m.The maximum thermal conductivity was obtained for the composite with 20% AlN/carbon tube calcined at1200 ?,the thermal conductivity of the phase change material was 0.409 W/m·K which was 1.67 times of paraffin.The particle size and crystallinity are critical to obtaining phase change composites with higher thermal conductivity.(4)The effects of different fillers on the heat storage properties of phase change materials were also studied.The addition of 8%,10%,12%,16%,and 20% self-made R12/graphite and R12/carbon tube fillers significantly reduced the undercooling of paraffin wax,indicating that the addition of thermally conductive fillers accelerated the heat cycle.The latent heat of the composites containing 8%,10%,12%,16%,and 20% self-made R12/graphite and R12/carbon tube fillers decreased from 174.7 J/g of pure paraffin to about130 J/g,but the shape stability of the composites did not meet the ideal requirements.