Formation of an icosahedral structure during crystallization of nickel nanoclusters

The crystallization of nickel nanoclusters is investigated using a molecular dynamics simulation with tight-binding potentials. The formation of a cluster structure depends on the cooling conditions. Slow cooling results in the formation of a face-centered cubic structure, whereas fast cooling, according to the data obtained in 40% of the simulation experiments, leads to the formation of an icosahedral structure. The molecular dynamics simulation experiments demonstrate the possibility of controlling the formation of a structure of nickel nanoclusters during crystallization.     

The state of the art and prospects of detonation-synthesis nanodiamond applications in Belarus

Technological features of the commercial production of detonation-synthesis nanodiamonds at the SINTA Joint-Stock Company and the characteristics of the nanodiamonds and diamond-containing mixtures produced are considered. Nanodiamond applications in the production of composite electrolytic coatings that are based on chromium, nickel, gold, and silver, exhibit good service properties, and save on the use of noble metals and electric power are exemplified. Nanodiamond applications for the modification of plastics, antifriction lubricants, and oxide coatings grown by microarc oxidation of aluminum alloys are also considered. The prospective application of nanodiamonds as a raw material in the synthesis of diamond powders and superhard composites by static and shock-wave loading is demonstrated.     

Effect of laser erosion on the copper and zinc concentrations in the surface layer of brass

A REMMA 102 scanning electron microscope equipped with semiconductor and wave spectrometers is applied to measure the copper and zinc concentrations in the surface layers of an M161 brass sample and the same sample subjected to a focused laser radiation. The results are compared with the results obtained with an MS3101 laser mass spectrometer having a laser-plasma ion source. The laser-assisted erosion of the surface layer in the brass is shown to significantly change the copper and zinc concentrations. It is found that, when the craters produced by laser pulses on the initial surface do not overlap, the copper and zinc contents in the laser-induced plasma correspond to their contents in the sample.     

Generation of a homogeneous plasma and wide ion beams in a penning system with a nonequipotential cathode

A study is made of the possibility of controlling the spatial distribution of the degree of ionization in a modified Penning cell with a cathode divided into several sections that are at different potentials. It is shown that an almost uniform plasma can be produced when applying an optimal potential of the control electrode. This enables the generation of wide ion beams in this system. An ion extraction efficiency of several tens of percent is achieved, which is substantially higher than in conventional ion sources.     

Asymmetric synthesis of 6-(2′,3′,4′,5′,6′-pentafluorophenyl)-δ-lactones via “allyl”boranes: application for the synthesis of fluorinated analog of key pharmacophore of statin drugs

Asymmetric “allyl”boration of pentafluorobenzaldehyde with various α-pinene based “allyl”boranes provides homoallylic alcohols in high de and ee; the alcohols have been converted into δ-lactones via acryloylation, ring-closing metathesis and hydrogenation. Pentafluorophenyl analog of key pharmacophore of statin drugs has been synthesized using diastereoselective epoxidation and regioselective reduction as key steps.     

Electrical Conductivity Oscillations in Laminated Charge-Ordered Crystals with a Monotonic Negative Reluctance

In the present paper, the Shubnikov–de Haas oscillation frequencies arising in laminated charge-ordered crystals with a monotonic negative reluctance due to scattering of current carriers on charged impurities with a short-range potential are calculated and classified. It is demonstrated that non-semiclassical oscillation frequencies can be a measure of charge ordering.     

On the Effect of the Strength of Acid Sites in Heterogeneous Catalysts on the Activity in the Skeletal Isomerization of n-Butane

The catalytic activity of three groups of acid catalysts different in the nature and strength of acid sites in the skeletal isomerization of n-butane was studied. It was found that the strength of the sites did not correlate with the rate of the reaction.     

The synthesis mechanism of Ca3Al2O6 from soft mechanochemically activated precursors studied by time-resolved neutron diffraction up to 1000°C

The reaction pathway for the Ca₃Al₂O₆ formation up to 1300°C, from mechanochemically treated mixtures of amorphous aluminum hydroxide and CaCO₃, was studied in situ by differential thermal analysis, constant heating rate dilatometry and time-resolved neutron powder diffraction. The experiment was carried out, in an open system, on a sample with the nominal Ca₃Al₂O₆ stoichiometry. The results obtained by neutron diffractometry and thermal analysis were in good agreement with the data obtained by scanning electron microscopy and X-ray diffraction on heat-treated and-quenched samples. The synthesis path implied the formation of cryptocrystalline Al₂O₃, crystalline CaO, CaAl₂O₄ and Ca₁₂Al₁₄O₃₃ as transitory phases. Finally the nucleation and growth of the single phase Ca₃Al₂O₆ took place at 1300°C and exhibited porous structure due to CO₂ and H₂O release.