Phase diagram oxides

A prerequisite for an effective fiber coating is chemical stability with the fiber and matrix phases of a composite. If reactions occur, the fiber-coating-matrix interface would become strongly bonded, and the composite would exhibit brittle fracture behavior. Based on currently available phase diagrams, oxide compounds have been identified that do not show compound formation with commercially available oxide fibers. Particular attention has been paid to fibers that show the highest temperature capability (alumina fibers, such as Fiber FP, PRD-166, and Nextel 610). Oxide compounds identified as stable with alumina included tin oxide, zirconia, titania (at temperatures below 1,150°C [2,102°F]), zirconia titanate (ZrXi04, also at temperatures below 1,150°C [2,102°F]), and possibly zirconia tin titanate (Zr(Sn,Ti)04). 

E. A. Brandes and R. E. Flint, Manganese Phase Diagrams, The Manganese Centre, Paris, 1980 L. B. Pankratz, Thermodynamic Properties of Elements and Oxides, Bull. 672, U.S. Bureau of Mines, Washington, D.C., 1982. 

Fig. 6. Phase diagram for three crystalline and two Hquid forms of phosphoms(V) oxide. To convert kPa to mm Hg, multiply by 7.5.

Table 1 fists the more important physical properties of calcium carbide. Additional properties are given in the literature (1). Figure 1 gives the phase diagram calcium carbide—calcium oxide for pure and technical grades. 

Fig. 1. Calcium carbide—calcium oxide phase diagram using A, pure CaC2, and B, technical-grade...

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. 

Over the years, Pourbaix and his co-workers in the CEBELCOR Institute, founded under his direction, extended these diagrams by including lines for metastable compounds. Figure 7.66 illustrates such a presentation for the Fe-O system over the temperature range 830-2200 K. Pourbaix used these diagrams as a basis for a discussion of the stability of metallic iron (solid, liquid and vapour phases), the oxides of iron as a function of oxygen pressure and temperature from which he explained the protection of iron at high temperature by immunity and passivation. He also pointed out the... 

There are two compounds possible, namely - LaAlOs and LaAlnOig. (How do we know - Consult the volumes published by the American Ceramic Society entitled "Phase Diagrams for Ceramlcists" for La20s and AI2O3 which show that only two compounds form when these two oxides are reacted). 

Early workers, and some later ones, ignored the fact that aluminium is always found in the orthophosphoric acid liquid of the practical cement its presence profoundly affects the course of the cement-forming reaction. It affects crystallinity and phase composition, and renders deductions based on phase diagrams inappropriate. Nevertheless we first describe the simple reaction between zinc oxide and pure orthophosphoric acid solution, which was the system studied by the earliest workers. 

Terrey (1950). In the case of the simple zinc oxide-orthophosphoric add system, but only for this simple system, these phase-diagram arguments are valid. 

Jameson, R. F. Salmon, J. E. (1954). Aluminium phosphates Phase-diagram and ion-exchange studies of the system aluminium oxide-phosphoric oxide-water at 25 °C. Journal of the Chemical Society, 4013-17. 

Rossmeisl J, Norskov JK, Taylor CD, Janik MJ, Neurock M. 2006. Calculated phase diagrams for the electrochemical oxidation and reduction of water over Pt(l 11). J Phys Chem B 110 21833-21839. 

While we have focused here on the oxygen adsorption at the electrode surface, in the following, we will discuss the part of the phase diagram shaded gray and labeled Oxide formation in Fig 5.10b. 

In the Pt bulk oxide range of the phase diagram, which is relevant provided that (5.26) is fulfilled, the bulk electrode is Pt oxide and no longer pure Pt. Therefore the corresponding term in (5.28) that accounts for the bulk electrode reservoir now has to involve Since the bulk electrode should be in thermodynamic equihbrium with the surroundings. 

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