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Title: A study of the synthesis of CoAI₂O₄ and the inducement of reactions and rearrangements in the solid state by mechanical milling
Author: Wynn, Paul G.
ISNI:       0000 0001 3573 6227
Awarding Body: Open University
Current Institution: Open University
Date of Award: 2006
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The nature of commercial samples of Co3O4, y-AI(OH)3 y-AIO(OH) and a-Al2O3 have been examined and the phase changes undergone by these materials as a function of heating in air examined ex situ and in situ by X-ray powder diffraction and by thermal analysis. The thermally induced reaction between the pre-milled cobalt- and aluminium-containing species, to form CoAI2O4 with a spinel-related structure, has been investigated. Pre-milling of the reactants facilitates the formation of CoAI2O4 in shorter periods of time. An attempt to produce a series of phases in the solid solution series CoxAI3-xO4 was not successful. Nanoparticle calcium stannate (CaSnO3) and calcium titanate (CaTiO3) have been prepared by the mechanical milling of mixtures of calcium (II) oxide with tin (IV) oxide or titanium (IV) oxide. The reaction of the rutile form of titanium (IV) oxide with calcium (II) oxide is faster than that between the anatase modification of titanium (IV) oxide and calcium (II) oxide. Nanostructured partially inverse spinel-related zinc ferrite (ZnFe2O4) particles have been synthesised from bulk normal spinel-related ZnFe2O4 by means of mechanical milling using a planetary ball mill. This process is shown by a combination of X-ray powder diffraction and Mossbauer spectroscopy to result in a rearrangement of the zinc and iron ions in the A and B sub lattices with the resultant change of magnetic properties from antiferromagnetic to ferromagnetic or ferrimagnetic. The changes in the local coordination of aluminium in y-AI(OH)3 when milled with zinc oxide has been monitored by 27AI MAS NMR spectroscopy. The results give evidence for the onset of the formation of a precursor to spinel-related ZnAl2O4 and may have implications for the more facile formation of CoAI2O4 by the calcination of pre-milled mixtures of cobalt- and aluminium-containing oxides.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral