Heavy Walter
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Quartz and molten sodium nitrite
Hi
I would appreciate any reference to potential chemical attack by molten sodium nitrite to quartz surface.
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Dan Vizine
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I was sure I could find something, but I really haven't yet. It's not so easy. I have reams of info on what resists what, and at what temperatures,
but nothing on this specific case.
Complicating it is the fact that all quartz is not the same.
[Edited on 20-12-2016 by Dan Vizine]
"All Your Children Are Poor Unfortunate Victims of Lies You Believe, a Plague Upon Your Ignorance that Keeps the Youth from the Truth They
Deserve"...F. Zappa
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Chemetix
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I have no references just experience in this case, but most glasses don't like sodium in high concentrations and high temperature for extended
periods. It tends to leave a milkiness on the surface. Quartz is tougher than most, but I do see signs of chemical change on quartz repair work I do.
Generally it's sodium hydroxide or sodium chloride residues that are the culprit. I guess your application would need some clarification about your
concerns? Is it optical damage you are concerned about, residue and contamination issues?
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Heavy Walter
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Hi Chemetix
This is the scenario: I cleaned a W deposit in a quartz window with sodium nitrite and after cleaning with water, I found the surface slightly milky.
I wasn't sure if it is due to the nitrite or the W itself.
As soon as I get a clean quartz window will check with nitrite alone.
Thanks!
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Marvin
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My thoughts were that as an acidic oxide contacting the salt of a weak acid it would form sodium silicate and nitrogen oxides. My memory of nitrate
melts is that they are in equilibrium with nitrite and oxygen, and that significant at higher temperatures nitrite melts are in equilibrium with
sodium oxide and nitrogen oxides. Rate of reaction per unit area might depend mostly on how soluble the silicate is in the melt.
I checked encyclopaedia of chemical reactions and couldn't find anything in relation to silica. Which surprised me. And irritated me, because that's
a dead end for what I have access to here. Nitrate/nitrite melts have been studied extensively for thermal storage and power generation, so the
information is out there somewhere...
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Fleaker
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Can't say I've ever tried this. What temperature do you need to be at? Pretty sure the aqueous nitrite salt isn't going to touch it. I doubt even
nitrite at its melting point is going to be highly aggressive.
Also, when I melt salt to mix with RhCl3 or Ir powder before chlorination, the tube stays fine even at 750 C with NaCl.
Usually what's wrecking quartz is alkali.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Heavy Walter
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Hi Fleaker
Sodium nitrite melts under a mild flame. When molten it dissolves easily the W deposit (a thin one, by sputtering).
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Chemetix
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When you say tungsten deposit, was it tungsten metal from some high temperature event or tungsten salts? High temperature nitrites are used to clean
metals usually.
I'm familiar with tungsten oxides being deposited by flame at high temperature, in fact I can put together a photoset of how to clean it. I recommend
using welders pickle. A preparation of 30% nitric and 9% hydrofluoric acids used to clean stainless steels after welding.
edit- Just saw the above post...sputtering! try the pickle it's quite gentle at the concentrations it's sold as.
[Edited on 21-12-2016 by Chemetix]
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Heavy Walter
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Hi Chemetrix
Will try!
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Fleaker
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if it's just tungsten or tungstic acid, just use hydrogen peroxide and skip the HF.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Heavy Walter
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Hi Fleaker
Just H2O2? No heat?
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Mesa
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With the thermal stabilty of quartz, you can also just hit it with a blowtorch for 20-30 seconds then wash it off with ammonia or NaOH solution.
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Heavy Walter
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Problem solved!
My experiment is on a discharge lamp that I am trying to recover after darkening of the quartz window due to sputtered W. My access to the inner side
of the quartz window is near none.
So I am dealing with it as a ship-in-a-bottle craftsmanship.
I sent a little of NaNO2 and melted it. The molten salt dissolved easily the W deposit.
Then I proceed to wash the rests of the reaction from outside, sending water with a needle.
At that moment I perceived a milky deposit. I imagined some alteration on quartz surface.
Today I have been able to melt a large quantity of NaNO2 on quartz. No attack at all. I realized that water dissolved the salt soon when was in powder
shape but the molten one was a lot harder to get rid of.
So, I am certain that the problem is solubility. The milky area must to be an unwashed deposit. I will move to the suggestions I received, leaving
aside the sodium nitrite.
My first move will be H2O2. I will report results.
Thanks!
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Fleaker
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35% w/v H2O2 usually works OK with powdered tungsten.
If more aggressive conditions needed, maybe it can be mixed with ammonia water.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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