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Author: Subject: Silver plating via Tollens' reaction
lahthffire
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[*] posted on 24-5-2006 at 11:16
Silver plating via Tollens' reaction


Addition of an aldehyde to Tollens' reagent (a silver-diamine complex) causes Ag to precipitate and plate onto the glass of the container, creating a mirror.

My questions are:

1. How tightly does the Ag adhere to the glass?
2. How would it adhere to alumina ceramic (Al2O3)?
3. How thick do you think the layer can be made?
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Cloner
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[*] posted on 24-5-2006 at 13:41


THe layer adhered poorly when I did it, though the mirror was perfect and the imperfections were on the dull side.
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The_Davster
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[*] posted on 24-5-2006 at 14:13


The testtube with silver on it from a tollens test usually requires concentrated nitric to get it off. In my experiance it does not seem to just scrape off.
2) Most likely, yes




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neutrino
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[*] posted on 24-5-2006 at 14:15


There was a good thread about plating silver onto glass either here or at RS (roguesci.org). Search around and you'll find it.



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[*] posted on 24-5-2006 at 14:35


Most instructions for mirroring glass require extreme cleaning of the glass first - using NaOH, then concentrated Nitric, then rinsed with distilled water. I guess any kind of crap on the glass will affect adhesion.



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triphenylphosphineoxide
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[*] posted on 25-5-2006 at 06:29


Follow the cleaning described above and make sure there are no suspended solids or surfactants in your solution these will also affect adhesion
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lahthffire
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[*] posted on 30-5-2006 at 04:40


Thanks for the responses. I'll give it a try later this week or next and report back.
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[*] posted on 1-6-2006 at 12:32


Make the solution fresh

mick


To the Safety-Net:

The January 8, 1996 issue of "Chemical and Engineering News" (see
page 2) had a letter to the Editor in the CHEMCIAL SAFETY section
which reported an explosion related to Tollens Reagent. The
letter was signed by G.S. Klinger, R.D. Scheele, and M.J. Steele
of the Battelle Pacific Northwest Laboratories. The letter
reports the following:

Tollens Reagent was being used as a semiquantitative test for
formaldehyde in water. An (unexpected) explosion occured as a
glass vial containing two-day old reagent was rinsed with
deionized water from a squeeze bottle.

Fortunately, there were no injuries and little damage. However,
this incident should not have occurred since the potential for
silver and ammonia (ie Tollens Reagent) solutions to form highly
shock-sensitive precipitates is well-known. The authors of the
above-cited letter did a post-incident literature search and
discovered a reference in the "Handbook of Reactive Chemical
Hazards" by Bretherick. There are more warnings to his effect in
the literature, including one I published in the Journal of
Chemical Education in the early 70's.

All of us who use to Net to stay current should file this in our
general awareness file. The possibility for this type explosion
exists in darkrooms, in glass shops where silver mirrors are
prepared, and in laboratories which use Tollens Reagent.

The proper procedure for working with silver - ammonia solutions
is to make the solutions when needed, use them immediately,
and destroy any excess solution immediately. The best method of
destruction is to carefully add HCl (hydrochloric acid) which
removes the silver as silver chloride and forms ammonium
chloride. The final pH should be around 4 - 7. If there is
sufficient silver present, the solution can be sent to a precious
metal recovery firm, under the Precious Metal Exclusion of RCRA;
otherwise, it must be disposed of as a hazardous waste because of
the silver.

(By the way, the cited letter refers to an "unexpected"
explosion. Most explosions in labs are, in fact, "unexpected"
and it is usually post-incident that the literature search is
done. I urge everyone with chemical research lab responsibility
to have a copy of Bretherick handy, and use it!)

Neal
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lahthffire
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[*] posted on 7-6-2006 at 13:24


I've done some plating. The adhesion to the testtube I tried first was OK, but nothing special. Interestingly, the silver seems to adhere to smooth HDPE (plastic).

It is adhering very well to the piece of alumina I've tried. I'm shooting for a coating of thickness ~.001 inch, though, and I don't think this, alone, is going to get me there. I've plated it 5 times and the silver layer is maybe .0001" thick. So, I think I'm going to have to use this as a base coat and electroplate to achieve the thickness.
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lahthffire
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[*] posted on 13-6-2006 at 16:21


More results in case anybody is interested:

After plating 5 times, the resultant layer was a pretty, silver layer, with a measured resistance of 1 ohm with the leads to my multimeter .25" apart, and 2 ohm with them 1" apart. My multimeter is a piece of crap, though, so I take that as only an indication that the layer is plenty conductive.

