TEM INVESTIGATION OF CORDIERITE CRYSTALLIZATION FROM A GLASS POWDER WITH COMPOSITION MG2AL4SI11O30

The crystallization of a glass powder with composition Mg2Al4Si11O30 t o beta-quartz(ss) and the transformation of beta-quartz(ss) to alpha-c ordierite were investigated by means of SEM and TEM. Crystallization o f beta-quartz(ss) starts at the surfaces of the glass grains. At first growth proceeds nearly isotropically, but due to mutual hindrance gro wth perpendicular to the surface is preferred when the beta-quartz(ss) crystals impinge on each other. Tile transformation of beta-quartz(ss ) to cordierite starts at the surfaces of the beta-quartz(ss) crystals . In a first stage the cordierite nuclei grow over long distances only along the grain boundaries of several beta-quartz(ss) crystals. On pr olonged annealing the cordierite rims grow dendritically, into the cor es of beta-quartz(ss), maintaining the same crystallographic orientati on.