Влияние предварительной сжимающей нагрузки на работу, производимую монокристаллами Cu-Al-Ni при взрывном восстановлении деформации памяти формы

The ability of martensitic single crystals Cu 82.5 wt.% - Al 13.5 wt.% - Ni 4.0 to perform work has been investigated. It is shown that weight placed on the crystal is transferred smoothly or by impact during shape memory strain recovery (SMS) Moving depends on the preliminary deformation of the crystal. An influence of the preload on this work is studied. It was found that the transition to the impact mode occurs after preliminary compression of the crystal to the full SMS (~ 9%), when the load is more than twice the stress of the detwinning of martensite. DSC calorimetry showed that after compression to 200–250 MPa and higher sharp narrowing of reverse martensitic transformation (RMT) peak takes place.

Preparation and Characterization of Indomethacin Supramolecular Systems with β-Cyclodextrin in Order to Estimate Photostability Improvement

Cyclodextrins have found wide application in contemporary chemistry, pharmacy and medicine. Because of their unique properties, cyclodextrins are constantly used in research on solubility or stability improvement, as well as other physicochemical properties of medicinal substances. Indomethacin (IND) is a photolabile molecule that also attracts the interest of researchers due to its therapeutic potential and the need to overcome its problematic photosensitivity. Supramolecular complexes of indomethacin with β-cyclodextrin (CD) are already known, and they show greater stability compared to complexes with other types of cyclodextrins. So far, however, the sensitivity to light of physical mixtures and inclusion complexes in the solid phase has not been studied, and their various stoichiometries have not yet been investigated. Due to this fact, the aim of the present study is to obtain supramolecular systems (inclusion complexes and physical mixtures) of indomethacin with three different amounts of β-cyclodextrin. Assessment of the photochemical stability of indomethacin-β-cyclodextrin systems in the solid state is performed in order to find the best correlation between IND stability and the amount of CD. Comparative analysis of physicochemical degradation for stoichiometry systems [CD:IND] = [1:1], [0.5:1] and [0.1:1] is performed by using ultraviolet spectroscopy, transmission—FTIR, reflection—ATR-FTIR infrared spectroscopy and DSC calorimetry.

Thermodynamic properties of single crystals based on lithium tungstate by reaction and DSC calorimetry

For the first time, single crystals of undoped lithium tungstate and lithium tungstate doped by 1.25% molybdenum were grown by the low-temperature-gradient Czochralski technique. The standard formation enthalpies, lattices enthalpies, stabilization energies, and the heat capacity were determined in the temperature range of 320-997 K. The lattice enthalpy dependence on Mo content was constructed.

Heat capacity of lithium tungstate single crystal by DSC calorimetry data in the temperature range of 319-997 K

The heat capacity of lithium tungstate single crystal (Li2WO4) was measured for the first time in the temperature range of 319-997 K. The experiments were carried out by DSC calorimetry. The Li2WO4 single crystal was first grown by low-temperature-gradient Czochralski technique with weight control. The temperature dependence of Li2WO4 heat capacity in the temperature range 319-997 K was monotonic. According to results of our studies, there were no phase transitions in Li2WO4 in the investigated temperature range.

Influence of aging on microstructure and hardness of lead-free solder alloys

Purpose The purpose of this paper is to carry out a study of the evolution of the microstructure and the microhardness of Sn-Cu-Ag alloys from as-cast condition and under artificial isothermal aging at different temperatures (100ºC and 180ºC) for a treatment time up to 500 h. A comparison with Sn-37% Pb eutectic solder samples was also made. Design/methodology/approach Sn-3.5%Ag, Sn-0.7%Cu and Sn-3.5%Ag-0.9%Cu were poured in two different cooling rate conditions and then aged at 100ºC (373ºK) and 180 °C (453ºK) during 500 h. Microstructural changes were observed by optical microscopy, scanning electron micrograph and energy dispersive X-ray microanalysis. Differential scanning calorimetry technique (DSC) was also used to confirm the obtained results. Findings A decrease up to 20% in microhardness respect to the value of the as-cast alloy was observed for both aging temperatures. These changes can be explained considering the coarsening and recrystallization of Sn dendrites present in the microstructures of all the systems studied. Originality/value There is no evidence of dissolution or precipitation of new phases in the range of studied temperatures that could be detected by DSC calorimetry technique. The acting mechanisms must be the result of coarsening of Sn dendrites and the residual stresses relaxation during the first stages of the isothermal aging.

Liquid-crystalline properties of 4-alkyl-, 4-alkyloxy and 4-halogene-4′-hydroxyazobenzene alkyloates

Twenty one esters, 4-alkyl-, 4-alkyloxy-, 4-nitro- and 4-halogene-4′-hydroxyazobenzne alkyloates have been synthesised. Basing on the DSC calorimetry and polarizing microscopy liquid- crystalline polymorphism was investigated. Five types of mesophases were identified: nematic, smectics A, C, F and unknown X (probably G).