Chromicoat L25 won't plate to 2024-T3 Aluminum

A. We suspect your pH measurement is slightly out of whack.

Dip out two buckets, then however you measure pH, raise the pH in one bucket by 0.3 with ammonium hydroxide, lower the pH in the other bucket with nitric acid, run three panels down the line, one in the tank, and one in each bucket. Observe the results.

If the above is no difference, then go back to the deox, make up a new solution in a bucket, make a 25% add to another bucket, run three panels, let us know what happens.

A. Edmundo

Have you always used the L25?
Have you been able to achieve favorable results on 2024-T3 before.

If yes to both, look for that which has changed (or could change) in your process... rack material, galvanic currents, aging chemistry, water quality, new chemical lot addition, new Al source.

If the L25 is new to your process, verify you can process 2024 by mechanically cleaning a coupon and immediately immersing in the L25 for your standard duration. If the coupons coats, start adding one of your standard steps and repeat until you find the problem.

A. Try skipping the etching process and use a little longer deox time. You may find it useful to have a sample analyzed by Oakite. You may find your chemistry is out of balance

A. Hi Michelle,

Look up the Qualified Product Database (QPD) on the DoD Assist Quicksearch for MIL-DTL-81706 [on DLA] . These are all products qualified to be used to produce coatings in accordance with MIL-DTL-5541 [on DLA]. From that list look at the Material Safety Data Sheet (MSDS) for information about the contents of the solution or ask the manufacturer of the product you are considering whether it contains HF.

A. You need to know the concentration of the HF in the product to really determine how serious a factor it is. I have used concentrated HF and I have the greatest respect for it. However a 0.1N solution is pretty much a pussy cat with the minimal amount of safety gear.
Your product starts with an L so I assume that it is a liquid. Note that they probably sell a similar product that is a granule. Therefore it will have a fluoride like sodium or potassium fluoride [affil links]. Does this scare you?? If not, why does it as HF scare you?
Environmentally, the chrome6 is more of a hazard.
This is my worker bee opinion.

Great advice (check the concentration in the product). The concern is hydrofluoric acid can cause severe chemical burn, but when skin receives the exposure, the burn/damage doesn't show up until many hours later.

Hydrofluoric Acid

from Wikipedia: In the body, hydrofluoric acid reacts with the ubiquitous biologically important ions Ca2+ and Mg2+. Formation of insoluble calcium fluoride is proposed as the etiology for both precipitous fall in serum calcium and the severe pain associated with tissue toxicity. In some cases, exposures can lead to hypocalcemia.

I am researching this for a company. I presume, due to the chrome, that PPE is used, so skin contact may not be very likely anyway.

A. A true HF burn is indeed very serious. Unlike strong acids, it tends not to have much pain associated with it until it has done damage.
You need to take a look at the first aid requirements. After normal flushing, it needs to have an injection of a material under the burn. I do not remember what it is, but it requires a prescription. It took a good bit of begging for the local ER to keep it on hand and to try to get them to know the appropriate treatment.

A. It's calcium gluconate. It deactivates the fluoride by precipiting the F-.

A. You can get tubes of Ca gluconate paste from Grainger under the trade name 'Calgonate'. It is intended to be used externally IMMEDIATELY upon dermal exposure to HF. The injectable stuff requires a trip to the ER. Use the paste to buy time while you're on your way to the parking lot...
IMVHO, if you're messing with concentrated HF, it is essential to keep a couple NON EXPIRED tubes in the first aid kit and check in with your nearest urgent care facility to make sure they are ready to deal with an exposure.
As an aside, you're just as likely to have HF in your desmut or satin mask... Even if it comes as a powder, check the MSDS for Fluoride salts.