| A New & Significant Australian
Technology - (Published - International Minerals
Magazine February 05) |
| What
is Graphite? |
Say "graphite"
and most of us think of pencils, fishing rods or
golf clubs. 
To engineers graphite is a common form of carbon
used extensively throughout industry because of
its inertness and its lubricating and electrical
qualities. So you may be shocked to know that each
year the world consumes more than US$38 billion
of graphite.
The industry is dominated by large manufacturers
located primarily in China (with 40% of world production
of natural graphite), India, Brazil, Mexico and
North Korea.
A recent major industrial mineral report(1) noted
that: "From 1992-2000 world production of natural
graphite has averaged 620,000tpa, with a maximum
annual variation of about 15%".
Graphite is widely used in metallurgical, chemical,
mechanical, glass and ceramic industries, primarily
as moulds, crucibles, electrodes and electrical
components. |
Graphite
plays an important role in a range of medical, environmental,
transportation and energy management technologies.
The same report (1) noted a growing demand for graphite
in new technologies. It said: |
| "Graphite
usage in battery manufacture shows significant
growth potential in both the USA and Asia.
There are hopes that fuel cells, in particular,
will brighten the long-term perspective. Demand
from this sector currently accounts for just
12-15,000tpa but some industry observers believe
that, in the long term, demand for high quality,
high carbon graphite in batteries and fuel
cells could increase to 100,000tpa or 15%
of present world production." |
|
|
What is VHD-Graphite and what are its advantages? |
| A research
group associated with the University of New South
Wales in Sydney has recently developed a new form
of very-high density graphite (VHD Graphite) that
is superior to conventional graphite in three key
aspects. |
| Porosity
and Composition: |
It is well-known
that commercially available graphite is highly porous.
Porosities above 25% are not uncommon. Graphite
with a porosity of 15% to 20% is considered to be
of high quality.
The VHD-Graphite has a porosity of virtually nil
and residual amorphous carbon is substantially eliminated.
Furthermore, VHD graphite does not have the dusting
associated with conventional graphite.
The composition and bulk density of VHD graphite
can be tailor-made to whatever is desired. |
|
|
| Electron
microscope photos illustrating the low porosity
and grain structure of VHD Graphite. Very good,
conventional graphite (about 15% porosity) left
vs VHD Graphite right. |
| Electrical/Thermal
Conductivity |
- VHD-Graphite
has a much more isotropic microstructure than conventional
graphite.
What this means in practical terms is: |
The electrical and thermal conductivity in the axial
(planar) direction is significantly higher than
for conventional graphite. The restitivity in this
plane is about 55mW per metre. |
|
The electrical and thermal conductivity in the longitudinal
direction is significantly lower than for conventional
graphite. In this plane restitivity is about 2.5
mW per metre. |
| This
could be commercially advantageous in a number of
ways: |
|
Enhanced electrical conductivity in electrical applications
(conductivity path is parallel with the axial direction)
such as brushes in electric motors, electrodes in
batteries, etc. |
|
Enhanced thermal insulation (hot face is perpendicular
to the longitudinal direction) in the case of graphite
refractory bricks. |
|
A novel heat storage device in which heat is introduced
or removed at the edge of a graphite brick array,
and can not escape through the face of the graphite
brick array. |
| Price |
VHD Graphite
can be manufactured at substantially lower temperatures
than conventional graphite and the processing time
is an order of magnitude shorter. No new specialist
infrastructure would be required.
Energy and capital investment savings will make
the cost of manufacturing VHD Graphite a fraction
of that for traditional graphite |
| Otherwise,
VHD graphite is similar to conventional graphite.
It can be manufactured in large cross-sections and
can be formed into complex shapes (within the usual
limitations). |
| Why
is VHD Graphite a significant development? |
| Professor
Chris Sorrell of the School of Materials Science
at the University of New South Wales described VHD
Graphite as a "generational breakthrough".
"It should revolutionize the way graphite is
manufactured and will make redundant all forms of
conventional graphite", he added. "In
particular, VHD Graphite is ideally suited for the
manufacture of batteries and fuel cells and should
replace conventional graphite in this application
within the next few years". |
| |
