Microstructure of alumina produced by millimeter-wave heating

Alumina ceramic synthesized by millimeter-wave (MM) heating at 1523 K for 60 min exhibits higher bending strength (800 MPa) than conventionally synthesized alumina. We analyzed the relationship between the bending strength and microstructure of both types of alumina samples. A transmission electron microscope (TEM) was used to compare the microstructures of samples synthesized by MM heating at 1523 K or 1573 K for various heating times with those synthesized conventionally at 1773 K. The TEM data reveal that the most significant factors influencing bending strength are not the grain size and grain boundaries, but rather, the pore size and distribution.