| NEWS & IDEAS |
News & Ideas is a guide to research in science, technology, management, architecture, and humanities and social sciences at Rensselaer. For details or photos, contact Marketing and Media Relations, Rensselaer Polytechnic Institute, Troy, NY 12180, (518) 276-6532, or e-mail us at nasons@rpi.edu.
February 1999
NEW ENERGY SOURCE:
Turning Heat to Power
PSYCHOLOGY:
Good Impressions = Profits
RECYCLING CELLULOSE:
Don't Call It Garbage
NEW ENERGY SOURCE:
Turning Heat to Power
Picture a small propane burner coupled with a radiator and an array of semiconductor
devices. No moving parts. No noise. Easy maintenance. Reduced air pollution.
No battery disposal problems. Just a steady flow of electricity to power
navigation and communications equipment on a sailboat, appliances in a remote
cabin, or electronic equipment for military ground troops.
Just as solar converters turn visible light into electricity, thermophotovoltaic
(TPV) devices produce electric power from infrared radiant heat. Rensselaer
Polytechnic Institute is playing a leading role in developing this new energy
source, which is rapidly moving from theoretical possibility to practical
consumer and industrial products.
Rensselaer will receive an additional $1.4 million over the next two years
from the Lockheed Martin Corp. for continued TPV research. The program already
has received approximately $2.4 million over four years for research that
has helped make the new technology more practical and cost-effective, said
Ronald J. Gutmann, who coordinates Rensselaer's TPV program. Hybrid Electric Cars
The first TPV device was marketed last year as a power source for equipment
on sailboats. Furnaces have been designed to power blowers and other electric
equipment with TPV units, eliminating the need for expensive wiring. The
technology also has major economic potential for recovering waste industrial
heat and recycling it into energy. In addition, TPV power is being considered
as a means of creating more practical hybrid electric cars in which battery
power is supplemented with TPV cells. While such an automobile is not
yet proven cost-effective, a prototype has been built.
TPV technology can have nearly 300 times the power density of solar devices,
said Gutmann, professor of electrical, computer, and systems engineering.
TPV arrays can generate up to five watts of energy per square centimeter,
compared to 15 milliwatts for a solar-cell array. A TPV array measuring
30 centimeters by 30 centimeters could produce more than four kilowatts
of electricity, enough to power major home appliances, Gutmann said. In
addition, TPV systems can supply heat and operate as needed at night or
on cloudy days.
TPV devices can be more efficient than traditional fuel-powered generators.
They also operate silently and with less pollution since they offer a
relatively "clean" burn without the incomplete combustion of an internal
combustion engine. Band Gap: One Size Doesn't Fit All
A TPV system consists of a heat source, often a burner for a fossil-fuel
such as propane, a radiator to transform the heat energy into appropriate
wavelengths of radiant heat, and an array of semiconductor devices that
convert the radiant heat to electricity. The key to practical TPV devices
is creating semiconductor materials with a band gap that corresponds to
the wavelength of the radiant heat, a challenge Rensselaer researchers are
tackling in several ways.
Electrons in the valence band of an atom cannot escape the atom, but if
the atom is struck with an infrared photon containing the right amount
of energy, an electron can be lifted to the conduction band and flow in
a circuit. The amount of energy needed to free an electron depends on
an electrical property known as band gap.
Silicon, with a band gap of 1.1 electron volts, efficiently converts radiant
heat the temperature of the sun - 6800 C - to electricity. A semiconductor
material with a much smaller band gap is needed to convert lower, more practical
temperatures created by terrestrial heat sources. Unfortunately, simple
binary compounds do not have the optimal properties, and researchers must
create more complex materials.New Materials Made to Order
At Rensselaer, Ishwara Bhat, associate professor of electrical, computer, and systems engineering, uses a process known as organo metallic vapor phase epitaxy to create thin layers of compounds such as gallium indium antimonide. While gallium antimonide, a material now used in some TPV devices, has a band gap of 0.7 electron volts, Bhat adds 20 percent indium and achieves a more ideal 0.55 electron volts, the band gap needed to convert radiant heat at about 1000 to 1200 C, temperatures that can be achieved easily in metal-mesh or ceramic burners.
While Bhat grows materials in a form known as epilayers, some researchers
believe lower cost TPV structures could be built from materials grown
as crystals, an approach followed by Aleksander Ostrogorsky, associate
professor of mechanical engineering. He and Partha Dutta, a post-doc in
his lab, have developed a process of growing semiconductor crystals that
is being patented by Rensselaer. Ostrogorsky's team has used it to grow
compounds containing two, three, and four elements, such as gallium indium
arsenic antimony. This process offers the possibility of lower cost TPV
cells, while allowing the energy gap to be customized for any application.
