A simultaneous thermogravimetric/differential thermal analyzer with a range from 20 to t600'C was used to study the oxidation ofTi 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 increasedwith higherinitialoxygen content, and the nature of the ignition processchanged:the transitionfrompassivity to combustion via a regimeof 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 characterizeits reactivity: simple measurable powder characteristics like particle size, surfacearea and oxygen content alone, are not sufficientfor the determination or powder reactivity.

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