Inert Gas That Will Not Impact Metal Alloys in Coins

I am not an expert in coin preservation, by any means, but helium is easily obtained and non-reactive. Argon is another possibility, also widely available. For ordinary uses in which you want to avoid oxidation, nitrogen is used, and that may be fine for coins, too. Helium and argon are both used as shielding gases in welding, so are non reactive with metals even at elevated temperatures.

Helium is too small a molecule - extremely difficult to seal for any significant time. Argon or Nitrogen would be much better. Another possibility would be CO₂. With a molecular weight of 44, it is much easier to seal than the other smaller molecules.

Yes, helium is leaky sneaky stuff!

I agree. Sealing a plastic container containing Helium would be tricky. Virtually any gas or gas mixture that doesnt react with either the metal or the PVC would be practical. The cheaper the better.

Nitrogen gas is readily available and fairly cheap. Since the main thing that would cause tarnishing (oxidation) of the coins is oxygen, most gases with low reactivity would work. Nitrogen is the most common.

The other thing I would make sure of is that you have a good tight seal on the chamber/case and that you make sure that you displace all of the air when filling.

Best Regards,

Mike

Argon is used when seals could leak do to its larger physical size. Look for the inert gases on the periodic chart and see what is biggest vs. what is cheap.

depending on the value of your Numismatic collection what is appropriate.

ps. design a low cost system and sell it to your niche market.

or not

good luck on your Numismatic venture

Brad

Excellent answer PW!

i personally would not use CO2 -- if there is any moisture left or diffusing into the bag - the CO2 will form carbonic acid

I agree that some care should be taken, but I am not as excited as Mr Slack. Having worked in industry for a decade or so I am a bit more - well - just take practical care.

I also am a coin collector. I am curious as to why you want to fill the container. There is no such thing as a leak proof container, so over time (especially a plastic, accessible container) the inert atmosphere will need to be re-established. Since there is no way easy way to monitor the environment within the container you will just have to establish some sort of PM program.

However, the evacuation of the atmosphere by vacuum is more achievable. Also a simple pop-up indicator will assure the negative bar atmosphere exists.

As stated O2 and H2O and to some degree UV are your enemies for an un-handled coin.

There are a number of gas dryers available and five 9 purity inerts too (99.999% pure) but the practicality is questionable from my perspective.

Review the products in magazines such as CoinWorld and CoinAge or Coin Collector or read any of the work of Scott Travers for what is on the market.

Perhaps a better product would include the packaging of five 9 inert gas into a small container such is used for air rifles, a bulb pump and a proprietary container. This gas can be 'pulled through' your container via a proprietary connection fixed to the container by means of a bulb pump vacuum. So that a negative bar atmosphere of dry five 9 inert exists within the container with a pop-up monitor device as a visual indicator of the internal environment.

I will sketch up something in a bit.

Hope this helps,

cr3

Hi gewoodfo.

By far, the best inert gas for protecting nonferrous metals is Argon! It is relatively cheap and easily available.

Spencer.

Determining a satisfactory gas environment is the easy part. Maintaining that environment in a plastic container over a long period of time is the challenge. I suggest you look at ASTM E595 (Volatile Condensable Materials) and NASA STD 6001 TEST 6 (Determination of Offgassed Products). Once you find plastic materials that don't outgas very much, you will find they are expensive and exhibit other undesirable properties. Glass and metals are easier to deal with and even they have significant problems. There is a web site that describes recent efforts to conserve the declaration of independence. I believe the work was done by NIST.

The idea is to be sure. An Argon filled 9mil mylar bag that will be heat sealed. For final storage put the coin/argon filled bag in a can or other sealed container to protect the bag and its' contents from UV radiation.

Don't worry about which gas is cheaper, you are seeking reliable performance not, "well this should work". Put the bag, coins and, heat sealer device in a homemade plywood box and reach through slits in the plastic sheet lid to seal the bag. The plywood box will be flooded with the argon. I know it seems like a waste but it actually isn't when you comare it to the future value of the coins. This box idea works for critical welding jobs too.

h2om@hotmail.com

Could you pull a vacuum on your encapsulation container? This might be simpler than injecting an inert gas...Just a thought.

I was reading through this thread and thinking to myself "Why use a gas?"

Most coin collections I've seen are sealed in a vacuum bag similar to vacuum packed food...

Just use a standard vacuum packing machine with heat sealing done! no hazardous gases or anything...

John.

Another issue with gas is when you expand it the new volume has the same relative heat in relationship to absolute zero. People have died from frost bite of the lungs just from trying to correct a leak in a room. If you open the door and there is fog (ice crystals) get out and take appropriate measures. Non recirculating refrigeration.

You wouldn't need much gas so something like a small sandblasting cabinet would work.

Argon is heavy so vent it high and purge the case to open it low, both to outside where it can disperse.

The chances of a problem are very slim but understanding the dynamics of a situation gives you options.

2bits

Brad

Argon is a inert gas that can be used. If the container is flooded with Argon. Some type of desiccant is placed inside to remove moisture. Then sealed should protect them for your life time.

Nitrogen is silent killer.Better use Hellium for this pupose.

Thanks!

Ramdas

What are you referring to? You breathe in more nitrogen with each standard breath than the amount required for several coin cases. Nitrogen is only dangerous if it reaches concentrations to exclude oxygen,

Thank you. Having worked with gaseous chemicals of the very worst type, I find it fascinating the fear some seem to have over a little N2.

Again, use practical safety precautions.

I keep waiting for one of these guys to try and sell me an N2 monitor for my basement.

cr3

Actually, with a molecular weight of 28, N₂ is slightly lighter than air (avg Mol Wt about 29), so with O₂ at 32, you may have to 'worry' about excess O₂ and diminished N₂ in the basement! So you really should watch for excess oxidation down there - maybe they will sell you a strip of iron encased in a fancy box with a photoemitter-detector pair connected to an alarm!

Dick