Nanocrystalline to microcrystalline transformation of ball milled vanadium carbon mixtures: The effect of temperature and pressure

Mechanically Enhanced Reactivity of Silicon for the Formation of Silicon Nitride Composites

“…R ECENTLY, high-energy ball milling has been widely used to produce supersaturated crystalline solid solutions, 1,2 amorphous phases, 1,3-5 nanocrystalline solids, [3][4][5][6][7][8] solid solutions containing two (or more) immiscible components, 9 and compounds through in-situ solid-solid, gas-solid, and liquid-solid reactions. [10][11][12][13][14][15][16][17][18][19][20][21][22] It is generally agreed that there are many processes occurring during ball milling. These processes include at least repeated deformation, fragmentation, cold welding, microdiffusion, amorphization, recovery, and recrystallization.…”

“…[23][24][25][26][27] In addition to the comminution process, ball milling also causes the following: an increase in the atomic-level strains 9,18 and the specific heat; 7 the generation of free radicals, unsaturated groups, and deformed bonds at the surface; [28][29][30] changes in grain-boundary energies; 6,7 the storage of considerable enthalpies; 6,7 release of gases; 31 localized temperature increases; [24][25][26]32 electrostatic charging, the emission of electrons, and the emission of light; 31 and solid-solid, gas-solid, and liquid-solid chemical reactions. [10][11][12][13][14][15][16][17][18][19][20][21][22] Because of these processes, the free energy of reactants has been increased considerably and the kinetic dependence on diffusion rates and diffusion through the product layer has been minimized. Furthermore, many of the aforementioned processes are shortlived, such as localized temperature increases with a time scale of 10 −3 -10 −4 s and triboplasma in the range of <10 −7 s. 31 Although short-lived, these processes are important in the sense that they trigger the reaction, thereby leading to the insitu formation of compounds during milling.…”