Sciencemadness Discussion Board - Atomic hydrogen

Atomic hydrogen

Fusionfire - 27-1-2012 at 23:05

Hydrogen is an ubiquitous and readily available molecule. On an industrial scale it can be produced easily by passing steam over coal, steam reforming of natural gas, incomplete combustion of hydrocarbons or by the electrolysis of water. It is the most common element in the universe, accounting for 75% of its mass.

Hydrogen atoms readily combine into hydrogen molecules, releasing 218 kJ/g of reactants or 436 kJ/mol of product.

In specific energy terms this is the most powerful non-nuclear reaction known to man. The closest contenders are gasoline 47.2 kJ/g, 700 bar hydrogen combustion 123 kJ/g, the combustion of beryllium 67.6 kJ/g and the combustion of boron 58.9 kJ/g.

Monoatomic hydrogen has other uses, besides a rich energy store. It can also be used as a strong reducing agent, capable of reducing Ag, Cu, Pb, Bi, Hg from oxides, K or Na from nitrates, nitrites or cyanides and producing NaH or KH. It can also produce H2O2 by reacting with oxygen.

The methods known to make monoatomic hydrogen are as follows:
1) High temperatures. 0.08% H at 2000K, 7.8% at 3000K, 62.2% at 4000K and 95.5% at 5000K.
2) Electrical discharge through H2 gas at low pressure.
3) Irradiating a mixture of Hg + H2 vapour with 253.7nm light from a mercury arc.

Does anyone have any suggestions on how to:
1) Efficiently make atomic hydrogen en masse. Efficiency here is defined as the yield in the context of the supplied energy vs. disassociation heat. So a 100% optimal process would use 436 kJ to get 2g of H from 2g of H2. A 50% optimal process would use 872 kJ.

2) Stabilise and store atomic hydrogen in large kg-size quantities.

Credits:
Thank you Mr. Wizard for drawing this fascinating atom to our attention

watson.fawkes - 28-1-2012 at 11:56

Quote: Originally posted by Fusionfire

Does anyone have any suggestions on how to:[...]
2) Stabilise and store atomic hydrogen in large kg-size quantities.

Don't try.

The suggestion that you can spin-stabilize the electrons in 1 kg of monoatomic H has no grounding reality. There's always population statistics involved, which means there's always some adjacent atoms with opposite 1s-electron spins. These will immediately combine, releasing heat, which leads to thermal runaway.

Fusionfire - 29-1-2012 at 07:00

Quote: Originally posted by watson.fawkes

Quote: Originally posted by Fusionfire

Does anyone have any suggestions on how to:[...]
2) Stabilise and store atomic hydrogen in large kg-size quantities.

Spin stabilisation is finicky to do on a dozen atoms let alone a mole. It won't work in neglected machinery in disrepair - a far cry from a controlled laboratory setting.

Keeping it as a hot plasma at 3000 - 5000K won't work because the black body radiation the body would emit would end up just eating up all the energy you're trying to store. For sure, we can generate it at that temperature.

Would continuously bombarding atomic hydrogen with photons of the Planck's constant x frequency of the ionisation energy of hydrogen work? That way the hydrogen is always kept as an ion and its electrons won't get a chance to form a duplet with another hydrogen atom. Any hydrogen ion that captures an electron and falls to ground state would emit a photon of the same frequency, and as long as you're not loosing photons too badly you will probably still have to invest a continuous power supply in stabilising the atomic hydrogen.

[Edited on 29-1-2012 by Fusionfire]

watson.fawkes - 29-1-2012 at 07:57

Quote: Originally posted by Fusionfire

Would continuously bombarding atomic hydrogen with photons of the Planck's constant x frequency of the ionisation energy of hydrogen work? That way the hydrogen is always kept as an ion and its electrons won't get a chance to form a duplet with another hydrogen atom.

No, and for two different reasons. First, you're always going to have some non-trivial population statistics, since this hypothetical radiation source isn't ever going to be ideal, nor is its absorption profile ever going to be ideal. So you'll still get recombination.

The second reason is that you're proposing a cold plasma of H, not atomic H. Even being charitable, and treating it as a source of atomic H to aim at something, above some critical beam density you're going to get very high rates of recombination, and at point you more-or-less have another atomic hydrogen torch.

condennnsa - 9-2-2012 at 17:09

A nice read http://www.gifnet.org/articles/Langmuir%20&%20Atomic%20H...

I find this very interesting. It's 4 am and I can't stop reading whatever i can find about the atomic H torch. Online info is very little on the subject.

I bet it shouldn't be so difficult for one to build his own torch. I would really like to try it, I have three 1mm diameter 17cm long tungsten rods, but can buy up to 4mm cheaply.

From what i read online the open voltage of the transformer needs be between 300-600 volts. It only needs to be so high to facilitate the striking of the arc. Well, where I live we got 240 mains so I might be able to get away with no transformer...
just hook the electrodes in series with a heating element,

The Hydrogen might be more problematic. I don't have a source for pressurised H2 gas cylinders, so I'd have to make it. Two options that come to mind would be either electrolysis, which would require a fairly high power consumption for a reasonable flow, or good old acid - Al or NaOH and Al.

