A study of the synthesis of CoAI₂O₄ and the inducement of reactions and rearrangements in the solid state by mechanical milling.

Wynn, Paul Grant (2006). A study of the synthesis of CoAI₂O₄ and the inducement of reactions and rearrangements in the solid state by mechanical milling. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000fe11

Abstract

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 Co_xAI_3-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.