Synthesis of Nanostructured Spherical Aluminum Oxide Powders by Plasma Engineering

Irregularly shaped aluminum oxide particles were plasma atomized resulting in narrow size range dis-tribution of spherical nanostructured powders. Cooling rates, on the order of 106 to 108 K/s, were obtained from the different quenching medias, viz. air, water, and liquid nitrogen. Plasma-engineered powder particles developed nanosize crystallites, while solidification provided insight into the mor-phological feasibility in refinement of grain size. X-ray diffraction (XRD) methods have been used to quantify the crystallite size obtained with different quenching media. Raman peak shift validated the X-ray analysis in anticipating the grain refinement with increasing cooling rates. Salient struc-tural morphology characteristics and a detailed understanding of spheroidized plasma-sprayed alu-mina powders were analyzed through scanning electron microscopy (SEM) studies. Formation of nanograins, novel metastable phases, and amorphous structure were endorsed by transmission elec-tron microscopy (TEM) investigations. I