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https://hdl.handle.net/2440/16726
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Type: | Journal article |
Title: | Phase evolution and kinetics of the oxidation of monosulfide solid solution under isothermal conditions |
Author: | Wang, H. Pring, A. Xie, Y. Ngothai, Y. O'Neill, B. |
Citation: | Thermochimica Acta, 2005; 427(1-2):13-25 |
Publisher: | Elsevier Science BV |
Issue Date: | 2005 |
ISSN: | 0040-6031 1872-762X |
Statement of Responsibility: | Haipeng Wang, Allan Pring, Yaning Xie, Yung Ngothai and Brian O’Neill |
Abstract: | Abstract In this work, the effects of stoichiometry on phase evolution during the oxidation of mss (monosulfide solid solution) were investigated. A series of mss samples, ranging from Fe7.9S8 to Fe2.37Ni5.53S8 were synthesized from pure components. Samples with grain size 53–90 μm were oxidized at 830 and 850 K in air in a muffle furnace. The Rietveld quantitative phase analysis method was used to identify and quantify the phase information from powder X-ray diffraction (XRD) profiles. Hematite was observed and accounted for most of the oxidized iron. Nickel in mss was not oxidized to NiO under current isothermal conditions; instead, it was finally transformed to Ni17S18. Hematite, Fe2(SO4)3 and residual mss were identified in the final phases after 24 h oxidation of the mss composition Fe7.9S8; hematite and Ni17S18 for compositions Fe6.15Ni1.54S8 and Fe2.37Ni5.53S8; hematite, Ni17S18 and pentlandite for Fe6.4Ni1.6S8. Given a constant iron to nickel atomic ratio of 4:1, the sample with lower metal concentration, Fe6.15Ni1.54S8, showed a faster oxidation rate than its metal richer counterpart, Fe6.4Ni1.6S8. The mean oxidation rates for these two samples are 1.85 × 10−4 and 1.22 × 10−4 s−1 respectively for 1.5 h heating at 830 K. Vyazovkin's theory of changing activation energy (Ea) with reaction extent (y) was employed in the current kinetic study. The activation energy was determined using a model-free method. The oxidation of Fe6.4Ni1.6S8 exhibited a higher Ea than Fe6.15Ni1.54S8 over the course of reaction. The activation energy increases with y from 67.1 to 103.3 kJ mol−1 for mss composition Fe6.15Ni1.54S8; 76.1 to 195.0 kJ mol−1 for Fe6.4Ni1.6S8. Bulk compositions Fe7.9S8, Fe2.37Ni5.53S8 were selected to give a constant metal to sulfur atomic ratio of 7.9:8. Oxidation of Fe2.37Ni5.53S8 achieved equilibrium within 1 h, compared to 5 h for Fe7.9S8. |
Keywords: | Kinetics Model free Monosulfide solid solution Oxidation Phase evolution |
DOI: | 10.1016/j.tca.2004.08.007 |
Description (link): | http://www.elsevier.com/wps/find/journaldescription.cws_home/500855/description#description |
Published version: | http://dx.doi.org/10.1016/j.tca.2004.08.007 |
Appears in Collections: | Aurora harvest 2 Chemical Engineering publications |
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