Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden. IV. Reaktionen 2. Art im System CoO-β-Ga2O3

The solid-state reaction of the second kind in a sandwich type diffusion couple of $\text{Co}{}_{\mathrm{1?z}}\text{Ga}{}_{\mathrm{<mtext>2z</mtext><mtext>3</mtext>}}\text{O}$ and β-Ga₂O₃ has been investigated between 1249 and 1550°C in air. The quantity z, which corresponds to the saturation concentration of β-Ga₂O₃ in CoO, was determined as a function of temperature by X-ray methods and the optical microscope; the homogeneity range of the spinel phase $\text{Co}{}_{\mathrm{1?y}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2y</mtext><mtext>3</mtext>}}\text{O}{}_4$ was investigated also. The growth of the thickness of the reaction layer follows a parabolic rate law; the activation energy is 71.6 kcal/mole. A comparison of reaction rate constants of the first and second kind in connection with experimental results, achieved with a modified marker technique, leads to confirmation of the Wagner mechanism for the formation of CoGa₂O₄ spinel as supposed before by Laqua. Reaction rate constants of the second kind, calculated from interdiffusion profiles in CoO-β-Ga₂O₃ diffusion couples, are in good agreement with experimental values. Presented data are used for estimating interdiffusion coefficients for the CoO-β-Ga₂O₃ system according to theoretical aspects developed by Pelton, Schmalzried, and Greskovich.     

Contributions on the Properties of Titanates with Ilmenite Structure. IV. The effect of an order-disorder transition on the high temperature electrical conductivity of NiTiO3

NiTiO₃ shows an order-disorder transition from an ordered ilmenite structure to a corundum structure at high temperatures. The transition is followed by a strong increase of the specific electrical conductivity. The conductivity was investigated as a function of temperature and oxygen activity. An order parameter according to common phase transition theories can be used to describe the behaviour of the conductivity in the transition region and vice versa. A model for the defect structure of NiTiO₃ is presented.     

Lineare Silizium-Photodioden-Matrizen mit parallelem Datenausgang als Strahlungsempfänger in der optischen Emissionsspektroskopie—II. Analytische anwendung in verbindung mit der glimmentladungslampe nach Grimm

A silicon photodiode array was placed in the focal plane of a spectrometer to detect the radiation. Three single diodes of the array, each 6.5 mm long and 19 μm wide, were connected to the three channels as described in Part I.The properties of the photodiodes were investigated with respect to their applicability in spectral analysis. Especially the spectral response, the dynamic range and the signal-to-noise ratio were of great interest. The quantum efficiency was found to be in the range from 300 to 800nm. The dynamic range, defined as the range from the noise level to the maximum permissible signal voltage extends over 5.5 decades and is a linear function of the radiative flux. The signal-to-noise ratio of systems using photodiodes depends on the wavelength of the radiation and, if high feedback resistors (≧10¹¹Ω) are used, reaches the same order of signal-to-noise ratio as that obtained by using a photomultiplier (EMI 9789 QB). To demonstrate the applicability of the photodiodes, the analysis of limestone was studied. The sample powder was mixed with copper powder, pressed into pellets, and the major constituents Al, C, Mg and Si were determined by means of a Grimm glow discharge lamp. The calibration curves obtained as well as the detection limits are reported.Furthermore, oxygen was determined in a series of synthetic samples using the line 777.2 nm.     

The application of an argon/nitrogen inductively-coupled plasma to the analysis of organic solutions

