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Problems in Acid Chloride Zinc Plating

A discussion started in 2001 and continuing through 2017 . . .


Q. 1. Minimum and maximum distance between anode to cathode.

2. Why to maintain this distance?

3. What is the principal to maintain proper distance.

4. How it works.

5. What is the purpose of using boric acid and how it works.

Can anyone suggest regarding this matter?

Mohanraj [last name deleted for privacy by Editor]
wire - Dubai, UAE


A. There is no real minimum or maximum anode-to-cathode distance. Whatever suits your condition should work. But in general terms, the larger the distance, the more solution resistance, so the more wasted power and heat. But the cathode must never touch the anode, and for shapes that are more complicated than wire, you may want a bit of distance so that the ratio of distance from the closest point to furthest point is as close as practical to unity.

As electrolysis proceeds, some water will be converted to H2 and 2OH-. The H2^ evolves as a gas and the OH- tends to raise the pH of the solution. Boric acid is a buffer to help stabilize the pH.

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


Q. Thank you Mr. Ted Mooney,

As you replied me when the pH of potassium chloride zinc plating bath increases we should add boric acid as buffer to maintain the pH. But why don't we use the same (boric acid) for ammonium chloride zinc plating bath.

Mohanraj [returning]
- Dubai, UAE

A. Buffers are to stabilize the pH rather than to raise or lower it. Hopefully a supplier will offer a more authoritative response here, but pending that: ammonium chloride is itself a buffer, eliminating the need for boric acid; I believe that ammonium chloride baths operate at higher pH than potassium chloride baths.

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


A. Mohanraj, use muriatic acid (HCl) diluted 50% with water to adjust pH down. pH of this bath should be 5.0-6.0. Boric acid is a buffer. Should be in a range of 3.5-6.0 oz/gal. Boric acid helps prevent burning of the parts. In a ammonia/potassium bath, the ammonia chloride replaces the boric acid. The mixed ammonia/potassium bath does allow higher current densities to be applied to the part. There are benefits with both baths. Temperature is also important when zinc chloride plating. Should be kept between 70-100 °F (don't have metric conversion available).

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan


A. NEVER add boric to adjust you pH! Keep boric within 22-25 gms / Lit for wire plating, otherwise higher boric will encrust upon your anodes which may be at the bottom of your tank!

Muriatic acid is called Hydrochloric acid in this part of the world. Please use it judiciously and do not lower the pH below 4.8 to 5.0 as you have to remember that you are doing wire plating and a pH lower than this will cause immense build up of iron!

Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

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Brown sticky slime on surface of chloride zinc plating tank


Q. We have made a few changes to our acid chloride zinc rack plating line. Increased our chloride to 20 oz/gal from 17 oz/gal. Increased our brightener additions from 1 gal every 25,000 amp hours to 1 gal every 8,000 amp hours based off of hull cell testing. Lowered our pH from 5.0 to 4.5 with diluted hydrochloric acid. Increased our bath temperature from 60 deg. F to 80 deg. F. Added more uniform air agitation. Our boric acid level is 3.3 oz/gal. Our zinc has increased from 5.6 oz/gal to 6.6 oz/gal in the last 7 months. Iron usually runs between 20 - 35 ppm. However, our parts look very good in appearance with no rejects since all of our changes. We conduct "non-air agitated" Hull Cells daily.

My question: Initially we noticed a very "dark" brown material across the surface of our bath - this stuff is extremely sticky - what could it be? Also, just recently the "dark" brown material seems to have changed to a lighter brown material.

Travis Crumrin
mfgr - Robinson, Illinois, USA


A. The bath is out of recommended range. First, pH should be 5.0-6.0. The crap on top of the tank is probably the wetter (carrier) portion that has "kicked" out at pH 4.5. Normally it won't at 4.5, right on the edge. When adjusting pH it is possible it was lowered to 4.0 or less. As you have found, it will not re-solubalize. Keep running and changing the filter.

The zinc metal content should be 3.0-5.0 for a rack bath. When the zinc rises above 6.0, the efficiency goes down ,i.e., when the bath is right, plate thickness is 6:1, high CD to low CD on the part. Metal above 6.0 may be 12:1 or higher high to low. You may be experiencing brittle plate with high zinc. You should decant the bath to reduce zinc.

To check for brittleness, run a 2 amp-30 minute Hull Cell, no agitation, do not nitric bright dip it. Just dry, and bend a corner over and back to see if it cracks.

