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Nucleation and Crystallization of NaNbO 3 from Glasses in the Na 2 O‐Nb 2 O 5 ‐SiO 2 System
Author(s) -
LAYTON M. M.,
HERCZOG ANDREW
Publication year - 1967
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1967.tb15133.x
Subject(s) - crystallization , nucleation , materials science , crystallography , transmission electron microscopy , viscosity , mineralogy , chemical engineering , analytical chemistry (journal) , thermodynamics , chemistry , nanotechnology , composite material , chromatography , physics , engineering
Transparent glass‐ceramics, in which the major phase was NaNbO 3 , were obtained by heat treatment of glasses in the Na 2 O‐Nb 2 O 5 ‐SiO 2 system. The structure of the glass and the changes occurring during crystallization as a function of temperature and heating rate were examined by X‐ray diffraction, transmission and replication electron microscopy, density, and other measurements. On heating, a rather abrupt formation of uniformly dispersed particles was observed. In the early stages of crystallization, these particles contained NaNbO 3 as loose, radially grown dendrites of identical crystal orientation which became dense during later stages of crystallization. The particle sizes ranged from 200 to 10,000 A, depending on the SiO 2 content of the glass. Transparency of the crystallized material was dependent on the particle size rather than on the amount of NaNbO 3 formed. The temperature at which crystallization occurred increased with the heating rate whereas the viscosity at crystallization decreased. For a given value of the rate of crystal formation per °C of temperature increase, the product (viscosity) n × (heating rate) was constant. The nucleation and growth phenomena which occurred in these glasses was attributed to microheterogeneities of higher Nb 2 O 5 content which formed part of the glass structure.