Non‐negative matrix factorization for the near real‐time interpretation of absorption effects in elemental distribution images acquired by X‐ray fluorescence imaging

Elemental distribution images acquired by imaging X‐ray fluorescence analysis can contain high degrees of redundancy and weakly discernible correlations. In this article near real‐time non‐negative matrix factorization (NMF) is described for the analysis of a number of data sets acquired from samples of a bi‐modal α+β Ti‐6Al‐6V‐2Sn alloy. NMF was used for the first time to reveal absorption artefacts in the elemental distribution images of the samples, where two phases of the alloy, namely α and β, were in superposition. The findings and interpretation of the NMF results were confirmed by Monte Carlo simulation of the layered alloy system. Furthermore, it is shown how the simultaneous factorization of several stacks of elemental distribution images provides uniform basis vectors and consequently simplifies the interpretation of the representation.     

Electronic structure of A15-type compounds: V<Subscript>3</Subscript>Co,V<Subscript>3</Subscript>Rh,V<Subscript>3</Subscript>Ir and V<Subscript>3</Subscript>Os

Band structure and Fermi surfaces of the A₃B compounds V₃Co, V₃Rh, V₃Ir and V₃Os are calculated in FP-LAPW calculations. From V₃Co to the V₃Os compound one observes a decrease of the overlap for d-states from both V and B atoms; the center of gravity of the d-band for V moves upwards, while for the B-atom it moves toward lower energies. Hence, despite the band widening, a weakening of interactions takes place throughout this series, which leads to a lattice expansion as experimentally observed. The bonding mechanism in these compounds is found to be dominated by the lower energy d-states. Comparatively, the DOS at E_F does not change appreciably between these compounds, except for V₃Os, where a sharp peak is observed at E_F. This feature leads to the highest electronic heat-capacity coefficient γ (2.31 ) in this compound, which otherwise possesses the smallest Bulk modulus (209.05 GPa). In V₃Os, for whom no report has been found, a stronger admixture between p-states from both metals near E_F is observed, and the Os d-states form a common d-band with the V d-states between 0.4–0.6 Ry. A stronger s–s hybridization is observed for V₃Co, which is in the source of the fact that this compound has an anomalously large quadrupole interaction and exhibits a positive Knight shift.     

Diffusion and electromigration on disordered surfaces

We study a one-dimensional disordered solid-on-solid model in which neighboring columns are shifted by quenched random phases. The static height-difference correlation function displays a minimum at a nonzero temperature. The model is equipped with volume-conserving surface diffusion dynamics, including a possible bias due to an electromigration force. In the case of Arrhenius jump rates a continuum equation for the evolution of macroscopic profiles is derived and confirmed by direct simulation. Dynamic surface fluctuations are investigated using simulations and phenomenological Langevin equations. In these equations the quenched disorder appears in the form of time-independent random forces. The disorder does not qualitatively change the roughening dynamics of near-equilibrium surfaces, but in the case of biased surface diffusion with Metropolis rates it induces a new roughening mechanism, which leads to an increase of the surface width as . Received 7 February 2000     

Investigation of shape memory characteristics and production of HfZrTiFeMnSi high entropy alloy by mechanical alloying method

High entropy alloy (HEA) with shape memory effect (SME) has been the subject of great interest for the past few decades. However, with the increased demands for new materials for high thermal applications, the research activities on the multi elemental high entropy shape memory alloys (HESMA) have been increased by many folds recently. The nano crystalline HEA powder with shape memory effect developed in this study, HfZrTiFeMnSi, was produced by mechanical alloying (MA) for the first time. In this method equiatomic ratio of Hf, Zr, Ti, Fe, Mn, and Si were mixed together and milled by MA process for 100 h. The powder formed was of amorphous in nature. Elemental mapping of the powder from SEM-EDS revealed homogeneity of the alloying elements confirming successful fabrication of HfZrTiFeMnSi HEA powder. The DSC studies from ambient to 500 °C of the annealed alloy powders showed reversible austenitic to martensitic (A↔M) transformations. The A↔M transformation hysteresis seemed to vary with the milling time and annealing temperature. The enthalpy values, ΔH, for the transformation were calculated from the DSC plots using tangent method for peak area calculation. Regardless of the annealing temperature, the thermal analysis revealed that the ΔH, equilibrium temperature (T₀), and crystallization temperature values decreased with the increasing milling time.     

SECM and SKPFM Studies of the Local Corrosion Mechanism of Al Alloys – A Pathway to an Integrated SKP‐SECM System

Scanning Kelvin Probe Force Microscopy and Scanning Electrochemical Microscopy were applied for the investigation of localized corrosion on heterogeneous aiming on the investigation of the possible correlation between the local surface potential differences, measured by the Kelvin probe technique in ambient conditions, and corrosion during immersion in a corrosive electrolyte. A model sample mimicking the interaction of Al and Cu in Al alloys was chosen to demonstrate the complementary nature of the information received from SKPFM and SECM. The necessary prerequisites for a future integration of SKP and SECM into a single set‐up are discussed.     

