Phase Equilibria in the System CaO‐PbO‐SiO₂

Abstract

Phase Equilibria in the System Ca0-PbO-SiOZ 157 Na,CO,j, and NaOH also indicates that an etching mechanism is predominant because Na is still present on all treated surfaces. Also, the Na,CO, and NaOH treatments were sufficient to remove the SO,-rich skin developed during fire-polishing, since the Ca and Mg in the bulk are now detectable. Electron micrographs (Figs. 8(A), 8(B), and 8(C)) indicate that the fire-polished surfaces are less planar than those obtained from the acid treatments ( Fig. 8 ( 0 ) ) and that residues are present on all surfaces treated in alkaline solutions. IV. ConclusionsThe combined techniques ofXPS and TEM of surface replicas of chemically and physically treated soda-lime glass surfaces clearly demonstrate that large variations in surface composition relative to the bulk glass result. Large surface compositional differences can exist without apparent microstructural differences and are readily detectable by XPS. The suggestion that the heated soda-lime glass acquires a surface film of Na,O in the range of 400" to 700°C'4 is supported by XPS data for the vacuum heat-treated surfaces. In general, the XPS results show that treatment in dilute acids and water results in a nearly pure SiO, surface, fire-polishing yields an Si0,-enriched surface, and dilute bases leach some of the network modifiers. There is little correlation between XPS and surface topography as determined by TEM. With the exception of firepolished surfaces, all treatments render the surface susceptible to the attachment of atmospheric COP; prolonged treatment results in the formation of alkali and alkaline-earth carbonates. These are the familiar weathering products of soda-lime as well as other glass surfaces. Direct surface analysis by XPS is in essential agreement with the inferred composition of soda-lime glass surfaces, as determined by chemical analysis of leachates.

Experimental study of phase equilibria in the systems PbO x -CaO and PbO x -CaO-SiO2

“…In contrast, The liquidus surface presented in the present study (Figures 5 through 8) differs significantly from that reported by Samanta and Hummel. [20] For example, the two previously reported ternary compounds Ca 3 PbSiO 6 and Ca 2 Pb 3 SiO 7 have not been observed in the present study despite the large number of experiments undertaken in that part of the system and the use of the EPMA technique.…”

“…This means that the system in air is not a true binary but part of the Pb-Ca-O ternary system. Studies on the activities [16][17][18][19] and on the phase relations in air [20] in the ternary system PbO-CaO-SiO 2 were previously reported.…”

Compositional Characteristics of 18th Century Derby Porcelains: Recipe Changes, Phase Transformations, and Melt Fertility

“…A phase diagram for this ternary system has been reported by Samanta & Hummel (1976). The bulk compositions of the sherds plot within the SiO 2 field on this diagram (Figure 2), well within the glassforming region defined by Samanta & Hummel (1976), and all phases plot on the SiO 2 side of the CaSiO 3 -PbSiO 3 join. For this reason, compositional data are plotted in the upper half of the CaO-PbO-SiO 2 phase diagram in Figure 2(b), although the full system is displayed in the inset (Figure 2(a)).…”

“…Furthermore, melts formed above the eutectic become depleted in PbO only gradually because of the close spacing of isotherms in the silica field (cf. Samanta & Hummel, 1976). For example, in the binary PbO-SiO 2 system, the melt formed 200 C above the eutectic (at 40 mol.% PbO) contains 37 mol.% PbO (Smart & Glasser, 1974).…”

Thermodynamic Optimisation of the Systems Cao-Pb-O and Pbo-CaO-SiO2

“…From these binary parameters, the quasichemical model was used to predict the thermodynamic properties of the slag phase in the PbO-CaO-Si02 ternary system. The initial computer modelling of the PbO-CaO-Si02 ternary system indicated significant discrepancies between the data previously obtained on the binary sub-systems and on this ternary system [13][14][15][16][17].…”