A STUDY ON THE MECHANISM OF CRYSTAL GROWTH IN THE PROCESS OF CRYSTALLIZATION OF GLASSES R.-G. Duan*, K.-M. Liang, and S.-R. Gu Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, P.R. China (Refereed) (Received November 26, 1997; Accepted February 3, 1998) ABSTRACT This paper investigates the CaO–Al 2 O 3 –SiO 2 system glass. When the glasses were heat treated at different temperatures and times, they crystallized from the surface. The main crystals were dendrites of anorthite (CaAl 2 Si 2 O 8 ). The morphology of crystallization was observed using scanning electron micros- copy, and the crystal size was measured by optical microscopy. It was found that the growth of anorthite (CaAl 2 Si 2 O 8 ) crystals was diffusion controlled. The apparent activation energy for crystal growth was about 581 kJ/mol. The rate of crystal growth was not constant during the growth process; the rate was highest at the beginning of crystallization and gradually decreased with increasing time. The higher the temperature, the less time required to complete crystal growth. The total process of diffusion may be determined by the diffusion rate of Ca 21 . © 1998 Elsevier Science Ltd KEYWORDS: A. glasses, B. crystal growth, C. electron microscopy, D. diffusion INTRODUCTION When glasses are crystallized, the crystal growth can be divided into two mechanisms: diffusion-controlled growth and interface-controlled growth [1]. For cases in which the size of the growing crystal particle is large relative to the characteristic diffusion distance, the *To whom correspondence should be addressed. Materials Research Bulletin, Vol. 33, No. 8, pp. 1143–1149, 1998 Copyright © 1998 Elsevier Science Ltd Printed in the USA. All rights reserved 0025-5408/98 $19.00 1 .00 PII S0025-5408(98)00105-6 1143