Untersuchung von Eisen(II)phosphiten im Hinblick auf die Ausbildung von Wasserstoffbindungen

Ferrous phosphites FeHPO₃·3 H₂O, FeH₂P₂O₅, FeH₄P₂O₆·1/2 H₂O and FeH₁₀P₄O₁₂·4 H₂O were studied using X-ray powder patterns, thermography, electron reflectance spectroscopy, magnetic susceptibility measurements andRaman and infrared molecular spectra. The results obtained indicate that all the phosphites studied contain an approximately octahedral coordination sphere consisting of oxygen atoms, which produces a weak crystal field around the iron atom. Phosphite FeHPO₃·3 H₂O contains an HPO₃ ^2– anion with the symmetry decreased from point groupC _3v toC _s. Ferrous diphosphite FeH₂P₂O₅ contains a non-linear P–O–P bond with a valence angle of 159°. The hydrogen bonds between the water molecule and the HPO₃ ^2– anion indicate a positive hydratation of the phosphite anion. Medium-strong or strong hydrogen bonds, 258–270 pm long, correspond to mutual interactions of the anions in the crystal lattice of hydrogenphosphites. Hydrogen bonding in hydrogenphosphites causes a decrease in theDq values.

     

Lithium insertion into titanium dioxide (anatase) electrodes: microstructure and electrolyte effects

Insertion characteristics of anatase electrodes were studied on single-crystal and polycrystalline electrodes of different microstructures. The lithium incorporation from propylene carbonate solution containing LiClO₄ and Li(CF₃SO₂)₂N was studied by means of cyclic voltammetry (CV), the quartz crystal microbalance (QCM) and the galvanostatic intermittent titration technique (GITT). The electrode microstructure affects both the accessible coefficient x and the reversibility of the process. The highest insertion activity was observed for electrodes composed of crystals with characteristic dimensions of ∼10^–8 m. The insertion properties deteriorate for higher as well as for smaller crystal sizes. Enhanced insertion was observed in Li(CF₃SO₂)₂N-containing solutions. Lithium insertion is satisfactorily reversible for mesoscopic electrodes; the reversibility in the case of compact polycrystalline and single-crystal electrodes is poor. The reversibility of the insertion improves with increasing electrolyte concentration. The lithium diffusion coefficient decreases with increasing x and ranges between 10^–15 and 10^–18 cm² s^–1. Electronic Publication     

Electrochemical processes during plating Fe powder particles by Ni and Ni/Cu coating in the fluidized bed

Ni electrodeposition on Fe powder was studied with respect to an inhibiting adsorbed hydroxycomplex layer. Its elimination was done in three possible ways: by increasing the rotation speed of the circular stirring of the suspension, by chemical dissolution of the adsorbed layer during interrupted electrolysis, and by addition of a complexing agent – sodium citrate into the electrolyte. The simultaneous deposition of a Cu/Ni coating was enabled by proper electrolyte composition as to the ratio of both metallic compounds and by the addition of a suitable complexing agent. The Cu/Ni ratio was influenced, beside electrochemical parameters, also by the particle size of the Fe powder and by the suspension density. Increasing the suspension density supports the deposition of Ni, and increasing the particle size supportsthe deposition of Cu. Electronic Publication     

Investigation of the reactivity of powder surfaces by abrasive voltammetry

The ability of abrasive voltammetry to reflect the reactivity of iron powder immobilized on paraffin-impregnated graphite electrodes was investigated. Normal pulse voltammetry was used as the preferred method. The peak shape and position on the potential/time axis reflected both the reactivity of iron powder particles as well as their size fraction. “Relative peak height” defined as peak height to area ratio, i.e., current to charge ratio, correlated well with the rate of the electrochemical dissolution process. It showed not only a decreasing dissolution rate with an increase in particle size, but also the differencies in the dissolution rate of iron powder of various reactive surfaces as a consequence of various pretreatment methods. It was found that chemical pretreatment of the powder always resulted in a faster dissolution process in comparison with other non-chemical pretreatment methods. Received: 30 June 1998 / Accepted: 30 September 1998     

Voltammetry of biologically active species and surfactants on new miniaturized and contractible (compressible) mercury electrodes

