-- The Home Page of the Finishing Industry

on this site
current topics
Live! From Pine Beach NJ: The world's most popular metal finishing website, and the internet's friendliest corner

topic 40095

Problems in Acid Chloride Zinc Plating


A discussion started in 2001 but continuing through 2019


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.
Pine Beach, New Jersey
Striving to live "Aloha"


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.
Pine Beach, New Jersey
Striving to live "Aloha"


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
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo

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.
Pine Beach, New Jersey
Striving to live "Aloha"

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
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

(you are on the 1st page of this thread)       Next page >

If you have a question in mind which seems off topic, please Search the Site

ADD a Q, A, or Comment on THIS topic START an UNRELATED topicView CURRENT HOT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices

©1995-2019, Inc., Pine Beach, NJ   -   About   -  Privacy Policy
How Google uses data when you visit this site.