An Experimental Study of Titanium Powder Reactivity in Gaseous Environments. Part II: Nitridation

Thermo-mechanical aspects of the heterogeneous ignition of metals

“…However, after the endothermic polymorphic transformation, αTi → βTi, with a latent heat of ∼ 59 J/g [23], is achieved, the reaction rate sharply increased. The link between the αTi → βTi transition and the ignition of titanium in nitrogen has also been observed experimentally [24]. Titanium powders (average size 24 and 67 µm) were heated in argon, which was switched to nitrogen at sample temperatures varying between ∼ 770 and 970 • C. When the switch of gases took place before the transition temperature was reached, no ignition occurred.…”

“…(13) and (14) are presented Table 3 The critical values of the oxide shell stress and pressure R 0 × 10 5 δ 0 /R 0 × 10 3 σ crit × 10 −8 P crit × 10 −5 (m) (N/m 2 ) ( P a ) in Table 3 for particles of varying R 0 sizes. It can be seen that for a titanium powder of the average particle size of 30 µm used in this work, as well for the titanium powders used before [24], the pressure drop existing at the point of the transformation α → β titanium does actually exceed the value of P crit , so buckling of the oxide shells is to be expected. As stated above, buckling should create numerous cracks in the oxide through nitrogen, which has good access to titanium, resulting in the fast nitridation of titanium.…”

Tailoring Titanium Hydride Decomposition Kinetics by Annealing in Various Atmospheres

“…An exception are ageing treatments between 1 and 12 h at temperatures between 560 C and 690 C, which were performed to realise difLehmhus, Rausch/Tailoring Titanium Hydride Decomposition Kinetics by Annealing in Various Atmospheres ferent levels of initial nitrogen content for further constant heating rate nitridation experiments. [31] Zhang and Kisi report both incorporation of nitrogen atoms into the titanium hydride lattice and formation of titanium nitride during mechanical milling in air; their studies show that interstitial nitrogen atoms are found in octahedral lattice sites, which would usually be occupied by hydrogen atoms following the first main stage of titanium hydride decomposition. [32] Finally, a recent publication on titanium thermal oxidation by Lenarduzzi et al shows that rates of surface oxidation depend strongly on the oxidising atmosphere, with oxygen levels of 20 % complemented by nitrogen leading to thinner oxide layers than a mere 1 % of oxygen complemented by argon, since nitrogen acts as diffusion barrier by occupying octahedral lattice sites in the titanium matrix.…”

An Experimental Study of Titanium Powder Reactivity in Gaseous Environments. Part I: Oxidation

“…The oxidation aspects are presented in this paper (part I) while the nitridation work is presented in Part II (cf. Rode and Hlavacek, 1994). The effect of powder characteristics such as initial oxygen and nitrogen content and particle size distribution and morphology were investigated.…”