Nitric storage issue

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MarcoP

Well-known member
Joined
Jan 22, 2014
Messages
735
Location
Sicily Island
Hi all, I'm not sure in which forum this topic fits the best, Chemicals or Safety.

My nitric acid container is discoloring and it is happening where the condense build up. Is this normal? Do I need to change container to avoid an accident waiting to happen?

It is 53% nitric, currently stored away from direct light and other chemicals.

Thank you in advance
Marco
 

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I would get it out of there ASAP... glass or 3xx stainless is the standard for nitric storage. I have mine in glass, which are then in a 5 gal bucket with some sort of funky gray cloth (thats what they had when I got them, no idea its composition, but I'm assuming it helps for insulation/ maybe to help absorb escaping gasses to prevent deterioration of its surrounding?...)

But nitric acid is ROUGH on plastic. So, I, personally, would make time to put it into another container unit, just because that will be much simpler than cleaning up a few gallon mess.

best of luck to you
 
You can prevent that happening by putting 5% F2 gas balance argon into the container for an hour or two.

Or, you can put it into stainless or glass bottles.

Overtime, you see the NO2 production slowly penetrate the HDPE.

Lou
 
Lou said:
You can prevent that happening by putting 5% F2 gas balance argon into the container for an hour or two. ...

Lou

That's a pretty good bit of interesting info Lou, I have a couple questions in regards to it, if you don't mind.

1. Does the addition of the 5%F2/argon create any unwanted contaminates that may taint the refinement of gold or other PM's?

2. Where would a guy go about finding F2 gas?

My nitric is in glass, but the caps are plastic, and I would hate for one of them to go bad and cause me problems in the long run, but, if the addition of gas would cause any unwanted problems in the second refinement of gold or anything else, I will just have to talk myself into using the nitric faster.

Thanks for the info, and any additional wisdom you may bestow upon me 8)

Beav3r
 
After reading your replies I started looking locally, to be as quick as possible, for a 304L container but I can only find 304. Would that be ok?

In Italy 304 and 304L seems to be under the same name, Inox 18/10.

Marco
 
304 is fine.

Dave

Edit: While 304 stainless is resistant to nitric acid, if it has been welded, it must be properly annealed to preserve that property. As Lou has stated below, 304L is preferable because of it's more forgiving properties during welding. See my post below for more information.
 
304 L is preferred for 16M on down nitric acid.


Lou

FYI, was joking about the fluorine thing. It does work and that's how they treat HDPE to fluorinate the inside for added chemical resistance.
I had a bottle of 99% nitric acid in FEP that slowly caused the bottle to blister!

Lou
 
99% Nitric? Ouch- the 70 something percent stuff is "interesting" enough to work with.
 
At the speed my chemicals are being used I need a long time storage option and since 304L is not easy available (tank and tap) I would definitively go for 25L narrow neck bottles, a small diaphragm pump and after those holidays I'll replace the plastic lid's bottle with proper rubber stopper.

By the end of next week it will have to be done. Unless there are unseen caveats I'll proceed this route.

Marco
 
Right, more over I've just searched for PTFE and Viton stoppers but to my surprise none available.

Reading about Viton, it says that unless its red fuming it is recommended with little or minor effect.
Could I just get a 0.5mm Viton sheet, cut to diameter and use it as a seal between bottle's mouth and plastic lid?

Marco
 
MarcoP said:
Could I just get a 0.5mm Viton sheet, cut to diameter and use it as a seal between bottle's mouth and plastic lid?
I've tried the same thing. I had an old bottle of nitric, and after opening it, the cap crumbled into pieces. I needed a quick solution and didn't have any proper containers. I was able to temporarily use a mason jar with a standard metal ring and lid by cutting a thin piece of PTFE to the same size as the lid and putting it on the jar, with the lid and ring on top. It lasted much better than I think a plain lid would have, but eventually the lid and ring still began to deteriorate.

Dave
 
Dave, that put me on a corner. I could just get a 304 tank and within few months I'll have to replace that with a 304L. Need to buy time to find one.

That's when studying ahead can simplify things, however I thought it would have lasted little longer (unless it was given to me an old stock).

Marco
 
Marco, the main problem with storing nitric in HDPE is that it causes the plastic to become brittle, which can lead to eventual failure. The key word is eventual. It doesn't happen overnight. If you check the charts of chemical compatibility, you'll find that HDPE is considered acceptable for storage of dilute nitric, but not concentrated acid.

You mentioned that your acid is 53%. Concentrated nitric is generally in the 68% to 70% range (about 15.6 molar), so I would consider yours to be slightly diluted. I don't know why you're seeing that discoloration so soon. It may just be bleaching the coloring agent, or it may indicate a more serious problem. I've actually had 10 molar acid stored in a heavy plastic bottle for about 40 years.

My first suggestion is to always have your acid container sitting in a second container that can capture the acid if the primary container fails. For a jug like that, I would suggest a plastic concrete mixing tub, which we have available in most hardware stores here. The potential danger is that if the jug has become brittle, it could fail if you try to lift it to put it in the tub. If you have some other HDPE or glass containers you can use for temporary storage, you can siphon the acid into them, put the large jug into a secondary tub, then return the acid to the jug.

