Technology
Saturday, October 13, 2007
Indians develop
new iron using ancient technology
By K.S . Jayaraman. Karnataka, India, 11:02 AM IST
http://www.indiaenews.com/technology/20071013/75049.htm
Indian
metallurgists have developed a type of corrosion-resistant
iron that construction engineers would love. And vital clues
for it came for Delhi's famous Iron Pillar that has been
standing tall for over 1,600 years.
Developed
by Ramamurthy Balasubramaniam and his former student Gadadhar
Sahoo of the Indian Institute of Technology (IIT) in Kanpur,
the iron contains phosphorus and shows remarkable resistance
to corrosion, especially in concrete.
'This
is a significant first step in the possible commercial (large-scale)
use of these irons,' Balasubramaniam, better known as Bala,
told IANS.
Most
steels today contain small amounts of carbon and manganese.
Modern steel makers avoid phosphorus because its segregation
to grain boundaries makes the steel brittle.
But
the IIT team successfully produced ductile phosphoric irons
by driving the phosphorus away from grain boundaries through
clever alloy design and novel heat treatment.
Ironically,
Bala's material is not new. It was being made by Indian
ironsmiths centuries ago.
Bala
says he got the clue for developing this material from the
six-tonne seven-metre tall Delhi Iron Pillar - a major tourist
attraction in the Qutb Minar complex -- that has been standing
for centuries in the harsh weather of the capital without
any corrosion.
'As
a metallurgist, I was intrigued,' Bala told IANS. And his
passionate quest to unravel the mystery that began in 1990s
has now culminated in phosphoric irons.
The
test samples developed by the IIT team remained fresh after
three months of being immersed in solution, simulating the
corrosive concrete environment, whereas the best commercially
available steels got rusted. In another experiment, they
embedded the samples in concrete to simulate actual conditions
and obtained similar results.
'The
work is especially important in regard to the widespread
use of steels in civil structures,' said Gerhard E. Welsch,
professor of Materials Science and Engineering at Case Western
Reserve University (Cleveland, Ohio).
'The
recent bridge collapse in Minneapolis has added new urgency,'
Welsch said in a congratulatory message to Bala. Seven people
died when the bridge across the Mississippi river collapsed
Aug 2, 2007.
Current
philosophies to tackle corrosion in concrete include the
addition of inhibitors to the cement mix, use of rebars
that are galvanised, epoxy coated, or micro-alloyed by the
addition of small amounts of chromium, copper and nickel
-- elements that are known to induce passivity in iron.
Their
high cost is a disadvantage, says Bala. 'Besides, we have
experimentally shown our phosphoric irons perform better.'
Bala's
real break came when he found that the iron used in the
Delhi pillar contained elevated amounts of phosphorus --
as much as 0.25 percent against less than 0.05 percent in
today's iron. He found this was a result of the ancient
process where iron ore is reduced in a single step by mixing
it with charcoal, without any limestone addition.
Modern
blast furnaces, on the other hand, use limestone yielding
molten slag and pig iron (high in carbon) that is later
converted into steel. Most phosphorus is carried away by
the basic slag.
Further
studies and analysing rust from the pillar showed that phosphorus
catalysed the formation of a protective passive film on
the surface of the pillar that acted as a barrier between
the metal and rust.
Tanjore
Anantharaman, author of the book 'Delhi Iron Pillar - the
Rustless Wonder' and Bala's former teacher at the Benaras
Hindu University, says phosphorus was long suspected to
be behind the pillar's corrosion resistance. 'It was Bala
who proved it.'
That
was in 2000. Actual material development and corrosion tests
were initiated in 2003 when Sahoo joined Bala for his PhD
that he completed in 2006.
'Our
papers based on the thesis are coming out now,' Bala said.
All the work, he said, was done with institute funds without
any external support.
'Certainly,
we are not claiming that this is the end of our studies,'
admits Bala. 'We have shown the usefulness of phosphoric
irons for concrete reinforcement applications. Now it has
to be taken up by more researchers for greater understanding.'
Bala
thanks his forefathers for the success. 'I am of the firm
belief that ancient Indian metallurgists had the empirical
knowledge that high phosphorus content ores resulted in
corrosion-resistant iron. They did not create this material
by accident.'
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