Papers by Keyword: Amorphous Solids

Abstract: Compared to information on nanocrystals, that on amorphous nanosolids is on the whole much less organized. On the other hand, growth of structural data in recent years on the latter, that deal with the range of atomic order (short range order and beyond), coordinations of core and surface atoms and similar aspects in amorphous nanoparticles through computer simulation and other techniques, has been very impressive. Similar generation of information is also true for physical phenomena like crystallization and melting. Finally, interesting properties revealed through experimentations point toward important applications. The present article makes a brief survey of these areas and attempts at reaching certain conclusions mostly specific for amorphous nanostructures with respect to the crystalline counterparts. The article analyzes the structural data to try and explain different properties of amorphous nanosolids and also their position in the applications scenario.

Abstract: In this study, Nb-Cr binary mixtures were prepared by mechanical alloying. And mechanical alloying process of mixed Nb-Cr(1:2) powders was studied, and the phases of milling powders analyzed by XRD and SEM. It has been found that the powders form solid solution first, then amorphous phase appeared gradually and crystallization of amorphous takes place with the different milling time. A thermodynamic model of MA of Nb-Cr system was developed based on Miedema Semi-experimental theory to explain the phase transformations of Nb-Cr system during milling. Using Miedema semi-empirical model the free energies of the ordered Laves-phase NbCr2 intermetallics, solid solution and amorphous alloy were calculated. From XRD and SEM analysis of Nb/2Cr powders prepared by mechanical alloying in a planetary ball milling, it was found that the calculated results were in accordance with the experiments.

Abstract: Changes in glass transition and ionic association of PPG/LiClO4 samples with increasing salt concentration have been studied using temperature modulated differential scanning calorimetry (TMDSC)and micro Raman spectroscopy, respectively. PPG, of average molar mass of 3000, was used as host for LiClO4 over the range O:Li = 35 – 4. The analysis of the Raman band, obtained at room temperature, associated with the ν1 symmetric stretching mode of ClO4 - anions, shows the presence of ionic association (ion pair) for electrolytes with salt concentration higher than O:Li = 8. The glass transition changes in the electrolytes were investigated using the differential of heat capacity with respect to temperature [dCp/dT], obtained from TMDSC. The analysis of the dCp/dT signal, by fitting with Gaussian curves, showed that there is a glass transition splitting in samples with concentrations higher than O:Li = 16, which indicates the presence of nanoheterogeneities in these amorphous electrolytes. Raman results pemit to affirm that this nanoheterogeneities were associated mainly with solvent separated ion pairs regions of different concentrations, and not with aggregate of ionic species.