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Offline dlt

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Zink plating
« on: December 11, 2007, 03:06:17 PM »
Hi,

I would like to try to zink plate some (iron) stuff that i fabricate for rust protection. I have read the page http://members.tripod.com/cb750k2/Technical/plating.html but doesnt really understand the chemistry involved. I have used electrolysis for rust removal which works fine and I understand it in terms of the reactions and voltage needed and would like to understand this as well.

The method involves dipping the part to be plated in NH4Cl + ZnCl (aq) and use a Zn-Anode. What part does the salts have in the reaction, are they only catalysts, current carrier or do they actually react?
With rust removal a voltage of 1.5V is enough to crack the solid FeO to bits and everything above will only create H2+O2, is there any threshold like that in this reaction?

Also, since I dont have any of the salts, would it be enough for me to buy NH3, HCl and a lump of Zn to create the salts in my bog standard garage, or will i die of toxic fumes? :-)

Second also - I have also found that you can use (NH4)2SO4 + ZnSO4 + NH4Cl as salts in the liquid doing the same thing. What is the difference?

Tnx / daniel

Offline Arkcon

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Re: Zink plating
« Reply #1 on: December 11, 2007, 04:58:42 PM »
Hi,

I would like to try to zink plate some (iron) stuff that i fabricate for rust protection. I have read the page http://members.tripod.com/cb750k2/Technical/plating.html but doesnt really understand the chemistry involved.

With you so far ...

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I have used electrolysis for rust removal which works fine and I understand it in terms of the reactions and voltage needed and would like to understand this as well.

Good.  That makes this simpler.

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The method involves dipping the part to be plated in NH4Cl + ZnCl (aq) and use a Zn-Anode. What part does the salts have in the reaction, are they only catalysts, current carrier or do they actually react?

Yes, yes and yes.  Zinc plates out on the cathode, from the zinc salts in solution, and the zinc salts in solution are replenished by dissolving the zinc anode.  The salts conduct the current, and complex the Zn ions, so the plating occurs slowly, with a smooth finish.  The particular salts, and their concentration are as important as correct wattage and surface area.  Irregular shapes of your cathode may pose problems.

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With rust removal a voltage of 1.5V is enough to crack the solid FeO to bits and everything above will only create H2+O2, is there any threshold like that in this reaction?

More careful control of wattage is important to get a smooth plating.  Notice I've said wattage twice already, the amperage is as important as the voltage, as the site you quoted indicates.

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Also, since I dont have any of the salts, would it be enough for me to buy NH3, HCl and a lump of Zn to create the salts in my bog standard garage, or will i die of toxic fumes? :-)

Toxic fumes are very likely, you should avoid trying to make these chemicals .  I can't guarantee you won't die if you avoid random chemical mixing, there are too many other variables.  :D

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Second also - I have also found that you can use (NH4)2SO4 + ZnSO4 + NH4Cl as salts in the liquid doing the same thing. What is the difference?

Yes, without the zinc anode, the plating bath gradually depletes itself.  This is OK for small items.

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Tnx / daniel


Seek out a better reference, a suitably thick book at the local library for instance.  You probably won't want to read a large technical manual, but you need to see how complicated this can get, so you'll appreciate how difficult your plan for home-grown zinc electroplating is going to be.

[EDIT] missed one misspell
« Last Edit: December 11, 2007, 07:01:12 PM by Arkcon »
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline dlt

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Re: Zink plating
« Reply #2 on: December 11, 2007, 05:53:24 PM »
Tnx for a  good answer Arkcon.

Now I'm a stubborn geek that doesnt give up easily without technical understanding and proof (or maybe hard convincing). Please give me more views of this, preferrable with some nice formulas and such. The ions traversing the salts i understand, them hooking up on the cathode, but what difference does the different contentrations or even ingredients of the salt make? Only speaking of ion travelling ordinary NaCl would do the job, right?

