Enhancing protective gas atmospheres: Influence of trace moisture on the oxidation of titanium in oxygen-free atmospheres

In this study, we systematically investigated the influence of residual water on the oxidation of titanium in an oxygen-free atmosphere at ambient pressure created using silane-doped argon. The study addresses a limitation of oxygen-free production: although molecular oxygen can be effectively scavenged by silane, residual moisture remains in the atmosphere and may act as an additional oxidising species for highly reactive metals. High-purity titanium samples (99.995%) were exposed for 10 min to oxygen-free atmospheres with controlled water concentrations ranging from 0.1 to 1.0 ppm. X-ray photoelectron spectroscopy (XPS) was used to analyse the resulting changes in the titanium chemical states and to determine the corresponding oxide thickness. In laboratory-scale reaction-chamber experiments, reducing the water concentration from 0.8 ppm to 0.2 ppm reduced the oxide thickness from 0.38 ± 0.09 nm to 0.12 ± 0.09 nm. In a glove box operated under comparable oxygen-free conditions, reducing the water concentration from 1.0 ppm to 0.1 ppm reduced the oxide thickness from 0.61 ± 0.09 nm to 0.23 ± 0.12 nm, corresponding to a reduction of approximately 62%. These results demonstrate that residual water causes measurable oxidation of titanium even after molecular oxygen has been removed and that moisture concentration is therefore an important process parameter for oxygen-free production. The findings show that further optimisation of oxygen-free atmospheres for highly reactive metals requires not only efficient oxygen scavenging but also stringent control of residual moisture.