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Name: Bill H.
Status: Other
Age: 50s
Location: N/A
Country: N/A
Date: June 2004


Question:
Why does molten glass stick to hot metal, but not to cold metal. I do lampwork with glass. I sometime use a stainless steel rod (1/16 inch diameter wire) to help shape the glass. If I keep the metal rod out of the torch flame the molten glass will not stick to it when they come in contact. But if I get the metal rod in flame (it then heats up), the molten glass sticks to the rod when they come in contact - permanently. Why does the temperature make a difference?



Replies:
In order for one object to stick to another, the atoms of one object must bond with some atoms from the other object. If you push two solid objects together they usually do not stick to each other because the atoms cannot rearrange their chemical bonds for sticking to occur. The atoms like to stay where they are. In hot molten glass, the atoms are moving around and ready to bond with other similar atoms that are put next to them. Two pieces of hot glass will quickly stick together. Two hot pieces of metal will often stick together if you bang on them with great force. When both objects are hot, the atoms attach to each other and stick, so the glass sticks to the metal.

Note that cold (or hot) steel or stainless steel is always covered with a layer of oxide, either chromium or iron oxide. Glass, which is an oxide, likes to stick to other oxides. When one of the objects is cold, the atoms do not have enough thermal energy to bond with other objects. The hot glass atoms are available for bonding, but the cold atoms on the metal rod do not have enough thermal energy to change their bonding. Thus the cold metal does not stick to the glass.

Bob Erck



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