The thermite reaction which is the reaction of aluminium and
iron oxide is used to make iron and because aluminium has
much stronger bonds to oxygen than iron that the reaction
produces an enormous amount of heat and you can use this
for welding pieces of metals together.
So this is a thermite mixture, it is a mixture of iron oxide and
aluminium powder and we are going to do some redox
chemistry and we are going to generate some molten iron
which will hopefully stream from the bottom of the flower
pot. So here you can see the black particles of the iron oxide
and the silver particles are the aluminium powder. So we get
some heat on this and we start an instantaneous redox
reaction so the aluminium and the iron oxide swap oxygens
so the aluminium will become oxidised and the iron will
become reduced hopefully we will generate a lot of molten
iron which should come from the bottom of the test tube …
of the flower pot.
Alright!
Right.
Now there is a story about students in Berkley that some
students, or group of students, decided to do a practical joke
on a tram of the sort that has one door where you go in and
another when you go out. So a big group of students queued
onto the tram and got into the front and there were enough
of them so they could actually come out at the end at the
other door and form a loop so they were just going round
and round and round so the tram could not leave because
they were just more and more people getting on.
We’re going to run out of tape.
And while they were doing this, other students went down
under the tram and set off two thermite reactions and welded
the metal wheels of the tram to the steel rails so that when
the tram tried to leave, when the students eventually stopped
going round and round, it was firmly welded to the tracks and
could not move at all.
It’s gone out.
Tell us about what is going on mate!
So instantly the thermite reaction starts and you can see that
it’s so hot that it burnt a whole through the bottom of that
terracotta flower pot. But if we go in close now Brady, you
can see all that really quite nice molten iron. Now that is so
hot that the iron itself has melted and it has formed this
really quite big goo in the bottom on the sand.
Do you encourage these sorts of practical jokes?
No, no, no, no ,no, our students are far more responsible.
So as soon as the fire work, or the sparkler, hit the top of the
thermite reaction, in the top of here, it started obviously,
instantaneous redox reaction. So this is where the metals
were fighting for the oxygen, the aluminium won that battle
and the aluminium came out of this reaction as aluminium
oxide. The iron was reduced and we can see that now in the
bottom which is really hot so I am not going to get too close
but you can see all of this really, really hot iron. The iron was
molten, it dribbled out through the bottom of the flower pot
and it is now cooling.
It didn’t dribble out of the bottom of the flower pot.
Well it smashed its way out of the flower pot.
Well you can say that iron is in my blood, it is in your blood
as well. It is iron that gives haemoglobin the red pigment in
your blood, its red colour.
So the reaction we saw was about 5 minutes ago and the iron
that was generated is still glowing red hot and you can see it
has fused itself to the bottom half of the flower pot, which it
broke in its tumultuous step forward.
It is an absolutely essential element to life, except for crabs
which use copper but you will have to hear about that later.
So iron is a really, really abundant metal which is used in lots
and lots of structural material, so you get to see lots of
pieces of iron around, some of the racking and even in fact
some of these pieces of equipment have got high iron
content. They have got other elements in them to form alloys
like stainless steel.
I have an extremely long standing interest in its chemistry
and in particular, I made one compound of iron so called iron
tetracarbonyl which had 4 groups round it and everybody had
expected that it would have a shape like one of these. Shaped
with tetrahedron like that whereas, in fact, it had a much
more irregular shape, the 4 groups were arranged like this,
and so every since this, every time I hear the word iron I get
quite excited.
So this is iron wire, ok, and as you can it is a very small wire.
It is 0.2 in diameter and you can see the shiny material
underneath is iron that has not undergone oxidation so this is
where it has been protected from the oxygen in the air now if
we look at the iron at the top we can see that this looks really
familiar especially because it looks like some of the rust which
we can see at the bottom of some of our cars. So here is
some iron oxide on top of the iron.
The very first chemical experiment I did the chemical reaction
was with iron and I think the same is true for many
generations of school children. I heated up iron and sulphur
together and made iron sulphide sort of blackish solid but
then we put acid on it and got a terrible smell of bad eggs
and this was my introduction to chemistry and I really loved
it.