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Title: The dispersion of divalent cation impurities in NaCl
Author: Quin, John
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1967
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Dielectric absorption in Ca2+ doped NaC1 was studied. In crystals which had been air quenched from temperatures greater than 200°C, the absorption was associated with the rotation of 2+ . Ca ion-cation vacancy pairs which probably formed on nearest neighbour lattice sites. Values for the activation parameters of the rotation were obtained. The total number of Ca2+ -vacancy pairs in air quenched crystals was a high percentage of total Ca2+ content. Some of the Ca2+ ions were probably associated with 011 ion impurities, unintentionally present in the crystals. The Ca2+-vacancy pairs in the air quenched crystals associate with ageing. Dielectric absorption measurements were used to study the ageing process. The initial decrease in pair concentration was associated with the formation of clusters of three pairs. At later stages in the pair aggregation, an aggregate of pairs was formed which could of itself contribute to the dielectric absorption. The final stages in pair aggregation were described by the addition of Ca2+-vacancy pairs onto existing aggregates. The density of divalent cation doped NaC1 was studied as a function of heat treatment and divalent impurity concentration. Ca2+ Cd2+ and Mn2+ doped NaC1 crystals were studied and only in Ca2+ doped NaC1 was evidence found for the precipitation of the divalent cation chloride. Differences between measured density changes and calculated density changes with increasing divalent cation concentration were interpreted in terms of lattice relaxations. In Ca24- doped NaC1 it was found that OH impurities contributed to the observed density changes. The effects of pair aggregation on the yield stress of Ca2+ doped NaC1 were studied. The yield stress was measured as a function of ageing time on an air quenched crystal, on which dielectric absorption studies had been previously made. It was thus possible to correlate yield stress changes with changes in Ca2+-vacancy pair concentration. Yield stress measurements were made at room temperature and at -196°C.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available