Iridite 14-2 Testing, pH Control & Maintenance

A. Hi Zander,
I just wrote out a long response and accidentally deleted it...

Short version:

I run 14-2. In almost 10 years I have NEVER adjusted the pH. Not once. I control my bath by annual ~40%ish decants.

Make sure you have a pH 1 buffer to calculate offset. Are your measurements correct?

Are you filtering your bath? DON'T. I typed out why but ... ugh.

When is the last time you did a 25-75% decant?

Have you checked for pinholes in your steam lines.

And if you are freaked out over pH because of test failures ... look skeptically at your deox. Is it strong? Fresh? Free of grease and silicon?

Is your line tech angry about anything? Ask them how they feel about their response time for Class 3. The bath pH has a wide range. But the ideal coating depends on so much more. And a good line tech will start grumbling the moment something ain't right!

Rachel Mackintosh
- Greenfield, Vermont
October 10, 2022

A. Mackintosh has told you all you need to know except for one thing, what is the pH of the rinse water you are dragging into the 14-2?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

A. Hi Zander!
I actually really trust the manufacturer data sheet. If you're staying towards the middle of their concentration / pH brain teaser, you're fine.

One thing I've been told to start up a new tank, is a small amount of sodium chloride (lab, not cafeteria). I made my last from-scratch tank this way after a steam line disaster that still keeps me up at night. I wish i could remember if this was from a macdermid chemist or an industry connection, nor what the amount was offhand, though im sure ive got it written somewhere. It sounds counterintuitive, right?

But the 2024 salt spray problem goes beyond the iridite tank. If i had a quarter for every full-sheet 3x10 sheared 3x10x.032 2024 that i got with massive surface defects, i could wash a load of laundry! Take a few of those panels and run them through tyII or II.5 anodize and ask the line tech how they were after etch, hard to deox, looked funky, just didn't sit quite right. Ive seen a lot with weird longitudinal granular inclusions that will pass salt spray on any type of anodizing, but absolutely crash in chemfilm salt fog.

Your best bet here IMVHO is to look around for alternate coupon sources, and at the same time also try to optimize your deox to be very clean. If you can filter it, that will save you more money in tank dumps and test failures than you will spend in the pumps. I believe the DeOx is the most important tank in a plating shop.

There is a place somewhere in Texas that offers DA sanded and ASTM spec solvent cleaned test panels that mimic an actual part freshly machined and degreased, which is what we all see for parts anyway. So that's arguably the ideal substrate to test on as well. I was DA sanding mine with AlOx (trust me) abrasive to break the mill finish previously, its definitely worth exposing actual true substrate so you don't have to etch so long all the hard to desmut junk gets brought to the surface.

Clean DeOx, clean panels, don-'t over-rinse after the Iridite unless doing that weird colorless spec, no filtering, maybe toss a couple aluminum rack bolts in to add to the voodoo sludge lol. Half kidding.

Half.

Take a sample now and test for chromium, iron, silicon, copper, and barium. Set it aside as your "fresh" tank. Cr and Ba will fall, Fe Cu and Si will rise. Keep an eye on those levels, and in a couple years of quarterly data set against salt spray results, you will be able to predict scheduled decants.

Good luck!

Sorry for the late response. Audit season.

Rachel Mackintosh
- Greenfield, Vermont

A. Mega too strong a hydroxide to raise the pH because it will precipitate some of the chrome out and it takes forever to come back into solution. I suspect that it adversely affects some of the proprietary stuff in the solution also. Why did you want to raise the pH that much? James Watts - Navarre, Florida A. I do not care what the supplier data sheet says, raise the pH with ammonium hydroxide NOT caustic! I suspect your pH measurement is not accurate, that low range is difficult, especially with single jointed probes. Dip out 5 gallons, raise and lower the pH in "apparent" increments of 0.3 until you find the right pH for your particular temperature and concentration. And be sure the deox is working. Robert H Probert Robert H Probert Technical Services Garner, North Carolina

A. I know this is a bit of an old thread but I have a couple things to add.
First, Robert is dead on the money about the NaOH being a less than ideal pH adjuster. There's already sodium in the tank in the form of sodium silicofluoride, but that doesn't mean that it can take a whole bunch more without throwing the chemistry out of whack.

If you are running Iridite you will ABSOLUTELY need to have a bottle of pH 1.0 buffer solution to check your accuracy. Calibrate your meter as usual with the two-point 7 & 4 buffers, then rinse the probe well and stick it in a small beaker [beakers on eBay or Amazon] of 1.0 buffer. If you can find 2.0 buffer, that will also work for this application. Give it some time to equilibrate. When the reading stabilizes, record the value. If your meter is anything like mine, it will not hit 1.0 on a two point calibration. So if your Buffer 1 reading is 1.2, apply a correction factor of 0.2 to your tank reading.

Another thing to note is that the correct pH of the solution is (according to the manufacturer) concentration dependent. So at 0.75 oz/gal the given target is 1.75. At 1 it is 1.6. At 1.25 it is 1.45. Do a titration to find your true concentration before you set the pH. Now, this is information directly from the tech sheet. I have had a consultant suggest a target of .85 oz/gal and pH 1.85, fresh from stock, without the addition of any old tank 'heel' or copper or chloride, just a little scrap aluminum to pre-condition the bath. At that combination the coverage and color is excellent. That was run as a bucket test which is a great way to evaluate your mix without committing to a whole tank.

Your stainless tank is not causing you any issues. Stainless steel tanks are fine for this material. There's ferrocyanide in the formulation. That being said, our tank has been in use over a decade and rather than pitting/etching into the metal, the solution tends to adhere and scale up on it. You'll see greenish residue which is reduced chromium and possibly some copper. The rack sitting on the lip of the tank aluminum-to-steel is fine.

Lastly, the reason you add DILUTE base rather than 50% is actually not to avoid precipitating out the chromium. In a hexavalent state, Cr+ stays put. In fact, a great way to get impurities out of a dichromate seal tank is to raise the pH to 8, drop the aluminum, decant the supernate, ship off the sludge, and return the seal to the bath. You'd see that the supernate naturally goes back down below neutral if you haven't added too much hydroxide, because the -OH is now stuck to the +Al in the bottom of the tank! The +Cr is still in solution. You would have to reduce it to tri with something like a permanganate to get it to form an insoluble hydroxide, which would drop out of solution as pH is raised.

You DO need to be concerned about messing with the activators, though! A large percentage of the Iridite is made up of a Barium salt, and Barium readily forms whitish hydroxides. You'll see almost neon-orange-Tang looking clouds where you pour in your pH-up. Avoid that by diluting it A LOT! I can't find a pH solubility curve for Ba(OH)2 but this would be my first concern. And regardless of pH, its solubility is MUCH greater in very hot solutions. Iridite is not all that hot. Or at least it shouldn't be!

Last, I can't emphasize enough the importance of testing your deoxidizer. Do a white glove test on parts coming out of it. Or use a white cotton towel. If you see ANY discoloration, increase your time, agitation, or concentration. Be sure you are having the aluminum content tested regularly and stay below the manufacturer's upper limit. Deox by its very nature (peroxides or persulphates) is unstable and is rapidly used up under workload and also air sparging will deactivate it slightly. Be sure you are titrating it a couple times a week for redox and once for acid content. Daily maintenance adds are advisable for a busy shop.

Anyway I hope you solved your problem and that this is helpful for future platers! :)

Rachel Mackintosh
- Greenfield, Vermont
April 11, 2016