Boric should be 4.0-6.0 oz/gal. When the zinc metal gets to 5.0-5.5 keep the boric at 6.0. No benefit to have boric higher.

Iron is good at 0-50 ppm. Is still OK at 50-100 ppm.

Chloride should be 17.0-19.0 oz/gal. When zinc is close to 6.0 oz/gal., chloride of 20.0-21.0 is OK.

The bath is most efficient at temperature 70-90 degrees F, 80 degrees is the best.

I don't know what brightener system (company) you use, but I am sure the salesman is smiling at a brightener add of 1 Gal. every 8,000 amp hrs.

Recommend you discuss with your vendor all the above. They should check for total organics, (wetter-carrier), this should be 4-6 %/vol.

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan


A. Hello Travis

It is possible that with the increase of Chloride in solution the wetter part of your brightener system is unable to " HOLD" in all the brightener that you have now started adding.

This phenomenon is sometimes called " Brightener Kick Out or Oiling out '

This question cannot be completely answered by this forum. Connect with your Brightener supplier and ask for service.
The only answer is to use a stable Brightener system that can work under your conditions mentioned .


Asif Nurie
- New Delhi, India

With deep regret we
sadly advise that
Asif passed away
on Jan 24, 2016


Q. Thanks for the comments - Our supplier has been notified - they always stress "consistency" and keeping the bath in "balance." We have had some different employees in and out of our shop which might have contributed to what's happening. Bill made mention of the pH maybe lower than the 4.5. I would have to agree that this is a strong possibility. We only add acid at the beginning of each day.

In regards to pH - Can you purchase a controller to constantly monitor the bath pH & automatically feed in acid to maintain a set pH? I've been told not to check pH while work is being plated - then I've been told it is ok?

Again, thanks for your comments.

Travis Crumrin [returning]
- Robinson, Illinois, USA


A. The temperature of 80° will cause "oiling out" in older standard baths.

You could also be overloading the wetter side of your brightener system.

Chris Snyder
plater - Charlotte, North Carolina


A. There was a great deal of information in the previous replies that is true and some which may not be quite so.
Firstly, zinc metal does tend to rise in chloride zinc solutions since the drag out is less that the drag in and the high anode efficiency leads to increasing metal. Most platers have to decant solution periodically. Secondly, it would seem that for a rack bath you are using an excessive amount of brightener from any vendor. Reduce brightener additions by at least half, treat the bath with potassium permanganate and carbon filter. The material you see on top of the bath is probably unsolubilized brightener. With most brightener systems you need to increase the quantity of carrier (aka starter, wetter) to provide enough solubilizer for the higher amount of brightener. This situation would be readily apparent if you ran a cloud point on your bath. Cloud point is a good indicator of low carrier and/or high total organics. You also should be having problems with yellow chromate adhesion at this high brightener loading. Finally, the suggested level of 4 to 6 oz/gal of Boric Acid is high since I believe this is beyond the solubility of boric acid at this operating temperature. If you wish to run boric acid at the high end of solubility (to help prevent burning and for improved conductivity) take an extra anode bag and fill it with boric acid, it will dissolve as much as possible for the temperature you are operating at. One caveat: if the temperature drops, the now insoluble boric acid will precipitate out and if not picked up by the filter will cause roughness.

One last thought, I hope you are running continuous filtration with a turn over rate (real time) of a minimum of 2.

Gene Packman
- Great Neck, New York

Operating temperature for acid zinc plating

July 13, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi, this is Danish. We manufacture sheet metal components and also electroplate them. What would be the optimum temperature for acid zinc plating if the capacity of tank is 500 ltr and per batch 25-30 kg material is plated? For a total of 6 tanks. Any advise will be highly appreciated.

Thanks and cheers,

Danish Jawed
- Karachi, Sindh, Pakistan

July 20, 2012

A. Dear Danish,

- The advised optimum temperature for acid zinc potassium electroplating bath is 22 °C. Over 28 °C there are (commonly) problems of over-consumption of brighteners, under 15 °C there are problems to level, low conductivity and low solubility of potassium chloride and boric acid (addition of these may be troublesome).

For 30 kg of material, 500 lt of bath seems good. If you have some small refrigeration equipment you may have no problems.

Best regards!

