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[en] In spite of extensive investigation and applications, influence of oxygen (O), and humidity on polyaniline (PANI) behaviour is not well understood. For this reason we have performed semi-empirical quantum mechanics, and ab-initio calculations of the pernigraniline base (PNB) PANI oligomers, of various lengths, before and after approach of H2O, O2 , and hydroxyl (OH −) group, and attachment of OH − and O to various molecular positions. Structure, charge and electrostatic potential distribution, relevant energies and enthalpies, infrared and electronic spectra of the PNB tetramer equilibrium conformation, and their changes induced by specific OH − , and O attachments are determined. These results provide identification of the most probable positions for O2 and H2O approach to PNB_PANI, enthalpies of OH − and O attachments to them, changes of molecular properties induced by the attachments, and infrared and electronic modes that are most suitable for the attachments detection. The results are compared to the existing experimental data, and the results of similar calculations, and implications for the PNB_PANI applications are notified. © 2019 Elsevier B.V.
[en] Highlights: ► Two experimental peaks observed in DSC of Fe75Ni2Si8B13C2 amorphous alloy. ► First peak deconvoluted into four steps and attributed to crystallization. ► Second peak deconvoluted into two steps and attributed to phase transformations. ► Thermodynamic and kinetic parameters of every individual process were determined. - Abstract: Thermally induced structural transformations of amorphous Fe75Ni2Si8B13C2 alloy have been characterized in terms of both thermodynamic and kinetic parameters of individual processes. The crystallization of the alloy occurs in temperature region around 500 °C with primary crystallization of stable α-Fe(Si) and Fe2B and metastable Fe3B phase, followed by transformation of Fe3B to Fe2B. The latter process exhibits the lowest values of apparent activation energy and change in Gibbs free energy of activated complex, as well as negative value of change in entropy of activated complex, indicating that this corresponds to transformation of one crystalline phase to another, making it the least complex of the four processes. Another set of transformations occurs around 700 °C, where two consecutive processes are observed: phase transformation of α-Fe(Si) to α1-Fe(Si) and subsequent transformation of a portion of α1-Fe(Si) to Fe2B. The consecutive nature of these processes is indicated by the fact that the first process exhibits significantly higher values of apparent activation energy and changes in Gibbs free energy and entropy of activated complex.
[en] Highlights: • Crystallization process was separated into two single-step processes. • Narrow distribution of Ea is indicative of homogenous structure of amorphous alloy. • Crystallites of α-Fe(Si) serve as nucleation sites for formation of Fe2B phase. • Mechanism of both crystalline phases corresponds to Šesták–Berggren model. • Relatively small difference between reaction mechanisms of different phases. - Abstract: Fe89.8Ni1.5Si5.2B3C0.5 undergoes multi-step structural transformations under thermal treatment. Crystallization process, occurring around 810 K, was separated into two single-step processes, corresponding to formation of α-Fe(Si) and Fe2B crystalline phases, respectively. Significantly higher value of activation energy obtained for the first crystallization step indicate that formation of α-Fe(Si) facilitates the subsequent formation of Fe2B phase, by increasing in boron content of the amorphous matrix at the crystal/amorphous interphase boundary, while α-Fe(Si) crystallites probably serve as nucleation sites for crystallization of Fe2B phase. Narrow distribution of activation energies for both crystallization steps, obtained using Miura–Maki method, is an indicator of very homogenous structure of as-prepared amorphous alloy. The mechanism of formation of both crystalline phases was modeled using the general Šesták–Berggren model, and it was found that there is relatively small difference between respective reaction mechanisms, which is expected, as both phases crystallize directly out of the amorphous matrix
[en] Highlights: ► No shift in Curie temperature after annealing below crystallization temperature. ► Structural relaxation increases magnetic susceptibility and electrical resistivity. ► Wide supercooled liquid region observed with relatively constant functional properties. ► Magnetic properties highly dependent on thermal history of the alloy. - Abstract: The influence of thermal treatment on functional properties of Fe75Ni2Si8B13C2 amorphous alloy was investigated, showing the change that resulted from thermally induced structural transformations. Thermal history of the sample was found to have a significant effect on magnetic properties. Structural transformations were identified using DSC and thermomagnetic curve and characterized using Mössbauer spectroscopy and X-ray diffraction. Further investigation of magnetic and electrical properties of the alloy showed that structural relaxation prior to crystallization affected both magnetic susceptibility and electrical resistivity of the alloy, leading to an increase in both. This was caused by a confluence of stress relieving and a decrease in number of defects and an increase in free volume in the alloy sample, not only enabling greater mobility of magnetic domain walls, but also decreasing electron density of states at the Fermi level. Annealing at temperatures below crystallization caused an increase in magnetic susceptibility of the alloy at room temperature, however, a shift in Curie temperature was not observed. The alloy also exhibits a wide supercooled liquid region before crystallization, where its functional properties remained relatively constant, exhibiting the low values of both magnetic susceptibility and electrical conductivity.
[en] Highlights: ► Cyclovoltammetric and in situ spectroelectrochemical study in aprotic and basic media. ► Proposed mechanism: an ECCEE reaction sequence. ► Keto–monoenol tautomerization as the chemical step following the first electron transfer. ► PM3 MO modelling accounts for the experimental results. - Abstract: Electrochemical and spectroelectrochemical study of the reduction of (Z)-2-(5-ethoxycarbonylmethyl-N-methyl-4-oxothiazolidin-2-ylidene) -1-phenylethanone in an aprotic solvent (dimethylsulfoxide (DMSO)) has been presented. The results indicate an ECCEE reaction sequence, whereby the chemical step is a protonation of the anion radical electrogenerated in the first electron transfer step by the enol tautomer of the substrate. The gas phase and solvent dependent PM3 semiempirical modelling allowed further rationalization of experimental data pertinent to the suggested electrochemical redox mechanism and the reactivity of the intermediate species involved.