In order to conduct heat treatments to obtain the desired microstructure, samples may be placed into a non-vacuum furnace. This can only be done successfully, and without oxidation, if the samples are first sealed into an ampoule which is evacuated of oxygen, and filled with an inert gas, such as argon. Encapsulation is the process of wrapping the sample in molybdenum foil before placing it into a quarz glass tube (sometimes along with a getter if the sample is suspected to have a high oxidation susceptibilty), evacuating the oxygen from it before filling it with argon, and heating and twisting the tube to seal the sample inside it, over a gas flame. The seal can be tested by submerging into water, to ensure no oxidation of the sample will occur in the furnace.
Figures
Figure One: Quartz Tube Encapsulation to prevent oxidation of samples (video here).