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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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