Time–Temperature–Transformation Diagrams for Borosilicate Glasses and Preparation of Chemically Durable Porous Glasses

Abstract

To clarify the effects of glass composition and heat‐treatment conditions on phase separation and crystallization, time–temperature–transformation (TTT) diagrams for the system (65 − x )SiO 2 ·25B 2 O 3 ·(10 − y )Na 2 O· y CaO· x ZrO 2 , which is used for fabricating alkali‐durable porous glasses, were determined. The microstructures and properties, such as resistance to alkaline attack as a function of ZrO 2 content, of the porous glasses fabricated on the basis of the developed TTT diagrams were examined. CaO and ZrO 2 additions were shown to affect the locations of the noses in the TTT curves for phase separation and crystallization. The substituting of CaO for Na 2 O was effective for retaining ZrO 2 in the skeleton of the porous glasses. The alkali resistance of ZrO 2 ‐containing porous glasses was 8–10 times superior to that of the porous glass without ZrO 2 . The results demonstrate that TTT diagrams can be used as guides for heat‐treatment scheduling in processing or predicting of glass‐forming ability and the onset of phase separation and crystallization in glass‐forming systems.