Tunthawiroon, Phacharaphon

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Tunthawiroon, Phacharaphon
Alternative Name
TUNTHAWIROON, Phacharaphon
Tunthawiroon, P.
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Email
phacharaphon.tu@kmitl.ac.th

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    Item type:Publication,
    Possibility of metallic cobalt formation in the oxide scale during high-temperature oxidation of Co-27Cr-6Mo alloy in air
    (2023-01-01)
    Wongpromrat, Patthranit
    ;
    Tunthawiroon, Phacharaphon
    ;
    Bumrungthaichaichan, Eakarach
    ;
    Ponpo, Phisan
    ;
    Nilsonthi, Thanasak
    Co-based alloys are known to be high oxidation-resistant material and used in several high temperature applications. During high temperature oxidation, duplex oxides containing Co and Cr were formed. It was thermodynamically elucidated that when the growing scale was thick enough, the partial pressure of O<inf>2</inf> in the scale dropped. Then, the reduction of CoO occurred for promoting O<inf>2</inf> which was responsible for Cr<inf>2</inf>O<inf>3</inf> production. This work experimentally proved this point by in situ char-acterising Co-27Cr-6Mo at high temperatures in air by X-ray diffractometer in a grazing incident mode and metallic Co was confirmed to be formed by the reduction of CoO consistent with the image taken and analysed by field emission scanning electron microscope, energy-dispersive X-ray, and electron backscatter diffraction. Furthermore, the change in lattice parameter and the phase transition were observed when the temperature was altered.
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    Evidence for chromium, cobalt and molybdenum volatilisations during high temperature oxidation of Co-27Cr-6Mo Alloy
    (2022-07-01)
    Wongpromrat, Patthranit
    ;
    Galerie, Alain
    ;
    Thublaor, Thammaporn
    ;
    Chandra-ambhorn, Walairat
    ;
    Ponpo, Phisan
    A Co-27Cr-6Mo alloy was oxidised in pure O<inf>2</inf> between 800 and 1000 °C for durations up to 96 h. The flow rate was varied between 2 and 5 cm.s<sup>–1</sup>. In these conditions, volatilisations of chromium, cobalt and molybdenum were observed. The chromium volatilisation values were in good agreement with calculations assuming (CrO<inf>3</inf>)g volatilisation limited by diffusion in the gas boundary layer. On the contrary, the measured flux of evaporated Co was higher than the calculated Co volatilisation flux from the metallic Co. The theoretical relation between the solid Co particle size and its vapour pressure was suggested to help explaining such difference.