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Molybdenum nitrides: structural and reactivity studies

Hunter, Stuart Michael (2012) Molybdenum nitrides: structural and reactivity studies. PhD thesis, University of Glasgow.

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Abstract

This thesis describes the preparation, structure and activity of a range of binary, ternary and quaternary molybdenum nitrides. It has been shown that all of the samples analysed can be formed through the reaction of the respective molybdate precursor with either ammonia or 3:1 H2/N2 gas mixture. The structures of the nitrides have been studied in detail. These structural findings were then linked to the activity potential of the materials to act as stores of activated nitrogen. The main body of work focused on the ternary molybdenum nitrides of cobalt, iron and nickel with a view to understanding their differences and similarities. Full structural analysis was performed using powder X-ray diffraction (PXRD) and neutron diffraction (PND). The activity of the nitrides was examined by reaction with 3:1 H2/N2 and with 3:1 H2/Ar at various temperatures. Particular attention was paid to the reactivity of lattice nitrogen. The cobalt molybdenum nitride was shown to be special case in this regard where the nitrogen is mobile and relocates within the lattice to a different crystallographic site. This mobility and relocation is concomitant with the loss of 50% of the lattice nitrogen from the system resulting in a phase change from Co3Mo3N to the unprecedented Co6Mo6N phase. The physical and chemical properties of this novel phase have been fully characterised and studied. Interestingly, the isostructual Fe3Mo3N behaves differently and the nitrogen remains fixed and the structure and stoichiometry constant throughout the testing procedure. Further studies of the ternary molybdenum nitrides extended to nickel molybdenum nitride, which was shown to be the least active when tested under both gas mixtures, and analogously to the iron molybdenum nitride the nitrogen is fixed within the β-Mn structured nitride. Further investigations were undertaken, resulting in the successful formation of a series of quaternary nitrides (Fe3-xCoxMo3N). These materials show properties similar to the Co-Mo-N system when the material is cobalt rich and behave similarly to the Fe-Mo-N system when iron rich.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Cobalt Molybdenum Nitride, Ternary Molybdenum Nitride, Molybdenum Nitride, Stuctural Study,
Subjects: Q Science > QD Chemistry
Q Science > Q Science (General)
Colleges/Schools: College of Science and Engineering > School of Chemistry
Supervisor's Name: Gregory, Prof. Duncan and Hargreaves, Dr. Justin
Date of Award: 2012
Depositing User: Mr Stuart M Hunter
Unique ID: glathesis:2012-3221
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 09 Mar 2012
Last Modified: 10 Dec 2012 14:05
URI: http://theses.gla.ac.uk/id/eprint/3221

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