Egidijus Griškonis

Electrodeposition of Zn–Mn alloys in the presence of thiocarbamide

Abstract The influence of thiocarbamide additions (0.5–2.0 g l −1 ) on the electrodeposition of Zn–Mn alloys from a sulfate–citrate bath is studied. Investigations of alloy composition were carried out by atomic absorption spectroscopy, EDX and XPS. The morphology of the coatings was studied by SEM. The crystal structure was investigated by powder and thin-film XRD. The corrosion behaviour of Zn–Mn alloys was tested by measurement of free corrosion potentials in aerated NaCl solution. The use of thiocarbamide allows higher Mn contents (70–80%) with respect to similar plating systems. High Mn deposits are composed of a nanocrystalline globular e phase. Air exposure gives rise to the formation of mixed Zn and Mn oxides. No carbon or sulfur incorporation in the bulk of the deposits was detected by XPS.

Molecular structure of mercury(II) thiocyanate complexes based on DFT calculations and experimental UV-electron spectroscopy and Raman studies

In this work, we report a combined experimental and theoretical study on molecular structure, vibrational and electronic spectra of [Hg(SCN)n](2-)(n) complexes (where n=2, 3, 4) in the aqueous solution. Molecular modeling of the mercury(II) complexes were done by the density functional theory (DFT) method using B3LYP functional with Stuttgart relativistic ECP 78MWB basis set for Hg and 6-311++G(d,p) basis set for all other atoms. The effect of different solvation models with explicit (ligand) and/or implicit water environment upon its geometry, vibrational frequencies and UV spectrum have been studied. The influence of H2O/D2O exchange on the experimental and calculated vibrational frequencies of studied complexes has been established. The double-peak character of the νHgS vibrational mode of the all analyzed mercury complexes and νCN mode of [Hg(SCN)3H2O](-) complex, respectively, were proposed here for the first time. The formation of four-coordinated Hg(II) complexes with thiocyanate and (or) water ligands was verified.

EVALUATION OF NEW TRANSPARENT TUNGSTEN CONTAINING NANOCOMPOSITES FOR RADIATION PROTECTION SCREENS

Evaluation of the new lead-free optically transparent nanocomposites is provided in this paper along with the introduction to their fabrication technologies and the results of investigation of their X-ray attenuating and optical properties before and after their exposure to high doses. These materials might be considered for the construction of X-ray protective screens that are used to protect medical personnel against scattered X rays during close-to patient operations. Rough selection of possible composites was performed according to X-ray attenuation modelling results. Experimental nanocomposites were prepared dissolving tungstates in different solvents or embedding tungsten structures into polymer matrix. It was found that the lead equivalent thickness of fabricated experimental samples varied from 0.15 to 0.75 mmPb and was higher for samples, containing polyanions of phosphotungstic acid. Transparency of the experimental samples to visible light varied from 20 to 60 % and was slightly increasing with irradiation dose due to radiation-induced processes in polymers.

Spectroscopic and structural investigations of iron(III) isothiocyanates. A comparative theoretical and experimental study.

A combined experimental and theoretical study on the molecular structure and vibrational spectra of [Fe(NCS)](2+) complex in the aqueous solution at the pH∼2 ± 0.1 have been performed. Experimental Raman spectra of the iron(III) isothiocyanate with higher coordination number in the acidic aqueous solution have been analyzed. Molecular modeling of the iron(III) monoisothiocyanate complex was accomplished by the density functional theory (DFT) method using B3LYP and PBE1PBE functionals. Theoretical vibrational spectra of the iron(III) monoisothiocyanate were interpreted by means of the potential energy distributions (PEDs). The influence of different solvation models and position of SO4(2)(-) ligand vs. NCS(-) ligand upon its geometry and vibrational frequencies have been evaluated. The effect of H2O/D2O isotopic substitution on the experimental and calculated Raman spectra of iron(III) isothiocyanates has been examined. Procedures of Raman spectra subtraction have been applied for the extractions of weak and/or obscured Raman signals. As a result, the presence of bound SO4(2)(-) ion and water molecules in the first coordination sphere in the acidic aqueous iron(III) isothiocyanate solution was confirmed. The vibrational assignments for the investigated iron(III) isothiocyanates were proposed here for the first time.

Investigation of X-Ray Attenuation Properties in Water Solutions of Sodium Tungstate Dihydrate and Silicotungstic Acid

Due to its outstanding photon attenuation features lead (Pb) is the most popular material which is used for radiation shielding and for radiation protection of individuals against ionizing radiation. However, Pb is very toxic and can cause serious health problems. Also recycling of lead containing materials is relative complicated. In order to overcome Pb related problems, researchers are looking for lead free materials possessing similar photon attenuation properties as lead and that can be used for the development and fabrication of radiation shielding elements and radiation protection equipment.

Graphite felt modified with electroless Co-Ni-P alloy as an electrode material for electrochemical oxidation and reduction of polysulfide species

Electroless deposition of a Co−Ni−P alloy on the surface of graphite felt filaments was performed in a low-temperature pyrophosphate solution under flow-through conditions. The loading, composition, morphology, and structure of electroless the Co−Ni−P alloy deposit on the filaments of the modified graphite felt were investigated by gravimetric analysis, energy-dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction, respectively. Electrochemical characterization of a graphite felt electrode modified with electroless Co−Ni−P alloy was performed by cyclic voltammetry, chrono-techniques, and the electrochemical impedance spectroscopy test in an aqueous solution of polysulfide composed of the mixture of 1 M Na2S, 1 M NaOH and 1 M S. It was found that the electroless Co−Ni−P alloy deposit on graphite felt has good cycling stability and high electrocatalytic activity toward reversible electrochemical redox reactions of polysulfide species. In comparison with the bare graphite felt electrode, the electrode modified with the electroless Co−Ni−P alloy showed five to seven times lower values of anodic and cathodic overpotentials in the aqueous solution of polysulfide. It is very likely that the good electrochemical performance of the modified graphite felt electrode is related to the high surface area of the electroless Co−Ni−P alloy deposit.