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I do a lot of short term ocean field deployments where system electronics are self contained in a submersible enclosure. A new project I'm working on requires a long term deployment in the deep ocean. Therefore, once the enclosure is deployed, I can not just go recover the instrument if something fails. I've spoken to a lot of colleagues about how they prepare electronic enclosures and one of the standard protocols is purging the enclosure of atmospheric air. For one, any moisture in the air can condense at cold, deep depths, which can cause electrical problems. I think another reason they do it is to reduce oxygen exposure. Typically the purging is done with argon from an air cylinder. However, this is something I don't have. Now I know I can go out and get one...that's not the point of this question. What I do have is a small nitrogen generator that was needed for other projects.

The question I would like to ask here is, can I use the 99.x% dry nitrogen air from the nitrogen generator as a substitute for argon? I know argon is denser than nitrogen, so clearly is a better choice, but I'm not concerned with the better choice. I want to know if I can use what I have at my disposal to achieve the same goal: replace atmospheric air with 99.x% dry nitrogen air?

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    $\begingroup$ It sounds like a costly project; seems strange they don't have a few dollars to rent a clean dry bottle of argon from a local weld shop supply. and know exactly what you have. $\endgroup$ Feb 11, 2021 at 0:22
  • $\begingroup$ What is the temperature in the ocean depths? If it is too low and the x in 99.x% is too high, the water vapor can condense on the equipment. $\endgroup$ Feb 11, 2021 at 12:33
  • $\begingroup$ Looks like the main issue is the presence of oxygen in the atmosphere of the enclosure. It looks like dense argon displaces more that just nitrogen. Nitrogen gas, even in the liquid form can hold a certain amount of oxygen. I recommend checking out dissolved oxygen topic at Science Direct. $\endgroup$
    – z1273
    Feb 11, 2021 at 12:42
  • $\begingroup$ A small bottle of highly pure argon will set you back perhaps 200 dollars, and that includes buying the gas bottle in the first place. Refills will be more like 60 thereafter. Just purge with argon like your colleagues - you want your experiments to be on your subject, not the best way to purge your enclosures... $\endgroup$
    – Jon Custer
    Feb 11, 2021 at 14:49
  • $\begingroup$ In my judgment, the water vapor in the nitrogen is also a major issue. $\endgroup$ Feb 11, 2021 at 18:10

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Using argon is, in effect, a costly physical path to remove oxygen, hence your interest in using nitrogen.

However, I suspect, a more efficient, cost-effective, and likely safe chemical path is also possible. For example, assuming a control structure (so as to mitigate potential deaths from O2 depletion, as has been reported, for example, among sewer workers working in a recently drained iron pipe), oxygen scavenging can result from a limited exposure to iron surface previously scrubbed with an acid. Here, lemon juice appears to be a friendly, pleasant, and effective choice.

Note, iron powder and ferrous salts have been used in the food industry to remove problematic oxygen (see, for example, THE USE OF OXYGEN SCAVENGERS AND ACTIVE PACKAGING TO REDUCE OXYGEN WITHIN INTERNAL PACKAGE ENVIRONMENTS).

One should be able to stoichiometrically compute, and experimentally validate, a safe amount of Fe (or its surface area) to employ. This is to limit a continuing unsafe scavenging action if, for example, subsequent maintenance work is required.

You can also employ commercially available products containing Calcium Chloride, for example, to remove water vapor.

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