Fe Nitride Formation in Fe–Si Alloys: Crystallographic and Thermodynamic Aspects

A Fe–3wt pctSi alloy was gas nitrided to study the effect of Si on the Fe nitride formation. Both ε-Fe3N1+x and γ′-Fe4N were observed at nitriding conditions only allowing to form single-phase γ′ layers in pure α-Fe. During short nitriding times, ε and γ′ simultaneously grow in contact with Si-supersaturated α-Fe(Si). Both nitrides almost invariably exhibit crystallographic orientation relationships with α-Fe, which are indicative of a partially displacive transformation of α-Fe being involved in the initial formation of ε and γ′. Due to Si constraining the Fe nitride growth, such transformation mechanism becomes highly important to the nitride layer formation, causing α-Fe-grain-dependent variations in the nitride layer morphology and thickness, as well as microstructure refinement within the nitride layer. After prolonged nitriding, α-Fe is depleted in Si due the pronounced precipitation of Si-rich nitride in α-Fe. The growth mode of the compound layer changes, now advancing by conventional planar-type growth. During nitriding times of 1 to 48 hours, ε exists in contact with the NH3/H2-containing nitriding atmosphere at a nitriding potential of 1 atm−1/2 and 540 °C, only allowing for the formation of γ′ in pure Fe, indicating that Si affects the thermodynamic stability ranges of ε and γ′.

SYNTHESIS, STRUCTUREAND PROPERTIES OF COMPLEX COMPOUNDS OF LANTANOIDES WITH 2-(METHYLAMINO) BENZOIC ACID

Synthesis of complex compounds of 2-(methylamino) benzoic acid (L) with ions of samarium (III), europium (III), terbium (III), gadolinium (III) and dysprosium (III). According to elemental analysis and thermogravimetry, the complexes obtained are hydrates of the composition LnL3 • nH2O, where n = 1-5. The area of their thermal stability ranges from 100 ° C to 240 ° C. Electronic and infrared absorptionspectra of the ligand and complexeswith rare-earth metal ions were measured. According to the IR spectra, coordination of the ligand with the metal ion is carried out on the carboxyl group. The carboxyl group is coordinated bidentately. A mercury lampwith a wavelength of 248 nm was used to excite the luminescence. The highest luminescence intensity is observed for the coordination compounds Eu3 +, Tb3 +, and Dy3 +

Stacking polytypes of mixed alkali gallides/indides A1–2(Ga/In)3 (A=K, Rb, Cs): synthesis, crystal chemistry and chemical bonding

The Ga/In phase width (y) and the distribution of the two triels within the polyanions of known binary (x = 1, 2) and new ternary ‘intermediate’ (x = 1–2) alkali trielides Ax(Ga1−yIny)3 (A = K, Rb, Cs) was investigated in a synthetic (slow cooling of the melts of the three elements), crystallographic (X-ray single crystal) and bond theoretical (FP-LAPW DFT bandstructure calculation) study. The Cs2In3-type structure (x = 2, series A, tetragonal, I 4/mmm) exhibits layers of four-connected closo octahedra [M6]4−. Ternary K compounds of this type were yielded within a large range (y = 0–0.87), whereas isotypic Rb/Cs trielides exist only at higher In contents (>52/69%). Geometric criteria determine not only the Ga/In stability ranges but also the occurrence of a commensurate superstructure at approx. 33% In (K2Ga2.17In0.83: P 42/ncm, a = 879.83(4), c = 1557.66(10) pm, R 1 = 0.0887), in which the octahedra are slightly tilted against the layers. Cesium compounds of the RbGa3-type structure (x = 1, C, tetragonal, I 4̅m2), which exhibits a 3D network of all-exo bonded closo dodecahedra [M8]2− and four-bonded M− anions, are stable throughout the whole substitutional range CsGa3–CsIn3. The maximum possible In content increases with increasing size of A+ (Cs: 100%, Rb: 30%, K: 8% In). The similarities between these two tetragonal structures are consistent with the occurrence of two new structure types of ‘intermediate’ compounds A7M15 (x = 1.4, 1B/2B), which differ in the stacking sequences of double layers of novel six-fold exo-bonded pentagonal bipyramidal closo clusters [M7]3− connected via four-bonded M− (e.g. 1B: Cs7Ga8.4In6.6, P 4̅m2, a = 656.23(3), c = 1616.0(1) pm, R 1 = 0.0742; 2B: Rb7Ga8.1In6.9, P 42/nmc, a = 665.64(2), c = 3140.9(2) pm, R 1 = 0.0720). The Rb/Cs compounds of these types are only stable in a limited Ga/In region and with a distinct Ga/In distribution within the [M7] clusters. According to the close relation between the structures A, B and C, the structure family is characterised by the occurrence of stacking faults and diffuse scattering, indicating the existence of further members of this series. The new compound Cs5Ga3.1In5.9 (x = 1.667, P 4̅m2, a = 654.62(2), c = 3281.5(2) pm, R 1 = 0.1005) is a reasonably periodically ordered stacking variant containing layers A and double layers B in parallel.

