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BromicAcid
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Electroforming is useful...
Electroforming is kind of like a beefed up version of electroplating. The difference being that the coating of metal deposited is significantly
greater then those coating achieved with electroplating.
Examples of useful electroforming to the mad scientist fall almost exclusively into apparatus manufacture. You could carve a retort out of wax then
paint it with electrically conductive paint (although some sources said a dusting of graphite could suffice) then coat that with silver and follow it
up with melting out the wax and viola, a silver retort. You could take a metal pipe endcap and electroform a layer of nickel on it, then pour some
HCl into it and dissolve out the iron and be left with a nickel crucible.
However from what I've read this process is very fickle and can be thrown off by variances in current of less then .2 A and that the coatings can
easily be stressed. I've read that the stress can be relieved by reversing the polarity and dissolving the cathode you are trying to build up
then reversing again and redepositing. Also I've read that the baths for electroforming are very similar to electroplating.
So what I'm getting to is, electroforming is useful and does anyone have any real world experience with it. We're not jewelers here, we do
not need that perfect finished surface, we just need a crucible or other vessel that will not crumble and will hold together. So what kind of power
supply would suffice and what kind of results should one expect from an at home operation. I've found kits to do this but as usual they
are beyond a humble mad scientist's budget.
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Tacho
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I did a small Garfield face (aprox 2x2cm) some years ago. It was after many failed tries. I remember that this one was left for something like a few
days under very small current, in acidic copper sulfate solution. In the end, the front surface (in contact with the conductive surface) was perfect
and beautiful, but the back was very irregular, covered with warts and lumps, but it was quite solid and resistant.
The problem, to me, seems to be the conductive paint. The result above was achieved using some plastic dissolved in acetone and mixed with powdered
graphite. To make the distribution of current more homogeneous, after the first layer of paint, I put some thin copper wires making a mesh, and then
another layer of paint. The existent conductive silver paints (find them at the local electronics hobby shop) are quite expansive.
I painted on a RTV silicone rubber “positive” mold, to be able to detach it and have a detailed “negative” conductive mold I could
electroplate on.
Recently I found out that rubber latex (a white goo, I found mine at a fiberglass supply shop), mixed with graphite, after dry, makes a good
conductive rubber. But my results with electroplating it were frustrating. But then again, ALL my experiments with electroplating are frustrating, so,
if you can already do decent electroplating...
I think the trick to decent electroplating is using cyanide salts, but I don’t want to buy that (dangerous), unless I’m sure it works.
Have you heard of electroless nickel plating? Take a look at the Hotblack thread at the Miscellaneous forum.
Edit: Many sources say that all you have to do is "paint" the mold with powdered graphite to render it conductive. And they mention it as a
trivial thing. Well, I wish luck to those who try. And please, post how you did it, because I could never make it work.
I always used the same powdered graphite I bought years ago, maybe is not the proper one.
[Edited on 10-5-2004 by Tacho]
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Saerynide
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How is the powered graphite supposed to stick to the mold if you're gonna dunk it into a solution?
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Tacho
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| Quote: | Originally posted by Saerynide
How is the powered graphite supposed to stick to the mold if you're gonna dunk it into a solution? |
Exactly!
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Saerynide
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Strange  I guess it might be possible if it was one of those
rubbery/jelly-like molds that stick to any dust/particles it touches and wont let go of them even when dunked in soapy water. Like the material they
use to make those sticky lizards kids throw against walls and they get stuck?
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axehandle
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Hmm. This has some relevance to one of my projects. I was thinking latex goo (the same that's used when making dildos) mixed with graphite.
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chemoleo
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The best one I found for moldmaking is alginate, and gypsum/plaster of paris.
Latex didnt work well at all, i.e. it takes forever to dry, and it becomes milky white if exposed to water for a bit... alginate is happy in water,
though. It doesn't redissolve, plus I am sure it is conductive (consisting 80+ % of H2O).
PS don't u mean condoms? There's a difference 
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Tacho
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I mixed latex goo with graphite to make a pressure-sensitive rubber. The idea was that it's electrical resistance would lower under pressure. It
does, but very irregularly.
A thin layer of my latex goo takes only a couple of hours to dry, but you have to paint many thin layers to have a resistent mold.
Salty alginate with graphite may prove to be good but, as I said, one must first be able to do decent electroplating.
Does anybody know a foolproof method for decent electroplating? Any metal will do!
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Organikum
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These coating methods sound incredible complicated to me.
I would suggest to get some zinc-spray, 99% zinc, at every automobile supply shop and to spray whats to plate. Bronze spray, aluminium spray, I have
even seen plain copper spray with 98% copper there.
Or do I overlook something here?
I remember I have read that cavities are a big probelem with this technique, which can be overcome by certain organic additives which cause a equal
deposition of the metal also in caves and in thicker layers. Forgot the name though, but can look it up if needed.
http://www.finishing.com
(the link is from memory and unchecked)
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axehandle
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If you find silver spray, contact me. I'm trying to make a very glittery piece of jewellry for my GF, based on Ti.
