Al-Mn-Ce quasicrystalline composites: Phase formation and mechanical properties

Aluminium-based composites with quasicrystalline particles as reinforcements were synthesized via the powder metallurgy processing route. In order to obtain bulk samples with a nanoscale microstructure most equivalent to that resulting from rapid solidification, powders of Al-Mn-Ce alloys were prepared by pulverization of melt-spun ribbons using a planetary ball mill. Significant differences in the phase formation upon quenching, composite microstructure and thermal stability of the microstructure were found for different alloy compositions. Severe grain growth during the subsequent consolidation by hot extrusion caused the formation of a micrometre-scale composite instead of the nanoscale phase mixture initially existing after rapid solidification. After hot extrusion, the specimens were deformed by compression at a constant compression rate at room temperature. With an ultimate strength of up to 975 MPa and a ductility of more than 4% the material yields excellent properties compared with conventionally produced aluminium-based alloys.     

Convergence of non-periodic infinite products of orthogonal projections and nonexpansive operators in Hilbert space

We provide sufficient conditions for strong and uniform (on bounded subsets of initial points) convergence of infinite products of orthogonal projections and other (possibly nonlinear) nonexpansive operators in a Hilbert space. Our main tools are new estimates of the inclination of a finite tuple of closed linear subspaces.     

Synthesis,Crystal Structure,and Selected Properties of [Au(S2CNH2)2]SCN: A Precursor for Gold Macro-Needles Consisting of Gold Nanoparticles Glued by Graphitic Carbon Nitride

A new preparation route is developed for the synthesis of needle-like crystals of [Au(S₂CNH₂)₂]SCN, which avoids disproportionation of the Au^I salt used as a starting material. In the crystal structure, the two crystallographically independent Au^III centers are in a square-planar environment of two S₂CNH₂ ligands. The Hirshfeld surface analysis reveals the presence of noncovalent intermolecular S⋅⋅⋅S interactions, which are essential for the spatial arrangement of the molecules. Density functional theory (DFT) calculations including dispersion and damping corrections result in a unit cell volume very close to the value determined experimentally. Thermal decomposition in an inert atmosphere generates black needles with lengths of up to 500 μm. X-ray powder diffraction and pair distribution function analyses demonstrate that the needles are composed of nanosized crystals with a volume-weighted average domain size of 20(1) nm. According to results of X-ray photoemission experiments, the black needles are covered by a nitrogen-rich carbon nitride with composition near (CN)₂N. ¹³C solid-state NMR investigations indicate that two different carbon species are present, with signals corresponding well to heptazine units as in melon and triazine units as in poly(triazin imide) type compounds. Scanning transmission electron microscopy tomography evidences that the needles are composed of slightly elongated nanoparticles.     

A mixed hp FEM for the approximation of fourth‐order singularly perturbed problems on smooth domains

We consider fourth‐order singularly perturbed problems posed on smooth domains and the approximation of their solution by a mixed Finite Element Method on the so‐called Spectral Boundary Layer Mesh. We show that the method converges uniformly, with respect to the singular perturbation parameter, at an exponential rate when the error is measured in the energy norm. Numerical examples illustrate our theoretical findings.     

Magnetomechanical training of single crystalline Ni-Mn-Ga alloy

A 5M Ni-Mn-Ga single crystal was investigated, supplied by Adaptamat Ltd, Finland. Especially low temperature magnetic actuation as well as cyclic tensile-compression tests revealed promising properties, which provide useful insights for training concepts in polycrystalline materials. Successive compressions lead to a significant reduction of the twinning stress by a factor of two.     

ORGANISCHE PHOSPHORVERBINDUNGEN 80 HERSTELLUNG VON TRIAZOLYLMETHYL-PHOSPHONATEN UND VON TRIAZOLYL-METHYLPHOSPHONIUMSALZEN UND DEREN VERWENDUNG IN DER WITTIG-HORNER REAKTION

Abstract

Attempts to prepare 1H-1,2,4-triazol-1-ylmethylphosphonates (4 and 5) by a Mannichtype reaction or by transesterification of 1-hydroxymethyl-1H-1,2,4-triazol 1 with tertiary phosphites failed. On the other hand 4 and 5 are obtained by a Michaelis-Becker reaction from 1-chloromethyl-1H-1,2,4-triazol 3 and sodium phosphites in high yield. The Michaelis-Arbuzov reaction is less suited for the preparation of 4 and 5. 3 is obtained in good yield as a water clear liquid, b.p. 52–54°C/0.2 torr, from the interaction of 1 with thionyl chloride followed by treatment with a base. On standing at 0° or 20°C it decomposes within hours and yields the unsymmetrical methylen-bis(triazol) 3a in addition to other products. However an acetonitrile solution of 3 is stable for months. Heating this solution with tertiary phosphines gives triazolylsubstituted phosphoniumsalts 6 to 8. The Wittig-Horner reaction with 4 to 6 gives the olefinically substituted triazols 9–12 as a Z/E mixture in high yield. Alkylation of 4 with methyl-and ethyl iodide gives the corresponding alkylated diethyl-1H-1,2,4-triazol-1-yl-ethyl-1-and-propyl-1-phosphonates 14 and 15 which on hydrolysis with HCI yield 1H-1,2,4-triazol-1-yl-ethyl-1-and propyl-1-phosphonic acids 17 and 18, respectively. Hydrolysis of 4 gives the unsubstituted 1H-1,2,4-triazol-1-ylmethyl-phosphonic acid, 16.     

Finite element approximations of a nonlinear diffusion model with memory

The convergence of a finite element scheme approximating a nonlinear system of integro-differential equations is proven. This system arises in mathematical modeling of the process of a magnetic field penetrating into a substance. Properties of existence, uniqueness and asymptotic behavior of the solutions are briefly described. The decay of the numerical solution is compared with both the theoretical and finite difference results.     

ORGANIC PHOSPHORUS COMPOUNDS 70 PREPARATION AND PROPERTIES OF NEW PHOSPHORUS CONTAINING CHELATING AGENTS FOR CALCIUM AND MAGNESIUM IONS

Abstract

Dedicated to Professor Martin Schmeisser on the occasion of his 65th birthday.

Several phosphonic acids of the type H₂O₃PCH₂OCHRCO₂H, R = H, CH₃, CO₂H; [H₂O₃P(CH₂)_x]₂ Y, x = 1, 2; Y = O, S; and [o-H₂O₃P(CH₂)]₂C₆H₄ have been synthesized and their capacity to chelate with calcium has been determined.