Yoshiaki Ouchi1, Toshiaki Yoshida2 and Eiichi Kato3
1The Casting Research Laboratory, Waseda University, Tokyo
The densities of melts in the PbO-MgO-SiO2, PbO-CaO-SiO2, PbO-SrO-SiO2, PbO-BaO-SiO2 and PbO-NiO-SiO2 systems containing 33 and 50 mol% SiO2 have been measured in the temperature range from 1000 to 1200°C. The Archimedean method was applied, and buoyancy measurement was carried out for each melt with both a small and a large bob. The measurement with a large bob was also carried out. The results obtained are summarized as follows:
There is little deviation from the additivity in the molar volume of melts for the pseudo binary systems PbO ⋅ SiO2-MgO ⋅ SiO2, PbO ⋅ SiO2-CaO ⋅ SiO2, PbO ⋅ SiO2-SrO ⋅ SiO2, PbO ⋅ SiO2-BaO ⋅ SiO2 and 2PbO ⋅ SiO2-2CaO ⋅ SiO2. Each of the Mg, Ca, Sr and Ba systems containing 33 and 55% SiO2, shows a linear relationship between the molar volume of the melts and the cube of the cation radius. The same relationship holds for the Ni system containing 50 mol% SiO2. The molar volumes of PbO-SiO2 melts containing 33 and 50 mol% SiO2 shift from the linear relationship to high molar volumes.
The results obtained are discussed on the basis of the thermodynamic model of silicate melts derived by the application of a quasi-chemical treatment to the random network model of silicates. It is shown that in the systems containing alkali earth metal oxide the accommodation of metal cations within the structure of lead silicate melts has direct effects upon the molar volume of these melts. It is also deduced from the results that the decrease of the oxygen density caused by the depolymerization of silicate anions has no effect upon the molar volume of these melts. In the PbO-NiO-SiO2 system containing 50 mol% SiO2, NiO in the silicate melts is found to behave as if it were an alkali earth metal oxide. The behavior of NiO agrees very well with that anticipated from the results of activity and viscosity measurements.
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