Passivation or not?

[TimCollins]

What are the groups recommendation regarding passivation of plates? I have just learned about this topic. So my question is, how much does the process cost? Can you do it yourself? Is it worth the effort?

[nst6563]

You should definitely passivate your plates. It's cheap, doesn't take long, and you can do it yourself at home with no worry about hazardous material. You can get the Citric Acid at any beer/wine supply shop. It's cheap too.

Here's what I do when passivating.
Wear latex gloves at all times. After putting them on, I run some distilled water over them to get rid of the powder crap.
Clean the plates with a vinegar bath, then acetone (you don't want any surface contamination as it will hinder the passivation process)
Mix your passivation bath in a plastic, acrylic, glass or stainless steel container.
I mix Citric Acid with distilled water - 15% Citric acid by weight.

When passivating the stainless steel the temperature of the citric acid bath should be kept between 140f to 160f for a period of 30-45 minutes. Longer could have negative effects, shorter could not give a complete passivation. If you're unable to heat the solution then let them soak at 70f-77f for a couple hours.

After they've soaked in the bath, take them out and rinse them with distilled water.
Then I put them in a bath of Peroxide (liquid oxidizing agent) for 30 minutes at room temp.
Take them out and rinse with distilled water.
Then I put them in an acrylic container which is hooked up to an oxygen concentrator to run pure o2 around them for a while (I normally just leave them in there with the o2 running overnight). If you don't have an O2 concentrator or source for pure O2, let them hang freely for a couple days as the oxidation process will occur from the O2 in the air.

From personal experience...if you don't get all the citric acid off, you will get discoloration from the residue of the acid. Not to mention that with acid residue left on the plates the surface will not oxidize completely like it needs to.

The peroxide bath I mention isn't entirely necessary - it's something I've been experimenting with as it's been mentioned in a few industry publications as providing a better oxidation layer to protect the SS. If this 'better' layer interferes with the hho production has yet to be seen/verified.

The oxidation process is very important and occurs naturally with SS. As soon as the SS comes in contact with O2 an oxidation layer begins to form. Aiding this process by removing surface contaminates (dirt, iron, other trace metals) improves the oxidation layer's effectiveness. Running Pure O2 over the plates speeds up the oxidation and prevents the chance of airborne contamination.

Do NOT store or get the plates near other metals during this process. I keep mine hung in a sealed acrylic container.

Here's a link to some documents I've collected with regards to passivation. None of them are very long, however one (from the aerospace industry) does go into some good detail as far as concentrations, temperatures, and the resulting thickness of the oxidation layers. It may help you with any questions you might have in the process.
http://www.mediafire.com/?bm1jwwwd5z5ht
At the very least I recommend reading the one labeled AAA passivation methods as it provides the most detailed information as well as some illustrations of tests using salt sprays (standard passivation test is to expose a stainless steel part to a salt spray for a period of 2-3 hours and then clean.). The Aerospace document is from Beoing in St. Louis MO and includes a comparison of Nitric vs Citric acid passivations and their effects on different grades of stainless steel.

[Stevo]

+1 to this post. This is the way to go and thanks for posting this. I too have tried passivation and can certainly vouch for it's effectiveness so long as you don't overdrive your reactor.

[myoldyourgold]

Hey Stevo, where you been all this time?? Any more ear drum damaging tests??

[TimCollins]

I am just learning of this process. I have run the generator a couple of times just horsing around, nothing extended just verifying it would work. Is it ok to passivate after the plates have been run a few times or is it too late? Also, my limited knowledge of this process seems to be that it just removes oxidizing impurities in the SS. If we did nothing and just dealt with some dirty/rusty water for a while wouldn't it eventually clear itself up? I need to dismantle the generator anyway so I will passivate the plates, these are just some questions I have... Thanks a ton for sharing your information!!

[Stevo]

Hey Stevo, where you been all this time?? Any more ear drum damaging tests??