/A
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BromicAcid
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| Quote: |
Have you heard of electroless nickel plating? Take a look at the Hotblack thread at the Miscellaneous forum.
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Yes, electroless nickel plating is good but the entire reason I wanted to do this electroforming was to make a silver retort for anhydrous hydrazine
production.
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axehandle
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Silver is (comparatively) cheap. And very malleable. Why not cast it?
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BromicAcid
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| Quote: |
Silver is (comparatively) cheap. And very malleable. Why not cast it?
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Also quite feasible, hence my U2U conversations with you, but if I had found a simple setup for electroforming the sciencemadness way that would have
been more enticing. Regardless, I'm in no hurry, it would be mostly for bragging rights anyways.
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axehandle
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I see. Well, electroplating is more entizing. Contact a jeweller's supplier and buy some silver cyanide. It works, but I'm afraid
you'll need a Pt or at least a platinized anode.
/A
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BromicAcid
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I thought that I could use a fine silver anode and that would replenish the solution as it took up the silver cations.
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axehandle
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Probably. But it will be a very thin layer of Ag.
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Tacho
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Organikum,
Are you talking about spray paints (cans) or the pure metal spray, done with a special high temperature gun? Most paints do not render conductive
surfaces, although, thinking about it, the zinc ones that claim something like “cold galvanizing” may worth a try, after all, galvanic protection
requires electrons moving from here to there.
Edit: You said somewhere that you were electrolyzing ZnCl and getting Zn metal. How does that metal deposit? Clean and shiny?
Axehandle,
You said the magic word: cyanide. Has anybody tried cyanide salt plating? I have a feeling that’s the easy way to go. But, cyanide is very
poisonous, releases very poisonous gas in acidic solution and so on...
Bromic acid,
I don’t know what's hydrazine, but if it requires pure silver, remember that's very hard to find. I’ve dissolved silver in nitric acid
many times, and the solution is always very blue, due to copper. To obtain pure silver, one way is to precipitate the silver chloride with table salt
and reduce using... using... eh...
I would start with molten NaOH (you know about that, don’t you?), or mix it with fine carbon then blowtorch it in a crucible. I’ve precipitated
the chloride (that's easy), but never reduced it.
[Edited on 11-5-2004 by Tacho]
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Saerynide
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Can you dissolve the silver in nitric acid to get silver nitrate, then stick a copper wire in to reduce the silver ions while creating copper nitrate?
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Tacho
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You can but, in my experiences, the silver deposit is in the form of a very fine loose black powder. In fact, looks like a black ink, mixing in the
solution. It didn't even decant overnight. Colloidal silver?
Eventually the copper ions will start reducing too if you don't use separate cells.
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Saerynide
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Really? When we did it at school, we got silver crystals that were very shiny and beautiful
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vulture
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AgNO3 forms an electric doublelayer with insoluble silver salts, keeping them in suspension. Maybe the same thing happens with Ag?
A large excess of indifferent electrolyte (KNO3, KCl, NaCl, etc) will fix this.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Marvin
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Bromic,
The silver mirror reaction I mentioned for coating the inside of glassware to protect from hydrazine attack (speculation this would work well), would
also work for producing a conductive coating on a non conductive former for producing silver containers. The surfaces need to be totally free of
greese to adhere. Watshed with dilute NaOH and scrubbed. I dont see how for the actual electroforming youd be able to avoid cyanide for a decent
plate though. When I did silver plating it was an everything in fume hood plus a great deal of paranoia job.
If you are willing to keep the current density very very low, something might be possible (eventually) with just silver nitrate, but it wont be good
mechanically.
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Tacho
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Sorry Saerynide,
I realize now that we are talking about two different things: you are talking about getting pure silver by reducing it with copper in the silver
nitrate solution. I've never done that but I've heard it is a common chemical demonstration.
I was talking about electroplating silver from silver nitrate solution. I used graphite electrodes, just to test the principle.
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BromicAcid
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| Quote: |
I don’t know what's hydrazine, but if it requires pure silver, remember that's very hard to find. I’ve dissolved silver in nitric acid
many times, and the solution is always very blue, due to copper. To obtain pure silver, one way is to precipitate the silver chloride with table salt
and reduce using... using... eh...
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I can buy silver ignot at my local jewlers shop for very near market value so fairly easy for mt to aqure. The problem with making anyhydrous
hydrazine that the silver poses the sole solution to is the distillation with a 3x stoichiomentric amount of NaOH or KOH. This mix eats glassware
more then usual and if the retort is made of some metal other then silver it easily catalyzes the explosive decomposition of the hydrazine thus
formed.
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Saerynide
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Oh, I thought you wanted to get pure silver for hydrazine production because the kind you buy isnt pure enough, so I was proposing a way to make pure
silver 
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