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 nitrog en content and the effects of heating rate and sample size were invest igated. All the oxidation experiments terminated at the sample ignitio n 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 tr ansition from passivity to combustion via a regime of gradual oxidatio n collapsed, bypassing the initial oxidation process observed for powd ers with lower initial oxygen contents. Cracking of the protective oxi de scale played an important part in this behavior. The complete histo ry of the powder needs to be known in order to characterize its reacti vity: simple measurable powder characteristics like particle size, sur face area and oxygen content alone, are not sufficient for the determi nation of powder reactivity.