Effect of temperature on solid-state formation of bulk nanograined intermetallic Al3Ni during high-pressure torsion

A bulk form of nanograined intermetallic Al₃Ni was produced by severe plastic deformation using high-pressure torsion (HPT). Powder mixtures of 75?mol% Al and 25?mol% Ni were processed by HPT at a selected temperature in the range of room temperature (RT) to 573?K under a pressure of 6?GPa. X-ray diffraction analysis revealed that the Al₃Ni intermetallic formed after processing for 50 revolutions at RT but, as the processing temperature increased, less revolutions (i.e. lower imposed strain) were required for the formation of Al₃Ni. Observations by transmission electron microscopy showed that the microstructure consists of ultrafine grains having a size of 300–2000?nm after 3 and 10 revolutions. Once the Al₃Ni formed after a higher number of revolutions, equiaxed nanograins with a size of ~30?nm prevailed with a significant increase in hardness. The increase in hardness was more significant when processed at higher temperatures because of increasing the fraction of Al₃Ni. It was shown that the solid-state formation of Al₃Ni occurred due to enhanced diffusion (i.e. decreased activation energy for diffusion) through the presence of high density of lattice defects.     

Efficient and solvent-free synthesis of bis-indolylmethanes using silica gel supported aluminium chloride as a reusable catalyst

Stable and non-hygroscopic silica gel supported aluminium chloride（SiO₂-AlCl₃）,which is prepared easily from cheap and commercially available compounds was found to be an environmentally friendly heterogeneous catalyst for the condensation of indole with aldehydes and ketones to afford bis-indolylmethanes at room temperature under solvent-free conditions.The catalyst can be reused up to five times after simple washing with ether.     

Uniform copper nanoparticles as an inexpensive and efficient catalyst for synthesis of novel β-carbonyl-1, 2, 3-triazoles in water medium

Copper nanoparticles as an efficient, inexpensive catalyst were prepared via ball milling for synthesis of β-carbonyl 1, 2, 3-triazoles from azido alcohol by click reaction in water. An extensive range of raw materials such as sodium azide, phenacyl bromide, epichlorohydrin, and terminal alkynes were used. Complete reduction of CuO in presence of NaBH₄ was done via ball milling with a ball-to-powder weight ratio of 50:1 under air atmosphere at room temperature. The final copper nanoparticles (Cu NPs) were characterized by SEM, EDX, XRD and FT-IR. The Cu NPs catalyzed one-pot three component synthesis of β-carbonyl 1, 2, 3-triazoles at room temperature with short reaction time and high product yields. The catalyst could be easily recovered and reused in several successive runs.

     

Some aspects of physical and numerical modeling of water hammer in pipelines

In this work, a computational method was used for the prediction of water transmission failure. The proposed method allowed for any arbitrary combination of devices in the water pipeline system. The method used was by a scale model and a prototype (real) system for a city main water pipeline where transient flow was caused by the failure of a transmission system.     

Electron-dislocation scattering and negative deviations from matthiessen's rule

It is shown that the negative deviations from Matthiessen's rule observed recently for the electrical resistivity of Al and of Ag can be explained quantitatively by including the effect of anisotropic electron-dislocation scattering.     

Backscattered indicatrix from surfaces with random impedance

Intensity enhancement in the retroreflection direction is studied for waves scattered by a random interface which has a bound state (surface wave). We have found that an enhanced backscattered peak appears as the result of competition of two mechanisms: multiple scattering of a surface wave along the interface, and its leakage to upper half-space. The last one is the important distinction of surface scattering, which shifts the diffuse pole and eliminates in a natural way the divergence of second moments, which is the crucial difficulty in existing theories. New results, valid when there is no real absorption in the medium, are obtained for the diffuse scattered intensity as a function of the angles near the antispecular direction.     

Rhodium-catalysed tetradehydro-Diels–Alder reactions of enediynes via a rhodium-stabilized cyclic allene

Efficient methods for the synthesis of fused-aromatic rings is a critical endeavour in the creation of new pharmaceuticals and materials. A direct method for preparing these systems is the tetradehydro-Diels–Alder reaction, however this is limited by the need for harsh reaction conditions. A potential, but underdeveloped, route to these systems is via transition metal-catalysed cycloaromatisation of ene-diynes. Herein, tethered unconjugated enediynes have been shown to undergo a facile room-temperature Rh^I-catalysed intramolecular tetradehydro-Diels–Alder reaction to produce highly substituted isobenzofurans, isoindolines and an indane. Furthermore, experimental and computational studies suggest a novel mechanism involving an unprecedented and complex Rh^I/Rh^III/Rh^I/Rh^III redox cycle involving the formation of an unusual strained 7-membered rhodacyclic allene intermediate and a Rh^III-stabilized 6-membered ring allene complex.

Room temperature Rh-catalysed tetradehydro-Diels–Alder reaction via an unusual Rh-stabilised allene.