Brigitte Bitschnau

Neutron scattering of a floating heavy water bridge

When high voltage is applied to distilled water filled into two beakers close to each other, a water connection forms spontaneously, giving the impression of a floating water bridge (Fuchs et al 2007 J. Phys. D: Appl. Phys. 40 6112–4, 2008 J. Phys. D: Appl. Phys. 41 185502). This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. In this work, the first data on neutron scattering of a floating heavy water bridge are presented and possible interpretations are discussed. D2O was measured instead of H2O because of the very strong incoherent scattering of H. The obtained data support the ‘bubble hypothesis’ suggested earlier (Fuchs et al 2008).

Two-dimensional neutron scattering in a floating heavy water bridge

When a high voltage is applied to pure water in two filled beakers kept close to each other, a connection forms spontaneously, giving the impression of a floating water bridge. This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. In this work, the first two-dimensional structural study of a floating heavy water bridge is presented as a function of the azimuthal angle. A small anisotropy in the angular distribution of the intensity of the first structural peak was observed, indicating a preferred orientation of a part of the D2O molecules along the electric field lines without breaking the local tetrahedral symmetry. The experiment is carried out by neutron scattering on a D2O bridge.

High purity pressurised hydrogen production from syngas by the steam-iron process

The production of hydrogen in a fixed bed reactor at a maximum pressure of 50 bar by oxidising an oxygen carrier (Fe2O3/Al2O3/CeO2) with 0.06 g min−1 of steam at 1023 K is discussed. Reductions were performed with synthesis gas at ambient pressure and 1023 K for 90 minutes. The influences of the elevated system pressure on the carbon contamination, the quantification of the contaminations in the produced hydrogen and the oxygen carrier conversion are analysed. The results show that small amounts of carbon depositions are formed during the reduction, which are re-oxidised with steam leading to the contamination of the hydrogen. The hydrogen purity obtained in the experiments is within the range of 99.958% to 99.999% with CO as the main impurity. The amount of contaminations as a result of the oxidation of the solid carbon is not influenced by the elevated system pressure, which confirms the suitability of the reformer steam-iron process in a fixed bed to produce pressurised hydrogen directly from a hydrocarbon feed. The oxygen carrier conversion displays an initial drop followed by a slightly linear decrease. Air-oxidations revealed a regeneration effect on the oxygen carrier conversion, which reversed a part of the conversion losses.

Intercalation behaviour of magnesium into natural graphite using organic electrolyte systems

The focus of this study is on the investigation of electrochemical intercalation and deintercalation behaviour of Mg2+ into natural graphite electrodes in organic electrolyte. We used as a conductive salt magnesium bis(trifluoromethylsulfonyl)imide (Mg(TFSI)2) dissolved in N,N-dimethylformamide (DMF) as organic solvent. By utilization of conductivity measurements within a broad temperature range (−20 °C to +60 °C), a conductivity maximum is to be found at a concentration of 0.5 M for all temperatures. Thus, in this study all electrochemical investigations dealing with magnesiation of graphite anodes are made with the electrolyte system 0.5 M Mg(TFSI)2/DMF. In three electrode cells (Swagelok© T-cells) we obtain cathodic and anodic currents, which are highly reversible and last for more than 100 cycles showing a coulombic efficiency above 98%. SEM images reveal a non-destructive intercalation of cationic species into graphite and the formation of a magnesiated graphite intercalation compound is confirmed by ex situ XRD diffraction measurements.

Charge-Induced Defect Formation in LixCoO2 Battery Cathodes: XRD and PA Spectroscopy Study

Lithium-ion batteries have developed into most advanced battery systems, e.g. laptops and mobile phones. LiCoO2 is a typical intercalation battery cathode material. However, reversible charge-discharge cycling of LiCoO2 is only possible down to 50% of the available Li-ions since further removal of Li-ions drastically reduces the capacity and cycle stability. The formation of vacancy-type defects during the charging process in LixCoO2 battery cathodes was investigated by XRD and position life-time spectroscopy and Doppler broadening of positron-electron annihilation (PA) radiation as defect specific techniques [1]. Li+-extraction, which in a battery mode corresponds to charging, was performed at 293 K under electrochemical control in a 3-electrode test-cell with a Maccor Series 4000 battery tester. The composition of the lithium-ion electrode material used was: 88wt.% LiCoO2 particles, 7 wt.% carbon black as conducting agent, 5 wt.% binder material (polyvinylidene difluoride hexafluoropropylene copolymer). Structural analysis of the electrode samples was performed by means of X-Ray diffraction using a Bruker D8 Advance diffractometer in Bragg-Brentano geometry with Cu-K -Theta angle range from 15° to 130° and were analysed by Rietveld refinement with the programs FULLPROF [2] and X’PertHighScorePlus (Panalytical). For positron annihilation measurements a positron source (22NaCl) was sandwiched between two identical LiCoO2 electrode samples. Positron lifetime measurements were performed with a fast-fast spectrometer with a time resolution of 221 ps. The spectra were analysed by using the program pfposfit [3]. Doppler broadening (DB) measurements were performed in a coincidence setup with two high purity Ge detectors.with energy -line in the detector system corresponds to ca. 0.88keV (FWHM). Both the Doppler broadening S parameter as we extraction; the S-extraction causes a decrease of S and ollowed by a re-increase for x<0.55. Conclusions: The regime of reversible charging is dominated by vacancy-type defects on the Li+-sublattice the size of which increases with increasing Li+-extraction. Indication is found that Li+-reordering which occurs at the limit of reversible Li+-extraction (x = 0.55) causes a transition from the two-dimensional agglomerates into onedimensional vacancy chains. Degradation upon further Li+-extraction is accompanied by the formation of vacancy complexes on the Coand anion sublattice.