Heating rate effect on nucleation rate measurements by Tammann’s development method: applications to crystallization of silicate glasses

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Abstract
10-081 Alexander Abyzov Abyzov, A.(National Science Centre Kharkov Institute of Physics & Technology); Montazerian, M.(Federal University of São Carlos (UFSCar)); Fokin, V.M.(Vavilov State Optical Institute); Zanotto, E.D.(Federal University of São Carlos (UFSCar)); For typical glass-forming liquids (such as silicate glasses or polymers) the experimental observation of the nucleated crystals is a quite difficult task: at high undercoolings, corresponding to the range of measurable homogeneous nucleation rates, the nuclei are undetectable by common experimental techniques. For these most typical cases, more than hundred years ago, Gustav Tammann proposed the following procedure, which is now known as the Tammann’s or ‘development’ method. According to Tammann’s proposal, crystals nucleated at a low (nucleation) temperature, Tn, are grown up to microscopic sizes at a higher (development) temperature, Td > Tn. The development temperature Td has to meet – according to Tammann – the following conditions for nucleation (J) and growth (u) rates: J(Td) << J(Tn) and u(Td) >> u(Tn) in order to be applicable. Numerical simulations were performed to take into account effect of development stage on the interpretation of nucleation measurements employing Tammann’s development method with a finite heating rates from Tn upto Td. The time-dependent cluster density, , is determined by solving a system of coupled differential equations. These equations were solved numerically for isothermal nucleation and then for heating to the development temperature, Td, at different heating rates. As a result of this research, (i) Parameters of the process of crystallization: the distribution function of the crystals, N(t) curves, nucleation rates and time-lag, are determined for silicate glasses. (ii) Algorithm of correction of the results of nucleation rate measurements employing Tammann’s development method at different heating rates is developed.
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