The adsorption of the polyether-antibiotic monensin from an aqueous solution on mercury was used to investigate the effect of the decreasing size of a stationary mercury drop electrode on the shape of the voltammetric desorption peak of the surfactant. The change of the i-E curve indicated an acceleration of the transport of the surfactant to the electrode as well as of time-dependent changes in the adsorption layer. A decrease of the radius of the hanging mercury drop electrode from 220 μm to 80 μm at a constant accumulation time of t_ac = 70 s resulted in an about 4-fold increase of the evaluated signal (i-E pre-wave) of monensin. A 7-fold increase of the voltammetric desorption peak of monensin at conc. 5 · 10^–7 mol/L was observed as result of a compressive accumulation of the surfactant due to a contraction of the mercury drop electrode. A scheme of an apparatus for voltammetric/polarographic measurements by means of the contractible (compressible) mercury drop electrode is described. The controlled contraction of the electrode surface is presented together with preliminary results covering a new way of accumulation of surfactants, new accumulation effects, effective in adsorptive voltammetry, and other electroanalytical techniques.     

Hydrogen photoevolution on InGaP polycrystalline and tandem-type electrodes

We report on preparation of p-In_1−x Ga _x P polycrystalline, p-In_0.5 Ga_0.5P/p-GaAs, and p-In_0.5 Ga_0.5P/n-GaAs/n-InP tandem-type cathodes. The photovoltaic efficiency of InGaP tandem type epitaxial electrodes is two times higher than that of polycrystalline photocathodes. The most significant advantage of epitaxial electrodes is in their markedly better corrosion resistance in comparison with polycrystalline photocatodes. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998.     

Mass spectrometric profiling of N-linked oligosaccharides and uncommon glycoform in mouse serum with head and neck tumor

N-linked oligosaccharides obtained from total serum of mice with implanted head and neck tumors were analyzed and compared with those from control samples of healthy mice. Methods used include a combination of a derivatization procedure with phenylhydrazine (PHN) and analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Oligosaccharides were enzymatically released from total serum with PNGaseF and purified by high-performance liquid chromatography (HPLC) on a reversed-phase column. Mass spectra contained ion peaks of labeled oligosaccharides and MS/MS experiments provided useful data for the structural elucidation of these compounds. More than 40 N-glycans with compositions characteristic of high-mannose, hybrid, complex, neutral, and sialylated structures were identified in the serum of tumoral mice. Significant differences between samples were observed with respect to the abundances of high mannose and hybrid glycans. These oligosaccharides showed higher relative intensities in the spectra obtained from the cancer sera. Complex sialylated oligosaccharides had similar abundances in both types of sera, with the exception of fucosylated biantennary disialylated oligosaccharide, which was mostly detected with lower abundance in control samples. In the MALDI spectra, several minor species corresponded to uncommon carbohydrates. These structures have been investigated in detail by MS/MS. Among these novel glycoforms, a few sialylated oligosaccharides without a free reducing end were identified. Also, glycans with an extra 60 u were observed and likely feature the presence of a 2-acetamido-2-deoxyoctose residue attached on antennae of 3- or 6-linked mannose.     

Piezoelectric and elastic properties of the nonlinear optical material bismuth triborate, BiB3O6

Piezoelectric, pyroelectric, dielectric, elastic and thermoelastic properties of BiB₃O₆, point group symmetry 2, are reported. The eight independent components of the piezoelectric tensor could be derived from first-order longitudinal and transverse electrostrictive effects, employing a Michelson interferometer. For the determination of the elasticity tensor ultrasonic resonances of plane-parallel plates of different orientations and, in addition, the resonant ultrasound spectra (RUS) of rectangular parallelepipeda were measured. For the evaluation of the elasticity tensor from these resonant frequencies the piezoelectric coupling had to be taken into account. BiB₃O₆ exhibits a maximum longitudinal piezoelectric effect of 39.5×10^-12 mV^-1 along the twofold axis, a value about 17 timeslarger than that of α-quartz. The longitudinal elastic stiffness attains a minimum of about 5×10¹⁰ N m^-2 along the same direction and a maximum perpendicular to the twofold axis of about 33×10¹⁰ N m^-2, one of the largest elastic anisotropies observed in ionic crystals. This behaviour corresponds to the earlier observed extreme anisotropy of thermal expansion. The phenomena can be qualitatively interpreted by structural details, especially the preferential orientation of the lone electron pair of Bi³⁺. PACS 62.20.Dc; 77.65.Bn; 77.70.+a