Free-flowing, transparent γ-alumina nanoparticles synthesized by a supersonic thermal plasma expansion process

Nanoparticles of crystalline, phase-pure γ-alumina is synthesized in a supersonically expanded thermal plasma jet assisted experimental chemical reactor, with good control over the average particle sizes independently with respect to plasma current, oxygen flow rate and the ambient pressure in the sample collection chamber. Most of the synthesized particle samples were seen to be transparent, which gets more transparent with decrease in the particle sizes. The lowest achievable pressure in the chamber had produced particles with average 10 nm sizes, which was best also in terms of narrow size distribution. Another important observation was the absence of serious inter-particle agglomeration, producing free-flowing particles. Optical emission spectroscopic technique was used to study the plasma chemistry of the reaction zone as well as the plasma jet.

► Crystalline, transparent, phase-pure γ-alumina nanoparticles by a plasma method. ► Control over sizes through plasma current, oxygen flow rate and chamber pressure. ► 9 mbar chamber pressure produced 10 nm sizes, smallest by a plasma method. ► Also, free-flowing, crystalline, best transparent with a narrow size distribution. ► Emission spectroscopy used for plasma diagnostics and to study the plasma chemistry.