Daniel Montanes
fasteners manufacturer - Canuelas, Buenos Aires, Argentina

pH Rises Even Though Boric Acid Is Right

June 27, 2013

Q. My question is that after having boric acid in range in acid zinc electroplating even then pH raises from 4.8 to 5.2 and above why? Please if you are capable tell the answer.

Dharmendra Chauhan
Chemist - Ludiana, Punjab and India

July 2013

A. Hi Dharmendra. It is normal for the pH to rise, and it is expected that you will need to add acid to maintain it. The plating is not 100% efficient, but releases some amount of hydrogen gassing at the cathode. When hydrogen gas is released from water, it leaves OH- in solution, so the pH rises.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Calculating / Analyzing Potassium Chloride in Acid Zinc Plating Bath

November 4, 2014

Q. We have a 17,000gal acid chloride zinc plating bath. I'm looking for a formula to help calculate the level of potassium chloride in the bath. I've been given a couple different formulas from but they produce completely different results. Hopefully a formula exists where we can input numbers from a quick titration rather than relying on an outside lab.

Thank you.

Chuck Hambly
- Cleveland, Ohio USA

November 15, 2014

A. Titrate the chloride via the silver nitrate method with chromate indicator. Determine the zinc content via EDTA titration. Calculate the ZnCl2 concentration by simple math...then get to the KCl concentration by subtraction. Helpful hint: run that KCl as high as you can get away with. (limitation, the KCl solubility) It helps improve the "throw" of the bath.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

November 25, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. How to check the zinc metal and total chloride in a zinc acid bath. Please tell me the procedure of checking in chemical, and also a shortcut to check.

naval dhiman
- Chandigarh ,India

November 2016

A. Hi Naval. As you see, we appended your inquiry to a thread where it is answered. If you have additional questions, please continue the discussion. But please tell us who you are and your situation (rack, barrel, or continuous plating; approx. tank size; what method you've used to date, etc.) so people can more immediately help you rather than having to concern themselves with all of the possibilities raised by abstract questions. Thanks!


pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Formula for acid zinc plating bath

June 30, 2015

Q. We are doing zinc electroplating using zinc chloride, potassium chloride and boric acid. Capacity of our bath/cell is 8920 Litter. Kindly suggest me the correct formula of preparing electrolyte solution using these chemicals. i.e what proportion of these chemicals will be used?
Thank You

Umer Draz
- Lahore, Pakistan

August 10, 2015

? Hello Umer!

Please provide more data:
- By the products you mention, you use a potassium-boric acid zinc bath. So, you have a vendor for brighteners for this bath, have you asked them? Or you make your own bath?

- Provide conditions: Time? Current? Conditions of the wire when you plate (straightened, in rolls...)? pH? Concentrations?

- Do you use chromate conversion coatings? Lacquers?

If you give us more information, we can assess you better. Hope you can solve your issue!


Daniel Montanes
- Canuelas, Buenos Aires, Argentina

August 14, 2015

Q. Thanks Mr.Daniel Montanes

Volume of solution (Zinc chloride + Boric acid + Potassium chloride) is about 6000 Litters. Conditions of process are:
Specific gravity = 20,
pH = 6
Temperature = around 30 °C
Cell dimensions are Length = 45 ft, Width = 4 ft, Depth = 1.75 ft
No. of amperes used per hour is round about = 5000A (it depends upon the load, i.e., no of steel wires passing through whole cell).
Straight wires are passing through cell and finally passed through dilute Nitric acid bath for finishing.
We are still not doing chromate passivation.
When wires at the end are passed through the nitric acid solution, they are bright; but with the passage of time, e.g., after one day, they begin turning black. I want to enhance two things: one is shine and the other is storage period. Kindly assist me.

Thank you

Umer Draz [returning]
- Lahore, Punjab, Pakistan

December 11, 2015

? Dear sir
Please tell us the process you're running, and after that the problem you are facing.

Mukesh k sharma
Mtech chemicals - Moradabad , Utter Pradesh , India

December 2015

thumbs up signHi Mukesh. Umer has told us that his problem is that the wire he is plating is not shiny enough after one day, and it turns black in a few days.

I think he needs to change his dilute nitric acid to a chromate treatment. What do you think?


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Removing organic contamination from acid zinc tank

December 20, 2015

Q. Hi all. I want to ask about how to remove organic contaminant in zinc solution tank. Size of tank is 7500 L; how many times we need to do cleaning for the tank if production is running 24 hours 7 days? Thanks.

best regards,

mohd solehin, industrial engineer
- perak malaysia

May 11, 2016

A. Dear mohd solehin,

According to your plant working period, you must refine the solution after max. 3 months by adding Hydrogen peroxide H2O2 0.1-0.5% of volume of tank, and give 48 hours for settling dissolved solids.

