Synthesis of several intercalating spinel cathode materials for secondary lithium cells by a simple low temperature procedure

Although several methods are available to prepare spinel cathode materials, a simple thermal method of low temperature inorganic procedure has been developed to synthesize these compounds of high purity, small particle size and good reversible behaviour on cycling. By this procedure, lithium based oxides, phosphates and boride materials were developed and these compounds can be used as secondary cathode electrodes for lithium cells. The procedure is very simple and novel. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Hindered motions in a ketonea-urea inclusion compound. An ESR and ENDOR study

We have studied by ESR and ENDOR spectroscopy the free radicals produced in γ-irradiated inclusion compound formed between the ketone 10-nonadecanone and urea. Only one type of long lived radical is formed by the removal of an α-proton from the ketone. The hyperfine (hf) coupling constants of the α- and β-protons of the radicals have been measured by ESR at different temperatures in the range 110–292 K and at different orientations of the crystals. The hf coupling of the γ-protons of the radical and of the urea protons have been studied by ENDOR. The temperature and angular dependences of the coupling constants have been analyzed in terms of the internal and overall motions of the radical inside the hexagonal channels formed by the urea molecules. It has been found that the radical cannot perform complete reorientations around the long molecular axis, but it undergoes restricted rotational diffusion. This process is explained by assuming a coupling between the rotational and translational degrees of freedom of the radical inside the urea channels.     

R.F. (280 MHz) EPR imaging of extended samples: Apparatus and preliminary results

This paper presents the preliminary results obtained using an Electron Paramagnetic Resonance imaging apparatus operating at 280 MHz. The acquisition technique and the procedure used to obtain the spin density spatial localization are presented and specimen images of extended samples are given. The accuracy of the images and the spatial resolution are also discussed.     

Spin-trapped hydroxyl free radicals studied at low field by Field-Cycled Dynamic Nuclear Polarization

The technique of Field-Cycled Dynamic Nuclear Polarization (FC-DNP) involves the EPR irradiation of a free radical solution and the subsequent observation of the NMR signal, the experiment being carried out at a range of magnetic field strengths in order to measure the free radical’s EPR spectrum. In this work FC-DNP has been used to study the EPR spectrum of DMPO spin-trapped hydroxyl free radicals at magnetic field strengths between 0.5 mT and 13.0 mT (5–130 Gauss). The low-field EPR spectrum contains six separate EPR lines, in contrast to the well-known X-band spectrum where only four are seen. Knowledge of the spin-adduct’s EPR spectrum will be of use to workers involved in low-field EPR, especially those conducting biological or in-vivo spin-trapping experiments.     

Summing the derivative expansion of the effective action

The derivative expansion of the effective action is a perturbative development in derivatives of the fields. The expansion breaks down when some of the derivatives are too large. We show how to sum exactly the first and second derivatives and treat perturbatively derivatives higher than second.     

Synthesis and conductivities of the apatite-type systems, La9.33+xSi6−yMyO26+z (M=Co, Fe, Mn) and La8Mn2Si6O26

Apatite-type oxides of formula (La/Sr)_10−xSi₆O_26+y have been attracting significant interest recently, because of their high oxide ion conductivity. In this paper we report the synthesis and conductivities of phases based on doping La_9.33Si₆O₂₆ with Co, Fe, Mn on the Si site, according to the formula La_9.33+x/3Si_6−xM_xO₂₆ (M=Co, Fe, Mn). Substitution limits observed were x≤1.5 (Co), x≤1.25 (Fe), x≤0.5 (Mn). Higher Mn levels could be achieved by substituting onto the La site, with it being possible to prepare the phase La₈Mn₂Si₆O₂₆. The highest conductivities were observed for the Co doped samples, although investigations into the dependence of conductivity on p(O₂) (0.2–10⁻⁵ atm.) indicated that the conductivity was dominated by the electronic component in these cases. In contrast, the conductivities for the Fe and Mn doped samples were mainly ionic in the same p(O₂) range. Experiments into varying the oxygen content of these doped phases indicated that increasing the oxygen content above the nominally stoichiometric O₂₆ appears to increase the oxide ion conductivity. Preliminary studies of the reactivity of the electrolyte La_9.33Si₆O₂₆ with potential SOFC cathode materials (La_1−xSr_xMO₃; M=Co, Fe, Mn) suggests that reaction can occur at high temperatures leading to the incorporation of the transition metal into the apatite electrolyte. However, the fact that these doped phases exhibit high conductivities suggests that this may limit any problems caused by such a reaction at the electrolyte-electrode interface. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Gasdynamische Untersuchung des Jouleschen Überströmversuches

Zusammenfassung Es wird die zeitabhängige Strömung beim Ausgleichsvorgang zwischen zwei endlichen Behältern untersucht. Den Überlegungen wird eine eindimensionale, reibungsfreie und quasistationäre Strömung zugrunde gelegt. Während bei überkritischer Strömung eine analytische Lösung möglich ist, wird das Problem bei unterkritischer Strömung numerisch gelöst.Dem Druckausgleich zwischen den beiden Behältern folgt ein isobarer Wärme- und Massenaustausch, bis sich das thermodynamische Gleichgewicht eingestellt hat.

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Gasdynamical investigation of Joule's overflow experiment

The time-dependent flow of an exchange process between two big insulated tanks is considered. The problem is treated on the basis of a one-dimensional, inviscid and quasi-steady flow. An analytical solution is obtained for supercritical flow, while for subcritical flow the problem is solved numerically.After the pressure-equilibrium between the two-tanks an isobar heat and mass exchange follows, until the thermodynamic equilibrium is reached.

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Formelzeichen a Schallgechwindigkeit - A engster Querschnitt - c Geschwindigkeit - c _p spezifische Wärme bei konstantem Druck - c _v spezifische Wärme bei konstantem Volumen - e innere Energie - i Enthalpie - m Masse - M Machzahl - p Druck - spezielle Gaskonstante - s Stromlinie, spezifische Entropie - t dimensionsbehaftete Zeit - T Temperatur - V Volumen - Konstante - Abkürzung - Volumenverhältnis - Verhältnis der spezifischen Wärmen - Dichte - dimensionslose Zeit Indizes 0 Zustand zur Zeitt=0 - 1 Zustand im Überdruckbehälter - 2 Zustand im Überströmbehälter - * Zustand im engsten Querschnitt - K kritisch - M Zustand bei Druckausgleich - E Endzustand bei Temperaturausgleich Herrn Prof. Dr. B. Schmidt in Dankbarkeit zum 60. Geburtstag gewidmet