So I mixed up some brush-electroplating solution, randomly deciding on 20 wt% AgNO3 in H2O, set the DC power supply on 6 volts, and tried plating with the brush plating anode I made by attaching a 1" x 1" x .375" square of graphite with rounded edges to the end of a nylon rod, running a lead to it, and wrapping in cotton.

And I burned up my Ag layer. It was just too much current for so thin of a layer, especially considering the poor thermal conductivity of alumina compared to metals.

So I tried again today. This time I did an even better job of cleaning and pre-plating with the Tollens' reaction deposition, and 4 iterations left me with a uniform, matte silver layer with a resistance measuring 0.3 - 0.4 ohm at .25" and 1" distance between leads, respectively.

I turned the voltage way down on the power supply and began plating, gradually bringing the voltage up to 3 volts, then back down to 2.7 V. I stopped when I ran out of plating solution (I'd only prepared ~5 ml of 8 wt% solution in a watchglass).

It worked well! My layer is .0005" thick; halfway to my target, and I have no doubt I can easily reach .001". It has a matte finish, but I scraped on a section of it with a stainless steel scooper to see if I could get it to chip or peel up (which I could not), and that left it shiny.

I think I'm going to work on a tank plating method rather than the brushplating, though, to facilitate control of the layer thickness.
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[*] posted on 13-6-2006 at 19:20


Of course we're interested! Check the number of "views" of this thread.

I've often wondered whether Tollen's reagent could plate substrates other than glass. Thanks for the results.

[Edited on 14-6-2006 by Twospoons]




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The Freak
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[*] posted on 29-3-2013 at 05:33


Has anyone ever tried plating stainless steel with tollens' reagent? I was wondering if this is possible, since I failed to electroplate it with copper. I know it can be done with cyanide, but I highly prefer not to.
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zed
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[*] posted on 29-3-2013 at 15:45


Should work. Simply activate the stainless by anodizing it for a little while. Then reverse polarity, and Bingo....copper should plate out.

Works nicely on Chromium; should work on stainless.
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[*] posted on 30-3-2013 at 05:40


Quote: Originally posted by zed  
Simply activate the stainless by anodizing it for a little while. Then reverse polarity, and Bingo....copper should plate out.

Works nicely on Chromium; should work on stainless.


What's the purpose of the anodisation?




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[*] posted on 31-3-2013 at 14:22


Hmm, create more oxide layer on the stainless? Isn't that making the problem worse? Not that I don't believe you, but I just don't see how that should help. Could you enlighten me/us on the working of this? Or do you know this to work mainly out of experience.
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[*] posted on 31-3-2013 at 16:04


if anodisation means to use the stainless steel as anode before plating then it is correct.finishing.com also recomends this to knock off the oxide protective layer before plating. one time i didnt change polarity when i gold plated a mixed stainless steel item and only one grade of stainless got plated but not the other.copper sulfate plates quite well on stainless steel.they told me to use stainless as anode for a couple of seconds in hcl and tartaric acid before gold plating.

[Edited on 4-1-2013 by cyanureeves]

[Edited on 4-1-2013 by cyanureeves]
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[*] posted on 31-3-2013 at 18:19


I have thought about the possibility of using chemical gold plating to form mirrors for a CO2 laser.

First, to dissolve the gold, it is placed into hydrochloric acid and chlorine gas is passed into the acid.

2Au + 3Cl2 + 2Cl[-] --> 2AuCl4[-]

Then, to precipitate the gold back out, an alkaline solution of H2O2 is used.

(2)AuCl4[-] + (3)H2O2 + (6)OH[-] --> (2)Au + (8)Cl[-] + (6)H2O + (3)O2

The gold usually separates out in a finely divided state, and appears brown by reflected light and greenish blue by transmitted light. If very dilte solutions are used, the gold sometimes separates out forming a yellowish film on the sides of the test tube.

[Edited on 1-4-2013 by AndersHoveland]
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[*] posted on 12-2-2017 at 10:28


Can Tollens' Reagent also be used to "plate" metal items (specifically brass)? Does anyone know how well the silver would adhere to brass?
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zed
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[*] posted on 16-2-2017 at 16:56


Ummm. Well, when the guys need perfect mirrors, they may resort to rinsing the glass for weeks with pure, running, H20.......And then deposit vaporized metal on the glass in a vacuum chamber. At least, that's the way I remember it.

Seems to me, the Hubble mirrors were crafted that way.

Can we do this at home?

https://www.youtube.com/watch?v=9ecyaal7DGs

http://aip.scitation.org/doi/abs/10.1063/1.354431

[Edited on 17-2-2017 by zed]

[Edited on 17-2-2017 by zed]
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[*] posted on 17-2-2017 at 07:06


I plated the inside of a test tube then poured in fiberglass resin so the Ag will be held in place, i'll upload a picture as soon as I get home.
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