Electrochemistry Can i use a plastic dish for a suphuric cell?

[mrrdan]

Hello all

This is my first post, but i have been reading the forum for months.

I am wondering if i can use a heavy plastic conainer for the sulphuric cell instead glass? They come is sizes and shapes that to me would seem more usful, and i would think the plastic would be safer since it doesn't break.

I am leaning towards rubbermaid type containers.

Any comments would be greatly appreciated

 

[publius]

I have not, as yet, set up my sulfuric acid cell. Concentrated Sulfuric acid scares me to death. It "wants" to suck the water out of every thing it comes in contact with. I suspect that as the acid becomes hotter with the amount of current introduced, that it could melt the plastic container, and if air or water got into your acid the oxygen available to the acid would begin to break down the plastic.

Not a good idea to use plastic, I think. Glass or china. Never metal.

Robert Jeffery, CWI

 

[NobleMetalWorks]

EDITED I would NEVER use plastic for any electrolytic cell unless it was specifically designed to withstand long term use at temps these cells can build up to.

EDITED Check out this table, notice as the sulfuric acid becomes more concentrated, there are only two types of plastic that are even partially resistant. Sulfuric acid in plastic at room temps is okay so long as the concentration isn't over a certain percentage and it is kept cool. But if you make, and run a plastic cell, eventually the plastic will give out.

The process builds up heat, heat concentrates acids, most plastic does not do well with the types of acids we use when it's concentrated. As heat builds up you run the risk of melting the plastic, as the plastic melts you could short out the two connectors, also as the plastic melts it folds in upon itself. This would trap small amounts of hydrogen gas and oxygen, the two gasses produced with a sulfuric cell. Add to that a spark from your anode and cathode shorting out and you have a bad combo. Imagine a small explosion, a failed plastic container, and sulfuric acid, seems like it would get all over the place.

Also, even using glass you MUST make sure it's tempered, this is the very reason why you see people using the glass Pyrex dishes for their cells. It's tempered and resists acid corrosion.

 

[etack]

the right type of plastic should not be a problem your sulfuric acid is in a plastic bottle. Here is a thread on a cell made of plastic.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=5092&hilit=tumbler+cell


Eric

 

[NobleMetalWorks]

the right type of plastic should not be a problem your sulfuric acid is in a plastic bottle. Here is a thread on a cell made of plastic.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=5092&hilit=tumbler+cell


Eric

That particular cell is a good design, it was originally intended for plating. Eventually however, the plastic bin will give out, and probably the plastic barrel as well. As the heat concentrates the percentage of acid, the plastic will resist it more and more until it finally fails.

The original poster is talking about using a rubbermaid container to use as a cell. He makes the argument that it will not break. It sounds like he's looking for a dish, not a tumbler. Notice in the link you posted that there is a huge surface area, and only the bottom part of the plastic cell is in the sulfuric acid. The large surface area, and the fact only part of the plastic is in the acid, and the fact it rotates and cools makes it a much better design, but even still, the acid over a period of time will still affect it.

If you used a plastic container, similar to a Pyrex dish, commonly used with cells, you have far less surface area to cool down the acid, the plastic container itself is almost totally full, so there is no heat dissipation there either, if the cell is not put in ice, it will heat up and could cause the plastic to fail. The scenario I wrote about, is very real. There is a type of poly that is acid resistant, you can Google it, but it's extremely expensive stuff, so not even worth talking about.

I edited and posted this above, but I am going to post it here as well so you understand what I am talking about. This is a chart for the different acids, and plastics, and rated to show how resistant different plastics are when exposed to different acids. Notice as the temperature rises, the acid resistance quality of the plastic comes into question, and also notice as the acid concentration goes up, so does the plastics ability to resist acid goes down. I think if you read this you will understand my point.

http://www.tedpella.com/company_html/PlasticsChemResistance.htm

STRICTLY for safety reasons, I will not use plastic for a cell, maybe for a tumbler like the one you posted a link for, but even still it will eventually fail.

