Oxidation of porous nanocrystalline titanium nitride. I. Kinetics

Abstract

We used the continuous weighing method to study the oxidation kinetics in air for TiN specimens pressed and sintered from nanocrystalline powders with particle size ≤55 nm. Oxidation was carried out at 500-1000°C for 240 min. By comparing with the oxidizability of compact titanium, we estimated the total reaction surface S of the porous specimens as a function of their oxidation conditions. The mass of absorbed oxygen Δm was calculated from the mass gain ΔP, taking into account the volatile component N 2 . We have shown that the maximum mass gain Δm at 600°C is due to reaction of oxygen with the largest reaction surface. Within 120 min, external pores close up, S decreases, and then a continuous oxide layer forms in which diffusion of oxygen is slowed down. At 700-800°C, the process of closing up of the pores is activated, and S decreases by an order of magnitude compared to 600°C. After the first 40-50 min, a continuous oxide film forms and virtually no further mass gain occurs. As the temperature increases, the oxidation rate increases. At 900°C, the reaction surface becomes equal to the external surface of the specimen, but the thickness of the scale increases linearly. We hypothesize that for T > 850°C, counterdiffusion of titanium ions is superimposed on diffusion of oxygen.

Oxidation of TiAl intermetallic

“…All this suggests that the oxidation mechanism of TiAl changes. Comparing the data on the oxidation of titanium [12,13] and its alloys [8][9][10][11], we may conclude that the cause of the change in the oxidation mechanism at t > 800°C is changes in the rutile lattice. According to [12][13][14], the lattice of nonstoichiometric rutile has both oxygen vacancies and interstitial titanium ions.…”

“…[3], Ni-Ti [8,9], Ti-Ni-Al [10], and TiN [11]. Depending on the composition of the alloy and scale, the temperature of transition from slow to fast oxidation is somewhere between 800 and 900°C.…”

“…The oxidation mechanism changes: the counterdiffusion of titanium ions is superimposed on the diffusion of oxygen. As a consequence, the oxidation rate of TiAl increases at t ≥ 850°C, as in oxidation of titanium [13] and its alloys [8][9][10][11]. This may be, according to [13], attributed to the fact that the diffusion rate of titanium ions in rutile is much greater than that of oxygen ions.…”

Unraveling the atomic structure evolution of titanium nitride upon oxidation

“…However, it is also susceptible to thermal oxidation corrosion that severely limits their applicability [17][18][19] . Early studies on TiN oxidation process and phase transformation suggest a series of titanium oxides might be formed 20 , including anatase TiO 2 18 , rutile TiO 2 21 , Ti 3 O 5 22 , and intermediate phase of TiO x N y 23 , etc. The oxidation of TiN appears to be complex because of the apparent disparity of the results, which mainly comes from the existence of variety of oxides with a stable structure.…”