Letter 22034

Consumption of nickel anodes  

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Hi

I have watt's nickel tank and my question is: the rate of nickel anodes consumption is very high so how i can control the rate of nickel anodes consumption . and what the optimum rate of consumption g/m2 of nickel anodes.

Thanks,

Aly Gomaa
Universal Co. - Giza, Cairo, Egypt

Mr. Gomaa,

Unless something is very unusual with your nickel plating process, all of the nickel that dissolves from the anodes goes on to the parts. So you need to approach it from the other direction, i.e., you have to decide how thick the nickel plating must be. Then however much nickel you plate is how much nickel anode you will consume.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Hi sir,

First I knew when the nickel anodes is dissolves the nickels ions is go to the cathodic parts. But you do not understand what I mean the rate of nickel anodes dissolve is very high which increase the nickel content in solution over the optimum point and decrease the area of anodes compare to the area of the cathodic parts. There is no equilibrium between the nickel consumption by parets area and anodes dissolve so I tend to add new anodes to adjust the ration of area between anode and cathode. So may be if the PH need to adjust or the brighteners need adjust too. But I need first the optimum rate of anodes consumption with thick 15 micro at current density 5 amp/dm2 finally.

Thanks,

Aly Gomaa
Universal Co. - Giza, Cairo, Egypt

Hi,

I'm with Ted on this one. The rate of anode dissolution is determined by Faraday's law, same as the rate of nickel plating. Anode current efficiency can be calculated the same as cathode current efficiency (actual weight dissolved/weight predicted by Faraday's law).

The pH etc has very little to do with the rate of anode dissolution. The corrosion of nickel in an anode basket is electrolytic, not chemical. One caveat to all of this. If, for some reason, your nickel is not corroding properly, you may be generating large amounts of anode residue, rather than having the nickel dissolve. Then you would need clean your basket more often and add more nickel squares, or whatever form you are using.

Don Piett
- Thompson, Manitoba, Canada

As I understand your problem, you are dissolving more nickel from the anodes than you are depositing onto the cathodes. As everyone above has said, nickel dissolution and deposition follows Faraday's Laws and both sides of the chemical reaction are pretty close to 100% efficient. If we assume you bath composition is basically in specification, then it must mean that your anode and cathodes are electrochemically out of balance. If that is not the case, then you must be depositing nickel onto something other than your workpieces. Have you checked for any unwanted nickel deposits in the tank caused by stray currents - if you have any, this will affect the apparent efficiency of your process tanks, because you will be applying a lower cathodic current density to what you were aiming for. Consequently, you will be taking out less nickel from the tank than you originally thought (and calculated for) and so when you calculate what you are actually taking out and what you are actually putting in, there will be a difference. Similarly, if you are only partially dissolving the nickel and getting lots of sludge in your anode bags, you will be losing more nickel from the anode than you are putting down on the cathode. However, if the concentration of nickel ions in solution is increasing, then you must be either dissolving the nickel anodes chemically, which is most unlikely if the electrolyte is in specification, or you have a stray electric circuit with a cathode that does not let the cations deposit onto it. Finally, are you sampling your bath at the correct tank volume - if there is a lot of water evaporation, which in Egypt I would suspect there is, you must make sure your tanks are kept at the correct volume or you will get misleading concentrations for all components of the electrolyte (except water!).

Trevor Crichton R&D practical scientist - UK

Very good answer, Trevor. Thanks!

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

Dear Aly,

What is the concentration of chloride ions in your bath check it. If you want to know with out analysis. Check the stress of your deposition if it high chloride is too high.

Raafat Albendary
- Cairo, EGYPT

Dear Sir,

Hi I think maybe you have a problem in your bath which leads to passivation of articles at cathode during plating. For ex. in case you have more brightener or overdosing in the bath the cathode will become passive very fast. So instead of nickel deposition the Hydrogen will involve at cathode so anode dissolves correctly but the deposition of nickel ion at cathode is not according Faraday law. please check the sign of passivity on nickel for ex. the chrome deposition, white stain,.. The other possibility can be stray current in the bath. if you have stray current in bath maybe instead of nickel deposition on some metallic device ( heater, heating coils,..) the hydrogen gas forms.

Reza Gharehdaghi
electroplating - Tehran, Iran

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