# NOx, put my mind at ease, smell PPM?



## snoman701 (Dec 6, 2016)

I've got a godawful cold.

I've been using nitric acid as of late.

Today the cold was ok in the morning, then got worse as the day progressed. 

I worked in the shop today, where I store my acid and glassware. 

You can see where I'm going. 

I have not performed any active reactions in well over a week, and they were all performed outdoors, but the glassware came back inside. Everything is capped (and seems secure) except a beaker that I use to transfer nitric, and that has a watchglass over it. My silver is sitting out drying (following copper nitrate cementation)

Shop has pretty good ventilation, but I'm still paranoid. None of the iron around the chemical storage area has rusted. No signs of a chemical leak anywhere, etc. 

I have exposed myself before on accident, so I know what nitrogen dioxide smells like....and I have not smelled it, but I can't figure out at what exposure you can smell it.


----------



## nickvc (Dec 7, 2016)

Most if not all the fumes from the reactions we create are best not inhaled at all but the truth is we all get some of them even when working with a fume hood. The point is to realise that you are in the danger area and to keep our exposure to a minimum, if your working in your shop open a window or the door and place a fan to blow the fumes out, it's a case of been careful and aware of the fumes that we are producing from any reactions we have going even ones we assume are over.
We are exposed daily to hazardous fumes from industry, cars, household products etc so just be aware of what exactly the fumes are likely to be and where from in your recoveries and refining and exercise caution and care as well as you can, if you get too paranoid about it you might as well give up this hobby/ pastime, study and read and learn what exactly is the likely fumes you are going to be around.


----------



## snoman701 (Dec 7, 2016)

The paranoia comes from last week. Had to take Dad out to mayo...didn't get the answers we were hoping for, but got the answers we've all been expecting. It's been a rough go.

I've been around chemicals all my life. I've done some stupid things, which I'm sure we all have at one time. I understand what I'm working with. The phrase I was looking for was "odor threshold" and it's 5 ppm. But what I was staring at was "death at 100+ ppm for a period over 1 hr". At my last real job, I set up an ethylene oxide sterilizer. Odorless, and carcinogenic. I had to perform exposure monitoring, and send the results off to be analyzed. I'll have to look in to NOx monitoring. 

The reality? I have a bad cold progressing in to bronchitis. It's worse because I flew last week and am under lots of emotionally draining stress. My lungs aren't eating themselves any more than normal. 

Thank you for your response.


----------



## anachronism (Dec 7, 2016)

I tried to find the level at which is its "smellable" Sno and I couldn't find it either. One thing to note, you mentioned that your steel isn't rusting in your shop, but don't take that as a marker of whether nitric is fuming or nox is being produced because it's the HCl that rusts the steel not the Nitric. 

I know where you are, I am paranoid about those fumes myself and aside from the fume cabinet extracting air at 1300 cubic meters per hour I also have exhaust fans (cheap ones) that cycle the air in all parts of the building more than once per hour.


----------



## autumnwillow (Dec 7, 2016)

Check your acid containers if they are sealed properly.

Hey, I sniff my scrubber exhaust fumes all the time just to check if the scrubber is working properly or not. I use my hand first to direct the fumes to my nose, if negative I put my nose closer to the exhaust port of my vacuum pump! Heh. So, I do not think that your illness is because of your exposure to nitric/hcl fumes. But also take note that I have only been refining for about 6 months.

You need a doctor, could be just a bacteria or a virus.


----------



## FrugalRefiner (Dec 7, 2016)

anachronism said:


> it's the HCl that rusts the steel not the Nitric.


Both will cause steel to rust.

Dave


----------



## snoman701 (Dec 7, 2016)

autumnwillow said:


> Check your acid containers if they are sealed properly.
> 
> Hey, I sniff my scrubber exhaust fumes all the time just to check if the scrubber is working properly or not. I use my hand first to direct the fumes to my nose, if negative I put my nose closer to the exhaust port of my vacuum pump! Heh. So, I do not think that your illness is because of your exposure to nitric/hcl fumes. But also take note that I have only been refining for about 6 months.
> 
> You need a doctor, could be just a bacteria or a virus.



