The mechanism of Fe induced bond stability of uranyl(v)

The stabilization of uranyl(v) (UO₂¹⁺) by Fe(ii) in natural systems remains an open question in uranium chemistry. Stabilization of U^VO₂¹⁺ by Fe(ii) against disproportionation was also demonstrated in molecular complexes. However, the relation between the Fe(ii) induced stability and the change of the bonding properties have not been elucidated up to date. We demonstrate that U(v) – oaxial bond covalency decreases upon binding to Fe(ii) inducing redirection of electron density from the U(v) – oaxial bond towards the U(v) – equatorial bonds thereby increasing bond covalency. Our results indicate that such increased covalent interaction of U(v) with the equatorial ligands resulting from iron binding lead to higher stability of uranyl(v). For the first time a combination of U M_4,5 high energy resolution X-ray absorption near edge structure (HR-XANES) and valence band resonant inelastic X-ray scattering (VB-RIXS) and ab initio multireference CASSCF and DFT based computations were applied to establish the electronic structure of iron-bound uranyl(v).

The role of Fe in the increased stability of uranyl(v) is clarified by using state of the art uranium metalorganic chemistry, advanced X-ray spectroscopic approaches and computations.     

Ueber Untersuchung von Jodoform und Jod enthaltenden Verbandstoffen und Arzneimitteln

Ohne Zusammenfassung     

Unusual nucleation and growth of γ′ iron nitride upon nitriding Fe–4.75 at.% Al alloy

The influence of substitutionally dissolved Al in ferritic Fe–4.75 at.% Al alloy on the nucleation and growth of γ′ iron nitride (Fe₄N_{1? x} ) was investigated upon nitriding in NH₃/H₂ gas mixtures. The nitrided specimens were characterised employing optical microscopy, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis and X-ray diffraction. As compared to the nitriding of pure ferrite (α-Fe), where a layer of γ′ develops at the surface, upon nitriding ferritic Fe–4.75 at.% Al an unusual morphology of γ′ plates develops at the surface, which plates deeply penetrate the substrate. In the diffusion zone, nano-sized precipitates of γ′ and of metastable, cubic (NaCl-type) AlN occur, having, with the ferrite matrix, a Nishiyama–Wassermann orientation relationship and a Bain orientation relationship, respectively. The γ′ plates contain a high density of stacking faults and fine ε iron nitride (Fe₂N_{1? z} ) precipitates, although the formation of ε iron nitride is not expected for the employed nitriding parameters. On the basis of dedicated nitriding experiments it is shown that the unusual microstructural development is a consequence of the negligible solubility of Al in γ′ and the obstructed precipitation of the thermodynamically stable, hexagonal (wurtzite-type) AlN in ferrite.     

Ueber die Untersuchung und Werthbestimmung von Phenolen

Ohne Zusammenfassung     

An NH-effect in iodometry,caused by N-S bond formation

Summary In titrations of iodine solutions with thiosulphate in the presence of ammonia or primary and secondary amines in near neutral solution (pH 5-7) sulphenamides are formed: This reaction competes with the formation of tetrathionate. The consumption of iodine is consequently up to double that expected for tetrathionate formation. The reaction is reversed by acidification, which gives tetrathionate and free iodine. The titrated solutions, containing no free iodine, retain their capacity to oxidise over long periods. They also retain the capacity to give the iodine-azide reaction, which is not given by tetrathionate. The stability of the sulphenyl-stage in the presence of amines can also be demonstrated in solutions containing an excess of iodine. In absence of amines the sulphenyl-stage in such solutions is known to disappear within minutes. The NH-effect is defined and its dependence on the pH, concentrations of titrants, iodide and NH-compounds is investigated. Other SH-compounds also give the effect, even at a lower pH, but this is often followed by irreversible oxidation by the iodine solution. The NH-effect of thioglycollic acid is only exceptionally (with morpholine) reversible by acidification. That of sulphide is not reversible and that of thioacetic acid is partly reversible. The postulated compound formed between thiosulphate and ammonia, NaO₃S-S-NH₂, sodium thiohydroxylamine-S-sulphonate, has been described in another context. The ready formation of an S-N bond, where an S-S bond would have been expected, should be considered in protein chemistry. The S-N compounds formed from thioacids and amino-acids should be of high interest.

