AN EXPERIMENTAL-STUDY OF TITANIUM POWDER REACTIVITY IN GASEOUS ENVIRONMENTS .1. OXIDATION

A simultaneous thermogravimetric/differential thermal analyzer with a range from 20 to 1600 degrees C was used to study the oxidation of Ti powder. The influences of powder morphology, initial oxygen and nitrogen content and the effects of heating rate and sample size were investigated. All the oxidation experiments terminated at the sample ignition point with an associated heating effect that induced sample melting. The ignition temperature for oxidation increased with higher initial oxygen content, and the nature of the ignition process changed: the transition from passivity to combustion via a regime of gradual oxidation collapsed, bypassing the initial oxidation process observed for powders with lower initial oxygen contents. Cracking of the protective oxide scale played an important part in this behavior. The complete history of the powder needs to be known in order to characterize its reactivity: simple measurable powder characteristics like particle size, surface area and oxygen content alone, are not sufficient for the determination of powder reactivity.