Paper VT-TuP4
The PM-IRRAS Study of Water Thin Film on Aluminum Alloy Surface with Vacuum Pumping Down Process Condition

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Baking is always a necessary step for achieving ultra high vacuum (UHV). For a previously baked system to have the vacuum parts replaced and to achieve the same level of vacuum without repeated baking is a challenge to today’s large vacuum system like synchrotron radiation facility. With ongoing study on ultra-dry parts replacement system, the need to understand how dry is enough becomes essential for both scientific aspect and cost of ownership aspect. Previous studies have shown a phase change for water on crystal Al₂O₃ (0001) near 10 torr. In our study, polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) results have shown a clear spectrum change at 8 torr on ozone water cleaned A6061-T6 aluminum alloy surface. We also measured the temperature change during pumping down process and found out the temperature can go as low as -30^oC for this adiabatic expansion process. This pumping down process could cause the water molecules on the surface to be frozen and then to be melted during the whole pumping down process. The PM-IRRAS study has shown the phase change result. A more detailed PM-IRRAS study corresponding to the pressure and temperature during pumping process will be shown in this presentation for both A6061-T6 aluminum alloy and crystal Al₂O₃ (0001).