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Zusammenfassung Bei der Titration von Jodlösungen mit Thiosulfat in Gegenwart von Ammoniak, primären oder sekundären Äminen in nahezu neutraler Lösung (pH 5–7) werden Sulfenamide gebildet: Diese Reaktion verläuft parallel mit der Bildung von Tetrathionat. Der Verbrauch an Jod ist folglich bis gegen das Doppelte desjenigen für die Tetrathionat-Bildung. Die Reaktion ist umkehrbar durch Ansäuern, wobei Tetrathionat und freies Jod gebildet werden.Lösungen, die mit Thiosulfat titriert wurden und die kein freies Jod enthalten, behalten ihre Fähigkeit zu oxydieren lange Zeit. Sie behalten auch ihre Fähigkeit die Jod-Azid-Reaktion zu geben, zum Unterschied von Tetrathionat. Die Beständigkeit der Sulfenylzwischenstufe in Gegenwart von Aminen kann auch demonstriert werden in Lösungen, die einen Überschuß an Jod enthalten. Es ist bekannt, daß die Sulfenylzwischenstufe in wenigen Minuten verschwindet, wenn keine Amine anwesend sind.Der NH-Effekt wurde definiert und seine Abhängigkeit vom pH, von der Konzentration der Titrierflüssigkeit, des Jodids und der NH-Verbindung wurde untersucht. Andere SH-Verbindungen geben auch den Effekt, sogar bei einem niedrigen pH, aber dies ist oft gefolgt von einer nicht umkehrbaren Oxydation durch die Jodlösung. Der NH-Effekt von Thioglykolsäure ist nur ausnahmsweise (mit Morpholin) umkehrbar durch Ansäuern. Der von Sulfid ist nicht umkehrbar. Der von Thioessigsäure ist teilweise umkehrbar.Die Verbindung zwischen Thiosulfat und Ammoniak, deren Bildung gefordert wird, nämlich NaO₃S-S-NH₂, Natriumthiohydroxylamin-S-Sulfonat, wurde schon in anderem Zusammenhang beschrieben.Die leichte Bildung einer S-N-Bindung, wo eine S-S-Bindung erwartet wird, sollte in der Eiweißchemie in Betracht gezogen werden. S-N-Verbindungen, die von Thiosäuren und Aminosäuren gebildet werden, werden von hohem Interesse sein.

     

Defect-dependent nitride surface layer development upon nitriding of Fe–1 at.% Mo alloy

Upon nitriding of binary Fe–1 at.% Mo alloy in a NH₃/H₂ gas mixture under conditions (thermodynamically) allowing γ′-Fe₄N_{1– x} compound layer growth (nitriding potential: 0.7?atm^?1/2 at 753?K (480?°C) – 823?K (550?°C)), a strong dependency of the morphology of the formed compound layer on the defect density of the specimen was observed. Nitriding of cold-rolled Fe–1 at.% Mo specimens leads to the formation of a closed compound layer of approximately constant thickness, comparable to nitriding of pure iron. Within the compound layer, that is, in the near-surface region, Mo nitrides are present. The growth of the compound layer could be described by a modified parabolic growth law leading to an activation energy comparable to literature data for the activation energy of growth of a γ′-Fe₄N_{1? x} layer on pure iron. Upon low temperature nitriding (i.e. ?793?K (520?°C)) of recrystallized Fe–1 at.% Mo specimens, an irregular, ‘needle-like’ morphology of γ′-Fe₄N_{1? x} nucleated at the surface occurs. This γ′ iron nitride has an orientation relationship (OR) with the matrix close to the Nishiyama–Wassermann OR. The different morphologies of the formed compound layer can be interpreted as consequences of the ease or difficulty of precipitation of Mo as nitride as function of the defect density.     

Normal and excess nitrogen uptake by iron-based Fe–Cr–Al alloys: the role of the Cr/Al atomic ratio

Upon nitriding ferritic iron-based Fe–Cr–Al alloys, containing a total of 1.50 at. % (Cr?+?Al) alloying elements with varying Cr/Al atomic ratio (0.21–2.00), excess nitrogen uptake occurred, i.e. more nitrogen was incorporated in the specimens than compatible with only inner nitride formation and equilibrium nitrogen solubility of the unstrained ferrite matrix. The amount of excess nitrogen increased with decreasing Cr/Al atomic ratio. The microstructure of the nitrided zone was investigated by X-ray diffraction, electron probe microanalysis, transmission electron microscopy and electron energy loss spectroscopy. Metastable, fine platelet-type, mixed Cr_{1? x} Al _x N nitride precipitates developed in the nitrided zone for all of the investigated specimens. The degree of coherency of the nitride precipitates with the surrounding ferrite matrix is discussed in view of the anisotropy of the misfit. Analysis of nitrogen-absorption isotherms, recorded after subsequent pre- and de-nitriding treatments, allowed quantitative differentiation of different types of nitrogen taken up. The amounts of the different types of excess nitrogen as function of the Cr/Al atomic ratio are discussed in terms of the nitride/matrix misfit and the different chemical affinities of Cr and Al for N. The strikingly different nitriding behaviors of Fe–Cr–Al and Fe–Cr–Ti alloys could be explained on this basis.