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Electrode polarization

 

What does electrode polarization mean?

Rahul Jairath
- San Jose, California


 

I read your question about polarized anode means I believe some kind of layer or film on anode to make anode to inactive.

Popat Patel
    plating shop
Roseville, Michigan

 

What the term means depends on the context. In one context--something wrong preventing proper plating--Mr. Patel's definition is correct.

In another context, though, anodes are always polarized,i.e., there is always an anode polarization which the plating voltage must overcome. In this context, you account where the rectifier voltage went: some went to anode polarization, some to cathode polarization, some to boundary layer ion depletion polarization, some to solution gradient polarization, etc.

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

 

Thank you all for the explanation.

Rahul Jairath
- San Jose, California


 

Hi,

There are two important types of polarization.1)Activation polarization and 2)Concentration polarization.

Activation polarization is caused by inhibition of the passage of potential determining ions through phase boundary i.e. the electrolyte double layer. With many electrodes a large polarization is observed at low current density,mainly due to activation polarization.

The inhibition of the transport of an ion through a layer contiguous to the electrode causes resistance polarization. The presence of foreign substances on the cathode surface may consist of electrolyte anions and cations,oxides or hydroxides, or other organic or inorganic components of the electrolyte. They are adsorbed at the electrolyte surface and when the electrolyte is completely covered by foreign substance ,it is passive. This gives rise to resistance polarization.Resistance polarization is also a type of activation polarization.

Concentration polarization is due to the concentration difference which develop at the anode and cathode during electrolysis and are caused by the inhibition of the transport process.

An increase in the concentration of the dissolved metal ions in the anodic diffusion layer causes diffusion polarization. Diffusion polarization is a type of concentration polarization.

Polarization can under certain circumstances be greatly increased by the addition of specific substances. Polarization increases with increasing c.d ,but decreases with increasing temperature and increasing agitation of the bath.

If we sees some examples Nickel bath has low concentration polarization and high activation polarization . Cyanide baths often have high concentration polarization .

Venkat Raja
  plating supervisor
Walkerton, Ontario, Canada

 

Hi,

A brief introduction to what I am trying to do....

In my experiemnt to measure zeta potential, by streaming potential technique, I pump aqueous surfactant solution (anionic or cationic) through a capillary tube at increasing pressure and try to measure the potential difference(which is called streaming potential) across the capillary due to the flow. For this I place an Ag/AgCl electrode at the beginning of the capillary(Lets call this electrode E1) and one at the end(and lets call this electrode E2). These are connected to a data aquisition system with high internal resistance(the potential developed is of the order of 100mV DC).

The problem......

The electrode E1 is always placed at the beginning of the capillary and electrode E2 is always at the end of the capillary. After using the electrodes this way for few days, the electrodes started showing higher potential than expected. ie, for example, If 1000wppm concentration of the anionic surfactant generates a voltage of -100mV DC and 1500wppm generates -150mV DC, I expect 100wppm to generate a voltage which is less than -100mV DC. But the electrodes actually are showing a value which is more than expected. The question.....

Is this because of electrode polarization? or is there some kind of ion accumulation taking place on these electrodes? I am not really sure what is going on. After each set of readings, I clean the electrodes and store them in 3M KCl solution as suggested by the manufacturer. Can some one throw some light on this issue....

Thanks,

Satish C Vishnubhatla
- Cincinnati, Ohio


Ed. note: We had an older thread on a similar subject, which we've now merged into this one in lieu of maintaining separately . . .
sidebar

(1996)

I am doing some numerical research on the mass transfer to a cylinder. The application of this work is the electroplating of cylindrical electric contacts (plugs), and in particular the gold plating of these cylinders. I am looking for some information about industrial situations, in particular : - concentration of gold solutions ? - current intensities (is it a limiting-current state ?) - what is the velocity of the pieces in the baths (laminar, turbulent, very turbulent) ? If anybody can tell me where I can find this information (and more; the more information I have, the better I can turn my research to possible applications) Thanks for the help.

Pedro Olivas -
Roy. Inst. Technology/dpt. Mechanics - Stockholm


Hello, Pedro. Many different gold plating solutions are used. Per the
, they typically contain 8 to 20 grams of gold per litre, with the higher concentrations used for higher speeds. Current densities range from 1 to 5 amps per square foot with no agitation, on up to 100 to 400 amps per square foot with violent agitation. Some proprietary gold solutions claim up to 2000 amps per square foot. Numerous technical papers have been published; a literature search incorporating
Plating & Surface Finishing
,
magazine, and Transactions of the IMF should give you plenty of background.

Good luck with it.

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


July 29, 2010

I would like to know the relation between the current Density and the Cathodic current Efficiency. In my undergraduate Laboratory of Copper Plating from Copper Sulphate solution, I am finding an Inverse Relation. Can anybody explain?

LAKSHMI NARAYANA
- Hyderabad, Andhra Pradesh, India


July 29, 2010

Hi, Lakshmi. Yes, the general direction that you perceive is correct, but it's not quite that simple or exact. Think of it this way --

Your power supply forces electrons to move from the anode to the cathode through the external wiring or bussing, and that causes things to happen at the anode, cathode, and within the solution to maintain an electrical balance. Ideally, at 100 percent efficiency, what would happen is that the metal of the anode would give up those electrons and dissolve into the solution as positively charged metal ions. Those ions would be attracted to, and migrate towards the cathode; and when they reach it, the surfeit of electrons there would cause the metallic ions to be reduced to metal.

But as you raise the current density, it becomes increasingly difficult for the migration of the metal ions to keep up. At the cathode, those electrons are demanding to be balanced, and if there are insufficient metal ions arriving fast enough, they start liberating hydrogen out of the aqueous solution.

Regards,

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


March 6, 2012

What is polarization ? What is polarization of electrode?

Gunjan Jadhav
- Mumbai, Maharashtra, India


March 6, 2012

Hi, Gunjan.

In view of the fact that the answer to your question is already on this page repeatedly, I don't understand your question. Sorry! Please do your best to phrase your question in terms of what you understood and still fail to understand. Thanks.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey

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