The Effect Of The Granularity And Content Of Graphite On Properties Of CNTs-Ag-G Composites

In this paper, graphite was comminuted by gas stream and ball-milled into finer particle. CNTs-Ag-G composite brushes were fabricated by means of powder metallurgy method. The process included mixing powder, pressing at 200 MPa, sintering for 1h in pure H₂ protective atmosphere at 700℃and repressing at 400 MPa. The distribution of graphite and CNTs was homogenous in the CNTs-Ag-G composite without obvious micropore and cluster.The effect of the process of comminuting and ball-milling on particle size of graphite was studied. The result indicated that the final particle size was decided by comminuting and centripetal air pressure. Higher comminuting air pressure and lower centripetal air pressure got finer particle size. The particle size was ball-milled into finer obviously at early stage. The shape of graphite particle was near to globular by ball-milled.The effect of graphite particle size on the densities, hardness and sintering contraction percentage of composites was studied. The density of composite with finer graphite was more than that with larger graphite. The composite with finer graphite had higher hardness and lower porosity than that with larger graphite.The effect of the graphite content on the electrical wear properties was evaluated. In the wear process, there were some conclusions followed. The friction coefficient and the wear volume loss of electrical wear were more than that of mechanical wear. Because the current caused the high temperature of the brush, and the lubrication film was then destroyed. So the wear volume loss of electrical wear was more than that of the mechanical wear also because of the additional electric wear, and the friction coefficient was same to the wear volume loss. The friction coefficient was lower with the higher graphite content but the wear volume loss and contact drop were contrary. Because graphite promoted the formation of the lubrication film, the composite with more graphite content could form thicker lubrication film. The wear mass loss of the positive brush was more than the loss of the negative brush because of the physical and chemical reaction on the interface and the existence of the metal transference.