sillicon tetrachloride

[zeocrash]

ok i was browsing through my big book of chemicals the other day when i came accross sillicon tetrachloride. among it's uses was millitary smoke screen.
i was wondering if anyone knew how this worked, i was thinking that maybe the sillicon tetrachloride decomposed to either sillica, sillicon or sillicon oxychloride (not sure if this exists). under heat. but i'm not sure.
any ideas

[yt2095]

The only reaction I remeber with SiCl4 was to do with bonding traits, we also compared it agains Carbon Tetrachloride.

the One test was reaction with water, SiCl4 + H2O left SiO2 + HCl

perhaps (and I`m guessing) that the SiO2 could be used if fine enough to create a white "smoke" effect in the air?
some type off reaction that emits water vapour as a combustion product while mixing with the SiCl4?

that`s the only Smoke like effect I`ve seen from SiO4, my logic is that the Silicon is critical, because if it wasn`t, then Carbon Tetrachloride would be used instead as it`s MUCH cheaper to produce and friendlier to handle (think Dry Cleaning fluid)

all the best anyway :)

[nbk2000]

Military smoke systems used ammonia gas in conjunction with the SiCl4 to produce the smoke screen. It would form particles of ammonium chloride and silicon hydrate that would form the obscuring smoke.

SiCl4, by itself in air, would form HCl by hydrolysis with ambient humidity, so it only works if there's moisture in the air. Dry air, like in deserts, greatly decreases such hydrolysis, making it ineffective.

Titanium Tetrachloride is much more effective as a chemical smoke agent.

[Mr Cool]

Sadly carbon tet can't be used, the poor little carbon has no d orbitals to accept electrons and form the intermediate in the reaction. I think it's to do with the d orbitals, anyway...
Plus CCl4 has a tiny little carbon atom surrounded by four huge chlorine atoms, so there's little room for attacking species to get to the carbon.
Pitty, isn't it? CCl4/NH3 smoke would be cheap.