Hey man. Mostly working a lot and switched to a new job not too long after hhounderground.com went under. I just recently started refactoring the last reactor and yes I do plenty more tests to come. :)

[Stevo]

Tim, if you wanted to you could use a higher than normal concentration of NaOH (28%) and run the reactor with than temporarily until you see quite a bit of "purple water" appear. Essentially it is all of the red rust bloom turning to black iron deposits so yes this process will remove a lot. Afterwards just clean the plates and proceed with the exact process mentioned above.

The reactor held up until I started overdriving it (on purpose) with 28% KOH at ~25 Amps (was only built for 14 A max. Just remember to stay at .5 A/sq. in. active surface area or below. What really seemed to cause the reactor to start churning up iron was when I went from 10 to 28% KOH by weight. Some subscribe to the 28% "rule", but I think it's exorbinantly too much for the stainless to handle regardless of preparation or grade.

[myoldyourgold]

Passivation has become more of an issue after finding the advantages of media blasting. There is something to be careful about though if you media blast your plates in regards to passivation. If you are to aggressive with the citric acid or strong NaOH you might damage the sharp points that have been made by media blasting and loose a major advantage of the media blasting. When you are finished everything your plate should make a good fine finger nail file and a paper towel will not slide off easily if at all when you stand the plate up vertically. The natural layer formed is extremely thin and does not affect the media blast texture.

[Darrell]

Just finished passivating my blasted plates. I was able to get the reactor up and running on the bench today. Nothing like seeing that crystal clear elite running thru her again and producing some good number as well.

Passivating is the way to go and I would never run another reactor without it. I would recommend everyone do it.

Stevo, Nice to see your still around.

Darrell

[TimCollins]

I am guessing that the steps are to media blast first, then passivate. Correct? Also, I am guessing the media blast is used to increase surface area. I dont have a media blaster. Would a good sand paper scrubbing achieve similar results, or is that a bad idea? So far, I have not done anything to the plates, they are smooth as glass...

[myoldyourgold]

I am guessing that the steps are to media blast first, then passivate. Correct? Also, I am guessing the media blast is used to increase surface area. I dont have a media blaster. Would a good sand paper scrubbing achieve similar results, or is that a bad idea? So far, I have not done anything to the plates, they are smooth as glass...

Tim, most do not have a sand blaster but find a powder coater and they usually do a good job of blasting. Make sure they understand if not done right the plates will get warped and ruined!!! Sanding with 8o girt sand paper in a cross hatch pattern is better than smooth. I think there is much more to media blasting than just increasing surface area and smaller bubbles releasing easier, just have not been able to explain it yet with good science. Your steps are correct because when you blast or sand you are removing some if not all of the existing passivation and if left alone it will not be even as it naturally passivates, making for an uneven performing plate. Using a controlled stripping of all the existing passivation and impurities and then controlling the process gives you a plate that is evenly passivated across the whole plate.

[koya1893]

For those of you who are as cheap as I am, I found White Distilled Vinegar works well doing passivation. I usually do that after the cell is build, then I use the test run as the cleaning phase. The plates must be media blasted, this is process everyone should incorporate during their build.

[TimCollins]

Any suggestions to properly dispose of this acidic solution after passivation. Is it safe to simply dilute with water and flush away? Citric acid does not sound too bad but if I am wrong please let me know. Wife would kill me if I melted her crapper or burnt her butt...:p

I went with the sand paper approach for this build. I will look for a powder coater for a future build.

[myoldyourgold]

Tim, remember critic acid is a food product. In a whole lot of things. So critic acid by itself is not a problem but what else is in your citric acid after using it to passivate the plates is unknown to me. Get it tested and let us know. I can say it will not melt your crapper. LOL What ever you do with it be responsible.

[TimCollins]

Well I completed the passivation process last night. So on with the build. I did not have the luxury of heating the solution so they simply soaked for two hours at room temp in solution. I followed all of the instructions so I presume all is good. From what I have read there is no real test to confirm the process was successful other than time will tell. If you know of any test, please let me know... Thanks a ton for all of your help and advice!