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Author Topic: Electro Co-deposition. Rate of Deposition reaction  (Read 806 times)

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bishopraj

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Electro Co-deposition. Rate of Deposition reaction
« on: July 11, 2018, 01:34:46 AM »

I hope to study the co-deposition of metals on mild steel as a means of producing superior anti corrosion surfaces. However, i am at a loss as to how to study the rate of deposition of each of the metals that would be co-deposited (e.g. Zn-Tn-Mg). If i have the ions of these three metals in an electrolytic bath, how would i determine the rate of deposition of each on the metal surface (or rate of disappearance form the bath solution)?.

Any useful suggestion would be appreciated sir.
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Enthalpy

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Re: Electro Co-deposition. Rate of Deposition reaction
« Reply #1 on: July 13, 2018, 01:45:23 AM »

A typical anticorrosion layer is thin, like 10 to 100┬Ám, so its deposition alters very little the composition of the bath, and the current and the mass losses at the counter-electrodes won't represent the deposited composition neither. I can imagine only to analyse the deposited layer.

Is Mg useful in an anticorrosion layer? Up to now, I've seen a protection only by elements that are themselves resistant to corrosion, like Cr, Al, Zn, Ni and others, but not Mg. I also suspect Mg is badly difficult to deposit electrochemically, especially from an aqueous solution.

And what do you call Tn? Is it Sn?

You might also want to decide if the metal layer shall resist corrosion by its redox potential, like Au does, or by its oxide layer, like Cr does. I haven't seen a deposited layer containing both up to now.

An other limit to electrolytic co-deposition is that the redox potentials of the elements (that's written too shortly) must not differ too much. Co and Ni yes, Cu and Sn yes, but Zn and Sn I doubt.
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Arkcon

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Re: Electro Co-deposition. Rate of Deposition reaction
« Reply #2 on: July 13, 2018, 04:11:26 AM »

When I worked at the plating bath company, a number of other metal, or metaloid ions were used in cobalt or chromium plating baths, as examples.  Such things would plate out as inclusions and would be analyzed by scanning electron microscope.  Any plating bath company should have access to an SEM to study crystal growth of samples, and perform other tests that I don't really understand.

If you want to make a superior surface coating, without this equipment and expertise, say, in a home lab, then I really don't know how to help.  Query: how will you analyze your bath depletion?  ICP-MS?  Ion chromatography?  Are you considering wet chemistry techniques?  Because you won't out perform any modern company that way.
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bishopraj

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Re: Electro Co-deposition. Rate of Deposition reaction
« Reply #3 on: July 15, 2018, 11:01:37 PM »

Thanks for your answers, observations and questions. I am aware that the layer would be thin and may have close to an insignificant effect on the concentration of the bath. However, i am interested in the Kinetics of the deposition process, in a Bath containing 3 major Cations (lets say Zn, Si and Tn), under normal electrolysis, you would expect that one of the metals would be deposited preferentially. But, literature reports that all three are co deposited (of course in the presence of boosters, and bath agitators). I still feel, the metals would not be deposited equally as their potential, and perhaps valency would have a say on the quantitative and qualitative deposition experienced.

Now, how to i measure the rate of deposition in the bath? this seems to be my question.
Are the assertions made above correct? Any twist or help?

really appreciate.
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Enthalpy

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Re: Electro Co-deposition. Rate of Deposition reaction
« Reply #4 on: July 16, 2018, 08:00:38 AM »

If the redox potentials of the metals (I formulate it incorrectly) are close enough and the current density big enough, you can hope to deposit several metals at the same time. Beware that a big current density make a rough layer.

But if the current density is small, or sometimes with no current at all, only the most noble metal deposits. This is how some metals are refined, notably Cu.

I don't understand your example. What is Tn? And if the electrolyte is aqueous, what kind of silicon compound do you hope to use, and why should silicon deposit? A silicon compound that dissolves in water without reacting isn't common.

To know the deposition speed, analyse the deposited film.
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