Gutmann and Jose Borrego, professor emeritus, have developed a technique
known as radio frequency photo reflection to help researchers understand
the electron recombination processes that limit TPV device performance.
Krishna Rajan, professor of materials science and engineering, has studied
the microstructure of the materials after processing to better understand
material defect structures. Putting the New Materials to Work
Other
Rensselaer work includes mathematical modeling of the devices, characterization
of the electrical and optical properties of various materials, and construction
of complete cells and devices. Rensselaer researchers have built devices
using materials grown on campus as well as four-element compounds grown
at Lincoln Labs in Boston. They also have built filters to return wasted
photon cells to the device so they can be reused, and they have worked on
radiators. Much of the work is aimed at building basic understanding of
the science, complementing development of TPV systems by industry.
As Gutmann explained, "Fundamental understanding tells you how to make
a better product, lets you know what to control in manufacturing, and
provides information about the operating life of actual systems." Such
fundamental information is needed by manufacturers, if TPV technology
is to reach full potential, he said.
Contact: Ronald J. Gutmann (518) 276-6794, rgutmann@unix.cie.rpi.edu
PSYCHOLOGY:
Good Impressions = Profits
Research at Rensselaer Polytechnic Institute shows that entrepreneurs
clearly profit by making a good impression.
"We found that financial success is definitely linked to looking good
and having good social skills," says Professor Robert A. Baron of Rensselaer's
Lally School of Management and Technology.
"That's not surprising," says Baron. "To be successful, entrepreneurs
have to convince investors to put hard-earned money into their idea, convince
people to come and work from them, convince customers to buy from them.
And if you're not good at managing how you come across to people and at
persuading people and being enthusiastic, your chances for success are
going to suffer."
The study showed a direct link between the financial success and social
competence of 75 high-tech entrepreneurs and 153 women who owned their
own cosmetic sales organizations.
Social competence, says Baron, includes skill at social perception (reading
people accurately), social adaptability (being able to work well with
many different kinds of people), and expressiveness.
"For years and years people have asked: 'Why are some entrepreneurs successful
and others are not?' This is a basic question in the field. And if we
can find the answers it would help us teach better. Now we have research
evidence that entrepreneurial success is due to more than just good timing,
or a healthy market, or a good business plan."
Because good social skills can be taught, Baron says the research might
encourage business schools to offer courses in "How to avoid the pitfalls
that will keep you from getting funding even if you have a very good idea."
Contact: Robert Baron (518) 276-2864, baronr@rpi.edu
RECYCLING CELLULOSE:
Don't Call It Garbage
Waste cellulose from paper mills usually ends up in landfills. But it could
be raw material for new plastics, says James Moore, professor of chemistry
at Rensselaer Polytechnic Institute.
Most plastics are made from petroleum-based products that are non-renewable.
Plastics made from renewable resources and waste products could be a real
boost to the environment, but the process must be profitable. That's what
prompted engineers from Biofine Corporation to talk with Moore and other
researchers at Rensselaer's New York State Center for Polymer Synthesis.
Specializing in environmentally-responsible products and processes, Biofine
engineered an efficient way to turn waste cellulose into levulinic acid
at a pilot plant in Glens Falls, N.Y. They knew that, historically, this
chemical had been used to create diphenolic acid, an ingredient once used
for producing polymers. But they needed to know if the levulinic acid had
significant value today, said Stephen Fitzpatrick, president of Biofine.
At Rensselaer's Polymer Center, Fitzpatrick learned that diphenolic acid
is very similar to bis-phenol A, a petroleum derivative that is a main ingredient
in LEXAN and other plastics.
"Early on, diphenolic acid was used in the polymer process, but it was very
expensive," said Moore. "Now the Biofine people have come up with a very
economical way to make levulinic that would give us diphenolic acid at only
a third of the cost of bis-phenol A. If diphenolic acid works as a substitute,
is cheaper, and can be derived from waste materials, we would have a very
attractive product," Moore said.
Moore and doctoral student Tanya Tannahill are now looking for a way to
process diphenolic acid into commercially useful polymers that may be less
expensive than but as good as LEXAN and other popular plastic materials.
That research is supported, in part, by the New York State Energy Research
and Development Authority.
Contact: James Moore (518) 2768481, moorej@rpi.edu
