Search results for "Metallurgy"
showing 10 items of 1419 documents
Influence of Compressive Stress on Dielectric and Ferroelectric Properties of the Na0. 5K0.5NbO3, Na0.5K0.5(Nb0.94Sb0.06)O3and Na0.5K0.5(Nb0.94Sb0.06…
2013
Good quality lead-free ceramics of Na0.5K0.5NbO3, Na0.5K0.5(Nb0.94Sb0.06)O3 and Na0.5K0.5(Nb0.94Sb0.06)O3 +0.5mol%MnO2 have been produced by a solid phase hot pressing sintering process at 1120–1145°C. The dependence of dielectric and ferroelectric properties on the uniaxial pressure (0–3000 bar) of the these samples was investigated, revealing a significant influence of the external stress on their properties. This includes a shift of the phase transition, a diffuseness of the permittivity characteristics, a change of the dielectric dispersion and a decrease of the polarization. We discuss our results based on hardening of the soft-mode and domain switching processes under applying of pres…
Conditioning following powder micronization: influence on particle growth of salbutamol sulfate.
2003
Micronization is a high-energy process that induces changes in the crystallinity of materials. As a result, the crystalline structures on the particles' surface are being destroyed and amorphous areas are formed. After micronization of salbutamol sulfate to be used in dry powder inhalers, only small amounts of amorphous material are produced. Nevertheless, even these small amounts can have important effects on the physical stability of the powder. The amorphous state is thermodynamically unstable and tends to convert to the stable, crystalline state. The recrystallization process of disordered regions on the particles' surface leads to particle growth of milled particles. In this case, brid…
Hydrogen Formation on Phase Boundaries of Sn/Al
2002
The present paper continues our earlier study of the embrittlement of Sn-Al eutectic alloy in water vapor and hydrogen emission from it, Atomically clean interfaces of solid phase joints of Sn with Al served as simple phase boundary models for this system. It was found by SIMS, X-ray and SEM techniques that the brittleness is caused by chemical adsorption of hydrogen on phase boundaries. This process is facilitated by structural defects. The reaction of hydrogen with phase boundary occurs first in regions of micro-and submicrocracks. The effect is irreversible one and it is associated with the formation of SnH4 that is instable and decomposes at the room temperature. The phase boundary of S…
The Role of Diffusion Accommodation and Phase Boundary Wetting in the Deformation Behaviour of Ultrafine Grained Sn-Pb Eutectic
2010
Mechanical properties, microstructure of the Sn–38wt. %Pb eutectic and the development of deformation - induced diffusion processes on interphase boundaries (IB) were investigated. Experiments were carried out both in deformed and annealed states of eutectic using micro- and nanoindentation, SEM, AFM and optical microscopy techniques. It was found that the deformation of the annealed alloy is localized at the Pb/Sn interphase boundaries and occurs by grain boundary sliding (GBS) accompanied by sintering micropore processes under the action of the capillary forces on the Pb/Sn IB. During severe plastic deformation of Sn-Pb eutectic phase transition in the Sn grain boundary occurs. This defor…
Experimental and Theoretical Study of Bi2O2Se Under Compression
2018
[EN] We report a joint experimental and theoretical study of the structural, vibrational, elastic, optical, and electronic properties of the layered high-mobility semiconductor Bi2O2Se at high pressure. A good agreement between experiments and ab initio calculations is observed for the equation of state, the pressure coefficients of the Raman-active modes and the bandgap of the material. In particular, a detailed description of the vibrational properties is provided. Unlike other Sillen-type compounds which undergo a tetragonal to collapsed tetragonal pressure-induced phase transition at relatively low pressures, Bi2O2Se shows a remarkable structural stability up to 30 GPa; however, our res…
Guanine Assemblies on the Au(111) Surface: A Theoretical Study
2013
It was found previously [Small2009, 5, 1952 and Angew. Chem., Int. Ed.2005, 44, 2270] that guanine molecules when assembled in a vacuum on the Au(111) surface at room temperature form a hydrogen-bonded network consisting of guanine quartets of the same chirality; this was supported by ground-state density functional theory (DFT) gas-phase calculations. In this Article, we re-examine this system and show that many more (almost equally stable) both homo- and heterochiral structures are possible; however, the homochiral structure observed experimentally becomes definitely the most favorable only if the vibrational contribution to the free energy is accounted for. Interaction with the gold surf…
Direct observation of strain-induced non-equilibrium grain boundaries
2015
Abstract The grain boundary (GB) wetting by the melt and second solid phase has been studied in the Sn–Pb system both in equilibrium conditions and during continuous strain. The percentage of Sn/Sn GBs completely wetted by the melt increases from 80% at eutectic temperature Te=183 °C to 100% at 220 °C. The percentage of Pb/Pb GBs completely wetted by the melt increases from 0% at Te to 100% at 270 °C. Below Te only incomplete wetting of Pb/Pb GBs by solid Sn and Sn/Sn GBs by solid Pb has been observed after long annealing. However, during strain the lattice dislocations are continuously absorbed by GBs increasing the GB energy. As a result, the complete wetting of such non-equlibrium Sn/Sn …
Up-conversion luminescence dependence on structure in zirconia nanocrystals
2013
The zirconia samples containing two different concentrations of Er and Yb dopants were prepared using the Sol–Gel method and up-conversion luminescence was studied using the time-resolved techniques. The up-conversion luminescence depends on the oxygen content in surrounding gasses during annealing as well as on the annealing temperature. These dependencies indicate that ZrO2 intrinsic defects annealing and generation, phase transition as well as dopant redistribution take place. The possible role of these processes on up-conversion luminescence is discussed. The results of experiments confirmed that the annealing temperature has a crucial influence on up-conversion luminescence for samples…
Influence of molecular weight and polydispersity on phase behaviour of polyesters with laterally fixed or cross-shaped mesogens
1991
Abstract To supplement previous studies of polyesters with laterally attached and cross-shaped mesogens the influence of molecular weight and molecular weight distribution on the phase behaviour has been investigated. For that purpose two polyesters have been fractionated by preparative gel permeation chromatography under high pressure and observed by polarizing microscopy and DSC measurements. A monotropic nematic polyester with laterally attached mesogens shows changing phase transitions up to a molecular weight of 10 000 (Mw); at higher molecular weight only the clearing transition is still slightly influenced. The molecular weight distribution at an average molecular weight of 15 000 (M…
Phase Transitions in Prequenched Mesomorphic Isotactic Polypropylene during Heating and Annealing Processes As Revealed by Simultaneous Synchrotron S…
2011
Time-resolved simultaneous synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) technique was used to investigate the phase transitions in prequenched mesomorphic isotactic polypropylene (iPP) samples during heating and annealing processes, respectively. For the heating process, it is shown that the mesomorphic-to-monoclinic phase transition is relatively faster for the mesomorphic iPP sample obtained with the high quenching rate than that with the low quenching rate. For the former, the stability of α-monoclinic crystals formed during heating is relatively higher. As for the annealing process, WAXD and SAXS data illustrate that the higher the annealing te…