Air-bubble entrapment due to a drop

Abstract

In 2001, an ultra-high-speed video camera of 1,000,000 frames per second was developed in Hydraulics Laboratory of Kinki University. The image sensor of the camera was the ISIS-V2, the In-situ Storage Image Sensor-Version 2. The camera has been applied to visualization of high-speed phenomena in various fields of science and engineering. We observed entrapment phenomena of bubbles resulting from thermal spraying of metals. Thermal spraying is used to improve solid surfaces by spraying melted metal or ceramic particles to the surfaces. One of the problems relating to the thermal spraying is entrapment of air bubbles under the metal or ceramic layers covering the solid surfaces. The bubbles decrease bonding strength of the layers made by the thermal spraying. The entrapment processes were successfully visualized by application of the ultra-high-speed video camera.

Thermal contact resistance between plasma-sprayed particles and flat surfaces

“…Thermal contact resistance between an impacting particle and a non-heated solid substrate has been attributed to the presence of volatile compounds on the surface, which evaporate under the hot splat and form a gaseous barrier between the two surfaces [2,5,34,35]. On heated or preheated surfaces, these adsorbates/condensates are almost completely vaporized [2,5,7,36], improving splat-substrate contact and greatly reducing the thermal contact resistance at the splat-substrate interface.…”

Effect of substrate oxidation on spreading of plasma-sprayed nickel on stainless steel

“…11B). Holes in the solidified splats have been attributed to the presence of gases entrapped between the splats and non-heated substrates [36,37]. Preoxidizing the surfaces at temperatures above 350°C, eliminated the appearance of these holes ( Fig.…”

Impact of plasma-sprayed metal particles on hot and cold glass surfaces

“…This suggests that thermal contact resistance between the cold glass and the splat is greater than that between the hot glass and splat. The cause of the increased thermal contact resistance on the cold surface is probably a gas barrier [20,21], formed after evaporation of adsorbed substances on the substrate beneath the splat. It is possible that heating the surface removes the adsorbed substances and gas barrier, producing better contact [2,9,22,23].…”