Sciencemadness Discussion Board - Using a(n Ag) mirror RBF to carry out reaction with fused alcali

Using a(n Ag) mirror RBF to carry out reaction with fused alcali

Keras - 24-10-2022 at 00:28

Folks,

This is very simple: I’m wondering if a glass RBF (or any vessel for that matter) covered in a thin metallic layer, such as the famous Ag mirror, could be used to perform reactions involving fused alcali such as liquid sodium or potassium hydroxide. It would provide a protective layer against the alcali, to avoid glass being attacked and dissolved.

Has anyone ever attempted that?

[Edited on 24-10-2022 by Keras]

j_sum1 - 24-10-2022 at 05:54

I doubt it would be physically robust enough.

Keras - 24-10-2022 at 06:12

Quote: Originally posted by j_sum1

I doubt it would be physically robust enough.

I never attempted making one (I have no silver, though I could buy some of course), but judging by what Nile Red says about it, i.e. that it would need a spatula or some other tool to be removed, it seems to be pretty solid.

Is there any alternative to it? Like stainless steel RBFs?

pneumatician - 24-10-2022 at 09:42

I think is not a question of thickness, ALWAYS the alkali eat something, your tolerance at this "something" is what matter.

Exist others combos to mirror glass, for example: Pt & Cu, Au & Zn and maybe...

I've a Bronica rotary finder where the mirror layer is corroded and I need to re mirror it, but someone known what type of combo use the Bronica camera or other brands?? What the combo is better??? what is better in light transmission?? all this is necessary to known before make a decision.

Old SCSI HDD use a glass plate mirroded with Pt... and what more??

Keras - 24-10-2022 at 10:35

Quote: Originally posted by pneumatician

I think is not a question of thickness, ALWAYS the alkali eat something, your tolerance at this "something" is what matter.

Exist others combos to mirror glass, for example: Pt & Cu, Au & Zn and maybe...

I'd be happy to know how to make other mirrors. I've tried CuSO₄ reduced by ascorbic acid, it makes very fine metallic Cu powder, but it doesn’t deposit on the surface of the glass. Pt seems difficult to summon to my needs. Gold mirror?

Twospoons - 24-10-2022 at 10:55

You should be able to electroplate other metals on top of a silver mirror

Fulmen - 24-10-2022 at 11:58

That's a very good idea. I think nickel is the best choice, at least among the non-noble metals.

pneumatician - 24-10-2022 at 15:51

Quote: Originally posted by Twospoons

You should be able to electroplate other metals on top of a silver mirror

to end in the same place, a mirror full of scales.

I think the best is, if can be done, Rh & Pt or one alone, Au... yes if you use Au for photo cameras you see the world yellow :-)

pneumatician - 24-10-2022 at 18:55

Au gilding of glass.

covert the part with a super-saturated borate de soda and applying Au leaf upon it. Afterwards is fixed by burning. Maybe if is for some interior thing like a photo finder, clean the glass and put Gold leaf.

The ass method is an amalgam with Ga? and heat...

Keras - 25-10-2022 at 00:23

Quote: Originally posted by Twospoons

You should be able to electroplate other metals on top of a silver mirror

That’s a good idea. It could certainly improve the chemical resistance, but I’m not sure about the ‘physical’ resistance, although I’m pretty sure the original silver plating is more than OK

Fulmen - 25-10-2022 at 00:58

I wouldn't put much faith in the mechanical strength of the silver coating. It is extremely thin, and pure silver is pretty soft. Chemically I think you're right.

Keras - 25-10-2022 at 02:59

Quote: Originally posted by Fulmen

I wouldn't put much faith in the mechanical strength of the silver coating. It is extremely thin, and pure silver is pretty soft. Chemically I think you're right.

Yet, how thick is standard gold plating in jewellery? And the protective oxide layer over an aluminium foil?

Fulmen - 25-10-2022 at 03:10

Only one way to find out I guess.

wg48temp9 - 25-10-2022 at 03:58

Quote: Originally posted by Keras

The glass needs to be very clean and for best results sensitized. For example:

From: https://www.researchgate.net/publication/274009270_Surface_m...

There is lots of info about silvering and electroless copper or nickel on the internet including youtube videos. The are also alternatives sensitizers to Pd but apparently Pd is the best.

Twospoons - 25-10-2022 at 13:24

Electroplating would allow the build up of a thick metal layer, such that the metal to glass adhesion is not really important and the glass merely provides mechanical support to a metal shell. Thermal expansion might become an issue though. This might be one of those times where soda glass is better than borosilicate.

paulll - 25-10-2022 at 14:09

Quote: Originally posted by Keras

Quote: Originally posted by pneumatician

I got some funky copper mirror reducing CuO with H2 in a dropping pipette.

j_sum1 - 25-10-2022 at 14:46

I recall reading once that a Cu mirror can be done using hydrazine. I have yet to try it.

WGTR - 26-10-2022 at 09:33

The difference in expansion coefficient between the metal and glass would be problem, especially since you are talking about molten hydroxide temperatures. Part of the problem with melting hydroxide in glass, is that the products of the reaction have a different expansion coefficient than the glass. Upon cooling, the glass cracks.

The metal layer would have to be very, very, thin and have excellent adhesion. It is difficult to make very thin, non-porous metal coatings outside of a lab. If you want to try a variety of metal coatings, I would suggest looking around for a good vacuum system to play with. We evaporate various metals (aluminum, chromium, gold, palladium/gold, copper, etc.) under vacuum by placing a small amount of the metal in a tungsten "basket". This is essentially a heavy tungsten filament. Since tungsten has such a high melting point, it is use to evaporate other materials onto our samples without introducing contamination. It's conceptually a very simple process.

There are several issues with evaporative coatings, however. First, the glass surface must be chemically clean for the metal layer to adhere. This means not only does it need to be aggressively degreased, but also needs to be free of adherent water vapor on the glass. The latter can only be achieved by heating over 100C under vacuum. The instant the glass is exposed to air again, it is "contaminated" with water vapor.

Second, a chromium "adhesion" layer is needed first, in order for things like copper or silver to bond to glass. The chromium cannot be exposed to air before the next metal is deposited, or the next metal will not stick. This means that both chromium and silver(etc.) sources would need to be present at the same time without breaking vacuum.

Third, evaporative coatings are usually too porous. It likely wouldn't be a good enough coating for what you're trying to do anyway. One other thing that I could suggest is painting the glass with a lead oxide enamel. The glass is heated up enough that the litharge fuses to the glass surface. Next, it is reduced with hydrogen or alcohol vapor. This should give you a thin layer of lead, suitable for electroplating. I have to run now. Have fun!

Keras - 27-10-2022 at 00:37

Quote: Originally posted by WGTR

…

Thanks for that very detailed input! Very clear and informative. TBH, it was only a hypothetic idea. Given the underlying complexity your process implies, I think the best way is to work out some sort of metallic container on which a standard glass adapter can be safely attached. That might still pose a challenge in terms of dilatation, but it’s probably much easier to address than using ultra-deep vacuum to deposit metallic vapours on an ultra-clean and dry glass.

unionised - 27-10-2022 at 04:23

Are you planning to stir the reaction?

Keras - 27-10-2022 at 23:59

Quote: Originally posted by unionised

Are you planning to stir the reaction?

Ideally, yes, and that’s the problem, really.

yobbo II - 29-10-2022 at 14:25

You can plate tantalum onto reaction vessells but that is not your original question.

Something like this.

https://www.sciencedirect.com/science/article/abs/pii/S02634...

Yob