The zirconia in a new coating for jet engine turbine blades chemically converts sand and other corrosive particles that build up on the blade into a new, protective outer coating.
airplane’s engines draw sand from a runway. Photo courtesy of the U.S.
Department of Defense.
Engineers at The Ohio State University are
developing a technology to coat jet engine turbine blades with zirconium
dioxide to combat high-temperature corrosion. The zirconia chemically converts
sand and other corrosive particles that build up on the blade into a new,
protective outer coating. In effect, the surface of the engine blade constantly
renews itself. Ultimately, the technology could enable manufacturers to use new
kinds of heat-resistant materials in engine blades so that engines will be able
to run hotter and more efficiently.
Sand as the Enemy
Nitin Padture, professor of materials science
and engineering at Ohio State, said that he had military aircraft in mind
when he began the project while he was a professor at the University of Connecticut.
“In the desert, sand is sucked into the engines during takeoffs and landings,
and then you have dust storms,” said Padture. “But even commercial aircraft and
power turbines encounter small bits of sand or other particles, and those particles
damage turbine blades.”
Jet engines operate at thousands of degrees Fahrenheit, and blades in the most
advanced engines are coated with a thin layer of temperature-resistant,
thermally insulating ceramic to protect the metal blades. The coating, referred
to as a thermal-barrier coating, is designed like an accordion to expand and
contract with the metal. The problem is that when sand hits the hot engine
blade it melts and becomes glass. “Molten glass is one of the nastiest
substances around,” said Padure. “It will dissolve anything.”
The hot glass chews into the ceramic coating, though the real damage happens
after the engine cools and the glass solidifies into an inflexible glaze on top
of the ceramic. When the engine heats up again and the metal blades expand, the
ceramic coating can’t expand because the glaze has locked it in place. The
ceramic breaks off, shortening the life of the engine blades.
ceramic coating destroyed by molten glass.
Zirconia to the Rescue
In a recent issue of the journal Acta Materialia
, Padture and his colleagues described how the
new coating forces the glass to absorb chemicals that will convert it into a
harmless-and even helpful-ceramic. The key, Padture said, is that the coating
contains aluminum and titanium atoms hidden inside zirconia crystals. When the
glass consumes the zirconia, it also consumes the aluminum and titanium. Once
the glass accumulates enough of these elements, it changes from a molten
material into a stable crystal and it stops eating the ceramic.
“The glass literally becomes a new ceramic coating on top of the old one,” said
Padure. “Then, when new glass comes in, the same thing will happen again. It’s
like it’s constantly renewing the coating on the surface of the turbine.”
Padture’s former university has applied for a patent on the technique that he
devised for embedding the aluminum and titanium into the zirconia. He’s
partnering with Inframat Corp., a nanotechnology company in Connecticut, to further develop the
technology. Padture stressed that the technology is in its infancy. He has yet
to apply the coatings to complex shapes, and cost is a barrier as well because
the process is energy-consuming.
His coauthors on the paper included Ohio State doctoral student Aysegul
Aygun, who is doing this work for her dissertation; former postdoctoral
researcher Alexander Vasiliev, who is now at the Russian Academy of Sciences;
and Xinqing Ma, a scientist at Inframat Corp. The research was funded by the
Office of Naval Research and Naval Air Systems Command.
coating designed to resist molten glass, which is in a thin layer at the top.
If the cost eventually came down and the
technology matured, the payoff could be hotter engines that burn fuel more
efficiently and create less pollution. Manufacturers would also be able to use
more sophisticated ceramics that boost the heat-resistance of engines.
Eventually, technology could go beyond aircraft and power-generator turbines to
extend to automobiles as well, Padture said.
more information, call (614) 247-8114, e-mail Padture.firstname.lastname@example.org or
Unless otherwise indicated, images are by Aysegul Aygun and
Nitin Padture, courtesy of The Ohio State University.