Study On The Preparation And Performances Of Thermal Conductive Silicon Grease Filled With AlN/Ag/Graphite

With the development of the economy and the improvement of the industrial level,more and more researchers pay their attentions to the high temperature lubricating issues.Many lubrication locations require the high thermal property,high insulation performance or high electrical conductivity of greases.In this paper,the thermal greases were prepared by choosing dimethyl silicon oil as base oil,alumina nitride and magnesium hydroxide and flake graphite and silver bars as thermal conductive fillers,fillers and polytetrafluoroethylene(PTFE)and lithium complex soap as thickeners.The thermal conductivity and volume resistivity of different thermal conductive greases were conducted using a heat conduction coefficient measurement and a resistivity tester,respectively.The tribological properties of thermal greases in absence or presence of electric field were performed by using a ball-on-disk reciprocating friction and wear tester(MFT-R4000).Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)were used to analyze the morphologies and elements of worn surfaces.The strategy to describe the objective spatial distribution configuration by the spatial distribution potential-energy function was employed,and a Monte Carlo controllable spatial distribution algorithm was designed,which can effectively create the RVE containing the network configuration with any mass fraction.Conclusions were as follows:1)Different proportions and mass fractions of fillers have a great influence on thermal greases’ thermal conductivity and volume resistivity.With the analysis of one-component thermal conductive greases,it can be found that the thermal conductivity of thermal conductive grease improves as the fraction of alumina nitride or magnesium hydroxide increasing.The silicon grease’s thermal conductivity can reach 1.218(W·mK)when the mass fraction of AIN is 80%.In two-component thermal conductive greases,with the increasing of the flake graphite,the thermal conductivity increases and volume resistivity decreases.However,adding the silver particles into grease results in the decreasing of the thermal conductivity.In the three-component thermal conductive greases,when the proportion of AIN,FG and Ag is 10:6:1,the thermal grease shows the best thermal property(the thermal conductivity is 1.623(W·mK)which is around 711%higher than that of silicon oil)and electrical property.2)By analyzing the results of tribological tests,it can be seen that the thermal conductive greases using PTFE or lithium complex soap as thickener show better friction reducing and anti-wear properties.The lowest mean friction coefficient and wear scar width are 0.091 and 0.227mm which are around 229%and 671%lower than those of silicon oil,respectively.Meantime,according to the analysis of the EDS,the fillers also play friction reducing and anti-wear roles during the friction process.PTFE can reduce the friction and wear because of its low shear force.With the function of electrical field,the friction coefficient and contact resistance of three-component thermal conductive grease are lowest because the good conductive layer containing AIN,graphite and Ag can make the two electrodes have a good contacting status which can abate the arc erosion on the friction contacts.3)Comparing with the traditional numerical methods,simulation results of finite element has a better agreement with the experimental data.The analysis of finite element shows that a given amount of mass fraction and relative effective distribution of particles are two essential conditions of the formation of the effective thermal conductive pathways.