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New Ceramic Is Super-Tough
When Michigan Technological University researcher
William Predebon and doctoral student Jim Staehler first tried to crush
the new ceramic material they had developed, they figured that something
had gone wrong. Subjected to stress that should have smashed it into so
much shattered crockery, it remained completely intact. The press they were
using simply wasn't powerful enough to crack the quarter-inch-thick disc
of high-strength alumina-a refined cousin of the same material used
Ghatu Subhash (left)
of Michigan Technological University and graduate student Brian Koeppel
measure ability of super-tough ceramic material to withstand stress under
heavy pressure.
to
make pottery and coffee cups-so they tried a larger press. Finally, after
applying about 50% more stress than alumina ever had withstood, the disc
fractured.
Not only did the disc resist more pressure than any alumina
tested in the past, it withstood sudden impacts better. Moreover, the tensile
strength is 50% greater, and it is 20% tougher than any previous alumina
by engineering standards, meaning the material is less likely to crack.
Predebon began researching the creation of a more-perfect ceramic
when he received a grant from the Honeywell Corp. to design ceramics that
could be utilized for armor. Despite some obvious shortcomings when used
for this purpose, ceramics have an important advantage-they weigh about
half as much as steel. A ceramic-plated vehicle would be far cheaper to
run and would have a greater range than conventionally armored tanks and
personnel carriers.
Predebon reasoned that, the purer the ceramic, the stronger
it would be, if processed under ideal conditions. He tracked down the purest,
finest alumina powder available, with an average particle size of less then
half a micron. Then he began processing it, using a vacuum hot press followed
by a hot isostatic press cycle.
When finally completed, the alumina was 99.6% solid and the
remaining 0.4% of empty space was inside the grains, not between then, where
the ceramic would be most likely to fracture. In the high-strength alumina,
the grains are uniform and lock together as tight as cells in honeycomb,
Predebon explains.
Because it wears better than traditional alumina, the new variety
could replace the ceramic coating now used on artificial hips. Due to its
strength and ability to withstand high temperatures, it could replace steel
in some engine components, such as pistons.
Reinforced with silicon carbide whiskers, it also could be used
as a cutting tool for high-strength steel. So much heat is generated in
the cutting process that the tool and the steel can melt; the new ceramic
would dissipate heat and allow for a cool, clean cut.
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