Phase sesquioxides

If Ac is excluded from the actinide series (based on the absence of an f electron), the first member of the actinide series to form a condensed-phase sesquioxide is Pu. The Am-Es elements also form stable sesquioxides presumably the Fm-Lr elements would also form sesquioxides. The sesquioxide is the most stable oxide for Cm, Cf, Es and likely would also be the most stable oxide for Fm, Md and Lr. The sesquioxide, or perhaps the monoxide, are the oxides expected for No. The Fm-Lr oxides have not been prepared or studied experimentally. 

In the sohd phase the most stable forms of Mn (ITT) are manganese sesquioxide [1317-34-6] M1I2O2, and its hydrate Mn202 and manganese... 

In an alternative industrial process, resorcinol [108-46-3] is autoclaved with ammonia for 2—6 h at 200—230°C under a pressurized nitrogen atmosphere, 2.2—3.5 MPa (22—35 atm). Diammonium phosphate, ammonium molybdate, ammonium sulfite, or arsenic pentoxide maybe used as a catalyst to give yields of 60—94% with 85—90% selectivity for 3-aminophenol (67,68). A vapor-phase system operating at 320°C using a siUcon dioxide catalyst impregnated with gallium sesquioxide gives a 26—31% conversion of resorcinol with a 96—99% selectivity for 3-aminophenol (69). 

This paper reviews data on certain thermodynamic aspects of the nonstoichiometric Pu-0 system, which may serve as a basis for use In reactor safety analysis. Emphasis Is placed on phase relationships, vaporization behavior, oxygen-potential measurements, and evaluation of pertinent thermodynamic quantities. Limited high temperature oxygen potential data obtained above the fluorite, diphasic, and sesquioxide phases In the Pu-0 system are presented. 

It should be emphasized that very little is quantitatively known about how the total pressures of plutonium-bearing species vary with oxygen potential, stoichiometry, and temperature in the bivariant region of oxygen-deficient plutonia between the phase limits at very high temperatures. New (though limited) oxygen potential data have been obtained in our laboratory above the fluorite, diphasic, and sesquioxide phases in the Pu-0 system at 1750, 2050, and 2250 K. 

Oxidation of these model sulfur compounds was studied without solvent to investigate the chemical structure of the products using S K-edge XANES. A solvent free tri-phase (organic/ H202aq./catalyst) was used under the described conditions. Figure 1 shows the XANES spectra from the organic and aqueous phases as well as reference materials. The thiophene oxidized to thiophene-sesquioxide [3a,4,7,7a-tetrahydro-4,7-epithiobenzo[b]-thiophene 1,1.8-trioxide ] first.. The sesquioxide solid precipitated from the solvent free reaction mixture and was identified by NMR, IR and C,H,S elemental analytical. The sesquioxide oxidized to sulfate. 2-MT and 2,5 DMT also oxidized to... 

Figure 8.23A shows a simplified Eh-pH diagram for the Mn-O-H system. Within the stability field of water, manganese occurs in three valence states (2+, 3 +, and 4+). Figure 8.23A shows the condensed phases relative to the three valence states as the hydroxide pyrochroite Mn(OH)2 (2+), multiple oxide haus-mannite Mu304 (2+, 3 + ), sesquioxide Mu203 (3 + ), and oxide pyrolusite Mn02 (4+). 

Kj, or the ratios of solution-phase solute concentration and adsorbed-phase concentration were calculated to estimate the relative affinity of the soils for phenolic acids. The Kj values for p-hydroxybenzoic acid, p-coumaric, vanillic, ferulic, and syringic icids were 67, 75, 69, 92 and 376, respectively for a 48-hr equilibration of 0.1 nmol mL phenolic acid solution with a sample of an alfisol preextracted in boiling water. The sorption capacity was greatly reduced by pretreatment of soil samples with sodium acetate-hydrogen peroxide to remove organic matter and metal sesquioxides. 

The most stable oxidation state of thuhum is -i-3. Only the tripositive Tm3+ ion is encountered in aqueous media. The metal also forms compounds in +2 and +4 valence states, but there is no evidence of Tm2+ and Tm + existing in aqueous phase. Thuhum is relatively stable in air at ambient temperature. However, it combines with oxygen on heating forming its sesquioxide, Tm203. 

The dioxide. PbiO. has rutile structure, and the compound is a strong oxidizing agent. It is also amphiprotic. giving unstable lcad(IV) salts with acids, and orthoplnmbates. M PbOa, or metuplumbates. M PbO.. upon fusion with alkalies. Lead dioxide dissolves in aqueous alkali with formation of the ion Pb(OH)6. the alkali salts of which are isomorphous with the corresponding stannates and platinates. Lead sesquioxide, PbiO,. has been shown not to exist as a stable phase. 

C. Boulesteix, Defects and phase transformation near room temperature in rare earth sesquioxides 321... 

Stable phases in the rare earth oxide systems are tabulated and discussed. New data on the structure of sesquioxides quenched from the melt are reported. The structural interrelations between the A, B, and C type sesquioxides and the fiuorite dioxides are pointed out. The sequences of several intermediate oxides in the CeO, PrO., and TbO, systems are observed to be related to the fluorite structure and the C form sesquioxide with respect to the metal atom positions. A hypothetical homologous series of the general formula Mn02n i, related to the fluorite structure and the A form sesquioxide with a more or less fixed oxygen lattice, is suggested. 

Ordered Intermediate Phases. Between the dioxides of Ce, Pr, and Tb and the sesquioxides discussed above is a sequence of oxides of intermediate composition. The best established of these are listed in Table I and shown diagrammati-cally in Figure 4. The existence of these stable intermediate oxides is indicated... 

Solid rhodium sesquioxide, Rh203, was first identified in 1927,1148 and has the corundum structure1149 (hexagonally close packed O2- anions distorted by the presence of Rh3+ cations in of the octahedral interstices). Each Rh is surrounded by six oxygens, three at 2.03 A and three at 2.07 A. An orthorhombic phase forms above 750 °C.1150... 

As Indicated previously, the tentative phase diagram of the Pu-0 system shows plutonium sesquioxide as a line compound from room temperature up to its melting point. During the course of the preparation of for low temperature heat capacity... 

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