Please avoid the direct "wiff" like that. Your method of using your hand is absolutely correct, but moving closer to the exhaust will exponentially increase the dose you absorb if for some reason your sniff test was wrong. 

I moved all of the chemicals outside today. After moving them all, I can almost positively tell you that I have not been exposed to anything recently....well, except a snot faced five year old. 

Would the NOx gas be a strong enough oxidizer to rust steel or iron? It would seem so, but my brain is a little foggy.

Thank you again for all of your responses.


----------



## autumnwillow (Dec 7, 2016)

NOx will oxidize iron, some types of steel, but not all.

I had a similar illness and was as paranoid as you thinking it has something to do with refining. I was feeling okay in the morning, in the afternoon I felt very weak and in the evening I had shivers. This went on for two weeks. I got myself checked up and it turned out to be just a urinary tract infection.


----------



## Topher_osAUrus (Dec 7, 2016)

Yes, NOx fumes will rust steel/iron, as Dave mentioned above.

You seem to be in the correct mindset though, any NOx in the air you're breathing, is too much.

But, like Nick said, we get horrible things in our lungs from our modern world too.. Car exhaust is a nasty one.


----------



## anachronism (Dec 7, 2016)

FrugalRefiner said:


> anachronism said:
> 
> 
> > it's the HCl that rusts the steel not the Nitric.
> ...



Nitric acid fumes or Nox Dave?


----------



## snoman701 (Dec 7, 2016)

anachronism said:


> FrugalRefiner said:
> 
> 
> > anachronism said:
> ...



Both.

Nitric acid fumes = strong oxidizer, so it's oxidizing the iron.

NOx fumes, I think, following same mechanism it does when it's in your lungs. Reacting with moisture to form nitric acid, thus oxidizing the iron. At least that's what my brain decided when I was driving home from the grocery store.


----------



## Topher_osAUrus (Dec 7, 2016)

If i was a betting man, Id say its probably the oxygen in the NOx fumes thats rusting the iron/steel.
Or, if were talking NOx fumes from AR, it could be the O or the Cl from the NOCl.


----------



## anachronism (Dec 7, 2016)

Topher_osAUrus said:


> If i was a betting man, Id say its probably the oxygen in the NOx fumes thats rusting the iron/steel.
> Or, if were talking NOx fumes from AR, it could be the O or the Cl from the NOCl.



I'm with you Toph on this one. My understanding which could be wrong is that NOx and water makes Nitric and Nitric with iron forms a layer of Iron Nitrate.

The rusting is caused by the HCl.


----------



## Topher_osAUrus (Dec 7, 2016)

If the oxygen dissasociates from the NOx and recombines with the iron, it in turn would be creating iron oxide, which as we all know is rust.

If chlorine attacks iron, it would be creating rust too, but (this is a guess at best) I think it would be creating ferrous chloride, which would then oxidize via atmosphere into iron oxide.

One of our chemistry guru's will certainly set us straight soon.


----------



## snoman701 (Dec 7, 2016)

anachronism said:


> Topher_osAUrus said:
> 
> 
> > If i was a betting man, Id say its probably the oxygen in the NOx fumes thats rusting the iron/steel.
> ...



Iron oxide does not form in the presence of just dry iron and oxygen. You need water. 

Iron alone will form a passivation oxidation layer, that will largely be unaffected by further oxygen exposure. You have to have a motivator. The nitric acid, HNO3, reacts to form HO and NO2...the hydroxide is what speeds the reaction along. 

Drop a piece of steel in to dilute or concentrated nitric...it will react....quite violently I might add (excluding a specific percentage). I made that mistake!


----------



## Topher_osAUrus (Dec 7, 2016)

The humidity in the atmosphere is generally enough I'd imagine.


----------



## snoman701 (Dec 7, 2016)

Topher_osAUrus said:


> If the oxygen dissasociates from the NOx and recombines with the iron, it in turn would be creating iron oxide, which as we all know is rust.
> 
> If chlorine attacks iron, it would be creating rust too, but (this is a guess at best) I think it would be creating ferrous chloride, which would then oxidize via atmosphere into iron oxide.
> 
> One of our chemistry guru's will certainly set us straight soon.



