Effective Injection of Ceramics Nanoparticle Pastes into Plasma Spray for Speedy Layer Formation

Abstract

Thermal nanoparticle spraying was developed to create fine ceramics layers on free surfaces. Resin slurry containing ceramics nanoparticles were atomized by a compressed air jet in a chamber, and the resulting micro mists of composited droplets were effectively injected from a tubular nozzle into the plasma flare. Alumina particles with average diameters of 200 nm were dispersed into the acrylic liquid resin at 40% volume ratio. The microsized mist droplets with average diameters of 20 μm were first formed using the compressed air jet under pressure of 2 atm, and then introduced into the arc plasma with an argon gas spray of 50 slpm in flow rate. The alumina layer of 300 μm thickness was formed successfully on the SUS-304 substrate of 50×50×5 mm in size, which was placed at a distance of 100 mm from the plasma gun, and a higher speed coating at the deposition rate of 50-100 μm/s was achieved. Crystal phases of the coated layer were analyzed by X-ray diffraction. The cross sectional microstructures were observed with optical and scanning electron microscopy. Porosities of the coated layers were estimated through dielectric constant measurements using terahertz wave spectroscopy.