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

The paper presents the results of the study of aluminosilicate glass that c ontains 0.77 wt% of F- anions. The results show that the critical size of g lass particles at which the surface mechanism of crystallization changes to volume crystallization is in the vicinity of 0.075 mm in this glass. The t emperature of the maximum nucleation rate was determined to be T-n = 680 de grees C, and it is higher than the transformation temperature T-g. At cryst allization temperatures up to T-c = 950 degrees C, the crystal phase of leu cite is formed, alone. Above this temperature, besides the main phase of le ucite, two other phases, diopside and phlogopite appear. The activation ene rgy of crystallization E-a = 319 +/- 23 kJ/mol was determined. The results also show that the activation energy does not depend on the crystallization mechanism in this glass. The value of the Avrami parameters is n = 1.45. M icrostructural studies confirmed the fact that volume crystallization of le ucite takes place in this glass. The leucite crystals grow in form of equia xial dendrites with pronounced anisotropy along the direction [001]. Kineti cal and microstructural studies show that the process of leucite crystal gr owth occurs at the smooth atomic scale-faceted crystal/glass interfaces and that it is controlled by volume diffusion. During the isothermal heat trea tment the structure of dendrites changes. (C) 2000 Kluwer Academic Publishe rs.