A Study On Preparation And Thermal Conductivity Of Silicon-Oil-Based Thermal Grease

Thermal interface materials (TIMs) play a very important role in rapid heat transfer between power component and heat sink. Thermal grease, as a member of TIMs, has good thermal conductivity and certain fluidity. Even a very thin layer of thermal grease can effectively reduce the thermal resistance at the contact interface. Therefore, thermal grease is promising in terms of rapid heat transfer.In this thesis, Al2O3/silicone oil thermal greases were prepared by simple physical milling. XRD and SEM were used to characterize two Al2O3 samples with different morphologies. FT-IR analysis was applied to investigate the surface modified Al2O3 particles. Thermal conductivity of the prepared thermal greases was measured by KD2 Pro conductometer. The results are as follows:Al2O3 particles can effectively improve the thermal conductivity of silicone oil. Spherical Al2O3 particles are better than non-spherical Al2O3 particles. However, the filling amount of the Spherical Al2O3 particles is less than that of non-spherical Al2O3 particles. Thermal conductivity of thermal grease increases with filing’ amount of Al2O3. Particle size of Al2O3 of the thermal grease also has certain influence on the performance of the thermal grease. In four different sizes of spherical Al2O3, the thermal conductivity of the thermal grease with 40 μm Al2O3 is the highest. Silane coupling agent (KH570) can effectively improve the thermal conductivity of the thermal grease. The prepared thermal grease exhibits the highest thermal conductivity when the mass fraction of KH570 is 1.7wt.%-2.5wt%. Hybrids of Al2O3 with different sizes are helpful to improve thermal conductivity of thermal grease. Thermal conductivity of the thermal grease with 63vol.% is up to 1.64 W-m’1·K-1, when the mixing ratio of 40 μm and 5 μm Al2O3 is 4:1. This is better than the system filled with Al2O3 of single particle size.Graphite fiber/silicone oil thermal greases of were also prepared in this word. The influence of graphite fiber content, silane coupling agent, silver coated treatment and hybrids with metal powers on the performance of the prepared thermal grease were studied. The results show that thermal conductivity of thermal greases can be improved by increasing graphite fiber content. The thermal conductivity is up to 1.21 W·m-1·`K-1 at the maximum graphite content of 56vol.%. The thermal grease has the best performance when the mass fraction of KH570 is 2 wt.%-3wt.%. Using silver coated graphite fiber, the thermal conductivity of the grease can be further improved. Thermal grease with mixed fillers has higher thermal conductivity than those with single filler. The best mixing ratios are 10:1 for graphite fiber/copper powder and 4:1 for graphite fiber/silver plated copper powder, respectively.System thermal resistance of thyristor radiator is related to water flow, pressure and heating power. Adding thermal grease can largely reduce system thermal resistance. In general,55vol.% thermal grease with graphite fiber and copper powder has higher thermal conductivity than 63vol.% spherical Al2O3 thermal grease.