The Preparation And Properties Research Of High-strength Nano-graphite Bulks

High-strength graphite bulks have good mechanical properties and low open porosity,and can be smoothly processed into products of high strengths and high densities,which are vital in nuclear industry,aerospace technology and high-tech for potential applications such as heating elements,electrode equipments and nuclear reactors,etc..In the past,aggregate(graphite or various cokes,etc.)and binder(asphalt,resin,etc.)were generally mixed as raw materials to prepare graphite bulk materials.This process leads to mounting energy consumption and serious pollution.People have long been searching for a way for producing high-strength bulk graphite by directly sintering graphite powders,which is,however,unachievable due to the high stability of graphite.With the development of high temperature nuclear reactors,the need for advanced high-strength graphite is growing faster than ever.Therefore the research on high strength graphite bulk materials is very important and extremely urgent.The purpose of this study was to prepare high density and intensity bulk nano-graphite materials and explored their mechanical properties and strengthening mechanism.Firstly,we used a mixture of many nano-diamond(ND)powders of various sizes as the precursor for the preparation of graphite bulk.We mixed diamond powders by a certain percentage.Then,graphite bulk materials were produced by hot pressing sintering in an atmosphere of argon by the spark plasma sintering(SPS),exploring the preparation technology and conditions of high-strength bulk nano-graphite materials.X-ray diffraction,scanning electron microscopy,transmission electron microscopy and Raman spectroscopy are used to characterize the microstructure of the samples.The results showed that the density of graphite bulks prepared by single crystal ND particles(average size 100 nm,50 nm,10 nm and proportion of 8:1:1)was highest(1.89g/cm3).The pellets were heated to 1600 ? at a heating rate of 150 ?/min with a pressure of 80 MPa and a soaking time of 5 min.The microstructure of this graphite particle is "onion grains".Secondly,combining with the preparation of high-density bulk nano-graphite,we explored the mechanical properties and strengthening mechanism of this graphites.Bending and compression tests,nanoindentation and scratch techniques are carried out to evaluate the mechanical properties.Results show as-prepared graphite has ultra-high bending and compression strength,modulus and microhardness,160 MPa,350Mpa,33 GPa and 2.5 GPa,respectively,due to its uniquely intrinsic structure.The nanosized graphite onion is quasi-spherical carbon nanoparticles with the nucleus of C60.The stress-strain state of the nano graphite onion model with more than 70 spherical shells has been researched by theoretical calculation,and the loading was carried out by hydrostatic method,which correctly represents the force load on the nano graphite onions.This graphite material may find important applications in wide fields due to its unique structure and excellent performances,such as high performance graphite bearings etc.