Effect of vacuum level on evaporation rate of magnetic fluids

One hydrocarbon-based and two fluorocarbon-based magnetic fluid samples were tested under four different vacuum levels. The weight losses of the samples were measured and the evaporation rates calculated. It was found that under higher vacuum levels (lower pressure levels) the evaporation rate of each sample was significantly higher than under atmospheric conditions, gradually reaching a saturated level while the vacuum level kept increasing. The Langmuir equation is modified to theoretically explain this phenomenon. It was also found that the fluorocarbon-based magnetic fluids are more suitable for ultra-high-vacuum applications.