Non-Equilibrium Reaction Milling and Nanomechanochemistry in Ceramics

Abstract

This article describes a nanomechanochemistry, from which to set up the phenomenology for the amorphization and nanocrystalline synthesis via non-equilibrium reaction milling in ceramics. When the instrumented rotating-arm reaction ball mill system is used, an amorphization by mechanical alloying (MA) the ceramic powder mixture is monitored through measures of temperature inside the tank and applied torque. This MA process is expressed by Johnson-Mehl-Avrami equation (JMA) of X=Kexp{1−(t−t_s)}ⁿ with K=K_oexp(−Q/kT); JMA exponent (n) is obtained at 0.5 and 1.7 for the nucleation and growth of amorphous (ZrO₂-3mol%Y₂O₃)₈₀(Al₂O₃)₂₀ and nanocrystalline (ZrO₂-3mol%Y₂O₃)₉₀(Al₂O₃)₁₀ respectively. On the other hand, for the mechanically driven amorphization of the covalent bond type ceramics, the new formula of d(V_f−V)/dN=−K_m(V_f−V) with the repeated impaction number N, as proposed on the basis of the first-order chemical reaction, is validated through a model experiment using planetary ball milling; the reaction rate constant K_m increases with decreasing powder amount and temperature, and in order of B₄C, ZrB₂ and SiC. Furthermore, far from equilibrium reaction milling provides a process window and control methodology for the glass formation in ceramics on the basis of the thermodynamic and kinetic considerations.