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Author: Subject: Electroforming is useful...
BromicAcid
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[*] posted on 9-5-2004 at 17:49
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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[*] posted on 10-5-2004 at 03:52


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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[*] posted on 10-5-2004 at 07:51


How is the powered graphite supposed to stick to the mold if you're gonna dunk it into a solution?



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[*] posted on 10-5-2004 at 07:53


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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[*] posted on 10-5-2004 at 08:38


Strange :o 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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[*] posted on 10-5-2004 at 09:01


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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[*] posted on 10-5-2004 at 09:20


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 :D




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[*] posted on 10-5-2004 at 09:55


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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[*] posted on 10-5-2004 at 13:19


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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[*] posted on 10-5-2004 at 13:34


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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[*] posted on 10-5-2004 at 13:45


Quote:

Have you heard of electroless nickel plating? Take a look at the Hotblack thread at the Miscellaneous forum.


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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[*] posted on 10-5-2004 at 14:11


Silver is (comparatively) cheap. And very malleable. Why not cast it?



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BromicAcid
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[*] posted on 10-5-2004 at 14:37


Quote:

Silver is (comparatively) cheap. And very malleable. Why not cast it?


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. :D




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[*] posted on 10-5-2004 at 15:18


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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[*] posted on 10-5-2004 at 15:28


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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[*] posted on 10-5-2004 at 15:33


Probably. But it will be a very thin layer of Ag.



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[*] posted on 11-5-2004 at 03:28


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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[*] posted on 11-5-2004 at 05:00


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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[*] posted on 11-5-2004 at 05:51


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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[*] posted on 11-5-2004 at 05:55


Really? When we did it at school, we got silver crystals that were very shiny and beautiful :o



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[*] posted on 11-5-2004 at 05:57


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.




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[*] posted on 11-5-2004 at 06:59


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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[*] posted on 11-5-2004 at 09:14


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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[*] posted on 11-5-2004 at 14:05


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...


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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[*] posted on 12-5-2004 at 00:14


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 :P



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