5. Titanium's resistance to gases other than air

5.1 Behavior in hydrogen

The titanium oxide layer acts as a barrier to gases such as hydrogen at room temperature. Any break in this film can lead to rapid hydrogen uptake as soon as the temperature exceeds 80°C. Hydrogen has a very low solubility in the alpha phase of titanium (20 to 150 ppm depending on the author); when this limit is exceeded, hydrides precipitate (see figure 6 ), and as these hydrides are brittle, ruptures can occur in stress zones and during shaping. At temperatures below 80°C, hydrogen diffusion is low and hydrides remain in the skin.

The use of titanium in pure hydrogen gas is therefore not recommended; however, the...