Mukundan, Mallika (2007-08). Phase control in the synthesis of yttrium oxide nano and micro-particles by flame spray pyrolysis. Master's Thesis.
The project synthesizes phase pure Yttria particles using flame spray pyrolysis, and to experimentally determines the effect of various process parameters like residence time, adiabatic flame temperature and precursor droplet size on the phase of Yttria particles generated. Further, through experimentation and based on the understanding of the process, conditions that produce pure monoclinic Y2O3 particles were found. An ultrasonic atomization set-up was used to introduce precursor droplets (aqueous solution of yttrium nitrate hex hydrate) into the flame. A hydrogen-oxygen diffusion flame was used to realize the high temperature aerosol synthesis. The particles were collected on filters and analyzed using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Individual process parameters (flame temperature, residence time, precursor concentration, precursor droplet size) were varied in continuous trials, keeping the rest of the parameters constant. The effect of the varied parameter on the phase of the product Yttria particles was then analyzed. Pre-flame heating was undertaken using a nozzle heater at variable power. Precursor solution concentrations of 0.026 mol/L, 0.26 mol/L, and 0.65 mol/L were used. Residence time was varied by means of burner diameter (9.5 mm and 1.6 mm ID). Large precursor droplets were removed by means of an inertial impactor. The higher flame temperatures and precursor heating favor the formation of monoclinic yttrium oxide. The fraction of the cubic phase is closely related to the particle diameter. All particles larger than a critical size were of the cubic phase. Phase pure monoclinic yttrium oxide particles were successfully synthesized. The end conditions included a precursor concentration of 0.65 mol/L, a pure hydrogen-oxygen flame and a 1.6 mm burner. The precursor droplets entrained fuel gas was passed through a round jet impactor and preheated at full power (130 VA). The particles synthesized were in the size range of 0.350 to 1.7 um.