Is the salt only interesting in a cleaning matter? Will the salt actually stick to the plating making it less than 100% Zn? I guess in that case the plating with NaCl would be pretty dirty, but it would still conduct? If thats the case, why not use 100% ZnCl in the bath, not bothering with the ammoniac chloride?

I clearly understand that the wattage might be a factor, especially if the cathode is of funny shape, but is it just a factor of time? If i use very low wattage and very long time it ought to be pretty nice, since the inner resistance of the bath wont be "saturated"? Do you follow me?

What title should I look for regarding this? As you can see I'm eager for info, and I grattitude everyone trying to help me with an imagined cup of coffee...

About the toxic fumes, where do they come from? I was thinking about NH3 + HCl -> NH4Cl and HCl + Zn -> ZnCl + H2. Never heard anyone dying from H2, unless exploding. Maybe you are thinking of HCl + Zn + stuck paint + grease on the Zn-blob -> ZnCl + H2 + VeryDeadlyGasFromThePaintAndGrease?

/ daniel

Offline Arkcon

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Re: Zink plating
« Reply #3 on: December 11, 2007, 07:34:53 PM »
Plating people have experimentally determined that the addition of the appropriate concentration of ammonium chloride is needed for proper zinc plating.  Following the recipe carefully is an important first step, you can make slight changes later if you feel like reinventing the square wheel, just to prove it doesn't roll. ;)

Controlled wattage is a prerequisite for proper plating.  But it isn't the entire answer.  I previously worked for a plating bath company, and a plating assay was one (ancient and now mostly superseded) quality control technique.  A carefully polished, flat, clean, piece of metal, immersed in an acid copper solution, held at a fixed wattage, will produce a bad plating of copper.  That's not a joke.  We wanted a sample to produce a bad plating, not terrible or flaking off in chunks, or not plating out at all, prior to shipment.  We knew that, to achieve a proper metal plating, the end user would add an abundance of organic modifiers.  You're lucky to have found an online source for zinc plating solution that is so simple.

Regarding the toxicity:  HCl produces a toxic vapor, as soon as you open the jug.  It reacts with pure ammonia (where're going to get that, clear household ammonia has detergent added) so rapidly, that it happens in the air above the respective jugs, producing a white smoke of NH4Cl crystals.  You shouldn't breathe those.  When you drop the zinc into the HCl, the bubbling hydrogen will spray the HCl out, so you'll have to watch that.  By the way, you're sure there's no open flames in the vicinity, right?  Having mixed the chemicals, you'll have to dry that to crystals so you can weigh them (you already own an accurate gram balance, right?  No point in starting to follow a recipe you can't do accurately.)  Anyhow, how will you dry them?  Hot plate or oven?  There will likely be an excess of one reactant or another, so something HCL, or ammonia, so those fumes will be present.  A little tip, NH4Cl sublimes (look it up) so you wont want to heat it to dryness -- even though you'll need it dry in order to weigh it accurately. 

You see, you mentioned the "bog standard garage", not the laboratory with fume hood or even the well ventilated work shed.  So I'm letting you know what you're in for. 

If I had to plate something homemade with zinc, I'd dip it in molten zinc.  At least there's fewer variables.

You asked if the impurities will stick.  That is correct, if the recipe is wrong, or the wattage is wrong, or the temperature is wrong, you will get inclusions.  Likewise if you use bog standard "drugstore grade" chemicals, instead of plating bath grade chemicals.  A textbook on plating chemistry will help you learn what to expect.  It's not at all uncommon for people to take this up as a hobby, there's a lot to learn, and it must be satisfying to achieve it yourself.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline 2beakers

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Re: Zink plating
« Reply #4 on: December 18, 2007, 10:42:56 AM »
Just found the forum and am interested in Zn plating. 

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I was thinking about NH3 + HCl -> NH4Cl and HCl + Zn -> ZnCl + H2. Never heard anyone dying from H2, unless exploding.

Can you not just buy the NH4Cl? 

http://cgi.ebay.com/Ammonium-Chloride-99-to-99-5-One-Pound_W0QQitemZ270197445221QQihZ017QQcategoryZ104233QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


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