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Chromic-Nitric Acid versus Triton X-100 scintillator grade.

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Proud Mary

Sun Sept 20 2009, 06:21PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

A grumpy old man tired of surface leakage across glass wants to know what other sufferers would consider the ultimate glass cleaning combinations.

Chromic-nitric acid on its own followed by copious irrigation with distilled water, chromic-nitric acid followed by prolonged irrigation, and then Triton X-100n SC.

Ordinary surfactants followed by Triton SC.

This leakage business is a bit like the fruit fly infestation of my best apple tree....

Bored Chemist

Sun Sept 20 2009, 06:34PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Very clean glass picks up a layer of water from the atmosphere.
You could try treating the glass with a solution of dichlorodimethylsilane in cyclohexane then with methanol followed by washing in water. That covers the surface with a bonded on layer of silicone.

Or you could try vaseline.

Proud Mary

Sun Sept 20 2009, 07:55PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thanks for those suggestions.

With things like electrometer valves, which you might as well put in the dustbin if they are but once touched by human hand, I use anhydrous calcium chloride as a dessicant inside gasket sealed die-cast boxes - mostly because it's cheap, readily available and not truly noxious like some of the more aggressive desccicants, so as to keep water adsorption on the glass to the lowest level possible.

I suppose that in a notional perfectly sealed box, that a state of equilibrium would be reached between the residual water adsorbed onto the glass, and the amount absorbed by the dessicator, mediated by the vapour pressure of water and temperature.

So now, by theory alone, we can shew that Schroedinger's wretched pussy died of thirst!

IntraWinding

Mon Sept 21 2009, 01:13AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

'Piranha' solution is impressive stuff. You add strong Hydrogen Peroxide to concentrated Sulphuric Acid (the opposite to the usual dilution method), wait for the reaction to settle a bit and then use. I'm sure it smells of Ozone, that's how reactive it is! Apparently they use it on wafers in the semiconductor industry. It is of course very hazardous to mix and use so if you're new to it start on a small scale and try to retain your sight! It might be a good cleaning step prior to silanizing/siliconizing, as described by Bored Chemist.
Alternatively, dissolve some sodium hydroxide in isopropyl alcohol and use that hot. Apparently it strips away a small layer of glass taking contaminants with it, as well as directly attacking organics.

I read that Chromic acid leaves a lot of Chromium ions attached to glass that take a long time to wash off. That might not be good for your application.

Bored Chemist

Mon Sept 21 2009, 05:57AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Just a thought Harry,
you might want to see if you can track down some molecular seive rather than CaCl2- it doesn't turn into a corrosive puddle when the tin leaks.

Another point is that if these valves run hot the silicone might not like it.
Piranha solution is certainly effective but it's nasty. Don't use it on anything that's actually dirty. The reaction with bulk dirt can be dangerous. Also don't try to keep it in a closed bottle.

Proud Mary

Mon Sept 21 2009, 06:57AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

IntraWinding wrote ...

You add strong Hydrogen Peroxide to concentrated Sulphuric Acid -

...on my way into the Night and Fog of the Terror Factory, I think, with those two.

It had struck me that chromic-nitric acid could leave chromium ions adsorbed onto the glass, once I'd thought about it, but having conc H2S04 and conc HNO3 under the same private roof sounds like another way to spend weeks in The Place Where No Darkness is, as Orwell had it. The discovery of some edible glycerin in the back of a cupboard, something left over from the royal icing in last year's christmas cake would make the case seem beyond doubt to readers of The Sun.!

Proud Mary

Mon Sept 21 2009, 07:01AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Bored Chemist wrote ...

Just a thought Harry,
you might want to see if you can track down some molecular seive rather than CaCl2- it doesn't turn into a corrosive puddle when the tin leaks.

Another point is that if these valves run hot the silicone might not like it.
Piranha solution is certainly effective but it's nasty. Don't use it on anything that's actually dirty. The reaction with bulk dirt can be dangerous. Also don't try to keep it in a closed bottle.

I don't suppose you could kindly suggest a suitable sieve number could you?

Bored Chemist

Mon Sept 21 2009, 04:50PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Any of them would do but I'd go for 3a or 4a.

aonomus

Mon Sept 21 2009, 05:05PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

For the love of god don't use pirannah solution. Many people have gotten badly injured from it. I recall there was one incident where a lab tech used a vacuum flask (erlenmyer with a sidearm) to collect pirannah solution by sucking it out of glassware that was filled with it, unfortunately there was a tiny bit of acetone in the bottom and when the pirannah solution went in, it exploded.

Also you should read

if you do decide to use it, make only as much as you need.

IntraWinding

Mon Sept 21 2009, 11:55PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Is silica gel not a good enough desiccant?
It's certainly cheap and easy to get.

I really don't like the idea of home science/technology enthusiast types 'self censoring' what chemical they'll use. I think the worst of the witch hunt mentality's over by now anyway, isn't it?

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