Oxidation of Niobium in the Temperature Range 350°–750°C

Abstract

The kinetics of the oxidation of niobium in dry oxygen at 1 atm pressure have been measured at temperatures in the range 350°–750°C with some additional measurements at 0.1 atm. At 350°C, in tests lasting 270 hr, the oxidation is protective, but at 400°C and above the metal oxidizes, apart from an initial period, at a constant rate with a second breakaway reaction (rate transition) at 450° and 500°C but not at higher temperatures. The anomalous temperature coefficient of the linear rate has been confirmed. The specific surface of the oxide scale has been measured and, apart from an anomaly at 400°C, is shown to decrease with increasing temperature of oxidation and this is ascribed to sintering. The oxidation kinetics of a purer batch of niobium were also investigated. The effect of moisture is to decrease the rate at 400° and 450°C, whereas at 600°C the rate is unchanged.

Reaction Sintering of AlMg–MgO for the Production of MgAl2O4‐Spinel‐Based Composite Ceramics

“…At higher temperatures increased diffusion rates and crystallization processes leading to transition phases as e.g. γ‐Al 2 O 3 are observed, while α‐Al 2 O 3 as the only stable oxide phase is achieved at temperatures beyond 750°C 1–6 . The progress of oxidation is then obstructed even at temperatures beyond the melting point of aluminum.…”

Tantalum, niobium and their alloys

“…Unfortunately, niobium is among the metals which are substantially oxidized at temperatures of 773 K and above. In the mid-temperature range the oxidation rate is at its maximum at 1023 K, after which it decreases up to 1093 K and increases again above this temperature [17]. The linear oxidation rate at various oxygen pressures as a function of temperature is shown in Figure 4 on the basis of results obtained by various authors [17 -22].…”

“…The oxidation rate of niobium as a function of temperature at various oxygen pressures •[20,21],[18], x[17], •[19]…”

Development of experimental verification techniques for non-linear deformation and fracture on the nanometer scale.

“…The oxide growth was shown by Aylmore, Gregg, and Jepson to follow a linear law with time between 500 and 550°C. [39] Using the linear law, the theoretical film thickness should be 35nm, 50 and 65 nm for 1, 2, and 3 hrs growth time at 500°C, respectively . The oxide thicknesses were measured using a Gaertner spectral ellipsometer, and were determined to be 25, 54, and 63 nm for 1, 2, and 3hr growth times, respectively .…”