June 15, 2024, 06:46:58 AM
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Topic: ?'s on silver and copper plating non-metallic items, and home distilling HNO3  (Read 31425 times)

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Offline jonogt

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Hi everyone,

          This is my first post on here and I read the forum rules, but if I violate something just lemme know.  I'm a soph in college majoring in engineering, but I have underlying passion for chem and functional art on the side. Lately I've been trying to find a way to copper and silver plate non metallic items for an effect of embedded metal.  Woodwork in particular is what I want to do this with right now.  The common procedure that I've heard and read some online about is

Cu(s) + 2AgNO3(aq) ---> Cu(NO3)2(aq) + 2Ag(s)

          I'm fuzzy on the exact science behind reduction/oxidation reactions, but I think I get the more macro principle:  Copper metal is higher on the reactivity series, so when in contact with AgNO3 solution it forms Cu+ ions which displace the Ag+ ions, precipitating silver metal out, taking the copper's place as the solid, which can occur as a surface layer are right.  No electricity needed; just uses higher reactivity.  Is that all correct?

          I took a metalsmithing class last year before I transfered schools, and we had crockpots filled with aqueous acid at ~140F.  I don't know exactly what the acid solution was that they used in that class, but from reading online I don't think there's a single magic recipe. Sparex might have been it... http://tinyurl.com/2thrtt ...I'm not certain, but I know it was a granulated compound that you just mixed in with water. I can't find much info on what exactly this acid is. Can anyone speculate? The main selling point seems to be that it's a safe alternative to H2SO4.

          After torch soldering your piece, you put it in this bath and the acid removed the mess of oxidation, flux, and any impurity deposits from the torch etc, leaving you with a slightly rough but elementally clean surface. The big common use one was so loaded up with copper ions that any metal workpiece (from what I saw and remember atleast) you put in it would grow that same layer of textured pink copper.

       ^ This incessant copper coating is what I what I think I need to recreate for the nonmetallic surface dillema.  In class we worked with plain copper, brass (copper, zinc), sterling silver (copper, fine silver), nickel silver (copper, nickel, sometimes zinc), and occasionally steel.  zinc nickel and iron all have higher reactivities than copper so it makes sense that they grow a layer, but why does the copper and sterling silver do it as well (fine silver reactivity < copper reactivity)?  shouldn't they be essentially stable in such a solution?  Is it reacting with the film of copper oxide that inherently forms when copper sets in air, and this lets it precip out enough Cu+ ions to give the same appearance?

          My TA (has no interest in actually teaching; very frustrating) said you can get or make something that can be painted onto non conductive items that will allow them to be plated in this manner, but I couldn't get anymore info out of him.  Since I'm applying it to wood it needs to be something that can work into the wood grain and be basically flush, not a paste that would need gobbing on.

          Correct me if I'm wrong: I basically need to get something of higher reactivity than copper into the target area, firmly deposited such that it's not going to just get washed out when immersed in the ionized acid bath?  Rough up the wood grain, then spray/brush a mild adhesive solution into the target area, either followed by the powdered reactive metal, with said metal in suspension with the adhesive, or both. I have flake aluminum powder around my house somewhere, but it's been temporarily misplaced.  Would iron oxide powder work, or will the oxide ion give me trouble?  What kind of adhesive would be good to use here that will keep the powder from washing out, but will also be porous and penetrable enough to let the reaction take place?  If I can get a powder caked into the grain and redoxed without washing out, I would think the copper would precipitate in its place with a more interlocked and crystalized structure.  Does that sound reasonable?

          After the copper gets plated on like so, then I'd go and basically repeat it with the AgNO3 solution to now replace the copper with silver.  I'd insulate the rest of the wood that wasn't being plated so it wasn't pointlessly exposed to acid each time.  I'm mainly wanting to do this for goblets and bowls that I turn on the lathe I'm getting soon, so after the target area is plated, I'll just stick it back on the machine and refinish it to remove the insulation and generally clean it up.

          So that's what I've gathered on this topic so far, for what it's worth.  Does anyone have a better idea for the base reactant isntead of trying to glue powdered metal in there?  I'd imagine there is something better, but I don't know what it is.  In my class they showed us a big electroplating machine that upper level classes use, where you could copper plate pretty much anything.  They had some wild flowers flawlessly plated as examples.  I don't have any access to a machine like this, but if I can get higher quality results and more efficient operation with an electrical setup, I could give it a try with a big battery and a lab beaker.  The items I'm wanting to plate are small enough that I could easily find a suitable container to do it in. 
          What would be the best acids for me to use?  The Sparex stuff  we had in class probably isn't the prime one to use for the intention of plating things in copper, or does it even really matter?  Can I substitute something for nitric acid for the AgNO3 solution?  I don't really have a good source for nitric acid, but I have ammonium nitrate and sulfuric acid, so I can theoretically distill it in my friend's retort. Problem is the sulfuric acid is the low quality stuff from the hardware store, "drain opener", and it's about 95% H2SO4, but it has 12 buffers that they add to keep it from damaging pipes. Does anyone know what these are, and will they compromise the quality of my HNO3 yield?