Alternately, if you have enough HDPE containers, you can transfer the acid to them, then store them in a similar tub, or smaller secondary containers. Use only thick containers. Milk jugs are HDPE here, but they're far too thin. You want something heavier.

You could also dilute the acid a bit more to buy more time if you have to store it in HDPE. For silver work, you're going to dilute it anyway. For gold work, a bit of dilution probably won't cause you any problems.

As I mentioned, the PTFE I cut for the mason jar did buy me extra time. It just didn't create a perfect seal, so eventually the fumes started to corrode the metal rings, but it bought me the time I needed.

Dave
 
It appears my knowledge of stainless steel varieties, and their resistance to attack by nitric acid was incomplete. After Lou specified 304L stainless, I went on a mission to find out why. I thought I'd share what I learned.

My recommendation of 304 in my post above was based on my belief that stainless steel beer kegs were made of 304 stainless, and that they were suitable for storing 68% to 70% nitric acid. I found the best, simple explanation in an article at Realbeer.com.

The corrosion resistance of stainless steel depends on the chromium.
Austenitic stainless is a super-saturated solution of chromium and nickel in
iron. It is actually a very high temperature phase that has been quenched to
preserve the distribution of elements. Austenitic stainless does not like
middling-high heat. It performs well up to 600F (315C), but higher
temperatures in the range of 800-1600F (425-870C) cause atom diffusion which
causes the properties to change. Temperatures in this range allow the chromium
to diffuse away from the grain boundaries to form chromium carbides, the
preferred crystalline structure in that temperature range. Exposure to the
temperatures that cause diffusion is referred to as being "Sensitized". The
diffusion of chromium away from the grain boundaries results in un-stainless
grain boundaries surrounded by stainless steel. This situation soon leads to
localized corrosion and rapid cracking of the grain boundaries. To correct
this, the metal must be heated to at least 1900F (1040C) for a period of time
in an inert gas atmosphere and then quenched to retain the austenite crystal
structure. Unfortunately, doing this heat treatment to a welded keg would
result in a lot of warping and distortion. It is better to get another keg
and start over.

Welding is a local melting/freezing process that creates high temperature
gradients in the metal around the weld. This Heat Affected Zone (HAZ) is the
region where unwanted atom diffusion can take place if it is hot enough, long
enough. There are time/temperature curves that describe this, and the curve
for alloy 304 is shown in Figure 2. This chart shows that for type 304
stainless (nominal carbon content of 0.08%), five minutes at 600C (1110F) or
above will cause chromium diffusion that will later cause cracking in service.
Type 304L stainless, "L" denoting less carbon (nominal 0.03%), is more
weldable and can spend about 6 hours at 600C before becoming Sensitized. Most
kegs (in North America) are made from 304L to facilitate the welded
construction.
So it appears our US beer kegs are indeed suitable for storing nitric, but they are now made of 304L, not 304. 304 is still suitable for nitric contact as long as it has not been welded, or, if it has been welded, it has been properly annealed. So a 304 cap and clamp are suitable for use on a 304L keg.

Sorry if I caused any confusion. :oops:

Dave
 
Nothing wrong. Continue to keep the nitric acid in the plastic canister. Discoloration of dye is the result of the reaction of acid vapors penetrating through the polyethylene into the surrounding air. Such processes are called diffusion. Diffusion of gases passes approximately 1,000 times faster than in liquids. So, discoloration occurred only in the upper part of the vessel, where is acid vapor but not liquid. Note the speed of the process depends on the material thickness. So, discoloration occurred symmetrically in thin areas canisters.
 
Viy said:
Nothing wrong. Continue to keep the nitric acid in the plastic canister. Discoloration of dye is the result of the reaction of acid vapors penetrating through the polyethylene into the surrounding air. Such processes are called diffusion. Diffusion of gases passes approximately 1,000 times faster than in liquids. So, discoloration occurred only in the upper part of the vessel, where is acid vapor but not liquid. Note the speed of the process depends on the material thickness. So, discoloration occurred symmetrically in thin areas canisters.
I'm not so sure that there's "nothing wrong" with storing nitric in plastic. If it was safe, industry would have done so right along.

My experience dictates that nitric degrades plastic, and does so at the expense of tensile strength (it becomes brittle). I shudder to think what would happen if a guy picked up a five gallon container that ruptured. We've all had a minor nitric burn, I'm sure, so you probably understand from where I'm coming.

In regards to the difference between 316 and 316L, the L designation is to signify a lower carbon content, which is already quite low in 300 grades of stainless alloy. 316 is reputed to contain .08% maximum, while 316L contains only .03%. While I am not implying that it makes no difference, pretty much any of the 300 series stainless alloys will suffice, and be far superior to glass, or, especially, plastic. Passivation of the 300 series of stainless is typically accomplished with nitric and potassium dichromate.

Harold
 
Marco, make sure you destroy that container when you find another one for your Nitric. Blue is usually a drinking water container and you wouldn't want someone to use it for anything really, after having Nitric Acid in it.
 
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