| In recent years,with the increasing demand for graphene composite materials in industries such as automobiles,ships,aerospace,and electronics,graphene core-shell nanocomposites have become an important research direction.The method of combining solid lubricant with hard ceramic material can make up the disadvantage of ceramic particle toughness and low thermal conductivity,so that the lubrication of soft particles and the strengthening of hard particles complement each other.By means of wet ball milling,the graphene coated silicon carbide(Si C)core-shell nanocomposite is synthesized in one step on a planetary ball mill.The effect of ball grinding speed on the number of graphene layers,quality and conversion efficiency was studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman spectroscopy,Fourier infrared spectroscopy(FTIR)and X-ray diffraction(XRD).When the speed is in the range of 160-240 rpm,with the increase of the speed,the number of oligo-layer graphene(?10 layers)increases from45% to about 70%;When the rotation speed is increased to 280 rpm,the proportion of graphene layers of 0-10 layers reaches more than 80%.The defect type of graphene in the composite material is the edge defect with the least impact,and it is almost not oxidized.In the range of 160-280 rpm,as the rotation speed increases,the intensity of the graphite peak gradually decreases,and the conversion efficiency of the number of graphene layers gradually increases.The effect on the layer number distribution,quality and conversion efficiency of graphene in composite materials was studied by using the ball mill rotation speed of240 rpm and changing the ball-to-material ratio is 20:1,30:1 and 40:1,respectively.According to statistics from TEM observation,when the ball-to-material ratio is 20:1,the number of graphene layers is 10-20,accounting for about 72%;When the ball-to-material ratio is 30:1,oligo-layer graphene(?10 layers)accounts for the largest proportion,about 70%;When the ball-to-material ratio is 40:1,the percentage of different graphene layers is similar to that when the ball-to-material ratio is 30:1,but the proportion of oligo-layer graphene decreases.Through Raman spectroscopy and FTIR testing,it can be seen that the defects of graphene under the three ball-to-material ratio are very small,and there is no characteristic peak of graphene oxide.Through XRD test analysis,when the ball to material ratio is 30:1,the conversion efficiency of graphene is the highest;When the ball-to-material ratio is20:1,the conversion efficiency of graphene is the lowest,which is also consistent with the experimental results of TEM.The motion state and pressure distribution of composite materials with different speeds and ball ratios in the grinding tank were simulated by Fluent software.A three-phase flow model of air-alcoholic Si C graphite suspension-silicon nitride grinding ball is created.When the rotation speed is 160-240 rpm,the movement mode of the grinding medium is the dropping type;When the rotation speed is increased to280 rpm,the pressure on the inner wall of the milling tank gradually increases,and the movement of the grinding medium is the throwing type.When the ball-to-material ratio increases from 20:1 to 30:1,the maximum pressure in the grinding tank increases significantly,the proportion of oligo-layer graphene increases from 28% to about 70%,and the grinding effect is significantly improved;When the ball-to-material ratio increases to 40:1,the maximum pressure in the grinding tank only increases slightly.At this time,the space in the tank is reduced,the movement state of the grinding medium is restricted,and the proportion of oligo-layer graphene is reduced,which reduces the grinding effect. |
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