Boric-Sulfuric Acid Anodizing (BAC5632) Problems & Solutions

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

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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.

A. If it were me, I'd trash the bath and start anew. I'm not very familiar with Boric acid anodizing, and the film properties it produces, especially when it comes to dyeing parts. You weren't too specific on the type of film properties you are trying to achieve by converting to sulfuric. I'm also assuming that you want to be able to repeat quality results -- how could you ever do that if you're basically starting off with an unknown from the get-go?

A. You need to discard that solution and start over. Since the bath is relatively dilute, you really aren't throwing away many dollars by discarding the bath or spending many dollars to waste treat it. So, don't feel too bad about getting rid of it.

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.

A. I think your problem is not related to anodizing. I had the same problem 4-5 months ago. I noticed the source of the problem was extrusion and storage conditions.

In longterm storage the profiles's surface was getting corroded. After caustic bath, these pits are revealed and after anodizing you can see it.

Solution: profiles not kept in storage a long time, avoid humidity storage. Q: also I wonder if you see these pits on bright profiles after anodizing? I don't see any so far ... because these profiles not treated with caustic?

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.

You can easily determine total acidity via a titration with 0.1N NaOH ⇦ on eBay or Amazon [affil link] to a phenolphthalein 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.

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

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.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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.

? 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.

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 neutralizing duration can be much more, like 5 min. Maybe profile's surface was dirtier than normal level so in that joint area it had the effect as we see in the picture.

  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 :-)

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.

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

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.

A. 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.

A. It is standard white polypropylene.

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".

Polypropylene Tanks & Anodizing Shop Fires Thanks Fauna. (Readers: that article can be found at https://www.pfonline.com/articles/preventing-electroplating-tank-catastrophes-in-surface-finishing-operations ) For several years I was 'the plating shop fire guy' for a fire investigation specialty service retained by insurance companies, so I visited a lot of plating shops which had suffered fires and I saw the causes and the results. The overwhelming majority of plating shop fires were caused by the use of electric heaters in polypropylene tanks. What happens is if the solution level drops, the electric heater gets very hot and radiantly heats the nearby are of the tank wall, melting it, then igniting it, and polypropylene is highly flammable. The first rule should be: never use electric heaters in polypropylene tanks unless 'armed to the teeth' (at least two, maybe 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 turned out okay for most of the tanks ... but the Electroless Nickel tank which was built of fire-resistant polypropylene had to be 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 or triple safeties, you essentially eliminate the problem of flammable polypropylene tanks. And I certainly saw many leaking steel and lined steel tanks in my career. A point to be inferred from the Products Finishing 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 absolutely 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. Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey Need quick confidential answers? $25 Need project assistance? $100/hr. Ed. update Dec. 2025: The phrase 'enshitification of the internet' entered the lexicon in recent months, meaning that registration is now required on nearly all websites, many pages are now considered "premium content", and the use of pop-up and sticky ads means the reader now often has to run a land-mined slalom just to try to read an article on line. The glory days of 'surfing the internet' are behind us, and enshitification is everywhere -- except right here, of course! finishing.com remains "no registration", available to everyone, with no "premium content" and no aggravating pop-up/ sticky ads  🙂 Although the URL listed above was available to all when we posted it, it has now been placed behind a "registration wall", so we've left the URL listed, but be removed the direct link.

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

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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.

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

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.

  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!

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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 ⇦ on eBay or Amazon [affil link] 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.