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Glass and Metal Adhesion
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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Update: June 2012
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