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Author: Subject: Electrodeposition How-To
elementcollector1
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[*] posted on 8-7-2012 at 18:36
Electrodeposition How-To


How do I electroplate metals out of solution with good results? I.e., shiny, good-sized 'plates' of metal?

I would like to plate chromium out of a Cr(VI) compound (sodium chromate) or a Cr(III) compound (probably chromium chloride), but a good how-to on what current, voltage to typically use would be nice for a general understanding.

From my experience, using a lot of voltage / amperage (12V/2 or 6A) has led to badly formed plates, which are almost never shiny or solid.

This has been the case for manganese (which is supposed to be hard to plate anyway, but they have to produce it somehow) and chromium (which strangely formed white crystals on the penny I tried to plate it on).

I know manganese plating requires some special conditions to work (mainly a tin-lead anode and a very cold temperature), but I still have not had much success with these darned transition metals.

Any advice?




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dann2
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[*] posted on 9-7-2012 at 05:46



Try downloading 'The Electroplaters manual'. There are a large variety of solutions/conditions that can be followed. Some metals cannot (as you probably know) be plated out.

One of my pet projects (it will never be done) is to plate Tantalum onto a steel vessel. A tantalum lined cauldron, hows that. It can be done from molten Tantalum Chloride AFAIK.
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elementcollector1
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[*] posted on 9-7-2012 at 08:54


Where do I find this manual?



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dann2
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[*] posted on 9-7-2012 at 09:51


Hear's some link's to get you started. I'm sure there are many's more's to get you started. ;)


http://archive.org/details/practicalelectro00bedeuoft

http://archive.org/details/polishingandpla00hawkgoog

http://4megaupload.com/electroplating-engineering-handbook-f...


The last type of link can be somewhat fustrating and they sometimes don't work.
Make sure you are not downloading some piece of software that the (bugger's) want you to download when you think you are downloading the book.


In the meantime you can read up on Ta plating (say Ta Ta) as there is some reading attached.
A Ta lined Fe Cauldron would be a big hit around here!
(THAT'S A CAPITOL c FOR cAULDRON!!!)

Dann2

Attachment: Tantalum Plating_smaller.pdf (1.1MB)
This file has been downloaded 901 times

[Edited on 9-7-2012 by dann2]
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elementcollector1
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[*] posted on 9-7-2012 at 16:29


These look useful for setup, but the only stuff I found about voltage was a battery labeled 1.9V, and a large amount of amps. So, does low-volts, high-amps give best results? If so, how do I modify my 12V, 6A car-battery charger to output at this level?

Furthermore, what are simple, ideal plating formulas for different metals? I know ammonium chloride, sulfuric acid, and others are included (for reasons yet unknown).




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[*] posted on 10-7-2012 at 08:49



Try here for more books.
http://www.en.bookfi.org/s/?q=electroplating&t=0

If using a car battery you need to put a resistor in series to keep current to sensible levels (or to put it another way) or to drop the voltage so that you only have low voltage accross you electroplating cell.
Look up Faradays law, Ohms law etc.

Basic primer on electricity here

http://www.oxidizing.110mb.com/chlorate/runtime.html

Don't start obsessing over the 'voltage required' to do the job. You do of course need a certain voltage to get the current to flow.
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elementcollector1
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[*] posted on 10-7-2012 at 22:35


Hmm... I'm getting my calculations all wrong. If I used 2 amps, that translates to how many coulombs?



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[*] posted on 11-7-2012 at 00:45


That's 2 coulombs/second, 120 coulombs per minute, 7200 coulombs/hour.

The concentrations of chemicals in your electrolyte determine the voltage you require to a point. Try source a variable power supply and work from say 1V upwards until you are achieving good results.
In some instances it would help to first plate on another metal such as copper or nickel before your intended metal (Cr). This would help with the integrity of your final plate. In most instances 'brighteners', which are manufacturer protected formulations, are added to obtain the desired reflective surface finish. Search for 'brighteners' and 'cyanide plating solution' on this site and elsewhere and you'll find some pointers. Look for data on temperatures, eg copper bath needs to be cool and a nickel bath needs to be hot.

There are so many factors effecting your setup it could take you hours and still not achieve the desired result.

Just in case you are not aware of the carcenogenic nature of Cr(VI) compounds please be careful.




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[*] posted on 11-7-2012 at 15:41


I am well aware of the dangers of hex-chrome, thanks.
How to get a good, cheap, thick plate then? Probably add acid (like HCl) to increase electrical conductivity...

EDIT: Trying a mix of sodium chromate and impure HCl, 3 volts (2 fat alkalines hooked together), can't remember the current, etc. Will see if I get anything shiny tomorrow.

EDIT #2: Shiny! :D

[Edited on 12-7-2012 by elementcollector1]

[Edited on 12-7-2012 by elementcollector1]




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[*] posted on 13-7-2012 at 02:17


Instead of using HCl,It is feasible to work with H2So4.



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[*] posted on 13-7-2012 at 07:04


I would, but the stuff's hard to buy around here. I guess I could electrolyze magnesium sulfate...



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[*] posted on 10-9-2012 at 21:24


Quote: Originally posted by froot  


Just in case you are not aware of the carcenogenic nature of Cr(VI) compounds please be careful.


Seriously? I always end up with orange hands when dealing with Cr VI!!!! Is that really really dangerous?

