Energy conversion is not an
efficient process. Only a small part of the energy that is produced is used
productively, the rest is wasted as heat. For example, when we burn fuel in a
car engine, only about 30% of the total energy content is used to drive the
vehicle. The rest is released as heat, which is wasted. It is possible to tap
this waste heat and use it for other meaningful purposes. It requires further
conversion of heat energy into something more convenient, like electric energy,
which can be used for various purposes.
Scientists have been trying to
tap this waste heat, and convert it into electrical energy, by utilising a
well-known physical phenomenon called thermo-electric effect. It has been known
for long that if two ends of a electrically-conducting material, like a metal,
are maintained at different temperatures, a current flows from the hot to the
cold end.
Although it may appear to be
simple, there is a huge obstacle. The problem is that most materials which
conduct electricity are also good conductors of heat. Such a material is
useless for thermo-electric effect because both the ends gets heated up and
there is no temperature difference to exploit.
Traditionally, thermo-electric
effect has been demonstrated by using two different metals joined together, and
by mechanically maintaining different temperatures at the ends. For the kind of
solution that is being explored for tapping waste heat, mechanical maintenance
of different temperatures at the ends is not possible. The quest, therefore,
has been to find a material that is a good conductor of electricity but a bad
conductor of heat. That is, it should have free electrons to move the current
but heating up one of its ends does not result in heating the entire thing up.
It is here that Dr Kanishka Biswas
and his PhD students at the Jawaharlal NehruCentre
for Advanced Scientific Research, Bengaluru, have managed to make a big
breakthrough. Biswas has synthesised a new material, Silver Copper Telluride
(AgCuTe), a compound of three elements, Silver, Copper and Tellurium, that has
this desired property — conduction of electricity but not of heat. Biswas says
this property is due to the unique structure of the new compound. While
electrons are free to move around ensuring electrical conductivity, the
lattices of Tellurium are unusually rigid. The lattices of Silver also vibrates
very slowly, thereby, inhibiting the conduction of heat. It is thus a good
candidate for exploiting thermo-electric effect. The team’s work has just been
published in the chemistry journal, Angewandte Chemie.
Biswas says the new material can
be extremely useful in big industries where the amount of waste heat generated
through various processes is huge, and the potential to convert it into
electricity is large. Of course, the engineering works to make the attachments
of this material is still to be done.
The research
Silver Copper Telluride is a good conductor of electricity and not of heat. The
new compound can now be used for thermo-electric effect.
Researchers:
Dr Kanishka Biswas and team Jawaharlal Nehru Centre for Advanced Scientific
Research, Bengaluru
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