Silica phase diagram

Fenner, C.N. (1913) The stability relations of the silica minerals Am. J. Sci. 36, 331. Gave the original version of the silica phase diagram. 

Figure 4.3. The borax-silica phase diagram showing the compositions of Vycor and Pyrex glass.

The surfactant-water-silica phase diagram is shown in Fig. 3b. Due to the stronger head-silica attraction as compared to the water-head attraction, we observe phase separation between the surfactant-rich, silica-rich and water-rich phases. Ordered phases that are observed at different regions of the phase diagram depend on the component concentrations spherical micelles are found at low to medium surfactant concentrations, bicontinuous structures are observed at high surfactant and intermediate silica concentrations, whereas cylindrical structures are seen at high surfactant and high water concentrations. 

The silica-alumina phase diagram ss denotes solid solution. (Adapted from F. J. Klug, S. Prochazka, and R. H. Doremus, Alumina-Silica Phase Diagram in the Mullite Region, /. Am. Ceram. Soc., 70[10],758 (1987). Reprinted by permission of the American Ceramic Society.)... 

Take the silica-alumina system as an example. It is convenient to treat the components as the two pure oxides SiOj and AI2O3 (instead of the three elements Si, A1 and O). Then the phase diagram is particularly simple, as shown in Fig. 16.6. There is a compound, mullite, with the composition (Si02)2 (Al203)3, which is slightly more stable than the simple solid solution, so the alloys break up into mixtures of mullite and alumina, or mullite and silica. The phase diagram has two eutectics, but is otherwise straightforward. 

The phase diagram for silica shows six different forms of the solid, each stable under different temperature and pressure conditions. 

As an example of binary clusters for magnetic applications, we present the study performed on Ni-Co alloy [78]. The Co-Ni phase diagram was investigated by performing sequential ion implantation in silica of Co and Ni at the same energy of ISOkeV (Rp 150nm) but with different fluences in order to have a constant total Co+Ni fluence (15 x lO ions/cm or 30 x 10 ions/cm ). For the 1 1 Co Ni ratio, we also performed sequential implants at... 

Recently, new ordered mesoporous silicas have also been synthesized by using self-organization of amphiphilic molecules, surfactants and polymers either in acidic or basic condition. A schematic phase diagram of water-surfactant is shown in the figure. 

We can start, as did the ancient craftsmen, with the fusion of the iron oxide, FeO, with silica, SiO . The phase diagram for those binary mixtures show that whereas Si02 fuses at about 1713 C and FeO at 13 9 C, mixtures containing between 20 and 40 weight percent FeO fuse below 1250 C. Complexing with additions of another iron oxide, Fe203, in amounts of up to 10%, can lower the fusion temperature to about 1150 C. 

Silica-CTAB-Water Phase Diagram at 150 °C Predicting Phase Structure by Artificial Neural Network... 

Silica and aluminum phosphate have much in common. They are isoelec-tronic and isostructural, the phase diagrams being nearly identical even down to the transition temperatures. Therefore, aluminum phosphate can replace silica as a support to form an active polymerization catalyst (79,80). However, their catalytic properties are quite different, because on the surface the two supports exhibit quite different chemistries. Hydroxyl groups on A1P04 are more varied (P—OH and A1—OH) and more acidic, and of course the P=0 species has no equivalent on silica. The presence of this third species seems to reduce the hydroxyl population, as can be seen in Fig. 21, so that Cr/AP04 is somewhat more active than Cr/silica at the low calcining temperatures, and it is considerably more active than Cr/alumina. 

Y-Ni-Sb. Figure 1 represents the isothermal section of Y-Ni-Sb phase diagram at 870 K (0-50 at. % Sb) which was studied by Zavalii (1982). The isothermal section was constructed by means of X-ray powder analysis of alloys, which were arc melted and subsequently annealed in evacuated silica tubes for 400 h and finally quenched in water. Starting materials were Y 99.8 wt.%, Ni 99.99 wt.% and Sb 99.99 wt.%. The ternary phase equilibria diagram is characterized by the existence of two ternary compounds YNi2Sb2 (1) and YNiSb (2). 

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