From: AHAHMA@kontu.utu.fi
Subject: Smoke bombs
Date: 30 May 90 16:15:01 GMT

>It also said that smoke bombs should be bought, because they were too
>difficult and dangerous to make.  Seems like I've heard several easy
>and foolresistant ways to make smoke-generating mixtures, though now
>that I think of it none of them included an oxidizer--they were just
>supposed to burn.  Is adding an oxidizer the dangerous part?
 
Smoke bombs usually do not contain any strong oxidizer and the mixtures
are seldom able to explode violently. However, some of them may self-ignite
and still be dangerous in that respect.

I can remember only a few effective and relatively safe mixtures, more
can be found in the pyrotechnics literature. Both of the following
mixtures are based on zinc. 

1. A stoichiometric mixture of zinc powder and hexachloroethane. This
mixture is very easy to ignite and gives a lot of grey and bad-smelling
smoke. The mixture also burns quite fast as an loose powder, but the
burning rate can be reduced by pressing the mixture to a hard "cake".
This mixture is also relatively unstable. The hexachloroethane sublimes
even at room temperature and is volatilized in few weeks or months, if
the mixture is not kept in a tight container. If the mixture gets some
moisture, the zinc will start reacting slowly and if the charge is
great enough, it may self ignite.  

2. A stoichiometric mixture of hexachloroethane, zinc oxide and
aluminum dust - much safer, but requires a pyrotechnic igniter charge.
Black powder will do just fine, if it is slow burning (no gunpowder
FFFF!). A gram of potassium nitrate-magnesium will ignite the stuff
even better. This mixture is used in smoke grenades and cans and it can
be stored for a few years without significant deterioration.(In tight
cans). This also gives grey smoke and is slightly more efficient than
the previous one.

In the first mixture zinc can be substituted for magnesium, and the
mixture will become even more unstable.

There are also numerous chemicals, that fume on exposure to air. To
mention a few: titanium, tin and silicon tetrachlorides, phosphorus
trichloride, chlorosulphonic acid, sulphur trioxide. All of these are
hydrolyzed by the moisture in the air and create a mist of
hydrochloric/other acid and a metal/other oxide. Just spray them in the
air and you get a very dense, white smoke. As a drawback, half of the
smoke is extremely corrosive acid.... Not to be recommended for
household use, outdoors only! :-)

A mixture of potassium chlorate with ammonium chloride and sugar also
generates smoke when burned, but is hazardous to use and even more
dangerous to store.  Chlorates should never be mixed with ammonium
salts, since ammonium chlorate is very unstable. This recipe can still
be found in some pyrotechnic books; be careful, if you try this or at
least use it immediately after preparation.

ArNO
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