Synthesis and structural characterisation of mixed-metal oxide pigment systems

Owens, Craig (2004) Synthesis and structural characterisation of mixed-metal oxide pigment systems. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The synthesis and characterisation of the NaCaV_1-xMn_xO₄ (x = 0, 0.02, 0.04, 0.06, 0.08 and 1.0) system has been carried out. Structural characterisation was performed through the use of powder X-ray diffraction, powder neutron diffraction and UV-Visible spectroscopy. These techniques reveal that the MnO₄^3- complex ion can be stabilised within the NaCaVO₄ structure by isotopic substitution of the VO₄^3- unit. The MnO₄^3- ion imparts it own coordination geometry upon the host lattice, with the effect of making the MO₄^3- a more regular coordination environment. The limit of substitution occurs at x = 0.08. Degradation of the colour over time makes this system unsuitable for use as a pigment.

The preparation of the solid solution Cu₂Al_1-xGa_x¹¹BO₅ has been successfully completed with colours ranging from dark intense green to a lighter olive green. Structural characterisation has utilised powder neutron diffraction and CIELab colour measurements. The replacement of Al³⁺ with Ga³⁺ enlarges the average metal-oxygen distances, which in turn alters the copper coordination and hence the observed colour. Cu₂Al₆¹¹B₄O₁₇ has been prepared by conventional solid state methods and has been structurally characterised using powder neutron diffraction.

The crystal structure of cobalt pyroborate (Co₂B₂O₅) has been further refined using powder neutron diffraction. The structure of Co_2.45BO₅ has been determined from a single crystal X-ray refinement and is shown to adopt the Ludwigite structure. The structure contains four distorted octahedral CoO₆ environments and planar BO₃ units.