Synthesis of nanostructured spherical aluminum oxide powders by plasma engineering

Abstract

Irregularly shaped aluminum oxide particles were plasma atomized resulting in narrow size range distribution of spherical nanostructured powders. Cooling rates, on the order of 10 6 to 10 8 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 morphological 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 structural morphology characteristics and a detailed understanding of spheroidized plasma-sprayed alumina powders were analyzed through scanning electron microscopy (SEM) studies. Formation of nanograins, novel metastable phases, and amorphous structure were endorsed by transmission electron microscopy (TEM) investigations.

Synthesis, Microstructural Characterization, and Mechanical Property Evaluation of Vacuum Plasma Sprayed Tantalum Carbide

“…Cooling rates were estimated from the XRD spectrum (Fig. 5) using full‐width at half‐maximum (FWHM) peak intensity, and also the crystallite size is determined from the peak characteristic as follows 6,7,21,22 : where is average crystallite size, k is shape factor (∼0.9), λ is wavelength, ( B − b ) is FWHM, θ is angle of diffraction, Q is the average cooling rate, n is cooling rate exponent (∼0.32), c is a material‐dependent constant (∼34) 6–7,21,22 . Average crystallite size was calculated to be approximately 60–90 nm in diameter, which matches with the crystallite size observed in the TEM images.…”

“…Vacuum plasma spray formed tantalum carbide (TaC) provides an alternative to overcome fabrication hurdle of high melting point materials and their brittleness. Plasma plume reaches temperatures in excess of 10 000 K and impacts the powders in molten or semi‐molten states generating typical mechanically bonded layered structure 4,6,7 . It is important to emphasize that much of the literature research material for the applications of TaC, because of military applications, is sparingly available 4,8,9 .…”

Role of carbon nanotube dispersion in fracture toughening of plasma sprayed aluminum oxide - carbon nanotube nanocomposite coating

“…Survival of CNTs was possible because of rapid kinetics inherent to the plasma spray processing. Laha et la has investigated CNT/metal interface in Al-Si/CNT system [43,44,118]. It was concluded that a thin layer of SiC on CNT is formed ( Fig. 2.21b) suggesting interfacial reaction which improved interface wettability required for .t-AI-Si matrix x 1 .…”

“…Basic challenge arising in the metal-CNT nanocomposite is associated with damage to CNTs at high temperature processing, as required for metal processing [43,44,118]. Secondary challenge includes low interfacial bonding strength between CNT and metal interface [156][157][158].…”

“…4 Overall plasma spraying parameters utilized in the optimization of depositing n-A1 2 0 3 coating are listed in Table 4.3. Processing parameters for plasma spraying of A-SD powder were selected based on earlier experience and exiting literature [39,118,[209][210][211]. Uniform coating thickness is observed in the plasma sprayed ASD coatings, as presented in Fig.…”