Keramische und elektrolytische Eigenschaften von Zirkonsilicat ZrSiO4 bei Temperaturen um 1600 °C

Überprüfung von Zirkonsilicat ZrSiO₄ im Hinblick auf seine Eignung als Festelektrolyt zur Messung der Sauerstoffaktivität in Metallschmelzen. Angaben über Zustandsbereich sowie Kristallstruktur, thermische Ausdehnung, Wärmeleitfähigkeit und mechanische Eigenschaften. Untersuchung des Sinterverhaltens, der Gefügeausbildung und der Temperaturwechselbeständigkeit. Messungen der elektrischen Leitfähigkeit von ZrSiO₄ sowie der EMK an Sauerstoffkonzentrationszellen mit ZrSiO₄ als Festelektrolyt in Eisenschmelzen. Nachweis einer überwiegenden lonenleitung bei 1600 °C.     

Desoxidationsgleichgewichte von Titan,Aluminium und Zirconium in Eisenschmelzen bei 1600 °C

Verwendung einer Doppelelektrolytzelle aus ZrO₂(CaO) mit ThO₂(Y₂O₃)-Beschichtung zur Untersuchung der Desoxidationsgleichgewichte Fe–O–Ti, Fe–O–Al und Fe–O–Zr bei 1600 °C über EMK-Messung sowie Probenahme und chemische Analyse. Ermittlung der Sauerstoffaktivitäten in Abhängigkeit vom Gehalt an Titan, Aluminium oder Zirconium in der Eisenschmelze sowie der Gleichgewichtskonstanten und Wirkungsparameter e^x_x. Vergleich der analytisch bestimmten und thermodynamisch berechneten Sauerstoffgehalte.     

Dual Stochastic Dominance and Quantile Risk Measures

Following the seminal work by Markowitz, the portfolio selection problem is usually modeled as a bicriteria optimization problem where a reasonable trade–off between expected rate of return and risk is sought. In the classical Markowitz model, the risk is measured with variance. Several other risk measures have been later considered thus creating the entire family of mean–risk (Markowitz type) models. In this paper, we analyze mean–risk models using quantiles and tail characteristics of the distribution. Value at risk (VAR), defined as the maximum loss at a specified confidence level, is a widely used quantile risk measure. The corresponding second order quantile measure, called the worst conditional expectation or Tail VAR, represents the mean shortfall at a specified confidence level. It has more attractive theoretical properties and it leads to LP solvable portfolio optimization models in the case of discrete random variables, i.e., in the case of returns defined by their realizations under the specified scenarios. We show that the mean–risk models using the worst conditional expectation or some of its extensions are in harmony with the stochastic dominance order. For this purpose, we exploit duality relations of convex analysis to develop the quantile model of stochastic dominance for general distributions.     

Thermomagnetic residual offset in integrated Hall plates

Integrated Hall plates show self-induced offset due to the current flow in their current leads. The magnetic field surrounding these current leads generates a magnetic offset signal, while their resistive heating causes thermoelectric offset voltages. This paper reports experimental results on these two effects. They are obtained using a novel test structure enabling to separate the two contributions. In addition, the experimental results concerning the thermal behavior of the test structure are compared with finite element (FE) simulations.     

Development of electrochemical silicon sensors for iron and steel melts

Based on the commonly used oxygen sensors with O^2- ion-conducting ZrO₂ electrolytes and solid metal-metal oxide references, new sensors have been developed for direct measurements of Si content in iron and steel melts. The sensors are designed in such a way that local chemical equilibrium of the reaction ZrO₂ + [Si] + 2[O] = ZrSiO₄ is established at the surface of the ZrO₂ electrolyte tube or inside a cavity adjacent to the ZrO₂ electrolyte sensor tip using a saturating ZrO₂-ZrSiO₄ mixture. Concepts and dimensions of the sensors were optimized in view of a fast EMF response upon immersion and the maintenance of a stable EMF recording over extended periods. Reliable measurements were performed in Fe-Si melts at 0.05 to 5 wt.-% Si.     

Vergleich experimenteller Ergebnisse und theoretischer Ansätze zur Verdampfung von Begleitelementen aus Stahlschmelzen

Auswertung von Schmelzversuchen im Vakuuminduktionsofen zur Verdampfung der Begleitelemente Kupfer, Mangan und Chrom aus Schmelzen des Stahles X 5 CrNi 18 9 bei Temperaturen von 1550 bis 1650 °C, Drücken von 10^?4 bis 50 Torr und Schmelzgewichten von 5 und 25 kg. Beschreibung des Verdampfungsvorganges anhand eines Teilschrittmodells, das Ansätze für die Diffusion durch die Grenzschicht in der Schmelze an die freie Oberfläche, die Verdampfung an der freien Oberfläche und die Diffusion durch die Gasgrenzschicht über der Schmelze vorsieht.     

Influence of aluminum and chromium on the activity of oxygen in nickel based melts at 1600?C

The activity of oxygen in technically important nickel melts containing 15 wt pct cobalt and 5 wt pct molybdenum has been determined at 1600‡C for various concentrations of chromium ranging from 0 to 30 wt pct and aluminum varying from 0 to 15 wt pct. The activity of oxygen was measured by an electrochemical technique using yttria-doped thoria electrolyte cells. The results obtained are analyzed in terms of activity coefficients of oxygen as a function of aluminum and chromium contents in the melts. Clear positive deviations of the experimentally determined from the calculated activity coefficients of oxygen were found when aluminum was added to Ni-Co-Mo melts with or without chromium. From the results obtained in the range between 1 and 10 wt pct aluminum, the following equilibrium constants for the reaction 2 [Al] + 3 [O] ⇋ Al₂O₃ in the nickel based melts at 1600‡C were calculated: loga ₀ =-2/3 log [pct Al] - 3.94 for 0 pct Cr loga ₀ = -2/3 log [pct Al] - 4.21 for 10 pct Cr loga ₀ = -2/3 log [pct Al] - 4.81 for 20 pct Cr loga ₀ = -2/3 log [pct Al] - 5.06 for 30 pct Cr.     

Hierarchies in nucleation transitions

We discuss the hierarchy of subphase transitions in first-order-like nucleation processes for an exemplified aggregation transition of heteropolymers. We perform an analysis of the microcanonical entropy, i.e., the density of states is considered as the central statistical system quantity since it connects system-specific entropic and energetic information in a natural and unique way.     

Physikalisch-chemische Eigenschaften oxidkeramischer Festelektrolyte bei Stahlschmelztemperaturen

Übersichtsbericht zur Beurteilung der Eignung von feuerfesten Oxiden, Mischoxiden und Oxidverbindungen als Festelektrolyte zur Sauerstoffmessung in Stahlschmelzen. Zusammenstellung und kritische Bewertung der physikalisch-chemischen Eigenschaften der in Frage kommenden oxidkeramischen Festelektrolyte.