Oxides phase composition

The development at FZJ Jiilich of a gas annealing treatment for FeCrAIRE alloys is described in detail in [23]. The twofold objectives of such a treatment in Ar -I- H2 mixtures were (a) the formation of a stable, thin, a-Al203 layer to prevent growth of transitional metastable aluminas at low temperatures, and (b) the removal of deleterious non-metallic alloy impurities (such as C, S, etc.). Pre-oxidation was undertaken primarily at 1200°C. Raman fluorescence spectrometry was used to establish the oxide phase composition, which... 

Many of the procedures used for technical analysis of aluminum hydroxides are readily available from the major producers of aluminum hydroxides. Phase Composition. Weight loss on ignition (110°—1200°C) can differentiate between pure (34.5% Al(OH)2) ttihydroxides and oxide—hydroxides (15% Al(OH)2). However, distinction between individual ttihydroxides and oxide —hydroxides is not possible and the method is not useful when several phases are present together. X-ray powder diffraction is the most useful method for identifying and roughly quantifying the phase composition of hydroxide products. 

In all of these oxide phases it is possible that departures from the simple stoichiometric composition occur dirough variation of the charges of some of the cationic species. Furthermore, if a cation is raised to a higher oxidation state, by the addition of oxygen to tire lattice, a conesponding number of vacant cation sites must be formed to compensate tire structure. Thus in nickel oxide NiO, which at stoichiomen ic composition has only Ni + cations, oxidation leads to Ni + ion formation to counterbalance the addition of extra oxide ions. At the same time vacant sites must be added to the cation lattice to retain dre NaCl sUmcture. This balanced process can be described by a normal chemical equation thus... 

Finally, oxygen is soluble in metallic titanium up to a composition of TiOo.s with the oxygen atoms occupying octahedral sites in the hep metal lattice distinct phases that have been crystallographically characterized are TieO, TisO and Ti20. It seems likely that in all these reduced oxide phases there is extensive metal-metal bonding. 

No other oxide phases below MO2 have been established but a yellow hydroxide , precipitated by alkali from aqueous solutions of chromium(II), spontaneously evolves H2 and forms a chromium(III) species of uncertain composition. The sulfides, selenides and tellurides of this triad are considered on p. 1017. 

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. 

All of the results discussed to this point infer surface coverages from gas phase composition measurements. Although these inferences are soundly based in the case of CO oxidation, we would be much more comfortable with direct measurement of the surface coverage. 

The spinel family of oxides with composition AB2O4 has the A and B cations distributed in octahedral and tetrahedral sites in a close-packed oxygen structure (Supplementary Material SI). Impurity doping can take place by the addition of a dopant to octahedral or tetrahedral sites. In this, the spinel family of compounds is quite different from the A2B04 perovskite-related phases of the previous section in that both cation sites are similar in size and can take the same cations. 

Seredych M, Mabayoje 0, Bandosz TJ. Interactions of N02 with zinc (hydr)oxide/graphene phase composites Visible light enhanced surface reactivity,/. Phys. Chem. C 2012,... 

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