Aluminium + water = Hydrogen, QUESTION

[Koen1]

Using aluminium in water to produce korund and H2 is not
a viable method to produce H2 gas cheaply.
It may seem so, but if you consider that aluminium takes
electrolysis during the smelting process to turn bauxite and basically
any aluminium ore, all of them mostly alumina forms,
and you calculate the energy we can get from oxidising the end product,
it is clear that we'd be better off skipping the entire aluminium
refining and oxidising part, and pump the electricity that would need
straight into H2O in an electrolysis setup.
The total amount of losses would be lower, and for the total amount
of energy input you'd get out a lot more H2 gas.

Btw, if you really insist on oxidising aluminium in water,
try using an allow of pure aluminium and gallium.
That speeds up reactions and allows all of the aluminium to
oxidise, not just its outer surface layer.

[Hydro-Cell]

i am going to use an aluminium/gallium alloy but theres a few more things in it than that.

you say it would be better to run all the energy that goes into smelting etc straight into an electrolyser, this may be true, but what i had in mind was mobile power. the sort of mobile power where you dont have acces to a wind farm or massive solar panels or even a neuclier power station.

what i had in mind was to have small cells containing a particular alloy that would react when water is passed over it. this will slowly turn the alloy into an oxide and reveal new alloy layers. this released hydrogen would then power either an engine or fuel cell.

according to my calculations, which i belive to be correct. a standard 5.5hp generator can run at 3/4 load for 1 week solid 24 hours a day on 35kg of aluminium, and double that time if run through a fuel cell
this may seem a lot of metal but there are a few things that need to be considered.

first off to run an engine on petrol for this long would consume 168 litres of petrol @ todays prices thats almost £150 and once its been burnt its gone forever
aluminium however is not it can be recycled, so therefore we can NEVER run out of the stuff

secondly the hydrogen engine run at cool temperatures produces no emmisions so can be used indoors.

thirdly, refining 350kg of alumina into aluminium creates only 1/3 of that when 350litres of petrol is burnt

all in all i think its a step in the right direction, aluminium and water are 2 of the most abundant elements on the planet so why not use them as fuel (i know water isnt an element lol)

[turbo]

Yes this is verry good topic

Some while ago i was thinking about a way to control the gas production by spraying the water KOH solution directly onto the aluminium.
My plan is to make a small HHO powerd moped 

The reaction is quite long lasting as you can see in these video's brought up by user Jetijs (THANKS ) from the energetics group:
http://www.youtube.com/watch?v=lmYgoGPmCok

And here is the same test after 5 days have passed:
http://www.youtube.com/watch?v=5zICEHEbAhs

I really like this methode because it does not need electricity.

Marco.

[Koen1]

Well... If you have a cheap source of aluminium you might be
ablee to produce H2 gas cheaper than buying it in a gas bottle...

But all in all it can never be more energy efficient to use aluminium
as medium for turning electrical input into H2.
The energy needed to refine aluminium is significantly more than
the energy that can be produced by burning the H2 gas that came
from the reaction between the water and the aluminium.

That said, if you want to produce a lot of H2 fast, in a relatively compact
and light weight portable system, then using pellets or grains of
GaAl alloy (Gallium-Aluminium) is a very good method indeed.
Normally a pure Al pellet would only oxidise on the surface layer of the
Al pellet, produce a little H2, and that's it. But with the Ga mixed in,
the Ga itself does not react with the water, but it does carry along
fresh unoxidised Al atoms and being a liquid metal at 30 degrees C,
it can almost be considered an "active" carrier of the Al atoms.
By cause of the action of the Ga, not just the outer surface layer but
now all of the aluminium can react and all of the Al atoms will oxidise.
Very good to make a lot of H2 fast.

But then you'll need to "recycle" as you called it the Alumina = Al2O3,
and it just so happens that electrolysis is the only way, the stuff
being the toughest solid material next to diamond.

So yes, good way of turning pure Al and H2O with Ga as catalyst
into a lot of Al2O3 and H2.
But no, not an energy efficient nor energy saving method if we
look at the entire cycle of producing the pure materials, performing
the reaction, and recycling the end products into pure materials again.
If you can find a source of pure Al that is really cheap, and that allows
you to buy and use pure Al as fuel in this way, while still being economical
for you, then you've certainly found yourself a good deal. And someone
somewhere in the supply chain must be losing money or getting free energy
somewhere, because someone's got to be paying for the energy loss
in the total cycle. But still, if you can find a supplier cheap enough,
you might indeed be able to save quite some money yourself.

Not sure how well it will work to just spray KOH onto Al though...
For each Al2O3 molecule formed, that would need 2 Al(3+) and 3 K(+)
and 3 OH(-), so after reaction of 4 Al atoms with 6 KOH we'd get
2 Al2O3 + 6 K(+) + 3 H2...
It seems to me that it would still be mostly the very outer layer, the
surface of the Aluminium plate, that oxidises, just like pure Al always
only oxidises the outer surface layer. The K will probably largely get
incorporated in the porous alumina, but without Gallium I am not sure if
your Aluminium will continue to oxidise.
So if your first test with spraying KOH onto Al pure doesn't produce
as much H2 as expected, you might want to try adding Gallium to the Al.
I don't really see it produce "HHO" or anything other than H2 gas,
but I suppose burning H2 gas with H2O vapour in it may give better
output than burning only the H2. Not sure.

Anyway, there's my 2 cents, hope it's of some use to you.