Computational and analytical approaches for investigating hydrates: the neat and hydrated solid-state forms of 3-(3-methylimidazolium-1-yl)propanoate

The interconversion pathways and stability ranges of OOCEMIM solid-state forms have been elucidated.

Complex cubic metallides AM~6 (A=Ca, Sr; M=Zn, Cd, Hg). Synthesis, crystal chemistry and chemical bonding

In a systematic synthetic, crystallographic and bond theoretical study, the stability ranges as well as the distribution of the isoelectronic late

Effects of Atmospheric Surface Layer Stability on Turbulent Fluxes of Heat and Water Vapor across the Water–Atmosphere Interface

Widely used numerical models to estimate turbulent exchange of latent heat flux (LE) and sensible heat flux H across the water–atmosphere interface are based on the bulk transfer relations linked indirectly to atmospheric stability, even though the accurate prediction of the influence of stability on fluxes is uncertain. Here eddy covariance data collected over the water surface of Ross Barnett Reservoir, Mississippi, was analyzed to study how atmospheric stability and other variables (wind speed, vapor pressure gradient, and temperature gradient) in the atmospheric surface layer (ASL) modulated LE and H variations in different stability ranges. LE and H showed right-skewed, bell-shaped distributions as the ASL stability shifted from very unstable to near neutral and then stable conditions. The results demonstrate that the maximum (minimum) LE and H did not necessarily occur under the most unstable (stable) conditions, but rather in the intermediate stability ranges. No individual variables were able to explain the dependence of LE and H variations on stability. The coupling effects of stability, wind speed, and vapor pressure gradient (temperature gradient) on LE (H) primarily caused the observed variations in LE and H in different stability ranges. These results have important implications for improving parameterization schemes to estimate fluxes over water surfaces in numerical models.

Strontium-Metallide im Bereich des Schnitts SrIn4 – SrHg4 / Strontium Metallides along the Section SrIn4 – SrHg4

In a combined synthetic, X-ray single-crystal and bond-theoretical study the phase widths of SrIn4 and the related Sr3In11 upon a sucessive substitution of indium against the more electronpoor, more electronegative and only slightly smaller element mercury have been studied. Along the 1 : 4 section Sr(In1-xHgx)4 the monoclinic structure of SrIn4 ( EuIn4-type structure) is stable up to x =0.14(1) ( SrIn3.44Hg0.56: monoclinic, C2/m, a = 1208.3(6), b = 502:5(2), c = 997.7(6) pm, b = 115.16(3)°, Z = 4, R1 = 0.0324). Further increased mercury content results in a distinct stability region of the very common BaAl4 structure type (tetragonal, I4=mmm, Z = 2), which starts at x =0.241(7) ( SrIn3.04Hg0.96: a = 4694(2), c = 1246.4(7) pm, R1 = 0.0374) and reaches up to the fully ordered compound SrIn2Hg2 (x =0.5: a = 456.4(3), c = 1273.5(11) pm, R1 = 0.0572). Unexpectedly, in the small composition range from x=0.68(1) to 0.758(6) ( SrIn1.16Hg2.84: a=1178.5(4), b = 495.20(12), c = 1016.8(4) pm, b = 119.67(2)°, R1 = 0.0542; SrIn0.97Hg3.03: a = 1167.30(4), b = 495.32(2), c = 1018.50(3) pm, b = 119.657(2)°, R1 = 0.0426) the EuIn4 structure type exhibits a further small stability range. The structures of the two slightly different In- and Hg-rich variants of the EuIn4 type are described and compared, indicating the similarities to the KHg2 (layers of folded In=Hg ladders) and the BaAl4 structure type (flat square pyramids) as well as to the structure of elemental mercury (rhombohedra). From samples of an intermediate In=Hg ratio (e. g. x =0.55), the new 1 : 3 compound SrIn1.2Hg1.8 (monoclinic, C2=m, a = 1168.5(13), b = 497.0(4), c = 1471(2) pm, b = 92.07(10)°, Z = 8, R1 = 0.0818) is formed. It crystallizes in a new structure type, which - according to the compound’s composition - can be described as a stacking variant of the EuIn4 and the KHg2 structure type. In contrast to the wide stability ranges of the 1 : 4 compounds, only a very small substitution of In ranging up to only 6% of Hg is possible in the binary indide Sr3In11 ( Sr3In10.32(8)Hg0.68(8): La3Al11 structure type, orthorhombic, Immm, a = 487:6(2), b = 1140.2(5), c = 1421.1(7) pm, Z = 2, R1 = 0.0703). The formation, stability ranges and the In=Hg ‘coloring’ of the polyanions are discussed for all compounds taking into account geometric (radius ratios, molar volumes, Sr coordination polyhedra etc.) and electronic aspects, which have been evaluated using FP-LAPW band structure calculations.