Zirconium carbide oxidation: Kinetics and oxygen diffusion through the intermediate layer

Abstract

Oxidation of hot‐pressed ZrC was investigated in air in the 1073‐1373 K range. The kinetics were linear at 1073 K, whereas at higher temperature samples initially followed linear kinetics before undergoing rapid oxidation leading to a Maltese cross shape of the oxide. The linear kinetics at 1073 K was governed by inward oxygen diffusion through an intermediate layer of constant thickness between ZrC and ZrO2 which was comprised of amorphous carbon and ZrO2 nanocrystals. Diffusion of oxygen through the intermediate layer was measured to be 9 × 10−10 cm2 s−1 using 18O as a tracer in a double oxidation experiment in 16O/18O. Oxidation at 1073 and 1173 K produced samples made of m‐ZrO2 and either t‐ or c‐ZrO2 with an adherent intermediate layer made of amorphous carbon and ZrO2, whereas oxidation at 1273 and 1373 K produced samples with a voluminous oxide made of m‐ZrO2 showing a gap between ZrC and the oxide. A substoichiometric zirconia layer was found at the gap at 1273 K and no carbon uptake was detected in this layer when compared with the top oxide layer. The loss of the intermediate layer and the slowdown of the linear rate constant (g m−2 s−1) at 1273 K compared to 1173 K was correlated with the preferential oxidation of carbon at the intermediate layer which would leave as CO and/or CO2 leaving a gap between ZrC and substoichiometric zirconia.

On the stoichiometry of zirconium carbide

“…ZrC commercial powder has, according to the manufacturer, a carbon content of 11.6 wt% (11.1% being combined and 0.5% being free carbon). The ZrC commercial powder analysed with the equipment used for this study showed a carbon content of 11.7 ± 0.1 wt% 35 , in line with the manufacturers' specifications. As described in our previous work 35 the hot pressed ZrC x pellets from Set A had a carbon content of 11.2 ± 0.1 wt%, while pellets from Set B had a carbon content of 11.9 ± 0.1 wt%.…”

“…The ZrC commercial powder analysed with the equipment used for this study showed a carbon content of 11.7 ± 0.1 wt% 35 , in line with the manufacturers' specifications. As described in our previous work 35 the hot pressed ZrC x pellets from Set A had a carbon content of 11.2 ± 0.1 wt%, while pellets from Set B had a carbon content of 11.9 ± 0.1 wt%. The stoichiometry of Set A and Set B from elemental analysis was reported as all other impurities were measured (oxygen and nitrogen) and an accurate (global) C/Zr atomic ratio could be estimated.…”

In situ single‐step reduction and silicidation of MoO3 to form MoSi2

“…However, nonisothermal oxidation studies related to the formation of SiO 2 and MoO 3 during MoSi 2 oxidation is scarce in the literature. Also, several research groups investigated the oxidation stability of a variety of materials through the TGA/DTG/DTA technique using an air atmosphere . So, it is crucial to study the nonisothermal oxidation behavior of MoSi 2 through the TGA/DTG/DTA technique.…”

In-Situ Investigation of the Oxidation Behaviour of Chemical Vapour Deposited Zr(C,N) Hard Coatings Using Synchrotron X-ray Diffraction

“…The oxidation behaviour of ZrC has been investigated in several studies on powder samples [13][14][15]19,20], as well as bulk materials [16,17,[21][22][23][24][25][26] and CVD coatings [15]. The oxidation mechanism of this system is generally described by the initial formation of a ZrCxOy phase, followed by the occurrence of amorphous or nanocrystalline ZrO2 [13][14][15][16][25][26][27]. This ZrO2 phase acts as an oxygen diffusion barrier and retards the oxidation process, leading to the precipitation of free carbon.…”