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Author: Subject: A breathable bomb (Rebreather)
Scratch-
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[*] posted on 4-6-2005 at 14:11
A breathable bomb (Rebreather)


Last night I had an idea for a rebreather using a mixture of potassium peroxide and superoxide. I have read about commercial rebreathers, and they use a mixture of calcium, sodium and potassium hydroxides. This is good for absorbing carbon dioxide but you need a seperate container of oxygen because the reaction:

Ca(OH)<sub>2</sub> + CO<sub>2</sub> => CaCO<sub>3</sub> + H<sub>2</sub>O

I was thinking that by using a mixture of oxides you could absorb CO<sub>2</sub> and replenish oxygen at the same time on a 1:1 ratio:

2 K<sub>2</sub>O<sub>2</sub> + 2 CO<sub>2</sub> => 2 K<sub>2</sub>CO<sub>3</sub> + O<sub>2</sub>
And
4 KO<sub>2</sub> + 2 CO<sub>2</sub> => 2 K<sub>2</sub>CO3 + 3 O<sub>2</sub>

So you would need 2 moles KO<sub>2</sub> to 1 mole K<sub>2</sub>O<sub>2</sub>.

And also it would absorb water vapor from your breath and convert that into oxygen:

2 K<sub>2</sub>O<sub>2</sub> + 2 H<sub>2</sub>O => 4 KOH + O<sub>2</sub>
And
4 KO<sub>2</sub> + 2 H<sub>2</sub>O => 4 KOH + 3 O<sub>2</sub>

Once most of the oxides have been converted to either carbonates or hydroxides, the mixture wouldnt release oxygen anymore. This could be detected by something sensitive to water because of the reaction:

KOH + CO2 => K<sub>2</sub>CO<sub>3</sub> + H<sub>2</sub>O

There are some questions I have about this though:

1. Is my reasoning correct and will the reactions work?

2. Will both the peroxide and the superoxide react at a similar rate? Will either the peroxide react too fast and you will black out from lack of oxygen, or will the superoxide react too fast and burst the container that holds the air when its not in your lungs?

3. What water indicator will work in dessicants like potassium hydroxides, and carbonates, not to mention strong oxidisers (And work well enough that you can tell when the rebreather is about to expire before you pass out)?

4. Finally, if this is doable, how can I make peroxides/superoxides fairly pure or in the porportions I need (There arent many posts on alkali peroxides or superoxides that I could find)?

[Edited on 6/4/2005 by Scratch-]
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[*] posted on 4-6-2005 at 14:50


I know that the superoxide idea is out there already, but I don’t know the specifics. Google will help you here.
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[*] posted on 4-6-2005 at 15:54


Yes, potassium superoxide is already used in space capsules and other situations, it's ability to both produce oxygen and trap carbon dioxide is of great utility in space and other enclosed applications.

On the subject of 'breathable bombs' have you ever heard of an oxygen candle? I always thought the concept of a pyrotechnic composition producing enough oxygen to survive on very interesting.

http://www.coaleducation.org/technology/chapter1/life.htm

This rebreather uses a bit of the oxygen candle concept and the use of superoxide.
Quote:

4. Finally, if this is doable, how can I make peroxides/superoxides fairly pure or in the porportions I need (There arent many posts on alkali peroxides or superoxides that I could find)?

I found some information a while back on the preparation of potassium superoxide by heating potassium hydroxide with oxygen, very simple although the posssibility was contested by some individuals. I have read a massive book on the alkali peroxides, superoxides and ozides and have several photocopies of pages that I can go though at a later date.

[Edited on 6/5/2005 by BromicAcid]




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[*] posted on 5-6-2005 at 04:33


Just remember that if the rebreather goes wrong you are in real trouble. An air tank is nice and simple. Even if it is a heavy pain in the neck to lug about it can't easily "go wrong".
What you really don't want is to be stuck under water with a decompression stop or two between you and the surface and with nothing to breath but caustic.
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[*] posted on 5-6-2005 at 05:37


How about a small reserve tank? Dont know if its commercially available, but could be.