TlCu5O(VO4)3 mit KCu5O(VO4)3‐Struktur – ein Thallium‐kupfer(II)‐oxidvanadat als Oxidationsprodukt einer Tl/Cu/V‐Legierung

TlCu₅O(VO₄)₃ with KCu₅O(VO₄)₃ Structure – a Thallium Copper(II) Oxide Vanadate as an Oxidation Product of a Tl/Cu/V Alloy Brown‐black crystals of the new oxide vanadate TlCu₅O(VO₄)₃ (triclinic, P1, a = 610.4(1) pm, b = 828.9(1) pm, c = 1075.3(1) pm, α = 97.70(1)°, β = 92.25(1)°, γ = 90.28(1)°, Z = 2) were obtained as a byproduct during the reaction of a Tl/Cu/V alloy with oxygen. The compound is isotypic with KCu₅O(VO₄)₃. All the crystals investigated were twins by non‐merohedry with [100] as the twin axis. The structure contains ladder shaped [Cu₁₀O₂₆]‐ribbons composed of edge‐ and corner‐sharing [CuO₅]‐polyhedra (tetragonal pyramids and trigonal bipyramids) and linked by vanadate groups. The thallium ions fill channels running along the a axis. No stereochemical activity of the thallium(I)‐lone pair is observed.     

Investigation of Nickel-Based Alloys Exposed to Supercritical Water Environments

Experimental tube reactors made of the nickel based alloys C-22 and Inconel 625 were exposed to supercritical water (SCW) environments. During this experiments, various inclusions and precipitates from a submicron size range to bulk scale-like layers were formed. The corrosion products and layers, located at the sub- and supercritical parts of the tubular flow reactors, were imaged and analyzed by field-emission scanning electron microscopy, combined with an energy-dispersive X-ray spectrometer (FESEM/EDX). The microanalysis was performed on metallographically prepared specimen. To obtain additional information regarding surface morphology, scanning force microscopy (SFM) and microhardness testing were applied at selected specimen.     

Electrocatalytic response of carbohydrates at copper-alloy electrodes

The voltammetric responses observed for carbohydrates and polyalcohols at 0.60 V in 0.10 M NaOH are significantly larger at preanodized CuMn (95:5) electrodes as compared to preanodized pure Cu electrodes. Apparent values for the number of electrons transferred (n_app) and the corresponding values of heterogeneous rate constants (k_app) are estimated for selected reactants from the slopes and intercepts, respectively, of Koutecký–Levich plots of background-corrected voltammetric currents obtained at CuMn and Cu rotated disk electrodes (RDEs). Values of n_app (and k_app) for sorbitol and glucose are 11.8 (9.2×10⁻³ cm s⁻¹) and 11.7 (8.0×10⁻³ cm s⁻¹), respectively, at a CuMn RDE. These are compared to the values 10.4 (1.8×10⁻³ cm s⁻¹) and 9.6 (2.0×10⁻³ cm s⁻¹) for sorbitol and glucose, respectively, at a Cu RDE. The larger sensitivities observed at the CuMn RDE in comparison to the Cu RDE are concluded to be the beneficial result of larger k_app values at the alloy electrode. Furthermore, the larger k_app values are speculated to result from enhanced preadsorption of the reactant species at Mn(IV) sites in the preanodized CuMn surface. In flow-injection measurements, the peak signals obtained for successive injections of glucose using a CuMn electrode (0.60 V vs. SCE) were quite stable with a standard deviation of 1.5%. However, large day-to-day variations (±15%) observed in the average peak signals are attributed to the temperature sensitivities of the k_app value and the diffusion coefficient for glucose.     

Ferromagnetic GaSb/Mn digital alloys

In order to realize spintronic devices in narrow-gap semiconductors, we have carried out studies on the well-known InAs/GaSb-based materials and structures. As a key component to such devices, GaSb/Mn digital alloys were successfully grown by molecular beam epitaxy. Good crystal quality was observed with transmission electron microscopy showing well-resolved Mn-containing layers and no evidence of 3D MnSb precipitates in as-grown samples. Ferromagnetism was observed in GaSb/Mn digital alloys with temperature-dependent hysteresis loops in magnetization up to 400 K (limited by the experimental setup). Magnetotransport studies were also carried out, both in the conventional Hall-bar configuration, and on gated Hall-bar structures. Both anomalous Hall effect and tunable ferromagnetism with applied gate bias were investigated. Annealing studies of the digital alloys reveal evidence of migration of Mn atoms at elevated temperatures.     

Magnetocaloric effect in high Ni content Ni52Mn48−xInx alloys under low field change

Ni-rich Heusler alloys Ni₅₂Mn_48−xIn_x (x=15.5, 16 and 16.5) were prepared by the arc melting method. X-ray diffraction analysis revealed that the martensite has orthorhombic structure (S.G. Pmm2) at room temperature. The only alloy with x=15.5 has structural transmission from martensite to austenite without any magnetic transmission. The temperature dependence and the field dependence of the magnetization measurement indicated that the magnetization increased with the decreasing of the concerntration of Mn. The lesser the Mn atoms located in the In atom sites, the weaker the total AFM interaction in the system. Giant entropy changes ΔS_M(T, H) were found in Ni₅₂Mn_48−xIn_x alloys with the maximum ΔS_M value of 22.3 J kg K for the sample with x=16.5 at 270 K under the magnetic field change of 1.5 T.