you may have heard there's been one of
the biggest diamond robberies in history
millions of dollars worth of diamonds
have been stolen from a hotel in monte
carlo and the reason that people
like diamonds
is because
they sparkle so much here i've got a
model of a diamond and the diamonds that
you see and the diamonds that are stolen
are
cut with these very precise geometrical
faces which is what makes them sparkle
and they sparkle so much much better
than this lamp of glass
because diamond has a very high
refractive index
it bends light very strongly
and although people don't realize it
they really value diamonds because of
its refractive index but chemists
think about diamond in a completely
different way they're interested in
diamond because of its structure
you can see here i've got a model of
diamond it's very strong
i can push hard on here
and it will
not distort at all so if you look at
this atom here
it is bonded to four other atoms one
here one there
the third one here and fourth one here
and each atom is bonded to four others
so you get a very strong structure
chemists value diamond because it's so
strong and they're two different ways
you can use it to be strong one way is
as a window to let light in or out of a
high pressure vessel so here
is a diamond window
which is mounted on a plate and the
whole thing fixed to a metal fitting for
high pressure work and if you look
through the diamond you can actually see
i can see brady's wedding ring i can't
remember whether it's platinum i think
it's palladium yes
so
i can just about see his lens now
the idea of this is that you can shine
light
through a very high pressure fluid and
look at the reaction under high
pressures not terribly high perhaps 100
atmospheres 200 atmospheres pressure
but if you use glass you'd have to use
really thick glass and that would
distort the experiment
the diamonds that are now used for
windows like that are usually synthetic
diamonds
though the structure is just the same
but the real power of diamonds is when
you need
very high pressures
and you do this with a diamond that is
tapered like this one you can see it
goes downwards down here and when you
have a shape like that if you press hard
on the top because the area of the top
is much bigger than the area of the
bottom
you increase the force as you push down
and multiply it so you get very high
pressure at the bottom
with windows shape like this you can get
a very high pressure on this tiny face
at the bottom
which has a special name it's called the
collet face of a diamond so you can take
a pair of diamonds like this one on the
top another one pushing up here
and push them together and this little
cell here has two plates one here and
one here which are pushed together and
pushed the diamonds together and the
force
comes from
screws that hold the plate together so
if i turn this over you can see there
are three screws which you can tighten
which force these together the amazing
thing with this tiny cell you can
squeeze a suitably small sample to
pressures of more than a hundred
thousand atmospheres
this is
really high pressures
so the way you use this cell is that you
take say a small crystal that you want
to
submit to a high pressure
and put it between the diamonds
surrounded by a small ring
made of tungsten so the liquid will
transmit the force from the diamonds
onto the crystal
because if you just put the crystal
between it it'll be crushed to bits
but if it's surrounded by a liquid the
pressure pushes from all sides
and all being well it just gets squeezed
some crystals it makes no difference if
you submit them up to pressure but if
you have quite a complicated molecule as
you increase the pressure it can change
its structure even the diamonds that are
used in labs are quite valuable
and so
sometimes
even our diamonds get stolen
but
the thieves are usually disappointed
because their value on the black market
is very small because nobody wants to
wear diamonds like this as jewelry
originally diamonds were made by heating
carbon at very very high pressure
and this was expensive
and you got rather poor diamonds modern
diamonds are made by so-called chemical
vapor deposition
where you take
a compound in the gas phase
at high temperature and it decomposes to
give a layer of carbon and if you do it
in the right conditions you can build up
diamond literally layer by layer so if
you want you can coat
metals with diamonds
or you can grow whole crystals of
diamonds rather like the ones here is
there a difference between manufactured
diamonds and diamonds that come out of
the ground
manufactured diamonds
do not usually have the same high
optical quality that makes
natural diamonds so beautiful
because natural diamonds have been made
under high pressure and sat under the
ground for millions of years
and the tiny
imperfections which don't really matter
to scientists have essentially
disappeared because the
diamond has been heated so long that
they can diffuse out and so you get
these really perfect crystals
so i don't think
that
the
high market
jewelry industry is yet being threatened
by synthetic diamonds