And please, if I am way off base here, someone call me out on it, I will apologize in this thread if I am wrong.

 

[mrrdan]

Thanks
I think i will be sticking to glass for the dish. The chart was very helpful, thanks SBrown, i see what you mean by the temp and concentration of the acid and the effects on plastic.

I was just looking for a dish that was a bit larger.

Hey quick thought, how about a crockpot vessel?

 

[etack]

A new crock pot would work. The problem with used or old ones is that the gazing cracks. This will allow your acid to seep though and eventually fail.

Good post Sbrown your chart is helpful. 8)

I was thinking that if I was to make a tumbler cell I would use a plastic drum. It would be spooky to have that much sulfuric acid ready to flow on to the floor.

Eric

 

[goldsilverpro]

When you buy concentrated sulfuric, it is shipped in DOT approved 55gal plastic drums. I would guess they are some form of PE.

I wouldn't use a crock pot or any other glazed container. Even the Pyroceram glaze will erode with hot concentrated sulfuric. What I have always used is a mild steel tank. I used the tank as the cathode.

I think any of those Nalgene or Tupperware containers are PE and would be OK to use. I would set them in a steel pan, just in case. Keep your temperature low by not using too much current or stripping too many parts at one time. I would keep the temp under about 130F and, preferably, under 110F.

 

[NobleMetalWorks]

If you are intent on using plastic for your cell, you might want to check out these that were made for plating. Not sure how they will do under heat or used in a deplating cell, but they are made to at least resist acid, specifically to resist acid.

http://www.usplastic.com/catalog/search.aspx?search=plating&page=1

 

[Palladium]

Even the Pyroceram glaze will erode with hot concentrated sulfuric.

So now you tell me! I guess that would explain a couple of things for me. :|

 

[NobleMetalWorks]

Even the Pyroceram glaze will erode with hot concentrated sulfuric.

So now you tell me! I guess that would explain a couple of things for me. :|

I bought my pyrex cells at thrift stores. I always run them in a bed of ice to avoid dissolving other metals into sulfuric, but also to cut down on the wear and tear on the Pyrex dishes.

Do you live in the SF Bay Area? I saw a craigslist post you made, from the area, and thought you might live nearby.

Scott

 

[Palladium]

Even the Pyroceram glaze will erode with hot concentrated sulfuric.

So now you tell me! I guess that would explain a couple of things for me. :|

I bought my pyrex cells at thrift stores. I always run them in a bed of ice to avoid dissolving other metals into sulfuric, but also to cut down on the wear and tear on the Pyrex dishes.

Do you live in the SF Bay Area? I saw a craigslist post you made, from the area, and thought you might live nearby.

Scott

Pyroceram and pyrex are a world apart. I pulled one of your tricks Chris and had to use an old Pryoceram dish for incineration the other day. I was a little weary as to how that might work out. I thought well…….. we will see !!!! It came through like a champ. After all i guess the tip of an incoming ICBM does heat up. :mrgreen:

I didn't have a post on Craigslist. That was a link i posted for reference to something. Nope i live in Bama.

 

[NobleMetalWorks]

I meant to say I saw that you posted a craigslist post on this forum, and that it was from the SFBay, not that you posted on craigslist yourself, lol. Oh man, I have to learn how to write better so people understand what I am trying to say, sorry about the confusion.

I was in Alabama not long ago, but only a day. Alabama, Tenn and Georgia are some of my favorite places in the US.

 

[Palladium]

Here's some info about Pyroceram http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_guid/shp/pyro.aspx

 

[NobleMetalWorks]

Here's some info about Pyroceram http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_guid/shp/pyro.aspx

I use them as temp shock buffers, and also bought them at thrift stores. But I haven't used them for anything else.

 

[mrrdan]

OK so now i am wandering about mild steel tanks. I am a fabricator and could make my own tanks out of what i have laying around. Is there a design that works better than others? More importantly is there any issue with the acid eating through the tank when it gets hot or just over time?

