Preparation And Properties Of High-performance Nanographite Bulks

High-performance graphite bulks play an indispensable role in the defense industry and specialty materials due to their special high temperature mechanical properties,low thermal expansion coefficient and good electrical and thermal conductivity.However,due to the layered structure of graphite itself,it is easy to dissociate along the(002)crystal plane under the action of external force,which limits the application of the product.Inspired by the mechanism of observing the trunk burls,the author creatively prepared a lattice-engineered high-performance graphite bulk.The main method is to introduce a trace amount of nanodiamond(ND)powder into the natural graphite powder.During the pre-sintering process,a small portion of the ND particles with sharp edges are pressed into the graphite layer,and the ND particles are phase-transformed into nanographite onions during the late sintering stage.These graphite onions,like expanded bolts,staple the graphite sheets together to form a unique "nanoburls" structure that imparts outstanding mechanical properties to the graphite bulk.This reinforcing mechanism is similar to the protrusion inside the trunk,so that the phenomenon that graphite is easily dissociated on the(002)crystal plane is prevented.At the same time,the phase transition of the ND particles between the graphite sheets can significantly reduce the sintering temperature of the graphite powder.The authors mainly discussed the effect of the content of ND particles in the composite powder on the microstructure and mechanical properties of the graphite bulk,The results show that when the ND content in the composite powder is 20 wt.%,the flexural strength of the sintered graphite bulk is comparable to that of the DS-4 type graphite.Its bulk density and flexural strength are 1.93 g/cm3 and 92 MPa,respectively.It is worth mentioning that this nanoburls structure significantly enhances the mechanical properties of graphite,and it is expected that this lattice engineering strengthening mechanism can not only change the microstructure and properties of graphite materials,but also apply to other layered materials.The authors also prepared high-performance graphite bulks by introducing a small amount of carbon nanotubes(CNTs)as precursors in the ND particles.Compared with the conventional process,the method not only reduces the anisotropy of the graphite,but also overcomes the problem that the graphite article is easily cracked by the large residual stress inside the graphite bulk after sintering by the single ND powder.More importantly,the introduction of a small amount of CNTs causes the ND particles to be arranged approximately in an orderly manner along the CNTs,so that the sintered graphite bulks have higher mechanical properties.The author mainly discusses the effect of CNTs content on the microstructure and mechanical properties of graphite after sintering.The experimental results show that when the content of CNTs in the composite powder is 5 wt.%,the prepared graphite bulk has high bulk density and mechanical properties;its bulk density,microhardness,Youngs modulus and flexural strengths were 1.78 g/cm3,3.3 GPa,20.7 GPa and 173.7 MPa,respectively.Its flexural strength is about twice that of DS-4 commercial graphite.