International audiencePellets of zirconium oxycarbide ZrC0.82O0.14, obtained by hot pressing of zirconia and zirconium carbide, were irradiated by an ytterbium-doped fibre laser in argon atmosphere (incident power density = 24.7 kW cm-2, beam diameter 0.7 mm). The surface of the samples, heated at 3300 C and more, i.e. near the melting, released its oxygen, leading to the carbide ZrC0.75 despite the presence of traces of oxygen in the cell of treatment (PO2 estimated around 1 Pa). A mechanism is proposed for explaining this result, based on the thermodynamical stability of the carbide, higher at these temperature and oxygen pressure than the oxide. Oxygen of the oxycarbide evolved in the form of the gaseous species ZrO, while the grains of the oxycarbide, converted into the carbide, grew from 2 to 20 lm. Similarly, the traces of dioxygen present inside the treatment cell react with the carbide, giving ZrO (gas), and do not form any oxidised solid phase. This opens interesting future prospects in the field of the production of oxygen-free zirconium carbide powders
This work compares the oxidation behaviour of three iron-based substrates (C40E,
Invar and 304L) in CO2 industrial gas, in order to determine the conditions for producing wüstite
(Fe1-xO), on the basis of kinetic and morphologic studies. For the three alloys at the beginning of the
reaction, wüstite formed under 105 Pa of CO2 following a rate law
RT
220000
10.2 P e
dt
d( m/S)
CO2 . For 304L, formation of a spinel phase chromite briefly
preceded it during a first step. Magnetite appeared for long times of experiment, in the case of
Invar and 304L. This can be explained by the stopping of iron outer diffusion. These results are
discussed according to the literature and thermodynamic data. They open new fields for coating
these alloys by plasma spray processes.
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