 

[FrugalRefiner]

mrrdan,

If I recall correctly, I believe GSP built his sulfuric cell with mild steel. Rather than hand you a fish, let me teach you a little about how to fish.

Find the search window somewhere on this page (it's location depends on the type of display format you're using for the forum - for me it's at the top right corner of every page). Click on Advanced search. On the advanced search page type sulfuric cell steel for the keywords you want to search for, and just below that type goldsilverpro for the author you want to search for. You'll find a number of posts in which GSP discusses his cells. :lol:

The search function is a wonderful tool once you get used to it!

Dave

 

[goldsilverpro]

I had a 1/4" thick 50gal tank made from mild steel. The tank was made the cathode. I used a 250A rectifier - 5A/gallon. The temperature never ran above 110F, even in the summer in sunny L.A. I mainly ran all-gold CPUs, which had had the lids and chips removed by melting the gold solder(s). They were run on homemade spring-loaded bare brass plating racks I built. I ran about 300 CPUs, per rack, every 30 minutes. I also ran many, many 100s of pounds of CPU lids, with gold braze on them, in a commercial tumbling plating barrel (about $2000 new). Most plated stuff was run in cyanide, although I ran pins occasionally in the sulfuric cell, especially the good stuff.

I spent a year researching a method of modifying the sulfuric cell so that it would strip the Au/Sn and Au/Si gold brazes that are on these CPUs. I can't tell you exactly what I added, but here's a hint. I added 2 different, very specific, halide compounds of certain quantities. Of course, the standard sulfuric cell will strip any gold plating, as long as you can make electrical contact to it, but not brazes, unless you want to take days. Even then, it's iffy you'll get it all.

 

[Traveller11]

When you buy concentrated sulfuric, it is shipped in DOT approved 55gal plastic drums. I would guess they are some form of PE.

I wouldn't use a crock pot or any other glazed container. Even the Pyroceram glaze will erode with hot concentrated sulfuric. What I have always used is a mild steel tank. I used the tank as the cathode.

I think any of those Nalgene or Tupperware containers are PE and would be OK to use. I would set them in a steel pan, just in case. Keep your temperature low by not using too much current or stripping too many parts at one time. I would keep the temp under about 130F and, preferably, under 110F.

Hello GSP
I am intrigued by the use of a mild steel tank as a sulphuric cell. Is the iron in the steel unaffected by this process?

 

[butcher]

Metals can react differently to different acids.
Acids of different concentrations will also act differently on a metal.

Lets look at sulfuric acid and iron.

I can take clean soft iron (transformer laminates), and 10% sulfuric acid and dissolve them quite easily, making copperas (ferrous sulfate), (iron sulfate),(FeSO4), if evaporated to crystals I could use these to test for gold in solution (brown), or use the copperas to precipitate dissolved gold from my solutions.
Now lets take the same iron and add 98% COLD H2SO4, now this iron will on its surface be quickly attacked by the sulfuric acid, but the attack will halt, the iron layer of oxidation will protect the iron from the acid, so basically the iron is passivated and the iron is protected from attack by the acid because of this passivated layer, the iron will not dissolve, unless I diluted the acid with water, sulfuric acid has an affinity for water and will absorb water from wherever it can, it will take water from the air so if we do not want the iron to be attacked by this cold sulfuric acid we must try to keep out the water., another thing is if we heated this concentrated sulfuric acid it would attack the iron (I am not sure of at what temperature?), the HOT concentrated sulfuric acid would begin to dissolve our iron making a solution of Iron III sulfate,Fe2(SO4)3, called ferric sulfate.

So the short answer is the iron can passivate in cold concentrated sulfuric acid and will not dissolve.


eddited to add another thought: as the cathode in a cell, the metals in solution wants to deposit its dissolved metal onto this layer of passivated iron, that also could help shield the iron vessel from further attack, of the acids.