Polverone - 27-5-2002 at 12:35
In private conversation I have recently been considering the vulnerability of borosilicate glass to hot NaOH and other strong alkaline materials.
Rather than continue to sling words back and forth, I sacrificed a single pyrex test tube to test things out.
What I found:
When the NaOH was just barely molten, hardly anything seemed to happen in the vessel. But as the temperature was raised, something clearly *was*
happening. Fine streams of bubbles began appearing from the interior tube surface where it was in contact with the NaOH. As the temperature increased,
this changed to vigorous bubbling. Water vapor condensed at the tube's mouth as this took place.
I withdrew heat after a while and cleaned the tube out. The glass had a distorted, wavy appearance where the NaOH had been. The etching was quite
similar in appearance to that I obtained from heating CaF2 and H2SO4 in an ordinary soda glass test tube.
I think it is quite safe to say that NaOH attacks borosilicate glass at elevated temperatures.
vulture - 28-5-2002 at 10:10
I have a prospect of Duran glass, which shows a the attack of glass by NaOH in function fo temperature and concentration. As it is an exponential
curve, your test results are reliable.
A related question...
Polverone - 28-5-2002 at 12:41
What does one use to handle molten NaOH/KOH? Glass won't work. I've used food grade stainless steel, but it is attacked by other things that I might
want to add at high temperatures (chlorides, sulfur, etc.) Would a higher grade of stainless steel work better? In my ideal lab I would of course use
platinum :-) I suppose I might be able to get away with using a sacrificial glass vessel and being careful to premix materials so they react right
away and there is little time for the material to interact with the glass. I'm especially wondering about the KOH since it has a higher mp than the
NaOH and, as you said, there's an exponential curve associated with the rate of attack on the glass...
Also, some of the materials I am interested in (sulfides and polysulfides) are themselves fairly corrosive, though I don't know what their effect on
glass/ceramics would be.
ray - 8-10-2002 at 04:48
Borosilicate glass ?
Molten ?
Is it possible, bound pure Si to a -OH group ?