Morphology of ceramic particulates formed in a premixed oxygen/acetylene flame from liquid precursor droplets

This study concerns high temperature flame synthesis of ceramic deposits utilizing a mono-disperse stream of droplets composed of an aqueous precursor. The droplets were injected into an oxy-acetylene flame. Mono-disperse droplets were generated with an electrostatic spray technique. High-speed droplet images suggest evidence of shedding of small particulates from the droplet surface as they enter the flame. Flame temperatures were measured by a spectroscopic technique utilizing chemiluminescence from the Q1 branch of hydroxyl (OH) radical A2Σ+ → X2Π(0, 0) rotational band. Scanning electron microscopic analysis of the extracted samples was performed to identify the types of deposits. The thermophoretically obtained samples show a morphology transition at flame equivalence ratios between 1.1 and 1.5. Large droplets in cooler flames impact onto the substrate as gelated material or liquid, whereas, smaller droplets traversing higher temperatures yield sintered poly-crystalline particulates. Raman analysis of multi-pass deposits indicates presence of tetragonal phase of the yttria-stabilized zirconia.