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Old 30th Nov 2017, 9:55 pm   #24
MotorBikeLes
Nonode
 
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 2,346
Default Re: Care of Rare Valves

Does glass continue to flow at room temperatures? It will certainly depend on the glass's formulation. I have done or overseen many hundreds of tests of thermal expansion of glasses. Ceramic glazes to be more specific. Back then, they were all lead glazes (glasses), and by varying the composition, significant changes could be seen. Generally a "softer" glass, typically higher sodium content, would have a higher thermal expansion and a lower softening temperature. Above 500 to 600 Celsius, the glass was obviously mobile, but on cooling from the higher temperature, a marked kink in the graph defined the "softening point" which we regarded as "no longer liquid". Our interest was to compare the difference of size on cooling below the softening point with that of the underlying ceramic body.
However if you move from lead glasses to the more common window glass, you were more a simple mix of sodium compounds and silicon dioxide (eg sand). Whilst I have not tested any window glasses, I know they have much lower softening points, are cheaper to formulate, and require lower kiln temperatures. If you move just a bit further, you have various sodium silicates which most will know as "water glass". Some with high sodium content (I have a jar full here) are so viscous that it is difficult to get any from the jar when required.
I have absolutely no doubt that a thin, high sodium glass is capable of slow viscous movement at room temperature.
Les
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