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topic 41155

Boric-Sulfuric acid anodizing BAC5632 Issues and Answers

A discussion started in 2005 but continuing through 2019


Q. We are having problems with our Boric-Sulfuric Anodize tank. We are getting some bad pitting and what looks like corrosion on our parts. This is the 2nd time this has happened in 3 weeks. The first time we suspected contamination of the bath, but now we have a brand new bath and it has my mind boggled. Please help me with any advice as to what our problem could be.

Tony Schmaltz
Plating Shop - Seattle, Washington USA


Q. Please send your answer for the problems of pitting in boric-sulfuric anodize process.

Kario Michael
- Lod, Israel


Q. We are having problems with our Boric-Sulfuric Anodize tank. We are getting some bad pitting and what looks like corrosion on our parts. I see same question but there was no answer.

Please, please, let me know why those pitting(or burning?) are generated and how to resolve this problem.

I.S. Hwang
Aluminum treatment - South Korea


Hello, I.S. There are several other letters on-line here about boric-sulfuric anodize, and several of them mention that the process is Boeing BAC5632. Are you following BAC5632?

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


Q. Yes, we perform Boric-Sulfuric Anodize in accordance with BAC5632 for Boeing parts.

I.S. Hwang
Aluminum treatment - South Korea


A. I.S.

It is a long shot but I would check for chloride contamination, particularly if the pitting coincides with a bath make-up or new solution(container) addition.

Willie Alexander
- Colorado Springs, Colorado

July 9, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir, we do Boric & Sulphuric acid anodizing.
After the process we get pits/ black pore-like things.
Please can you throw light on this?
Thanking you,

- Bangalore, Karnataka, India

July 11, 2013

A. We really need more information on your process parameters in order to come up with an insightful response but I have found that when I have had pitting problems they usually come from either too weak of a deox/desmut solution or too much time in the deox/desmut solution.

Tim Hamlett
Tim Hamlett, CEF
aerospace metals distributor - Tamarac, Florida, USA

July 25, 2013

A. I think your problem is not related to anodizing. I had had same problem 4-5 month ago. I noticed source of problem was extrusion and storage conditions. Long time storage profiles's surface getting corroded. After caustic bath, these pits reveal and after anodizing you can see it. Solution: profiles not to wait too long time; avoid humidity storage; and also I wonder do you see these pits for bright profiles after anodizing? I don't see so far... because these profiles not treated with caustic.

Alaattin Tuna
- Sakarya, Turkey

Boric Sulfuric Acid Anodize tank analyses

May 10, 2016

Q. I am looking for a titration procedure with factor for boric acid and sulfuric acid. I am having difficulty getting the correct concentration for each and I've tried three different methods

Christy S
lab tech - Savannah, Georgia

simultaneous May 10, 2016

A. Christy, it would be helpful to know what 3 methods you have tried, so that your follow up reply is not I tried that and it does not work.
If this is to a Boeing spec (since they patented it) then they will have a specific way to test for it.
I will speculate that it would require a very good pH meter and possibly an autotitrator using a weaker titrant than what you are using. Boric has 3 inflection points that might be hard to find. Impossible with a rapid titration or normal 1.0N sodium hydroxide.

James Watts
- Navarre, FL

May 10, 2016

You can easily determine total acidity via a titration with 0.1 N NaOH to a phenolpthalein endpoint. I imagine that you could isolate the boric by titration to a method orange endpoint with the same solution. Plenty of stirring and slow the titrant.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

May 11, 2016

thumbs up signThank you for all your help. Yes, I am using a Boeing spec for the titration procedure. The Procedure No. I used is B-281A of which uses 1.0 N NaOH as the titrant. I have started over and redone the procedure and finally got my end results in reason from what they were. I appreciate all the advice on this and will utilize it to my advantage. Thank you!

Christy Sanchez [returning]
- Savannah, Georgia

Pitting under the rack marks in Boric-Sulfuric anodizing

August 22, 2018

Q. We are experiencing pitting under the rack marks. This is a boric/ sulfuric process. It is only occurring on this part configuration. Does anybody have any suggestions as to what might cause this?

41155-1c   41155-1b   41155-1a  

Brandon Boyd
metal finishing - Holdenville, Oklahoma U.S.A.

August 24, 2018

A. Such big electrical contact, maybe acid residual when drying leads to these pits.

Tingqiang Wang
Zhejiang XIZI Aviation Industry Co., Ltd - Hangzhou, China

August 2018

A. Hi. The pictures might be deceiving me but those pits look so deep & severe that in my limited experience it doesn't seem likely they would happen in a short time solely from chemical reaction. I get the feeling something electrical is happening like a momentary short circuit, or dirty contacts not carrying any current during ramp-up then suddenly breaking through at higher voltage.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

August 24, 2018

A. The cause could be a poor electrical contact, probably the surface is uneven so only a small area is doing the electrical contact and that produces the burns.

