Crystallization of leucite as the main phase in aluminosilicate glass with low fluorine content

Abstract

The paper presents the results of the study of aluminosilicate glass that contains 0.77 wt% of F− anions. The results show that thecritical size of glass particles at which the surface mechanism ofcrystallization changes to volume crystallization is in the vicinityof 0.075 mm in this glass. The temperature of the maximum nucleationrate was determined to be Tn = 680°C, and it ishigher than the transformation temperature Tg. Atcrystallization temperatures up to Tc = 950°C,the crystal phase of Lucite is formed, alone. Above this temperature,besides the main phase of lucite, two other phases, diopside andphlogopite appear. The activation energy of crystallization Ea = 319 ± 23 kJ/mol was determined. The results alsoshow that the activation energy does not depend on thecrystallization mechanism in this glass. The value of the Avramiparameters is n = 1.45. Microstructural studies confirmed thefact that volume crystallization of leucite takes place in thisglass. The leucite crystals grow in form of equiaxial dendrites withpronounced anisotropy along the direction ‹001›.Kinetical and microstructural studies show that the process ofleucite crystal growth occurs at the smooth atomic scale-facetedcrystal/glass interfaces and that it is controlled by volumediffusion. During the isothermal heat treatment the structure ofdendrites changes.