The effect of energy deposition on the formation of nanoscale alumina particles in the electrothermal plasma synthesis of nanomaterials

Abstract

The electrothermal gun is a relatively new technology that produces various types of plasma vapor using high current pulsed power. A dense metal vapor plasma at extremely high temperature and high velocity is discharged from the electrothermal gun, and introduced into the background gas in the reaction chamber. Then; the discharged metal plasma vapor reacts with background gas and produces nanoscale ceramic particles. Although this method can be applied to make a variety of nanosized ceramic materials by choosing different metals for the cathode/anode/bore ablation and different gases in the reaction chamber, in this investigation, nanoscale alumina particles have been produced by letting a highly ionized aluminum plasma vapor react with oxygen gas in the reaction chamber. The synthesized alumina powder has been-characterized by X-ray diffraction, BET, SEM, and TEM. XRD patterns confirmed that low. energy firing of 44 kJ energy deposition produced high purity gamma-phase alumina nanoparticles, which sizes ranging between 5,and 50 nm with an average particle diameter of 26 urn. By contrast, a high energy shot of 96 kJ produced alumina particles of 41 nm average particle diameter and a small amount of delta- and alpha-phase contents were found even though gamma-phase alumina was still dominant. In addition, high-speed video imaging revealed delayed turbulent mixing and reaction between aluminum plasma vapor and oxygen gas to several milliseconds after approximately 1 ms current pulse duration.