Vaporization And Precipitation Characteristics Of Cerium Nitrate Precursor Droplets Heated By Monochromatic Irradiation

A novel experimental setup using radiative heating has been used to simulate the high heating rates of solution precursor plasma spray process and understand the thermophysical phenomena inside cerium nitrate precursor droplets. CO2 laser having a heating rate comparable to that of the plasma has been adapted to heat pendant precursor droplets generated at the tip of a micro-needle. The process has been imaged with a high speed video camera. The images have depicted two distinct phases during the entire heating process. In the first stage, the surface evaporation is predominant while the second phase is dominated by precipitation phenomena. Inside the droplet during the heating process formation of explosive bubbles resulting in severe instability and shape deformation has been observed. The droplet deformation was found to be dependent on heating rate and solute concentration in the precursor solution. High laser power (high heating rate) makes the droplet prone to deformation while high concentration precursor solution being highly viscous increases the resistance against instability and deformation. It was also observed that the precipitate transitions through a series of chemical transformations from the initial gelatinous phase into the final solid agglomerate during the last part of the heating process. The SEM images of the precipitate showed a porous morphology. However high concentration precursors with low heating rate resulted in dense microstructure. It was also observed that the micro-structure exhibited irregular patterns, which is evidence of the presence of multiple nucleation sites. The number of nucleation centers increased with the increase of solute concentration and laser power, while XPS analyses confirmed the presence of Ce3+ and Ce4+ in the residue. © 2009 Elsevier B.V. All rights reserved