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Title: Synthesis and characterisation of inorganic pigments
Author: Hughes, Eric Martin
ISNI:       0000 0001 3583 7693
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1999
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Inorganic materials, with potential application as pigments, have been synthesised in a wide range of phosphate, silicate, titanate and zeolitic systems and characterised in terms of their structure and physical properties using powder x-ray and powder neutron diffraction (PXD, PND), EXAFS, UV visible spectroscopy, colour measurements electron microscopy and thermal analysis. Complex cobalt phosphate materials, (M,M')₃(PO₄)₂ (M,M' = Co, Mg or Zn), have been prepared by precipitation from the metal ion solution with (NH₄)₂HPO₄ followed by calcination. The cation distribution of the five and six coordinate sites was determined and Co was shown to prefer the five coordinate site in the (Co,Mg)₃(PO₄)₂ system, and an almost random distribution in the (Co,Zn)₃(PO₄)₂ system. CsCoPO₄ was synthesised via conventional solid state synthesis for the first time and was found to adopt the zeolite ABW structure with tetrahedral CoO₄ units giving an intense dark blue colouration. The material was found to undergo a phase transition to higher symmetry at ca. 171°C. The commercial pigment Manganese Violet has been synthesised and EXAFS studies of the local manganese environment has shown it to be a distorted 4+2 octahedral Mn (III) centre coordinated to phosphate oxygen atoms. Variable temperature PXD has shown that the weight loss on heating at 100-250°C is likely to be loss of surface water as the diffraction pattern remains unchanged. The blue transition metal silicates Sr₂CoSi₂O7 and MCuSi₄O10 (M = Ca, Sr, Ba) have been synthesised. Structural characterisation shows that substitution of larger alkaline earth metals increases the lattice parameters and effects the tetrahedral geometry in the cobalt system thus influencing the colour. The colour in the copper system changes as a result of the smaller dipole between the larger metal ions and the copper centre with the copper square planar geometry being relatively unperturbed. Commercial transition metal substituted rutile materials (Ni,Sb,Ti)O₂ have been studied and the colour was shown to arise from Ni(II) d-d and Sb(V) charge transfer transitions. The colour was shown to be dependent on the relative atomic ratios of Ni and Sb. The novel (Ni0.25Ti0.25Nb0.5)O₂ has been synthesised and the green/yellow material was found to adopt the rutile structure with a = 4.69702(2) Å and c = 3.02411(2) Å.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Structure; Colour; Neutron; X-ray