Chemical Engineering September 2014 - 12

ChementatoR
This process realizes large costs savings for manufacturing silicon wafers
C
rystal Solar Inc. (Santa Clara, Calif.;
www.xstalsolar.com) is preparing for
high-volume production of silicon wafers
using a process that forms the wafers
directly from trichlorosilane (TCS)
gas using a chemical vapor deposition
(CVD) epitaxy process that can significantly
lower the manufacturing costs
for solar photovoltaic cells.
By eliminating several steps used
in the traditional solar-wafer manufacturing
process, including melting
down polysilicon pieces, formation of
a monocrystalline silicon ingot and
slicing the wafers, Crystal Solar's " Direct-to-Wafer "
technology allows for a
50% reduction in the wafer's production
cost, which represents almost
half of the cost of the final solar cell.
" Epitaxy has been well known for
silicon production in the past, " says
T.S. Ravi, Crystal Solar co-founder
and CEO, but the approach has not
been economical for use in solar cell
applications because growing the
silicon layer has been too slow, and
conversion rates from TCS to solid Si
have been too low. " The key for us was
to find good solutions to the problems
of how can you grow the wafers faster
and how can you achieve higher conversion
rates? " Ravi says.
By using a vertical reactor concept,
the company has been able to achieve
40% conversion rates of TCS to silicon,
with the ability to make several hundred
wafers at a time at atmospheric
pressure. The reactor combines solarThis
portable device measures Hg+2 in water samples
A
n ultra-sensitive, low-cost and portable
system for detecting mercury in water
has been developed by University of Adelaide
(Australia; www.adelaide.edu.au)
researchers, in collaboration with the
Universitat Rovira i Virgili (Tarragona,
Catalonia, Spain; www.urv.cat).
Project leader Abel Santos, of the Adelaide's
School of Chemical Engineering,
says there are systems capable of monitoring
mercury at trace levels, but they are
huge, expensive machines and are complicated
to use. Also, samples require chemical
treatment before analysis in such instruments.
" Our system, on the other hand,
is very cost-competitive, only as big as a
mobile phone and easy to use, " he says.
The researchers have engineered a nanoMercury
reMoval (Continued from p. 11)
sulfide material into the clay particles.
After blending and milling processes,
the AS-HgX product can be injected
into fluegas streams, where it reacts
with mercury to form mercuric sulfide,
a very stable and insoluble compound,
notes Butz. By altering the structure of
the metal sulfide and the manufacturing
process, Novinda can make related products
using the same product platform.
Novinda has partnered with several
manufacturers of injection systems that
grade TCS gas with hydrogen to deposit
monocrystalline silicon on top of
a porous silicon release layer.
Capital costs associated with this
production method are said to be half
what is required for traditional polysilicon
plants. Another advantage of
the Crystal Solar method is its amenability
toward automation, Ravi notes.
The technology was developed in part
as a component of a National Renewable
Energy Laboratory (Golden, Colo.;
www.nrel.gov) program, and has garnered
an R&D 100 award in 2014.
Crystal Solar has been making wafers
in a pilot phase, and generating
positive feedback in tests with cell manufacturers,
Ravi says, and the company
is gearing up to add capacity now.
(Continued from p. 11)
porous material, called nanoporous anodic
alumina, to make a special structure called
a rugate filter. The surface of the filter has
been modified to make it selective to mercury
ions. As water flows through the pores,
the mercury ions become attached to the
surface. Reflection spectroscopy measures
the amount of mercury present.
The system has a linear working range
from 1 to 100 µM of Hg+2. Its low limit
of detection is 1 µM of Hg+2 ions. Tests
were successfully carried out at the River
Torrens, demonstrating the suitability of
the system for developing environmental
point-of-analysis systems. The system
also proved to be highly selective in a
complex mixture of other metals and environmental
samples.
work well because the dispersal of the
material in the fluegas is a key factor in
the product's effectiveness.
Novinda's product has been tested in
full-scale coal power plants burning several
types of coal in various locations, and
has shown the ability to remove over 90%
of mercury present in plant fluegas, Butz
says. He adds that the tests suggested
that AS-HgX is particularly effective in
plants that use dry scrubbing to remove
SO2. In the future, AS-HgX may also be
applied for mercury removal in fluegas
from industrial boilers and cement kilns.
12 ChemiCal engineering www.Chemengonline.Com September 2014
than alternative reduction
catalysts that are based on
gold or silver. the results are
described in the July 30 issue
of Nature Communications.
. . . and CO2-to-methanol
meanwhile, a new catalytic
system that directly converts
Co2 into methanol has been
developed by scientists at
the U.S. Dept. of energy's
brookhaven national laboratory
(Upton, n.Y.; www.bnl.
gov), in collaboration with researchers
from the University
of Seville (Spain; www.us.es)
and the Central University of
Venezuela (Caracas; www.
ucv.ve). the catalyst is composed
of copper and cerium
oxide (ceria) nanoparticles.
the research team found
that the interface of the two
types of nanoparticles is
critical to the reactivity of the
catalyst system. laboratory
studies showed that the catalyst
converts Co2 to methanol
more than 1,000 times faster
than plain copper particles,
and almost 90 times faster
than a common copper/zincoxide
catalyst currently used
industrially. the results are described
in the august 1, 2014
issue of Science.
http://www.xstalsolar.com http://www.nrel.gov http://www.adelaide.edu.au http://www.urv.cat http://www.bnl http://www.us.es http://www.ucv.ve http://www.Chemengonline.Com
Chemical Engineering September 2014

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