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Title: Redox and mixed valence in some solid state systems
Author: Whittle, Karl R.
ISNI:       0000 0001 3567 6201
Awarding Body: Open University
Current Institution: Open University
Date of Award: 1998
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The silver amalgamation process whereby silver sulphide ore is converted to silver metal using copper chlorides and mercury proceeds through a redox process. The process involves the transformation of Ag2S to AgCl with a corresponding reduction of copper from Cu2+ to Cu+ and subsequent oxidation of Cu+ to Cu2+ by atmospheric oxygen. The AgCl is then reduced to Ag by mercury to form an amalgam. It has been found that the process proceeds similarly when iron replaces copper and involves a reduction of Fe3+ to Fe2+. The doping of SrFe12O19 by europium and lanthanum to form compounds of the type Sr1-xMxFe12O19 (M=Eu,La) has been achieved by three different methods, the calcination of oxides at 1250°C, calcination of a gel at 925°C, and hydrothermal processing of metal nitrates at 220°C. X-ray powder diffraction (XRD) indicates the formation of similar materials by each method. X-ray absorption fine structure (XAFS) has shown that the La3+ ions substitute for Sr2+ ions. The particle sizes of the Sr1-xMxFe12O19phase have been found by Scherrer analysis of the X-ray powder diffraction data to increase with the temperature involved in the synthesis method. The results show that the materials formed by the calcination of oxides have a size ~800 nm, while those made by hydrothermal processing are ~300 nm. 57Fe Mössbauer spectra collected at various temperatures have shown that the dopant has negligible effect on the magnetic properties of the system. The results show a gradual coalescence of hyper fine fields as the temperature is decreased from 298K to 25K. Magnetic susceptibility measurements have shown that Eu- and La-doped SrFe12O19 prepared by the co-precipitation of a gel has a greater magnetic coercivity than those prepared by other methods.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Hexaferrite; Strontium; Silver; Amalgamation