Mass Transfer in High-Temperature Laser Confocal Microscopy

High-temperature laser confocal microscopy allows in situ observation of the sample surface while the temperature and gas atmosphere are controlled. Because of the relatively small sample size (diameter around 5 mm) mass transfer between the sample and the furnace atmosphere can be rapid. When studying liquid steel samples, evaporation from the steel surface can be sufficiently rapid to influence observations. In previous work, magnesium oxide inclusions (at the surface of liquid steel) were shown to shrink by dissolution, during observation by laser confocal microscopy. Inclusion dissolution was driven by evaporation of magnesium from the steel surface. In the work presented here, the rate of sample-gas mass transfer in a high-temperature confocal microscope was measured based on evaporation of manganese. The mass transfer rate can be estimated by simple static diffusion from the sample surface.