May 08 2012

Glass Ceramics Are So Cool

Published by jfrank at 1:22 pm under Uncategorized

How do you make very hard glass ceramics with low coefficient of thermal expansion (CTE)?

Answer: Take a combination of SiO2+Al2O3 (about 80%-90%) some TiO2+ZrO2 (about 4.5%) and LiO2 (also about 5%). Heat it to 1650 C.

Anneal it at 650C for two hours.

Raise the temp slowly to about 680C and hold it for an hour while crystal nucleation begins, then up to about 850 to transform the glass into a few different crystals, ceramizing it.

Now the CTE of the final product will be the amalgam of the CTE’s of the component parts, possibly even producing a material with a negative coefficient! Imagine something that shrinks when you heat it.

I’d love to make some some day, however the temperatures involved are extreme.

Microstructure and Properties of Li2O-Al2O3-SiO2-P2O5 Glass-Ceramics

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