why do some metals wet glass?

[hermanntrude]

gallium and indium in the molten state and also galinstan all wet glass, but not plastics... this means they're behaving a bit like a polar liquid... but a liquid made of an element cant be polar, can it? so what causes gallium to wet glass but not mercury?

[ChemSiddiqui]

mercury is a liquid metal (only liquid metal), it has mettalic bonding and surface tension is great in mercury so Cohesive forces in mercury are much more dominant than the adhesive forces with the wall of the glass. so mercury form 'bead' rather than stick to the wall of glass and make it wet.

[hermanntrude]

mercury is a liquid metal (only liquid metal), it has mettalic bonding and surface tension is great in mercury so Cohesive forces in mercury are much more dominant than the adhesive forces with the wall of the glass. so mercury form 'bead' rather than stick to the wall of glass and make it wet.

 

mercury is the only pure liquid metal at 25°C, but at 29°C, gallium melts, and if you make alloys, there are several ways of making metals which are liquid at room temperatures. Gallium particularly will wet glass... now why would it do that when mercury doesnt?

[ChemSiddiqui]

I think even though what you said above may be correct, if the adhesive forces between the glass and liquid are dominant than cohesive forces in the liquid itself then some of the liquid will stick to the wall and make it wet, but if the cohesive forces (attractive forces b/w like molecules) in liquid are dominant than the adhesive forces b/w wall of glass and the liquid as is the case with mercury, surface tension will make the liquid to occupy the minimun surface area and hence will not allow it to stick to the wall.

[Justonium]

I don't know why gallium does wet glass, but I do know that mercury also wets glass when you cool it down to near its melting point. Gallium probably wouldn't wet glass if it were heated sufficiently. But yea, It doesn't make sense how metals near their melting points actually stain glass, when glass is polar and they are not.

[UC]

http://www.freepatentsonline.com/6706980.html

 

According to this patent (and a few others out there), the problem is that gallium and indium oxide (even in very small amounts) massively lower the surface tension of the molten metal and allow it to adhere to other surfaces. The same is obviously not true of, or less true of mercury.

 

I did notice this with gallium when melting it down. It came to me moderately oxidized and a bit grungy, but after cleaning, it stuck to platic a lot less when melted. I used a brand new pasteur pipette to break up the cleaned 20g of metal I had into some smaller pellets and it stuck, but not really badly to the glass.

[ArbitraryRenaissance]

I know this is a 6 year old post, but I found the answer after a bit of digging. It's because gallium and other liquid metals oxidize rapidly. The material that wets the glass is not the base metal itself, but the oxidized form, which understandably will have relatively stronger intermolecular forces with materials like glass due to polarity. Mercury is more resistant to oxidization, so it is less prone to wetting.

Edited August 4, 2015 by ArbitraryRenaissance