Investigations On The Microstructures And Properties Of Ball-milled Expanded Graphite And Its Metal (Oxide) Composites

It is extremely easy to introduce a lot of strain, defects and nanoscale microstructuresin materials during high-energy ball milling process. Therefore, high-energy ball millinghas become an effective method to control nanostructures and properties of materials andproduce various nano-materials. Carbon nanostructure is always the research focus ofmaterial fields due to its unique structure, outstanding performance and huge applicationprospect. Investigations show that high-energy ball milling is an effective method toproduce carbon nanomaterials. Up to now, many carbon nanostructures have beenproduced by ball milling of natural graphite, such as carbon nano-arc, carbon nanoscroll,carbon onion and carbon nanotube etc.Expanded graphite (EG) is a novel carbon material which is produced by naturalsquama graphite through oxidation, intercalation, washing, dryness and expansion. EGkeeps the layered structure of natural graphite mainly, but its carbon nanosheets possess athinner thickness and show excellent flexibility and elasticity. Up to now, bothhigh-energy ball milling and microstructure evolution of EG have just been receivedattention. The carbon nanostructures produced by ball milling EG has been barely reported.Therefore, this dissertation takes EG as the object of study. The microstructure evolutionof EG and the formation mechanism of carbon nanostructures during ball-milling processwere studied. In addition, the applications of ball milled EG-metal (oxide) composites intribology and energy fields were also investigated. The main research works and resultsare listed below.Graphite nanoshteets and their derived structure-columnar carbon nanosrolls (CNSs)are produced by vibratory milling of EG. The columnar CNSs are formed by bilayergraphenes. The formation mechanisms of graphite nanoshteets and columnar CNSs arestudied. The effect of the characters of nanosheets (thickness and intralayer defects) on theformation of columnar CNSs is also investigated. Results show that the ultrathin lamellarthickness and the intralayer defects play a decisive role of the formation of columnarCNSs. On the other hand, compared with the lamellar and tubular carbon nanostructures, columar CNSs has a lower flexility.Ball milled EG-Cu self-lubricating composites are fabricated by powder metallurgyusing ball milled EG and electrolytic copper powders as raw materials. The effect of theEG nanosheets on the hardness, bending strength, and tribological properties of ball milledEG-Cu composites are investigated. The abrasion mechanism of the ball milled EG-Cucomposites is also investigated. Results show that the ultrathin thickness of carbonnanosheets determines it has excellent tribological properties. With the content of EGnanosheets increasing, the hardness and bending strength of ball milled EG-Cu compositesgradually decrease, and the tribological properties are first improved and then deterioratedslightly. Adding a proper amount of carbon nanosheets can improve the tribologicalproperties of ball milled EG-Cu composites efficiently, and reduce the drop of the bendingstrength of ball milled EG-Cu composites.Ball milled EG-SnOx(x=0,1,2) composites are produced by ball milling andannealing of EG and Sn powder mixture. The effect of ball milling time and annealingtemperature on the component kinds and microstructures of ball milled EG-SnOxcomposites is investiagated. The effect of annealing temperature on the electrochemicalperformance of ball milled EG-SnOxcomposites is also investigated. Results show thatmilling time has the ability to control the porous rate, the microcrystal thickness and thecontent of oxide of ball milled EG. Annealing temperature has the ability to improve thedisordered structure of ball milled EG, and to control the process of carbothermic(reduction) reaction. Ball milled EG-SnOxcomposites with various component kinds andmicrostructures can be produced by controlling ball milling time and annealingtemperature. Compared with the ball milled EG-SnOxcomposites produced by18h ballmilling unanealed and annealed at800℃for4h, the ball milled EG-SnOxcompositeproduced by18h ball milling and annealed at600℃for4h has a better electrochemicalperformance.