Chlorine as a gas does attack iron, very violently. Pretty cool...look it up on youtube!

However, I think you speak of hypochlorous acid, not chlorine gas. If chloride + iron = iron chloride, all the cars in Michigan would be rusting to iron chloride, not iron oxide. (due to our use of salt on roads)


----------



## anachronism (Dec 7, 2016)

snoman701 said:


> Drop a piece of steel in to dilute or concentrated nitric...it will react....quite violently I might add (excluding a specific percentage). I made that mistake!



I'm not entirely sure what you dropped into the Nitric but I don't think it was steel. I've stripped loads of gold from steel using Nitric. The steel is fine and dandy.


----------



## FrugalRefiner (Dec 7, 2016)

anachronism said:


> snoman701 said:
> 
> 
> > Drop a piece of steel in to dilute or concentrated nitric...it will react....quite violently I might add (excluding a specific percentage). I made that mistake!
> ...


Do you mean steel, or stainless steel?

Dave


----------



## Topher_osAUrus (Dec 7, 2016)

snoman701 said:


> Topher_osAUrus said:
> 
> 
> > If the oxygen dissasociates from the NOx and recombines with the iron, it in turn would be creating iron oxide, which as we all know is rust.
> ...



Well, there *is* a reason why vehicles get (more) rust damage when they are closer to the oceans, or in colder climates (that's why -salt).

I think you overlooked one line of my post. (underlined)
Where the ferrous chloride (ferric?) would then disassociate with the chlorine and combine with the oxygen in the air to become iron oxide.


----------



## anachronism (Dec 7, 2016)

Dave, steel, stainless steel and ferrous derivatives such as Kovar.

Edit: For example look at how reverse AR works.


----------



## FrugalRefiner (Dec 7, 2016)

anachronism said:


> Dave, steel, stainless steel and ferrous derivatives such as Kovar.
> 
> Edit: For example look at how reverse AR works.


Those are far different animals. Reverse AR works on stainless steel because the nitric acid passivates the chromium in the stainless. Without the chromium, the steel will not survive. There is a reason nitric acid is shipped in stainless steel containers, not mild steel or carbon steel.

Dave


----------



## snoman701 (Dec 7, 2016)

Topher_osAUrus said:


> snoman701 said:
> 
> 
> > Topher_osAUrus said:
> ...



I saw it.

The chloride ions increase the conductivity of the electrolyte on the surface of the iron. This increase in conductivity increases the speed of the reaction between water and iron.


----------



## g_axelsson (Dec 8, 2016)

Chloride is way worse on rusting stuff, the chloride ions work almost as a catalyst and attacks iron. Similar to how copper chloride etch works according to some sources.

It seems like the chloride ion is able to break down the protective surface of oxides and 
Just google "chloride-induced corrosion" and you will find a lot of information.

One of the areas that deals with chlorides and their effect on iron objects are marine archeologists. Objects found in the sea is infused with chloride ions and one step in the conservation of iron is to remove the chloride ions.

The process where HCl is accelerating the corrosion of iron is basically :
1. Fe+2HCl -> FeCl2+H2
2. 4 FeCl2 + 10 H2O + O2 = 4 Fe(OH)3 + 8 HCl
The HCl is free to go back to dissolve more iron. It doesn't improve the situation that the iron chloride salts are hygroscopic and sucks moisture from the air.
More about marine archeological treatment of iron objects here
http://nautarch.tamu.edu/CRL/conservationmanual/File9.htm

I once saw a spectroscopic lab on the university where a 500g cylinder with HCl gas had sprung a leak over the weekend. The only metal thing they managed to save was a wrench and that was all brown from rust. The five HP IR-spectrometers in the lab were all scrap.

Göran


----------



## snoman701 (Dec 8, 2016)

Chloride is especially responsible for the pitting and undermining of the surface. 

When I age steel, I spray it in HCl, then I sprinkle table salt on it. Wherever the table salt crystals settle, you get a really nice pit. 

Chemistry is fun!


----------



## goldsilverpro (Dec 8, 2016)

Yes, nitric will dissolve steel and other iron alloys, except for SS. 

