I posted this originally on sci.chem and physics but it seems to
belong here too for different reasons. Is anybody else familiar with
this phenomena?

I was at a teacher training camp in materials science this last summer
and I saw something extraordinary in a science demo. What I saw seemed
to be a thermite reaction initiated by an impact. The trainer had two
large steel ball bearings, ~ 2 inch diameter, that were rusty. Here is
what I observed:

What makes you think you need to figure energy converted to heat?  Why
not just assume that at the molecular level it was simply kinetic
energy directly applied to a chemical rxn?  More efficient in getting
over the hump than heat, I would think.  The Al atoms are being rammed
straight into Fe2O3 molecules.

Robert

"michalchik" <michalc... at (no spam) aol.com> wrote in message

news:32a4cc82-6058-47fb-85b1-8dcd74e0f664 at (no spam) r2g2000yqm.googlegroups.com...

I posted this originally on sci.chem and physics but it seems to
belong here too for different reasons. Is anybody else familiar with
this phenomena?

I was at a teacher training camp in materials science this last summer
and I saw something extraordinary in a science demo. What I saw seemed
to be a thermite reaction initiated by an impact. The trainer had two
large steel ball bearings, ~ 2 inch diameter, that were rusty. Here is
what I observed:

*** Snip some very interesting observations:

This is not what you are asking but maybe you will find this article
interesting.

http://www.mms.gov/tarprojects/405/Final%20Report-2002_1.pdf

Tom

You are thinking along the lines I was thinking. Heat may not be the
best way to describe the initiation of the reaction, but I have
never
seen a scientific treatment of impact triggered chemical reactions.
Is
ramming molecules together en mass actually different from heating
them together? I really don't know. At first glance it would seem
that
in either case you are talking about molecular collisions so heat
energy and kinetic energy would seem to be equivalent, but other
factors might come into play. Is a self reinforcing shock wave
generated at the point of contact? Are the bonds stretched in some
unusal way that makes them more suceptible to reactions, such as
concerntraing the enrgy in breaking the bonds of certain atoms?

Welding - which is really placing two or metals in solution with one-

What makes you think you need to figure energy converted to heat?  Why
not just assume that at the molecular level it was simply kinetic
energy directly applied to a chemical rxn?  More efficient in getting
over the hump than heat, I would think.  The Al atoms are being rammed
straight into Fe2O3 molecules.

Robert

You are thinking along the lines I was thinking. Heat may not be the
best way to describe the initiation of the reaction, but I have never
seen a scientific treatment of impact triggered chemical reactions. Is
ramming molecules together en mass actually different from heating
them together? I really don't know. At first glance it would seem that
in either case you are talking about molecular collisions so heat
energy and kinetic energy would seem to be equivalent,

michaelmichalchik<michalc... at (no spam) aol.com> fired this volley in
news:c181a9a5-3327-4935-9a4f-c480f58239b7
at (no spam) w41g2000yqb.googlegroups.com:> You are thinking along the lines I was thinking. Heat may not be the
best way to describe the initiation of the reaction, but I have
never
seen a scientific treatment of impact triggered chemical reactions.
Is
ramming molecules together en mass actually different from heating
them together? I really don't know. At first glance it would seem
that
in either case you are talking about molecular collisions so heat
energy and kinetic energy would seem to be equivalent, but other
factors might come into play. Is a self reinforcing shock wave
generated at the point of contact? Are the bonds stretched in some
unusal way that makes them more suceptible to reactions, such as
concerntraing the enrgy in breaking the bonds of certain atoms?

Welding - which is really placing two or metals in solution with one-
another to form a new alloy - may be done by impact.  That's how
modern US coins are laminated.

But there may be another phenomenon at work -- think "Diesel".

Tiny pockets of air trapped at the point of impact may be compression-
heated above the ignition temperature of the surrounding reactants.

LLoyd

Feel free to improve on this calculation.