A good source for filaments
Posted: Wed Jun 06, 2007 4:00 pm
Kurt J Lesker actually sells big tungsten filaments pretty cheaply (about $5 ea) as evaporation sources. They tend to be a little too beefy for most small power supplies, but you may not need to heat these huge things up to white hot, either.
I have another source telling me the reason tungsten isn't good in hydrogen (or water vapor) is that it reacts, not sputters, with hydrogen, which makes a volatile compound that then evaporates. With water vapor, what happens is the water H and O get back together on the glass, leaving the tungsten there. It is supposedly one reason Edison didn't use the stuff, there weren't vacuum pumps good enough then for it to have a better lifetime in use.
I know I've burned out a few small ones pretty fast in the vacuum produced by a new Sargent-Welch 2 stage pump, and was not even bringing them to full brilliance. At orange heat, 1 mil wire is lucky to last one hour.
Hydrogen (or helium) is what you have in the tank if you want a glow but *no* sputtering, except with tungsten.
I have another source telling me the reason tungsten isn't good in hydrogen (or water vapor) is that it reacts, not sputters, with hydrogen, which makes a volatile compound that then evaporates. With water vapor, what happens is the water H and O get back together on the glass, leaving the tungsten there. It is supposedly one reason Edison didn't use the stuff, there weren't vacuum pumps good enough then for it to have a better lifetime in use.
I know I've burned out a few small ones pretty fast in the vacuum produced by a new Sargent-Welch 2 stage pump, and was not even bringing them to full brilliance. At orange heat, 1 mil wire is lucky to last one hour.
Hydrogen (or helium) is what you have in the tank if you want a glow but *no* sputtering, except with tungsten.