I once spent quite a bit of time working on a process using nitric to dissolve the very heavy silver layer from steel aircraft bearings. If I remember right, there was about 1/2 oz Ag on each half bearing. We had many, many drums of these bearings. I found that, if I used straight concentrated 70 percent nitric, it would dissolve the silver without attacking the steel. With even a 2 or 3 percent addition of water, the steel would react vigorously. The fly in the ointment was that, as the silver dissolved, it would heat up the solution slightly and then, after a few minutes, this would make the steel would start dissolving. The bearing halves were about 3" dia. X 4" and I was experimenting in a 4 liter beaker. I was sitting there watching it and, after a few minutes, there seemed to a simultaneous flash over the entire steel surface and then it would all start dissolving. Failure - I never could tame it. We ended up chucking 2 bearing halves together in a lathe jig and cutting the silver off.

Another time we had many drums of silver plated kovar electronic lead frame scrap. The silver ran 7 percent, or about 1 troy oz Ag/pound - good stuff. The kovar was 54 iron, 29 Nickel, and 17 Cobalt. Here again, the same thing - concentrated Nitric would dissolve the silver but not the kovar. This wasn't quite as sensitive as the bearing steel, but you couldn't run too much at one time or the solution would get too hot and attack the kovar. We also let it cool between batches. If I were to run these or the bearings again, I would use a heat exchanger and keep the solution cool.

I have always promoted the use of about 40 percenthot nitric to dissolve the kovar on TO5's and ceramic CPU packages.


----------



## Lou (Dec 8, 2016)

Not to derail the thread much further, but that phenomenon is passivation and that's what's related to the concentration of the acid. 

and when de-passivation happens, then you have the big time NOx issue. 

So when GSP is talking about the fly in the ointment being the heat, I somewhat agree as that can shift the potential curve. What really is the true fly in the ointment is that as silver dissolves in concentrated nitric acid water is produced:

Ag + 2 HNO3 = AgNO3 + H2O + NO2

and therein lies the issue.


----------



## snoman701 (Dec 8, 2016)

Thanks for the response!

Had he simply used excess nitric, he would have likely been fine. 

Although with that much silver, mechanical removal does certainly seem better. Then final removal of intermediate layer can be refined in a more controlled manor.


----------



## kurtak (Dec 9, 2016)

Snowman 

Something I do in my lab to monitor/check if I am having a problem with acidic fume in my lab is leave 3 or 4 pieces of pH paper sitting out at different locations in the lab

Due to the fact that I keep/let my fume hood run 24/7 I have little or no problem with fumes building up in the lab (according to the pH paper) also I have tools (iron) & copper (used for cementing) that has been in my lab since the day I built the lab (about 4 1/2 - 5 years) that show no sign of corrosion 

I actually have more of a problem with tools & other iron corroding outside the lab (in the shop &/or storage area) during the summer when humidity often runs high then in my lab --- so apparently not only does keeping my hood running 24/7 keep fumes out &/or from building up in the lab - but it also helps to keep the air dry

Therefore IMO whether iron is corroding or not is not really a good indicator of fumes or no fumes (especially if you live in a high humidity area) because it will certainly corrode even if there are no acid fumes

pH paper sitting out on the other hand will tell you if you have a fume problem - even if the fumes are low level you will see a color change in the pH paper in a relatively short time - depending on fume level the pH paper will change color within a few minutes to within a few hours

Example #1 put a piece of pH paper on the work bench - open a jug of acid next to it for 10 - 15 seconds - the pH paper will change color in a few minutes (or less)

Example #2 put a piece of pH paper on the bench - take the cover off a waste bucket 5 - 10 feet away for about an hour & put it back on - at that point you wont really see a change in the pH paper - come back 4 - 5 hours later & you will see "at least" a slight change in color if not a full color change

IMO pH paper is a great indicator for telling you if your chem work/storage area is within safe parameters & of course a "good" fume hood is a must for keeping it safe - never turn the hood off 

Kurt


----------



## snoman701 (Dec 9, 2016)

Thank you Kurt...that is an excellent idea!


----------



## anachronism (Dec 9, 2016)

Kurt's full of excellent ideas. He's one of the guys who has worked hard at the "coal face" so the speak and his posts come from hard earned experience.


----------

