I would like to study the effect of corrosion (on the cell or in the electrolyte) in my electrolysis cell with different materials for the electrodes:
- SS316
- Hastalloy H or B
- alloy 42
- Nickel Foil
- and maybe a Sintered Mesh material
On top of that, I would like to determine the effect of pre-operational conditioning of the electrodes which may include cleaning of the electrodes and reverse potential treatment.
Can anyone offer any information or suggest a design experiment to effectively carry this out. With polarization curves maybe.
The reason for these tests is to create a cell that will produce hydrogen for over 10 years within an enclosed environment without any maintenance except the periodic addition of de-ionized water. The cell already contains 20% w/w KOH solution at startup. Theoretically, only H2 and O2 is bubbling out of the cell and no other chemicals or substances should be entering the cell. Thus, corrosion is my only problem. If anyone has any input on how to minimize this corrosion or ideas of experiments with the aforementioned materials and preconditioning, it would be of great value to me.
There should not be any corrosion just as long as the water doesn't contain any contaminants...
The reason I ask is that after two or so years of running this electrolyzer with SS316 plates, a black sticky goo is found to be left on the bottom of the cell. I don't really know what this is.
well If the plates were not conditioned properly than I would say it was the Impurities of the surface layer of the plates. If they were then I have no clue. Are you using pure KOH?
The KOH comes from a stock supply and are diluted from 40% w/w to 20 ish with deionized water. Anyways, I would have to run some tests to see.
I am running an experimental cell with 2.5 meg Ohm /cm ID water with NaHCO3 650g : 2g an after only a few kW it looks like pond water, 304 SS, 5A @ 10V!! I am going to look at a acid cell next.
By any chance are the stainless tubes propperly passivated and re-annealed after cutting?
Quote from: Duranza on September 14, 2007, 08:59:25 PM
By any chance are the stainless tubes propperly passivated and re-annealed after cutting?
Do you know what the recommended post processing procedure is? To be honest all I have done to date is de-burr degrease and go!
Best, HTwoGo
The way I did mine was to anneal them and then soak them in lime juice ( citric acid ) over night. Then let them dry completely and wash them to stop the passivation. Some people do a 2nd soaking in KOH overnight, but i feel that's unnecesary for my Meyer replication. It might work for you though since you are using KOH anyways....
...how do you do the annealing?
Best, HTwoGo
Well you need a furnace to do that... Try to look for a metal working shop and have them anneal them for you. You must get all the stress out of the metal. After they are annealed you can't modify them anymore without re-annealing them...
?the furnace is not the problem, I?ve got a small tool room furnace good to 1100deg C but we have no experience of SS, with out any other input I would take the plates to 900C no soak needed as they re so thin and then let them cool in the furnace until back to ambient. Should I give it a try?
@HTwoGo,
You have a furnace, an electronic balance, lab software, power sources, calibrated instruments and many more... Obviously, a very nice lab! Above all, excellent skills and fine researcher abilities and knowledge. It?s a real honor and pleasure seeing you around!
I know it?s off-topics here but anyway, since I?ve noticed that you came and go, probably without digging through too many threads, do you mind having a look at http://www.overunity.com/index.php/topic,3086.msg49853/topicseen.html#msg49853?
It?s an interesting theory and I still hope in successful experiments, although I haven?t reached that point as of yet?
Tx,
Tinu
You have to dwell them at temperature between 1060-1120 C for at least 30 mins and back down to just bellow 1000 C for 30 mins and do this cycle 4-5 times to anneal them properly. Your furnace sounds like it will do the job. Remember to let them cool inside the furnace without opening the door after the completion of the process.
Quote from: Duranza on September 16, 2007, 11:08:30 AM
You have to dwell them at temperature between 1060-1120 C for at least 30 mins and back down to just bellow 1000 C for 30 mins and do this cycle 4-5 times to anneal them properly. Your furnace sounds like it will do the job. Remember to let them cool inside the furnace without opening the door after the completion of the process.
?okay I have run two test pieces, of 304 S/S plate, one I ran the protocol above at 1100 C and I will know the results tomorrow morning.
The other I followed a more convention protocol i.e. quench from full heat 1100C per this link? http://www.azom.com/details.asp?ArticleID=965#_Heat_Treatment
The quenched plate suffered badly from distortion and (probably my carelessness) if it proves the better protocol I will need to somehow control this, perhaps a sandwich between some slabs of 310 S/S, this I have done before but in a production setting with controlled atmosphere.
Once I have both samples ready I will be passivating in 20% nitric acid at 50-60C for 30 min.
Best, HTwoGo
Remember that they need to air cool inside the furnace without opeing the door.. You are not looking to harden them by quenching. The property of the SS has to remain unchanged...
I wanted to condition some 3 inch square SS plates that I had made. I didn't have plate material, but I had SS tubes, barely noticed by a magnet, so I guess 316. I cut the tubes into 3" lengths, cut a slot down the tube, and pounded them out flat with a heavy hammer.
I knew I had introduced plenty of stresses so I wanted to do a full anneal, but I don't have a suitable furnace. The best I could do was heat them to bright orange with oxy/acetylene and then quickly stick them into a cavity in my casting sand and slap a cover over them to slowly cool.
The problem I ran into was in heating them with the torch. They badly distorted, undoubtably because of uneven heating. So I have a bunch of warped plates that need pounding again.
Thought I would post this so anyone else thinking of annealing plates in this fashion might want to think again, especially if they are nice, flat, store-bought plates.
HTwoGo>>>>>
If ur furnace cannot accommodate inert atmosphere annealin>>>dont try it!
Process>
Place tubes in furnace>>>>>purge in Pure Nitrogen / Argon gas>>>donot open furnace after dis
Have leakage gas flowing continuously through the annealin process.
Heat to required temp>>>hold for time of specific grade*
Let the furnace cool 2 atleast 100-150 deg C befor u remove d pipes
Inert gas (leak) has to run till pipes cool of & u open d furnace
Incase u get an oxide coat>>>>ur inert gas wasnt sufficient!>>>>> u'll have to sand d tubes n start all over!
* 304L >>> 1050 deg C for 70 minutes
* 316L >>> 1050 deg C for 90 minutes
d hold time varies on thickness aswell>>>for pipes upto 2mm thick above time's ok!
Gh. J.
?I have decided to abandon this trial until I can get some sort of controlled atmosphere in place, the contrast between the exposed an protected surfaces of the slow cool sample is so much I must conclude there would be little worth knowing from going any further.
Best, HTwoGo