Umer Draz
Electroplating Plant Engineer - Lahore, Pakistan

April 28, 2016

Q. I use a zinc/potassium chloride/boric acid plating tank of 800 liters to electroplate small items like bolts, nuts, washers etc. Even though I get fairly good deposit on the workpiece, I do notice excessive foaming sometimes in my tank without warning, after some time it disappears. This development baffles me and keeps me searching for ways to solve the puzzle. In as much as I cannot say for certain the exact values of the constituents because I have not done the analysis for a while now, their values run within these ranges: zinc metal -28 g/l; chloride -122 g/l; boric acid -10 g/l. pH -5.4; temp. -30°C. For brighteners, I use 650M&R (Growel). I would appreciate it if you could suggest the possible causes of such excessive foaming.

zinc chloride barrel plating of bolts and nuts, etc. - Igbo-Ukwu, Nigeria

August 31, 2016

A. Dear Louis,

You said zinc chloride composition is 28 g/L. It's very low composition. Your zinc anode, you might notice, will highly melt down or transfer high current, and solution temperature is also going to increase. This is causing foaming in solution. You should enhance composition of zinc chloride up to 60 g/l and boric acid composition up to 20 g/L. Your Foaming problem will be solved and finishing of product enhanced as well. Also maintain the composition of brighteners according to such composition.

Warm Regards

Ingr.Umer Draz
QAQC & Electroplating Engineer - Lahore,Punjab, Pakistan

August 9, 2016

Q. Dear friends
We do acid zinc plating on ms wire. I am able to achieve 1 micron now. How can I increase the plating thickness to 5 microns? The running time of the wire in the tank is 15 seconds, the tank length is 12 feet, the zinc metal is 130 g, ammonium chloride is 230 g and boric is 20 g ,current is 450 amps please suggest.

A m khan
- kerla , india

A. Hi, A.M.
Faraday's Law says that the deposit thickness is directly proportional to the ampere-seconds applied. There might be some small variation based on the cathode efficiency of the solution, but essentially the only way to get 5X more thickness is to apply 5X more ampere-seconds. Unfortunately, you'll probably find that you can't increase the current much without causing burning, and the answer is going to be that you need to run the wire at 1/5 the current speed and produce only 1/5 as much wire.


pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

"Black Tar" on surface of Acid Zinc Chloride bath

March 2, 2017

Q. I have a customer whose acid zinc chloride bath develops a tar-like substance that settles out atop the bath. The color is a dark brown, but the colloquial "in-house" term is "black tar".

This is a barrel plating operation in a shop that has a history of inconsistency, but is making very fast strides toward best-practices.

For the sake of spitballing, I'd like to ignore the inconsistency possibility and ask about the possible nexus of this substance.

Has anyone faced this substance? What is it's nature? How can it develop? How can I advise them to eliminate it for now, and prevent it going forward?

Thanks to anyone who takes the time to reply!

Keith Bowers
Technical Service Engineer - Versailles, Kentucky, USA

March 4, 2017

A. You might consider having a lab do IR spectroscopy on the mystery tar.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

March 9, 2017

A. I would investigate possible gross overdosing with organic additive (brightener)

geoff smith
Geoff Smith

March 9, 2017

Q. The substance was analyzed, containing the following peaks in order of amplitude:

1. Carbon
2. Oxygen
3. Chlorine
4. Sulfur
5. Potassium
6. Zinc
7. Titanium
8. Iron

The corresponding solution contents are as follows:

Zinc: 3.04 oz/gal
Chloride: 20.34 oz/gal
pH: 5.85
Boric Acid: 1.65 oz/gal
Carrier: 7.62%BV
Iron: 17 PPM
Manganese: 3.0 PPM
Magnesium: 20.0 PPM


I have a conclusion of my own, but I'm interested in others' conclusions without influence of my own.

Thanks to all in advance!

Keith Bowers [returning]
Tech Svc Engineer - Versailles, Kentucky, USA

March 9, 2017

A. Hi,
I think it is too much of breakdown products from the the additive in the acid zinc and following rinses.

I suggest to do a analysis of these breakdown products.


anders sundman
Anders Sundman
    Sundman & Nylander AB
Arvika, Sweden

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