Devitrification behavior and preferred crystallization mechanism of glasses based on fluorrichterite (Na2CaMg5Si8O22F2) composition

Abstract

Devitrification behavior and preferred crystallization mechanism of glasses based on fluorrichterite (Na 2 CaMg 5 Si 8 O 22 F 2) composition.

Surface and volume crystallization in fluorrichterite based glasses

“…The thermal stability of the glasses can be evaluated from the relative positions of the characteristic temperatures, viz. T g (glass transition temperature), T x and T p (onset and peak crystallization temperatures, respectively), and T m (melting temperature) [18,21].…”

“…In previous papers, we stated the concurrence of surface and bulk crystallization in the devitrification process of Na-fluorrichterite glasses [17]. Surface crystallization mechanism predominates at the beginning of the crystallization process; however, volume crystallization attains significance with increasing fluorine content in glass composition [18]. The purpose of the present paper is to studythe crystal growth in the initial steps of devitrification of glasses belonging to the SiO 2 -CaO-MgO-Na 2 O-F system with variable fluorine content.…”

“…In order to minimize residual stress and to avoid glass devitrification, bulk glasses were annealed at a temperature of T g -100ºC for 2 hours. For each glass composition, T g was previously determined from differential scanning calorimetry (DSC) on glass samples with the same chemical composition (18). The T g values determined for the RE, R6, R8 and R10 glasses are 565º, 560º, 550º and 535ºC respectively.…”

Kinetic study of the transformation of sodalite to nepheline

“…Differential thermal analysis (DTA) is extensively used as a rapid and convenient instrument to study the crystallization kinetics in glasses, to determine homogeneous crystal nucleation rates and, to obtain the activation energy for glass crystallization assuming that the crystallization process is a first-order reaction. [17][18][19] In the case of nepheline, thermal analysis has been used to determine the activation energy for crystallization of glasses prepared from rice husks ash 20 and from fly ash and metallurgical slag. 21 However, to the authors' knowledge the kinetics of the thermal transformation of sodalite to nepheline using DTA technique has not been previously reported in the literature.…”