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SOME NOTES ON CARBON AT HIGH TEMPERATURES AND PRESSURES
Read before the Royal Society, June 21th, 1907
Following
the subject of my paper of 1888 to this Society, which will be referred
to in a subsequent communication, attempts have recently been made to
melt carbon by electrical resistance heating under pressure, and the
following is a short summary of the results of about one hundred
experiments.
The
procedure has been on two lines. In the first, carbon is treated in
bulk in a thick tube of 8 inches internal diameter of gun steel closed
below by a massive pole of steel insulated from but gas tight with the
mould and above by a closely fitting steel ram packed by copper rings
imbedded in grooves in the ram or by leather and steel cups according
to whether solids, liquids or gases are to be contained. The bore of
the mould is generally lined with asbestos and after being charged the
whole is placed under a 2000-ton press, the head and baseplate being
insulated and connected to the terminals of a 300-kilowatt storage
battery with coupling arrangements for 4, 8, 16 or 48 volts.
It
was hoped that the greater thermal and electrical conductivity of steel
as compared with carbon or graphite at moderate temperatures would with
the help of water jackets keep the outer layers comparatively cool, and
that the increased conductivity of the central portions consequent on
their higher temperature and conversion to graphite would so centralise
the current on the core lying between the poles as to melt it.
Further
concentration of current was obtained in the initial stages of heating
by packing the central portion with carbon rods on end or by a
compressed graphite core, and filling in around with coarsely broken
arc-fight carbon, or with wood charcoal (which is a bad conductor until
highly heated).
With
pressures of about 30 tons per square inch, and currents commencing at
6000 amperes, increasing up to 50,000 amperes, with about 2 volts
between the terminals of the mould, the carbon rods were partially
converted to graphite and firmly welded together; in the case of the
graphite core the flakes were much increased in size.
The
heating was in all cases limited by the melting of the steel poles and
resulted in short circuits in the mould from the permeation of the
asbestos by the molten iron. Neither the internal water jacketing of
the poles nor the substitution of copper poles for steel have remedied
this trouble.
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