A 4-kW argon/nitrogen inductively-coupled plasma (ICP) is used for multielement trace determinations in organic solutions. After optimization of the pneumatic nebulizer and ICP parameters, trace determinations at sub-mug/ml concentrations with relative standard deviations of 1% are possible. The first application described is the determination of a series of metals (Cd, Cu, Fe, Mn, Zn) after their isolation from the sample matrix by extraction of the ammonium pyrrolidinedithiocarbamate complexes into methyl isobutyl ketone. Alkali and alkaline-earth metal salts at 50-g/l. concentrations do not affect the method, which can be applied to trace determinations in industrial waste waters having high salt contents. The second application is the multielement analysis of oils. The samples are diluted 1:10 with xylene, and the detection limits for Al, Cu, Fe, Mg, Mn, Si and Zn are in the sub-mu/g range. The superior detection power of spectrographic ICP methods in comparison with photoelectric techniques using a monochromator and a polychromator is discussed. Oils of different viscosities can be analysed with use of the same calibration graphs. From experiments with a computer-controlled polychromator with background measurement facilities, it is concluded that the accuracy is improved if background measurements are made at wavelengths near the analytical lines, for each sample independently.     

Electron-Bernstein-wave current drive in an overdense plasma at the Wendelstein 7-AS stellarator

Electron-Bernstein-wave (EBW) current drive in an overdense plasma was demonstrated at the Wendelstein 7-AS stellarator for the first time. The EBWs were generated by O-X-B mode conversion. The relatively high current drive efficiency was consistent with theoretical predictions. The experiments provided first investigations of EBW phase space interaction for wave refractive indices much larger than unity.     

Beiträge zu den Eigenschaften von Titanaten mit Ilmenitstruktur. II. Zur Thermodynamik und elektrischen Leitfähigkeit von NiTiO3 und anderen oxidischen Phasen mit Ilmenitstruktur

Contributions to the Properties of Titanates with Ilmenite Structure. II. Study on the Thermodynamics and the Electrical Conductivity of NiTiO₃ and Other Phases with Ilmenite Structure NiTiO₃ shows a phase transition at high temperatures (T_c = 1290°C). The standard enthalpy and entrop of the reaction NiO + TiO₂ = NiTiO₃ was estimated for temperatures above and below the transition temperature using emf-measurements based on the following solid state galvanic cell: Ni,TiO₂, NiTiO₃|ZrO₂(+CaO)|Ni,NiO. The transition enthalpy was found to be 18 ± 2 kJmol^?1, The transition entropy is 12 ± 1 JK^?1mol^?1. This is in good agreement with the calculated entropy change for an order-disorder transition (11.5 JK^?1mol^?1). The influence of other cations like Mg²⁺ and Co²⁺ on the transition temperature was investigated by measurements of the electrical conductivity as a function of composition. Ni_1?xMg_xTiO₃ shows a strong shift of the transition to higher temperatures if a small part of the Ni²⁺ was replaced by Mg²⁺. A linear correlation between the temperature shift and the amount of Co²⁺ was found for Ni_1?xCo_xTiO₃. Thermoanalytical investigations reveal an endothermic peak during the heating period some degrees below the melting point of CoTiO₃. The substitution of Ge⁴⁺ for Ti⁴⁺ is without any influence on the transition temperature. By doping the NiTiO₃ with Ga₂O₃, the anomalous increase of the electrical conductivity with temperature is shifted to lower temperatures.     

A microcomputer-controlled dual-channel monochromator for plasma atomic emission spectrometry with time-constant and transient signals

Concept and operation of a microcomputer-controlled dual-channel monochromator system are described. A 0.9-m Czerny-Turner monochromator is equipped with two stepping motors: one for wavelength adjustment by rotating the grating, the other for driving a quartz refractor plate as a means for flexible background measurement. Instrument control as well as data acquisition and processing are performed by a 16 bit Intel 8088 based microcomputer system. The whole system is operated via a console keyboard with a simple dialogue. Main topics of the software are: setting operational parameters; automatic wavelength access using a peak searching routine with a screening window down to 0.05 nm; simple line intensity measurement; line and background measurement alternatively in one channel and simultaneously in two channels with a wavelength distance up to ± 0.05 nm using the quartz refractor plate, and stepwise intensity measurement (“profiling”) with an increment down to 0.0007 nm. Intensity values are acquired with a 12 bit resolution. Results are printed on a console typewriter. The performance of the instrument is demonstrated by applications in inductively coupled plasma atomic emission spectroscopy (ICP-AES) with steady and transient signals.