1995 Volume 59 Issue 10 Pages 1030-1035
Molten iron was evaporated in cold gas stream of argon+oxygen mixture in order to investigate the influence of vapor condensation in a reactive gas on evaporation rate. Iron was levitation-melted in argon+oxygen (PO2=0.0∼0.6 kPa) flows at a given temperature (2173∼2273 K) keeping total gas flow rate of 1.67×10−4 m3·s−1 (STP).
The evaporation rate was discussed with using the counter diffusion model of iron vapor and oxygen within gaseous boundary layer. Oxygen diffused beyond the site where iron vapor nucleated in argon. The oxygen reacted with the iron vapor in the boundary layer. The boundary layer thickness for iron vapor decreased with an increase of the oxygen partial pressure, so that the evaporation rate in argon+oxygen was larger than that in argon and increased linearly with the oxygen partial pressure. When the oxygen partial pressure exceeded a certain value, the evaporation rate became constant regardless with the oxygen partial pressure because the boundary layer thickness was unvaried with the oxygen partial pressure.
In this experiment, ultra fine particles were prepared due to rapid cooling of vapor and condensed particles. The condensed particles obtained in argon were α-Fe, on the other hand the particles in argon+oxygen were Fe3O4. The mean diameter of Fe3O4 was ca. 57 nm and it was unchanged with oxygen partial pressure and temperature. Although variance of particle size disribution of Fe3O4 was unaffected with oxygen partial pressure, it increased with temperature.