Yohands Rey
- Chihuahua, Mexico

August 27, 2018

A. Brandon

What does the surface of the contact plate look like? Does it have the same pitting?

Have you tried unracking the parts prior to seal to see if the problem originates in the anodize bath? If you have residual acid trapped between the part and contact point, elevated temperatures might cause the pitting you are experiencing.

Willie Alexander
- Green Mountain Falls, Colorado

August 29, 2018

A. I don't suppose this appearance is "pitting" ... pitting is completely different. We can say "stain" as described. My advice: you can change rack design, or degreasing and neutralize duration can be much more, like 5 min. Because maybe profile's surface was dirty from normal level so in that joint area had effected as we see picture.

alaattin tuna
- Turkey,sakarya

August 2018

thumbs up sign  Hi Alaattin. Agreed that this is not what we usually call a "pitting defect", but it sure looks to me like quite deep etched craters, not a surface stain. Pictures can be deceiving: one of us sees stains, but one of us sees deep corroded indentations :-)


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

September 4, 2018

A. Hi Ted, yes, I agree with you about "point of view" issue for some problems like this one ... but I think solution of this problem should be "one". In this situation I follow this way:
1- How often does this problem occur? for example, every rack or some racks ... also does the same problem occur on different profiles?
2- one of the key words in this situation is "survey". Is this problem emerging before/after anodizing or etching ... also sealing.
So we can collect and filter all the results and diagnose; after that, of course, treatment.

alaattin tuna
- sakarya,TURKEY

September 19, 2018

A. We have had the same problem as Mr. Boyd, however, not just on the contact areas. The deep pits in Mr. Boyd's photos are all too familiar to me while using boric/sulfuric anodize. I have never been able to nail down a cause. My tank will produce perfect parts for three months straight - then, without warning, an entire lot of parts will exhibit those monster-pits. The pits will appear at contact points AND at random areas all over the anodized parts. The pits are quite deep and generally will cause the entire lot of parts to be scrapped. Our parts are racked on clean and deoxidized racks and the contact points are as small as possible to reduce the likelihood of trapped solution. Pre-clean includes a deionized water rinse after deox.

Steven Haubeil
Aerospace - Wantagh, New York USA

November 16, 2018


To avoid confusing newcomers, please note that we are speaking of Boeing BAC5632 boric-sulphuric anodizing on this page. Boric acid anodizing is actually a very different process used for applications like electrolytic capacitors.

Q. What is needed to start up a boric acid anodizing tank. Does it need to be chilled or any type of special liner like a lead liner. Going to be using it per the Boeing Spec BAC5632.

Roger Leon
- tustin California

November 16, 2018

A. Assuming you mean Boric acid-Sulfuric acid anodizing, as that's what the referenced spec covers, there is no special liner: we have ours in a poly tank.
There are specific cathodes that must be used, which is specified in the spec & subsequent PSD's.
You will need a heater and a chiller, as it has a tight temperature requirement.

Fauna Tester
- Seattle, Washington, USA

November 16, 2018

Q. Fauna Tester, I appreciate your response. Is the poly tank the gray color that is more resistant to chemical?

Roger leon [returning]
- Tustin California

November 19, 2018

A. It is standard white polypropylene.

Fauna Tester
- Seattle, Washington, USA

sidebar2 November 19, 2018

A. However, I just received the latest addition of Products Finishing, which rates polypropylene the worst.
It states to "rely on the expertise of your supplier".

Fauna Tester
- Seattle, Washington, USA

November 2018

A. Thanks Fauna. (Readers: that article can be found at

For a number of years I was 'the plating shop guy' for a fire investigation service for the insurance companies, so I visited many plating shops which had suffered fires and saw the causes and the results. The overwhelming majority were caused by the use of electric heaters in polypropylene tanks. The first rule should be: don't use electric heaters in polypropylene tanks unless 'armed to the teeth' (at least two or more separate safety devices).

There are fire-resistant grades of polypropylene (infused with bromine fire retardants) but, besides adding a lot of cost, they can leach the bromine chemicals into the process. We used them on one process line and the bromine was a bit worrisome but turned out okay for most of the tanks ... but the Electroless Nickel tank which was built of fire-resistant polypropylene had to be simply scrapped.

Every material has its advantages & disadvantages and I personally feel that if you don't use electric heaters, or you use them only with the greatest care and double safeties, you eliminate 95% of the problem of flammable polypropylene tanks ... and that's a darn good start in any undertaking in my book. And I certainly saw many leaking steel and lined steel tanks in my career.

A point which ought to be inferred from the article is that only experienced plating tank designers should build plating tanks. In my career I designed many thousands of plating tanks and although I do not agree with the author of that article that you need automated welding, you do need competent engineers, broad experience with plating tanks, and skilled craftspersons regardless of the material of construction of the tanks.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

Copper contamination of boric-sulfuric anodize process

December 2, 2018

Q. Hello,
I am trying to identify any impact on parts caused by increasing dissolved copper content in a boric-sulfuric acid anodising tank. Our tank is currently around 200 ppm, but I wanted to know if there was any impact if the concentration was higher (say around 300 ppm). Any information or guidance would be much appreciated.

