Electrodeposition of yellow bronze from acidic sulfate baths containing polyether laprol and micromolar additives of halides

The composition of yellow bronze coatings deposited from acidic sulfate solutions added with polyether laprol and the electrodeposition conditions are studied by voltammetry and XPS. It is found that halides in rather low (micromolar) concentrations affect significantly the partial electrodeposition processes. Chlorides increases cathodic polarization, widen the current window of the yellow bronze electrodeposition, and favor the increase in tin content of the coatings. Bromides narrow the current window, lower the tin content in the coatings, and hinder the yellow bronze surface oxidation. Iodides inhibit the copper electroreduction markedly, which makes the yellow bronze deposition practically impossible. Original Russian Text ? Z. Mockus, S. Kanapeckaité, V. Jasulaitiené, A. Survila, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 5, pp. 526–531.     

Mössbauer study of the Ge two-electron donor centers in PbSe

Mössbauer emission spectroscopy at ⁷³As(⁷³Ge) is used to show that the charge state of the ⁷³Ge antisite defect formed in the anion sublattice after the radioactive transformation of ⁷³As is independent of the position of the Fermi level. In contrast, the ⁷³Ge center in the cation sublattice of PbSe is an electrically active substitutional impurity. For the n-type samples, the spectrum corresponds to the neutral state of the donor center (⁷³Ge²⁺), and for the p-type samples, the spectrum corresponds to the doubly ionized state (⁷³Ge⁴⁺) of this center.     

A physically based approach to granular media mechanics: grain-scale experiments,initial results and implications to numerical modeling

It is generally appreciated that the mechanical behavior of granular media depends fundamentally on the interaction of the constituent particles, and that the validity of numerical models of granular media would be greatly improved with knowledge of the grain-scale mechanics. However, most supporting experimental work has been conducted on highly idealized materials, and a limited amount of information exists on grain-scale force–displacement relationships for naturally occurring materials. To address this shortcoming, we are conducting a program that integrates laboratory experiments on grains of naturally occurring aggregate with the discrete element modeling method, with the goal of relating the grain-scale physical and mechanical properties of granular media to bulk behavior. The paper describes the equipment and methods that have been developed to conduct close-loop controlled, grain-scale experiments under monotonic and cyclic loading conditions, and presents results from an initial set of experiments on unbonded grains. The implications of the grain-scale results to the discrete element model are discussed. Discussions center on the applicability of a physically based approach to the mechanics of granular media in general. In light of future exploration missions and the resulting need to predict the mechanical properties of lunar and planetary regoliths, the paper examines the potential usefulness of our physically based approach to the problem of predicting the behavior of the types of materials found in those environments.     

Synthesis of ductile titanium-titanium boride (Ti-TiB) composites with a beta-titanium matrix: The nature of TiB formation and composite properties

The study focused on the in-situ synthesis of titanium (Ti)-titanium boride (TiB) composites with β phase in the matrix by reaction sintering of TiB₂ with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds of powder mixtures: (1) β-Ti alloy powders and TiB₂; (2) α-Ti powder, a master alloy (Fe-Mo) powder containing the β-stabilizing elements, and TiB₂; and (3) α-Ti powder, a β-stabilizing elemental powder (Mo or Nb), and TiB₂. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at processing temperatures ranging from 1100°C to 1300°C. The morphology, size, and distribution of whiskers were found to be influenced by the powder-packing conditions. A large particle-size ratio in bimodally packed mixtures led to the formation of a TiB monolithic layer around β grains. With a relatively finer starting powder, smaller size ratio, and trimodal packing arrangement, the TiB whiskers were found to be distributed more homogeneously in the matrix. The study also used the X-ray direct comparison method and the structure factor for the β phase to determine the volume fraction of TiB phase from X-ray data. Tensile tests and fractographic investigations were carried out on selected composites. The evolution of the composite microstructure, the influence of powder-packing variables, and the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.     

A Shortcut Method for Estimating the HETP of Structured Packed Distillation Columns at Elevated Pressure

A shortcut model is developed for predicting the HETP of a structured packed distillation column operating at elevated pressure. The proposed model incorporates the geometrical parameters of the packing, physical properties of the vapor and liquid phases, and the hydrodynamics of the two‐phase flow. The proposed model is tested and validated by comparing the predicted results with the present experimental data and some published HETP data. The results show that the proposed model can predict the experimental data with a deviation smaller than 20 %.     

Threshold behavior of the formation of nanometer islands in a Ge/Si(100) system in the presence of Sb

Atomic-force microscopy is used to study the behavior of an array of Ge islands formed by molecular-beam epitaxy on an Si (100) surface in the presence of an antimony flux incident on the surface. It is shown that, as the Sb flux increases to a certain critical level, the surface density of the islands increases; however, if this critical level is exceeded, nucleation of the islands is suppressed and mesoscopic small-height clusters are observed on the surface. This effect is explained qualitatively in the context of a kinetic model of the islands’ formation in heteroepitaxial systems mismatched with respect to their lattice parameters.