Introducing water vapor into a high vacuum chamber at AEDC.

A powdered form of calcium sulfate dihydrate (CaSO₄2H₂O) was heated to provide water vapor in a vacuum chamber for an experiment seeking to study cryodeposit thin films of ice at the Arnold Engineering Development Center (AEDC) in Tullahoma, TN. However, after the test was conducted, calcium sulfate deposits were found on all surfaces inside the vacuum chamber. It became clear that a new procedure for introducing the water vapor into the vacuum chamber needed to be developed. Calcium sulfate dihydrate, cobalt(II) chloride hexahydrate and 3 angstrom zeolite molecular sieves were investigated to determine how they could be used to deliver water vapor into a vacuum system. An inductive heater was used to heat the samples, a residual gas analyzer to see what gases they released, and a microbalance to measure the mass of the samples as they were being tested inside the vacuum chamber. The 3 angstrom molecular sieves proved to be the most suitable material for these purposes, and a new method that uses them to deliver water vapor to a vacuum system was developed and has been tested in a vacuum chamber at the University of Tennessee Space Institute's (UTSI) Center for Laser Applications (CLA). This method, with the water source located in an external canister that allows the source to be replaced without breaking the vacuum of the vacuum chamber, has been successfully implemented at AEDC.