          Anything else anyone can offer I would much appreciate

           Thanks for any help
           -Jon

Offline Borek

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You are more or less correct, although some details are wrong (it'll be Cu2+, not Cu+).

Apart from using electrolytical methods you may look for alternative - I have seen (on Discovery channel?) program about a man who patended something giving similar effects. It was something like a paint, that could be polished after drying. I suppose it was some mixture of epoxy resin and metal filings, but I can't remember neither man name nor product name. He was showing his product at some inventors show in UK - if I recall correctly.
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Offline hmx9123

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You may want to check out the computer industry.  Specifically circuit board manufacture.  Circuit boards are dipped into a tin bath, or perhaps it's tin spots on a circuit board are dipped into a different bath (it's something to do with tin), and the metal is exchanged in a useful manner.  Those green circuit boards aren't conductive, so that may help.  Wood is a much larger problem because it is porous.

Also, beware that plating out silver from copper solution will probably give you the black form of elemental silver, not a nice shiny coating like you're probably hoping for.  You may want to look into very thin metal sheeting, or perhaps even using your medium as a target in a sputtering application, if that's feasible.

Offline Borek

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You may want to check out the computer industry.  Specifically circuit board manufacture.  Circuit boards are dipped into a tin bath, or perhaps it's tin spots on a circuit board are dipped into a different bath (it's something to do with tin), and the metal is exchanged in a useful manner.

I can be wrong but I think they are covered with copper foil first - then etched. Using tin soldering alloy is some later step, done when copper tracks are already in place. At least that's how it works for small scale manufacturing.
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Offline jonogt

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Cu2+, my bad  ;D  thanks Borek

HMX,

I have heard of the problem sometimes encountered with the black silver... what is the chemical difference in it?  Unwanted particles from the air and such getting into the reaction? 

I was concluding that this would work out for this specific procedure from a blurb on United Nuclear's product listing of dry powdered AgNO3.  One of the experiments it mentioned that's interesting is if you leave a piece of copper wire in its solution undisturbed for several hours, it will grow an intricate tree of crystalized silver branching off from the wire.  Does this not actually work?

what exactly do you mean by a sputtering application?  I don't think I'm familiar with that context.

I'm gonna be stubborn and refuse to try metal sheeting, because if I can get a process down, I want to do the same thing in more complicated engravings and such, like with a dremel tool.

The idea of using tin is good though!  It slipped my mind what a low melting temp it has for a metal.  Still might be a bit of a stretch for wood though, trying to find the middle ground to get it deposited while still liquid, and not scorching the wood.  Are any of those metals with weirdly low melting temps higher in reactivity than copper?  Something around 100C would be ideal I think.


If anyone comes across what that paint-on material is that the guy patented for electroplating, I'll be forever greatful for a link or a name   :)  Sounds like a much better alternative to my current plans of action.


thanks for the help guys,
-Jon

Offline Borek

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I have heard of the problem sometimes encountered with the black silver... what is the chemical difference in it?  Unwanted particles from the air and such getting into the reaction?

In both cases you have metallic silver, just it is either in the form of fine powder (that looks black) or in the form of flat plating (that looks lustrous).
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Offline jonogt

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Okay I see what you mean now.  So the concern would be whether the silver would precipitate as a cohesive layer or if it'd just be a soggy powdery mess.

I'm not a pro on the topic or anything, but I think just giving it time to sit without any movement is the key for most things like this.  I used to have one of those Smithsonian crystal growing kits when I was little; the things where you mix up a solution and suspend rocks and such in it and they grow crystals over a week or so.  They always worked a lot better when I set it up before we went out of town, because if I was home I'd always get ADHD and go screw around with it  ;D  Hopefully something like this wouldn't take that long.  I only need a tiny layer of metal, not crystals big around as your pinky.

As long as it grows atleast decently cohesive, even if its rough, I have all shapes and sizes and materials of wire brush to clean it up with.  I'm leaning toward trying the epoxy resin saturated with metal filings.  It should hold the pieces in place well, and protect the wood to a degree so the grain doesn't raise and splinter a lot from being in moisture and acidity.

Any thoughts on what acids to use?  Can I use HCl for the copper part?  Nitric seems to be what people use for silver, so if I get everything I need I'll probably try my hand at distilling some.  Are the lead-acid battery top-off products that you can get at auto parts stores very pure?  It's 35% sulfuric by volume and the rest is water, so it's substantially weaker, but I can't find anything about it containing "buffers" like the drain opener solutions do.  Is there any reason other than inconvenience to not distill it from these weaker solutions?

