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New anodizer needs info about water for 10% sulfuric acid solution

Hi!
I want to start anodizing of commercial parts and couldn't get the water specifications required to make up the required solution that is 10% sulfuric acid solution. Can anyone help me out in this regard. Can I use tap water, distilled water or demineralized water? If demineralized water that what should be the TDS level?

Jawad Javaid
New Anodizer - Pakistan
2007

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Purified water is preferred; effects of impurities vary greatly. The Surface Treatment and Finishing of Aluminum and Its Alloys, 6th Edn., page 478, mentions detrimental effects above the following levels: chloride 200, Cu 125, Fe 50 and Pb 50 mg/Liter.

Not harmful: nitrate up to 1000 mg/L (in 20 wt% sulfuric acid electrolyte), carbonate (dry ice is added in one hard anodizing process) nor K, Mg or Na up to about 2 g/L (these sulphates have been included in hard anodizing electrolytes), ibid., page 768.

Note that alloying elements will accumulate in the anodizing solution: Cu and lesser amounts of Fe are present in many heat-treatable wrought alloys and many casting alloys. Try to use electroplating grade sulfuric acid; if necessary to use technical grade, ask for an analysis and verify that it is colorless.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007

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2007

Thanx alot for the very kind reply.
I have purified water from RO process with chlorides less than 12 ppm. Can I use it for the process.
Also should I use the same water for the rinsing operations, the tap water contains TDs 360 ppm. please advise.
Regards,

Jawad
- Pakistan

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The RO water is sufficient quality for the anodizing solution and its replenishment. Presuming periodic partial dumps of the solution to keep [Al] below 20 g/L (15 g/L for hard anodizing), the [Cl] should remain well below 200 ppm.

The 360 ppm tapwater is possibly OK, but high [Ca] & [Mg] may cause sulphate precipitation within the anodize pores which interferes with dyeing. Worse at high [Al] levels in the anodizing solution. Some anodizers use the same RO or DI rinse tank before & after anodizing [eliminates both drag-in & precipitation problems]. Others rinse the anodize in flowing tapwater but follow with a dilute nitric acid solution to clean out the pores (if dyeing).

In any event, DI water should be used prior to and for dyes and seals.

Run test coupons to compare RO and tapwater rinsing on dyeing and salt spray corrosion test results.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007

Thanx alot Ken.

Jawad
- Pakistan
2007

Our lab tests samples daily for aluminum concentrates in the sulfuric bath tanks. We reduced the frequency of dumping by simply running a cartridge-type filter pump during processing. We later added a skimmer to the pump to remove any carry-over oils (which can ruin the finish). Consult your pump manufaturer to ensure the pump materials are acid-proof. Our pump is polypropylene/PVDF, self priming, seal-less with magnetic drive and has held up quite well. We also use the same model in our rinse tanks to reduce the amount of fresh water used.

Derek Suddreth
anodizing shop - Kings Mountain, North Carolina, USA
2007