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[*] posted on 5-6-2005 at 17:11


Scratch-,

Your idea is plausable, but your methodology is worrying.

You can't trust a contrived chemical reaction on its own to balence the oxygen level. However close you think you have the mixture to where you think it needs to be its going to drift one way or the other. The only sane solution is to under produce and have a feedback mechanism with an electronic oxygen sensor and another source of oxygen, or overproduce with a hydroxide scrubber and switch the ratio of air that goes through each. In addition to an emergency oxygen backup.
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[*] posted on 6-6-2005 at 13:21


With this sort of complexity, it might be easier to evolve gills.:)
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[*] posted on 7-6-2005 at 19:48


Actually, I reaalllyy wouldnt want to use this underwater. If a little water gets down in the chemicals it would explode with a mixture of steam, oxygen and alkali oxides and hydroxides.

These are all great ideas, I think an oxygen candle would be the easiest to do (Since I'm not a great electrician or craftsman). Although I might be able to rig up something that traps the CO<sub>2</sub> and then an oxygen candle that releases oxygen at a speed enough to keep the pressure constant. I'll have to give it some thought.

On the subject of my methodology, I'm more of a logical person. My mind thinks that 1 + 1 should equal 2, not somewhere between 1.5 and 2.5, depending on whose doing the math, temperature, pressure, position of the moon, etc. Its not so in chemistry I guess.
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[*] posted on 8-6-2005 at 12:36


1+1 is still 2 in chemistry. The problem is that you don't know if you are metabolising fats, carbohydrates or what. The ratio of CO2 produced to O2 consumed varies with the "fuel".
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[*] posted on 8-6-2005 at 19:17


Oxygen candles were used on the MIR space station as an emergency backup ,
and IIRC they had opportunity to use them . Checked and before 1997 the lithium perchlorate oxygen candles were used as the primary oxygen source on MIR . The shuttle Atlantis delivered an electrloysis unit which then became the
main source .

[Edited on 9-6-2005 by Rosco Bodine]
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[*] posted on 9-6-2005 at 11:11
rebreather


Hi Basically patent us3809746 explains production of potassium superoxide
2KOH + 2H2O2 > K2O2.2H2O thats high test hydrogen peroxide combined under vacuum.
The product is heated to drive of the entrained water to give the anhydrous product.

These patents us4490274 us4731197 discuss some improvements for its use for rebreather technology. One drawback being that the oxygen production reaction takes a while to begin (several minutes)so manganese salts are dusted on the surface which helps decompose the superoxide when its moistened with breath. Possible use for fire use but no way would I use it underwater. youd be strapping the equivalent of a hydrogen peroxide rocket motor on your face. Most people building rebreathers use gas bottles.Cheaperand safer by far. Even then its a dangerous pastime and id have a backup air tank. Still interesting




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[*] posted on 18-7-2005 at 09:55


re: underwater use, things get complicated due to the need to maintain appropriate concentrations (partial pressures) of O2 and diluent gas - too low and you pass out; too high and you get O2 poisoning which can cause seizures. This is why underwater rebreathers use Ca(OH)2 to absorb CO2 and separate O2 and (usually) nitrox tanks to add gas to the system as you descend.

For surface use I think it's difficult to get O2 poisoning (maybe impossible at 1 atm) so rebreathers tend to be non-feedback O2 bleed systems. In this setting I think the superoxide system should work as well. You could use a commercial O2 sensor to tell you when your charge is getting exhausted, or possibly devise a redox indicator/pH indicator sensitive to good/bad atmosphere.

As mentioned above, there is the issue of the superoxide system taking a bit of time to start producing.

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[*] posted on 18-7-2005 at 16:47


I believe the following quote from yakattack is misleading:

"Hi Basically patent us3809746 explains production of potassium superoxide
2KOH + 2H2O2 > K2O2.2H2O thats high test hydrogen peroxide combined under vacuum.
The product is heated to drive of the entrained water to give the anhydrous product.
"

K2O2 is potassium peroxide, not superoxide.

According to several chemistry texts I have read potassium superoxide, KO2, is produced by burning potassium metal in an excess of oxygen. In fact this is given as one of the main uses for pure K.




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