I heard useing cyanides are good for electroplating purposes because it deposits evenly and at the same time the leftover anions won't corrode the newly formed plate much often.
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[*] posted on 11-9-2012 at 07:21


Um... yes? You do wash your hands after, right? If not, INCOMING CANCER.
Cyanides are good for electroplating, but they are also heavily toxic (and the symptoms of the corpse are not pretty). For chlorides, ammonium chloride is a good anolyte component.




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[*] posted on 6-10-2012 at 18:31


Sorry to revive this, but after quite a bit of research and reading, I still can't understand what is needed for a firm, thick, easily removable plate of metal.

For manganese (because I'm still stuck on that, and want a backup plan in case thermite really fails), I understand a cold solution is needed to stop the manganese from reacting severely with water, and a lead-tin anode is needed to prevent MnO2 forming on the anode (and thus wasting available manganese).
Other helping agents are acids (can I add sulfuric acid in small amounts to the anolyte of manganese chloride and the anode of lead-tin without causing too many unfavorable side-reactions?), ammonium chloride (wastes ammonia and hydrochloric to make).

How does concentration of the aqueous salt affect electrical needs and overall performance?
Why do my manganese coats appear to "burn" (oxidize, blacken) when the current and voltage are increased in the cell?
How do I prevent this?

So many questions...

[Edited on 7-10-2012 by elementcollector1]




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[*] posted on 6-10-2012 at 19:21


Are you sure that the manganese "burns" when the current and voltage are increased?

It may simply be that the texture of the depositing crystals is changing. I remember playing around with reclaiming bismuth metal through electrolysis, and I'd get this dark gray, spongy-fuzzy material that looked nothing like bismuth. However, hit it with a torch, and it would melt into beautifully shiny, pure bismuth metal. Thus, it seems it was just the extremely fine texture of the crystals that made it look dark.

I've noticed the same thing with grinding up metals. The smaller the particles, the more black they look. I've always wondered what that was about. Something to do with trapping light in the high number of crystal faces, maybe.

Anyway, go look for NurdRage's video on electrodeposition of silver from silver nitrate solution. He demonstrates the effects of changing concentration and current on crystal growth and texture.

Edit: Here's the video: http://youtu.be/fnyBldC4Ra4

[Edited on 10/7/2012 by Sublimatus]
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[*] posted on 7-10-2012 at 03:47


Quote: Originally posted by elementcollector1  
Why do my manganese coats appear to "burn" (oxidize, blacken) when the current and voltage are increased in the cell?
How do I prevent this?


if you can see gas bubbling at the cathode, then the current is definitely too high. usually each type of electroplating bath has max current per surface area, beyond which the results become very poor. don't sacrifice quality for speed. slow and steady wins the race =)

i don't know about manganese, but i had the same problem with copper and nickel. industrially, 'brighteners' (usually organic compounds) are used in order to obtain a smooth surface. make sure the cathode substrate is compatible with Mn.

you can also try brush plating, saves on amount of solution, although the throughput is very small, but it gives you a Mn base on which to plate a thicker layer.
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[*] posted on 7-10-2012 at 09:35


I'm pretty sure it is 'burning', although from what I know now, you may be right about that crystalline light refraction. Of course, I can't exactly melt any manganese produced to check...

I'm planning to do a bright, shiny 'strike' of Mn using a 9V battery, and then move on to more powerful stuff.
The cathode I'm using is carbon, to limit current and voltage on the cathode (one HUGE resistor).

That gas bubbling is a good rule of thumb, thanks! Two half-cells for electrolysis should further limit current and voltage, correct?

Watched NurdRage's video (always good), and determined that he was using a 6-volt power supply with a 470-ohm resistor to limit current. Also, if the current goes slowly in a saturated solution, the crystals are larger, with probably better adherence to the cathode, whereas if the current is faster, with no limitations, the crystals are small (and in Mn's case, probably badly oxidised). I'm thinking of placing a running ice-water bath around the cell, so as to lower temperature and limit the reaction between Mn and water.

Brush plating would be good for the initial 'strike' deposit, but I don't think I'd want to set up all that just for the initial layer which is only a few atoms thick. Thanks anyway.

You know, I've ground up aluminum and magnesium and experienced the same phenomena. Initially they stay shiny, but over time as the particles get finer they turn dark gray. I always assumed that was the layer of aluminum or magnesium oxide at work...




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[*] posted on 7-10-2012 at 11:06


It happens with bismuth too. Grind it small enough and it looks nearly black. I think this is due to particle size, rather than a chemical reaction, seeing as bismuth doesn't oxidize at any appreciable rate under standard conditions.

Is this the same dark color you see with your manganese?
http://en.wikipedia.org/wiki/File:Manganese_electrolytic_and...
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[*] posted on 8-10-2012 at 15:36


...Sort of. I don't think I let it go quite that far.
Well, I'm waiting until I can get some better equipment (a water-circulating tank, etc.). What would be a good metal for a flat cathode to plate this onto? I have cobalt and copper available as flat surfaces. (the cobalt, in a twist of irony (cobalty?) was electrowon from solution.)




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[*] posted on 5-11-2012 at 22:08


Again, necrosis powers!
Anyway, I think I'll actually try to make an official plating tank, instead of a beaker setup. Also, I've learned that:
1) Cathode and anode need to have roughly the same area.
2) Cathode and anode need to be very far apart, to the point where there is no bubbling on either of the electrodes.
3) The manganese cell, of course, still needs to be water-cooled for higher (ish) efficiency.

My end-goal (if all goes miraculously right):
http://upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Man...

or

http://unitednuclear.com/index.php?main_page=product_info&am...

(Terrible at uploading photos or embedding images. Sorry...)

[Edited on 6-11-2012 by elementcollector1]




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