lahthffire
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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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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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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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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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Twospoons
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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.
Helicopter: "helico" -> spiral, "pter" -> with wings
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triphenylphosphineoxide
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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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Thanks for the responses. I'll give it a try later this week or next and report back.
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mick
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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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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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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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Twospoons
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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]
Helicopter: "helico" -> spiral, "pter" -> with wings
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The Freak
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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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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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blogfast25
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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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The Freak
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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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cyanureeves
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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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AndersHoveland
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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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Jacob_Shin
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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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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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Chlorine
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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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