Only one more day of classes after this and I'll be home for thanksgiving.  Unless there are some underlying hazards with trying to do this that can't be avoided with normal lab precaution, I'll probably try some small scale test pieces.

thanks for the helps
-Jon

Offline Borek

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I think just giving it time to sit without any movement is the key for most things like this.

Just keeping it still is not enough. See http://en.wikipedia.org/wiki/Nucleation - if the process is too fast you may get many small crystals, if the process is slow enough, you will get less but larger ones. There are many effects playing their roles here.

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As long as it grows atleast decently cohesive, even if its rough, I have all shapes and sizes and materials of wire brush to clean it up with.

Layer created by electrolysis can be thick enough for further polishing. Layer created just by replacement reaction is so thin (around monoatomic) it will be destroyed when you touch it.
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Offline hmx9123

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http://en.wikipedia.org/wiki/Sputtering

You'd need some specialized apparatus for it, but it can be done.

Offline billnotgatez

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I Googled -making circuit boards from scratch-
There are probably better sites and a better combination of words to get a better search


http://www.everything2.com/index.pl?node_id=1164175

They used to put silver on glass for photography - I can see why you get the black color

http://en.wikipedia.org/wiki/Collodion_process


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Just use conductive silver on billboard, you can make all the circuit boards you want that way. Or let go of $10 at radioshack and get yourself a nice breadboard to screw around on.
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Offline jonogt

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Sorry I've not been back here to post a reply the last few days.

You're right Borek; I suppose the process I was analogizing to doesn't really apply very well; I want replacement, not simple deposition. 

A site I was reading noted that Copper doesn't react with HCl as it's non-oxidizing, but H2SO4 will with heat applied.  Does anyone know if the sulfuric acid available for topping off car batteries is reasonable to use for this?  Is it clean?

If I succeed at epoxying a ground metal to the wood, my procedure for a basic electroplate would be to attach my (-) lead to the piece i want plated, and the positive side to a piece of solid copper immersed in the solution?
I know that in any electrical application, the current is going to flow in the path of least resistance, and the resistance is going to increase the farther away the area is from where I connect the lead.  Any idea if this difference will be enough to cause a problem with the evenness of the plate? 

To get a stable build of crystals doing this, wouldn't my challenge would be finding the right combination of molarity and current to pace the reaction for even and metallic finish?

Offline Borek

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A site I was reading noted that Copper doesn't react with HCl as it's non-oxidizing, but H2SO4 will with heat applied.  Does anyone know if the sulfuric acid available for topping off car batteries is reasonable to use for this?  Is it clean?

I am almost sure it is clean enough, however, for dissolving copper I would rather go for nitric acid. You may also consider hydrogen peroxide and hydrochloric acid, although I am not sure about details (for sure it was H2O2 in low pH). Hot sulfuric acid - when reasonable alternatives exist - is not on my list of favorite reagents.

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If I succeed at epoxying a ground metal to the wood, my procedure for a basic electroplate would be to attach my (-) lead to the piece i want plated, and the positive side to a piece of solid copper immersed in the solution?

Yep. But if you will connect it wrong you will be aware of the fact immediately.

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I know that in any electrical application, the current is going to flow in the path of least resistance, and the resistance is going to increase the farther away the area is from where I connect the lead.  Any idea if this difference will be enough to cause a problem with the evenness of the plate?

Could be. Mixing and slowly moving plated object will help.

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To get a stable build of crystals doing this, wouldn't my challenge would be finding the right combination of molarity and current to pace the reaction for even and metallic finish?

Exactly. But I believe these things must be covered in textbooks - concentration and current density are very basic parameters here, so you should be able to find them.
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Offline jonogt

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Thanks a lot for the help.  I'm really more interested now in just experimenting with this process and basic applications than going straight to my woodwork. 

Nitric acid for copper I can go with; Is it reasonable to distill that myself with the H2SO4 and NH4NO3 like I mentioned earlier, rather than buying it?  It's pretty expensive around here and you have a HAZMAT charge on top of the intial cost, not to mention I'd like the experience of doing it.  What kind of concentrations do you suppose I could expect yielding from a basic retort setup?  50% if I'm careful?

What is the reaction between H2O2, HCl, and Cu?  I can't find any concrete info about it, and neither of these attack copper separately, but a video I found shows they certainly react... to a green (aq) solution?  In the mean time I'm gonna go try it for myself  :)

Offline Borek

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No idea about nitric acid...

What is the reaction between H2O2, HCl, and Cu?  I can't find any concrete info about it, and neither of these attack copper separately, but a video I found shows they certainly react... to a green (aq) solution?  In the mean time I'm gonna go try it for myself  :)

Something like:

Cu + 2H+ + H2O2 -> Cu2+ + 2H2O
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