From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: sci.chem
Subject: Re: Thermite question?
Date: Sat, 23 Oct 1999 03:00:32 GMT

On Fri, 22 Oct 1999 14:19:51 -0400, Bill <bhw@wam.umd.edu> wrote:

>
>
>Uncle Al wrote:
>
>>
>> One does thermite over a pan of DRY sand.
>>
>
>
>Absolutely not.  This generates the danger of spattering molten glass.
>We'd use a cone of thick paper or cardboard in a ring stand over a metal
>or asbestos plate, all enclosed by a transparent plastic shield covered
>with metal screen.  No pot to crack, no sand to spatter, no way for bits
>of flying white hot iron to burn your eye out.

I have to agree with Uncle Al. All the procedures I recall were done
using dry sand as the secondary container.

I had one of these assigned in a synthetic inorganic chemistry course.
I suspected later that it was because one of the professors wanted
some metallic chromium. I know for a fact that was why I had to
prepare anhydrous FeCl3.

At any rate...... The prep used a mixture of granular and powdered
aluminum metal, Cr203 and CrO3. It turned out that the addition of the
Cr03 was the key to getting a good yield.

The well mixed ingredients were placed in a Hessian crucible which was
sunk into sand up to the level of the mixture. The sand was in a metal
bucket.

The reaction was initiated by lighting a magnesium ribbon inserted
into the mixture. Once the ribbon ignited we ran like hell. This was
all done out doors and preferably where there were no onlookers.

When the reaction took off it was quite spectacular as there were a
few odds and ends erupting out of the crucible. This was definitely a
reaction to run outside particularly with the hoods available at that
time.

The yield was pretty good and consisted of a single crystalline glob
that was quite pure.

There was no splattering of molten glass from the sand. The Hessian
crucible occasionally cracked but remained intact. The sand did not
reach the melting point.

>That, and UV protective sunglasses - after all, we were doing this in
>the middle of my freshman dorm room.

Safety glasses of course but at the distance we achieved during the
fuse burn we were well protected from UV by the inverse square rule
and the depth of the crucible and sand bucket.