A Study of the Volatilisation of Lead Oxide from Lead Oxide–Silica Mixtures

JSGT_1935_V19_T296_T311

The mixtures ranged in composition from 53·96 to 99·80% PbO (24 to practically 100 mol%) and by rapid cooling could be obtained as glasses up to 90·05% PbO. The initial rates of volatilisation in mg/cm²hr ranged from 0·10 to 11·6 at 900°, 0·20to 80·0 at 1000°, 1·1 to 250at 1100°, and 2·0 to 254 at 1200°. The high volatility of the last two members of the series precluded any measurements beyond 1100° and the first two members were devitrified at 900°. The temperature–volatility relationships approximated to a vapour pressure law. The relationship between loss by volatilisation and concentration indicated the existence of the silicates PbO.SiO₂, 2PbO.SiO₂, 4PbO.SiO₂, and further relationships involving the progress of volatilisation with time confirmed this view. The combined heats of decomposition and evaporation were, in the order given, −36,000 −49,000 and −30,000 cals. per gram molecule. respectively. Density effects in the melts marred the ideal conditions for the volatilisation, but the results obtained were a general confirmation of earlier work on alkali–silica glasses.  At 1200° the calculated vapour pressures of PbO ranged from 0·7 to 72 mm. Hg for the first twelve glasses. At 1100° the vapour pressure of pure PbO was calculated to be 70 mm. Hg.

Eric Preston & W. E. S. Turner