[Edited on 10-2-2012 by condennnsa]

Mr. Wizard - 9-2-2012 at 18:04

Thanks for the nice link, it is a good read.

condennnsa - 10-2-2012 at 02:17

Surprisingly there is a youtube video of the beast too: http://www.youtube.com/watch?v=Mks09XPvYYw
most of you probably watched it too

Now if that doesn't look cool than what is

I wonder if the yellow large cone after the white arc zone is actually the place where the hydrogen recombines to H2. Or maybe it's just the flame of H2 burning in air?

edit:
now here is a real gem I found: :cool:

Phenomena, atoms and molecules
book written by the man himself in 1950, Irving Langmuir.

http://ia700407.us.archive.org/21/items/phenomenaatomsmo00la...

In pages 100 to 217 the behaviour of atomic hydrogen is documented in amazing detail, lots of tables of power per area and the like.

you're welcome, cheers

[Edited on 10-2-2012 by condennnsa]

watson.fawkes - 10-2-2012 at 04:10

Quote: Originally posted by condennnsa

From what i read online the open voltage of the transformer needs be between 300-600 volts. It only needs to be so high to facilitate the striking of the arc. Well, where I live we got 240 mains so I might be able to get away with no transformer...
just hook the electrodes in series with a heating element,

The power supply needed is much like for TIG welding. These machines use an HV supply to start the arc and then a much lower voltage to sustain it.

It's possible a TIG supply would work as is; I don't know. The old heavy ones are fairly cheap on the surplus market, as gear based on semiconductor switches have completely displaced the old transformer-based ones. The old ones are easier to modify, as they're internally much simpler machines.

The old HV supplies are deadly simple; they use a spark gap. Their manuals also have extensive instructions on how to deal with the resulting EMI and RFI emissions; small wonder.

Mr. Wizard - 10-2-2012 at 08:24

Electrical discharges through gas are more complicated than just high voltage and transformers. The conductivity of the gas changes as it becomes ionized after an initial high voltage (open voltage) 'strike' or breakdown spark. This happens in fluorescent lamps, neon tubes, arc welders, arc lamps, and most gas discharge devices. As the current flows, many more current carrying ions form, which lowers the resistance of the spark and it becomes an arc, and the voltage across the arc drops. Once this happens the arc and the power supply are mismatched in their impedance, and the 'load' or arc is now essentially a short circuit hooked up across the output of the voltage source. Ohm's law says the heat will develop where the resistance is. This is most likely the power supply, not where you want it. To prevent the overheating of the supply, it must be either able to handle the high current, as in an arc welder, or have some way to limit the current, as with 'ballast' transformer in a fluorescent light. Hooking up mains to a gas discharge will quickly lead to high current flow, and the 'weakest link' will burn up. I don't know what the current and voltage characteristics are in an H/H2 arc. Maybe the resistance of the arc stays high and limits current, but almost all other gasses quickly ionize and require some sort of current limiting device. Designing some sort of current limiter into the circuit would be prudent. Even a simple resistance appliance, like an electric space heater, or a large wattage light bulb will provide some measure of current limiting.

The concept of impedance matching, or matching the transfer of energy from one place to another is important. Imagine trying to hit a golf ball with a sledge hammer. The ball won't go far, and you might throw your shoulder out. The mismatch between the weight of the hammer head and the golf ball prevents efficient transfer between the two objects. Billiard balls represent an efficient match, of weight and velocity, and transfer of energy. The same concept applies to electrical loads, you can't connect 9 AA batteries to a 12 volt car starter and expect it to transfer energy. The batteries will get hot because their internal resistance is about 1.5 ohms and the resistance of a starter is in the .01 ohm range. Current will flow, but all the heat will be generated in the resistance of the batteries. Match the source and the load.

Slight correction, the resistance of each cell of the 9 cell AA battery is about 1.5 ohms at 1 amp, so the whole battery would have an internal resistance of approximately 12 ohms.

[Edited on 10-2-2012 by Mr. Wizard]

[Edited on 10-2-2012 by Mr. Wizard]

watson.fawkes - 10-2-2012 at 09:28

Quote: Originally posted by Mr. Wizard

As the current flows, many more current carrying ions form, which lowers the resistance of the spark and it becomes an arc, and the voltage across the arc drops. Once this happens the arc and the power supply are mismatched in their impedance, and the 'load' or arc is now essentially a short circuit hooked up across the output of the voltage source. [...] To prevent the overheating of the supply, it must be either able to handle the high current, as in an arc welder, or have some way to limit the current, as with 'ballast' transformer in a fluorescent light.

Before I get into this, I have to agree with the overall point. Using direct mains voltage to cobble up an AH torch is not a good idea.

TIG welders use a constant current (CC) supply for exactly the reason stated, that there must be some way to avoid arc current from blowing out the power supply. With a CC supply, once the arc is going the supply lowers the output voltage, keeping the total current constant. Sometimes you see CC supplies referred to as VV, variable voltage. In addition, the length of the arc changes as the operator moves the tip with respect to the work surface. A constant current through an arc discharge that's changing length corresponds roughly to a constant ionization rate per length of arc.