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Silicon and silicon chemicals

High quality local raw materials underpin the local manufacture of
silicon eroded by the energy-intensity.

Silicon is used in metallurgical and chemical applications for which
different quality products are required.

Metallurgical grade silicon is used for producing alloys with other
metals such as aluminium. It has the effect of strengthening and
hardening aluminium to improve its suitability and resistance to heat
for specific applications. Silicon is used in the production of both
primary and secondary alloys where only the highest purity of
metallurgical silicon is required to produce primary alloys.

Chemical grade silicon is used in the production of silicone. Silicone
is the precursor used in the production of commonly used products such
as polishes, lubricants, greases, hydraulic fluids, insulators, semi
conductors, adhesives, medical implants, medical and surgical aids,
cosmetics, paints, silicon chips and photovoltaic or solar cells. The
major users of chemical grade silicon require product qualities to
meet their specific process needs.

Since the early 1980's western world consumption of silicon has grown
at an average annual rate of 5% with the largest driver of growth
being demand from the chemical grade market. Industry experts are
forecasting continued growth into the next decade with the stronger
growth in demand from the chemical industry. International research
and ****ysis of western world silicon demand and supply, suggests that
about a 30% increase in western world silicon capacity is required by
2005 to adequately satisfy demand.

Other silicon chemicals

Carbon
The manufacture of high purity charcoal suggests potential for high
quality activated (commonly with steam) carbon used in the gold
extraction industry. (Though the carbon is of a specific form and
hardness that is commonly produced from coconut shell, there are price
premiums for superior-performance forms. The prospects for
manufacturing special grades of carbon are described.

Pyroligneous chemicals
Producing charcoal from timber generates substantial amounts of
pyroligneous tars and volatiles that are recycled as fuel by Simcoa.
Whereas up to 10 per cent by weight of wood tar is produced, the only
one-time commercially viable by-products are methanol, methyl acetate
and acetic acid (as once produced at Wundowie, east of Perth) that are
now more cheaply produced in large scale petrochemical plants.

High purity silicon
The silicon produced by Simcoa is suitable for metallurgical purposes
and for the manufacture of silicones. Semi-conductor devices require
an even higher purity form of silicon than produced by Simcoa. Such
grade of silicon is normally produced by its conversion to silanes
(being organochlorine derivatives of silicon as used in the production
of silicones) and then distilled and pyrodecomposition to silicon
metal. Given the proximate location of the chloralkali plant, that
produces both chlorine for the SCM plant and hydrogen as a currently
low value by-product, the prospect for adding value to the silicon by
further purification should be evaluated. It is worth noting that the

Silicones
Silicones are used as greases, sealants, adhesives, coatings, and
chemical specialties. Silicones are produced in many locations by some
seven major companies using technology that is not freely available.

Silicones are produced from silane monomers (including methyl-,
ethyl-, phenyl-chlorsilane), from which silicone compositions are
produced by hydrolysis. Until the early 1980s, Dow Corning produced
silicones in Australia from partly manufactured silane monomers
imported from its blank company in the USA. The reduction in the
levels of import tariffs led to the closure of the plant confirming
the Australian market is simply too small to support local
manufacturing without a substantial comparative advantage. It is
useful to note that the current owner of Simcoa has interest in
silicone manufacturing operations in Asia.
Activated and fumed silica

Activated silicas are high surface area silicas used as fillers,
drying agents, carriers, for fusing to high performance optical
lenses. Fumed silica is used for similar applications and in rubbers,
plastics, paints and adhesives. World consumption of such silica is in
excess of 1 million tonnes p.a. valued at around A$1500 per tonne.

About 40 percent of the quartz starting material is converted to
"silica fume", a solid aerosol, with particle size less than 1 micron,
comprising mainly silicon dioxide and some flux-wood ash. There are
conflicting reports on whether the silicon dioxide particles in the
silica fume are entirely amorphous silica, which is relatively
harmless; or whether containing up to 10 percent crystalline silica
which is carcinogenic.

Production may be from;
bullet Silicon tetrachloride reacted with oxygen and hence broadly
similar to the titanium dioxide operation (adjoining the Simcoa
silicon plant). The silicon tetrachloride is produced from silicon
with hydrochloric acid or silica with chlorine and carbon.

bullet From sodium silicate reacted with hydrochloric acid where the
sodium silicate is produced by reacting silica with caustic soda at
high temperatures.
A typical plant would produce around 10 000 tpa largely for export. It
is relevant to note that Western Australia has large deposits of high
quality silica.

Fused silica

The world market for fused silica is about 200 000 tpa of which 60 per
cent is for the electronics industry growing at 20 per cent per year.
The other market is for precision investment casting (ie. avoiding
machining costs) growing at 6 per cent.

Fused silica is manufactured by the fusion of high quality silica sand
in an electric arc and/or resistance furnace at temperatures of around
2000C (electricity typically represents 12.5 per cent of production
costs at a scale of 5 000 tpa. The fused silica is crushed to market
specifications.

http://www.chemlink.com.au/silicon.htm