What grade sulfuric acid is acceptable for PAA process line?

[KirbyWan]

Howdy all,

So my purchaser calls me and says "they don't have 3 ppm sulfuric acid. Can we use 6 ppm instead?" My first thought is ppm of what? So I review the specs and we run out PAA line per BAC5555 which indicates to use sulfuric acid per A-A-55828 Type I Class 1. I review this Commercial Item Description and it indicates that for this type and class the maximum Arsenic concentration must be 3 ppm. It also indicates that non-volatile matter must have a maximum % by weight of .025%. I ask the seller to clarify what the ppm is of and they don't know and need to check with someone technical. I get back from them a typcial spec sheet for E-grade (Electrolytic) sulfuric acid which I have attaced below. It lists Arsenic at 1 ppm so I'm good there, but it lists the non-volatile matter as 300 ppm max which is higher then the .025%, which I assume is equivalent to 250 ppm. The normal certs that come with it would not normaly have this much detail, just % Assay HsSO4, Specific Gravity and Iron specs. So my questions are:

What is non-volatile matter and for this specific application, PAA processing of aluminum for adhesive bonding of aircraft structure, would the slight increase of non-volatile matter be a significant problem?

How do you order this material? How do your specify it and what certs do you normaly require?

What else should I be asking? What do the grey beards know that a newbie needs to learn. What's that tribal knowledge that can be passed from tribe to tribe etc.

Thanks all,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[WKTaylor]

Exactly what is the sulfuric acid used for?

PAA anodize solutions normally run with a mixture of deionized/pure H2O and Orthophosphoric acid. period.

Is this a deoxidize solution? Aprocess control chemical?

Ref SAE ARP1524 Surface Preparation and Priming of Aluminum Alloy Parts for High Durability Structural Adhesive Bonding

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

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[KirbyWan]

Wil,

Per BAC5555 this is used for the Sufuric Acid/Sodium-dichromate Deoxidize tank, after degrease and before the Phosphoric Acid Anodize. BAC5555 allows other deoxidize systems but I think this is the most common system and is based on the FPL etch system.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[WKTaylor]

OK, I get it...

De-Ox process per BAC5765.

Are You talking about allowances for deoxize-bath contaminates build-up... or fresh process solution A-A-55828 that may be out-of-spec?

As I understand it, Boeing qualified processors have to stick with the requirements right-down-the-line... unless waived by Boeing (which is rare).

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[KirbyWan]

Wil,

This is for the quality of new Sulfuric Acid used to charge or recharge a Deox tank as needed to keep the tank within the specs laid out in BAC5555. We are not at the moment Boeing Qualified, but we plan on getting there so if that is what it takes we'll set that requirement. Note BAC5555 has all the process control for the Deox step and does not call out BAC5765. So I've not familiar with it, but I'll check it out now.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[KirbyWan]

Wil,

The solution controls in BAC5555 for the deox tank, solution 1 in the spec, are identical to BAC5765 solution 10 for sodium-dichromate and sulfuric acid concentrations, though given in different units. BAC5555 has a max copper of 180 ppm and max iron of 180 ppm which BAC5765 does not mention. BAC5555 has a max aluminum of 17.2 g/l while the BAC5765 has a minimum aluminum of 1.5 g/l. and the temperatures and etch rates are just a bit tighter on the BAC5555. The one significant difference is that where BAC5765 calls out the same Commercial Item Description, A-A-55828, it does not list a type or class so I would assume the less restrictive class 2 of A-A-55828 would be acceptable which does not have a limit on Arsenic and the Type II which permits .05% non-volatile matter.

Does anyone have experience with a PAA line controlled to BAC5555?

Thanks all,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[KirbyWan]

I finally got them to state that the ppm that they state for the ordering, 3ppm vs. 6ppm or higher is of Fe. Since the CID calls for controls only for Arsenic and the tank control indicates a maximum of 180 ppm iron I ordered the sulfuric acid with the higher iron rating, which is all they had to offer anyway. Even at 8 ppm of iron I will be diluting the iron in the tank which is over 100 ppm, but within the BAC5555 limits.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[WKTaylor]

As I understand it Boeing is extraordinarily fussy about details, and strict adherence to processes, when certifying vendors.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.