This Small Business Innovation Research Phase I project will use pressureless reaction sintering to generate transparent aluminum oxynitride samples with a minimum of 80 percent in-line light transmission and a maximum of 10 percent haze. A thorough microstructural evaluation of AlON samples synthesized in an earlier program will be carried out by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, and electron probe microanalysis. The effect of MgO addition on microstructures and nanostructures, the lattice structure, and the lattice parameters will be clarified. The nature of grain boundaries, i.e., the presence of a second phase, will be investigated. The solid solubility limits for MgO in AlON will be determined. The information gained will be used to slow down the fast grain-boundary movement, which causes excessive grain growth and pore entrapment within the grains, thereby preventing full densification and causing loss of transparency. A stepwise reaction sintering will be used to improve the densification-rate-to-reaction-rate ratio. Because pressureless sintering is used to manufacture AlON, processing large panels with curvatures will be practical. Sintered AlON is expected to cost 50 percent less than hot-pressed MgAl2O4 of comparable size because of the ease of manufacturing AlON by pressureless sintering. Potential applications include high-temperature windows (AlON is also infrared transparent),high-pressure lamp envelopes, transparent armor, watch glass (AlON's high hardness makes it scratch resistant), furnace windows, and radiation windows in next-generation fusion reactors.
