Papers by Keyword: Surface Nucleation

Abstract: The nucleation and crystallization kinetics of P2O5-B2O3-ZnO-BaO-Al2O3-TiO2 crystals in bulk glass in which this crystals were found to crystallize in the heating process of the glass, were studied by non-isothermal measurements using differential thermal analysis (DTA). A nucleation rate-temperature was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/Tp, or the height of the crystallization peak, (*T)p, as a function of nucleation temperature, Tn. The temperature where nucleation can occur for this glass ranges from 700°C to 890°C and the temperature for maximum nucleation is 760±5°C. The correct activation energy for crystallization, Ec, for this glass is the same for surface and/or bulk crystallization, and is 533±15°CkJ/mol. The analysis of the crystallization data with the Kissinger equation and the Marotta equation yields the correct value for Ec only crystal growth occurs on a fixed number of nuclei. The crystallization process of a sample heat treated at the temperature of the maximum nucleation rate was fitted to kinetic equations with an Avrami constant, n ≈2 and a dimensionality of crystal growth, m ≈2.

Abstract: We apply the lattice instability analysis to homogeneously strained single crystal with a flat or defected surface to demonstrate that, in the process of emission of dislocation by an unstable surface, prior to the breaking of atomic bonds, a vibrational mode localizes, foretelling the location and the manner of the impending microscopic catastrophic event.