The distributions of polyanions in binary phosphate glasses of sodium, cadmium, magnesium and lead oxides were determined by a paper chromatographic technique. The effect of making these glasses with rigid exclusion of moisture and the effect of quenching rates on the constitution of these glasses were investigated. The results indicate that the distributions are a function of cation and the mean chain length E. The breadth of these distributions is directly related to thw shape of the heat of formation curve for the glasses (from the constituent oxide), and to the cation radius to charge ratio of the cation to the extent this determines the heat of formation. The glasses made under dry conditions and also' •by fast quenching had anion distributions the same as those made in the conventional manner. The thermodynamic properties of PbO, Pb0+Si02, PbO+ P205, Pb0+B203 and PbO+PbF2 melts were obtained by measuring the emf of the cell, Pb / Pb0 containing melts / 02 : Pt The measurements were usually carried out in the temperature range 850°C to 1050°C. From the emf and its dependence on temperature the activities of PbO, and the partial free energies, heats and entropies of solution of Pb0 in Pb0 SiO2' Pb0 + P205, Pb0 + B203 and Pb0 + PbF2 melts were derived. The corresponding thermodynamic properties of the other components in these binary were derived using the Gibbs-Duhem relationship and these were combined with those for Pb0 to obtain the integral thermo-dynamic properties. The interpretation of observed Pb0 activities for the lead borate and Phosphate melts, more basic than the ortho composition, in terms of structural models seems to indicate the presence of three and four coordinated boron atoms in the borates and the possible existence of five coordinated Phosphorus atoms in the phosphate. The structural information gained on the phosphate glasses has been extended to the silicate and borate systems. Various available models, which relate the thermodynamic properties and structure of these polyanionic melts are assessed;It seems that Meadowcroft and Richardson's model is the only one capable of relating quantitatively the structure and thermodynamic properties of such melts. The thermodynamic data obtained for Pb0 PbF2 melts shows these to be regular solutions, with an ideal entropy of mixing as defined by Temkin. Unsuccessful attempts to study the anionic distribution in silicate glasses by a chromatographic separation technique are described in the appendix.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:622969 |
| Date | January 1967 |
| Creators | Sridhar, Ramamritham |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/17578 |
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