Stephen Brown
- Sydney, NSW, Australia

December 4, 2018

A. The spec states 237 ppm max, so I wouldn't recommend it.

Fauna Tester
- Seattle, Washington, USA

December 5, 2018

A. If you run the 2000's, there is nothing you can do to prevent copper, it plates out when the current is on, it partially re-dissolves when the current is off, so take the sample shortly after starting the current on; it does not hurt anything.

robert probert

Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

January 17, 2019

A. Copper in anodizing baths tends to lower salt spray resistance.

drew nosti
Drew Nosti, CEF
Ladson, South Carolina

January 20, 2019

A. It is possible to remove copper from this anodize bath by electrolysis with a high surface area cathode. This is preferable to decanting or dumping a portion of the bath in order to control copper.

Lyle Kirman
consultant - Cleveland Heights, Ohio

February 14, 2019
I am working on the implementatation of the boric-sulfuric anodizing system, then it is doubtful if it is strictly necessary the addition of an organic compound such as benzoic acid or sodium benzoate in order to inhibit the biocontamination.

That is to say, according to the norm, it is "possible" to add said compound, but is it really common for biocontamination in these types of anodizing tanks or can the addition of such an additive be dispensed with?

Thank you so much, I waiting for your answers

Q. Estoy trabajando sobre la implantación del sistema de anodizado con bórico-sulfúrico, luego cabe la duda de si es estrictamente necesario la adición de un compuesto orgánico tal como Ácido benzoico o benzoato de sodio a fin de inhibir la biocontaminación.

Es decir, según norma se "puede" añadir dicho compuesto, pero ¿realmente es común la biocontaminación en estos tipos de tanques de anodizado o se puede prescindir de la adicción de tal aditivo?

Muchas gracias, espero sus respuestas

Carla Castañeda
- Huelva, España

July 16, 2019

Q. Hello,

I'm looking for a way to analyze for copper and NaCl in a Boric Sulfuric anodizing Tank.

I must keep the copper to 235 ppm and the NaCl to .1 g/l

Thanks in advance,

Micheline Forth
Edwards Interiors - Rincon, Georgia

October 30, 2019

Q. Hello,

I was wondering if anyone knew of a way to analyze NaCl in a Boric/Sulfuric anodizing bath. I must not exceed 0.1 g/l of NaCl.


Micheline Forth [returning]
- Rincon, Georgia

October 2019

thumbs up sign  Hi Micheline. While we're waiting and hoping for a response, I see that you have reframed it in more limited fashion since last time. Please share what if anything you have learned about analyzing for copper in this bath. Thanks!


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

October 31, 2019

thumbs up sign Ted,

I have not found a great solution for copper. I do like to do everything in house if it is cost effective. I found a lab to do it for now but they say that they cannot do NaCl.


Micheline Forth
Edwards Interiors - Rincon, Georgia USA

November 6, 2019

A. Hi, Micheline

NaCl in aqueous solution would be present as Na+ and Cl-, so it might be better to ask to analyse for those ions (as NaCl itself would technically not be present).

Something like atomic absorption spectroscopy could probably do it. Salts can be pretty harsh on some forms of mass spectrometers and HPLC, so that may be why the lab can't do it.

Ben OShea
- Katikati, New Zealand

November 13, 2019

thumbs up sign  Thank you so much for your response. I will work hard to get a solution. It may involve buying our own equipment

Micheline Forth [returning]
- Georgia, USA

July 28, 2020

Q. Can you please help me out. I want to see what is needed to start a boric acid sulfuric anodizing tank. Per Mil-A-8625 [link is to free spec spec at Defense Logistics Agency,] type IC. If you would please help me I would appreciate it. Thank you in advance for your help.

Roger leon [returning]
- Tustin California

July 2020

A. Hi. Fauna previously answered you that a standard white polypropylene tank would be okay, and I think he's right. He also said that Boeing Spec BAC5632 requires very tight temperature control with both heating and cooling. If you are not working to BAC5632 I'm not really sure that MIL-A-8625-1C is truly very meaningful because it says you can only use it if the procuring activity agrees, and it doesn't specify boric-sulfuric anyway, just mineral acid or mixed mineral-organic acid; I think Airbus might use neither chromic, nor boric-sulfuric, but phosphoric acid for similar applications.

There may be shops who do MIL-A-8625-1C boric-sulfuric without adhering to BAC5632 but I don't know, and I don't know of a good way of figuring out ideal heating, cooling, and cathode material, concentrations, etc. without either simply following BAC5632 or being lucky enough that such a shop responds :-)

Sorry, & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

July 28, 2020

A. I believe that purchasing the most current copy of BAC5632 would behoove you. It is the governing spec for Boric Sulfuric Anodizing.

Taylor Clarke
- Minden, Nevada


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