Development of high strength ferritic steel for interconnect application in SOFCs

High-Cr ferritic model steels containing various additions of the refractory elements Nb and/or W were studied with respect to oxidation behaviour (hot) tensile properties, creep behaviour and high-temperature electrical conductivity of the surface oxide scales. Whereas W additions of around 2 wt.% had hardly any effect on the oxidation rates at 800 and 900 °C, Nb additions of 1% led to a substantially enhanced growth rate of the protective surface oxide scale. It was found that this adverse effect can be alleviated by suitable Si additions. This is related to the incorporation of Si and Nb into Laves phase precipitates which also contribute to increased creep and hot tensile strength. The dispersion of Laves phase precipitates was greatly refined by combined additions of Nb and W. The high-temperature electrical conductivity of the surface oxide scales was similar to that of the Nb/W-free alloys. Thus the combined additions of Nb, W and Si resulted in an alloy with oxidation resistance, ASR contribution and thermal expansion comparable to the commercial alloy Crofer 22 APU, but with creep strength far greater than that of Crofer 22 APU.     

The Energy Concept Adviser—A tool to improve energy efficiency in educational buildings

Educational buildings such as kindergartens, schools and universities display many similar design, operation and maintenance features in most countries. The two most noteworthy similarities amongst these building types are the high energy consumption and the necessity for retrofitting many buildings within this sector. However, studies have shown that during retrofit, energy saving measures are only rarely applied, because the decision-makers lack knowledge of investments and the efficiency of potential energy saving measures. The main goal of the International Energy Agency ECBCS Annex 36 is to provide the educational building decision-makers with sufficient data, information and tools to improve their learning and teaching environments by improving the energy efficiency of their buildings.     

Ion track-based electronic elements

In the past years, fundaments were set for a new type of electronics which is based on tracks in insulators formed by individual or multiple swift heavy ions. Due to the possibility of inserting any (semi)conducting material into these tracks, various active and passive electronic devices can be created. Among them are also transistor-like and Esaki diode-like elements. As many of these structures have sensing properties and the capability to undergo logic decisions, autonomous intelligent sensors appear to be a favourite field for future application. The use of liquid conductors may even expand the range of applicability towards medical implants.     

Rotor position and velocity estimation for a salient-pole permanentmagnet synchronous machine at standstill and high speeds

This paper addresses self-sensing (“sensorless”) control of salient-pole permanent magnet synchronous motors (PMSMs). The major contribution of this work is the introduction of a simple-to-implement estimation technique that operates over a wide speed range, including zero speed. The technique achieves simplicity by decoupling the inherent cross-coupling in PMSMs. The technique utilizes the dependence of inductance on rotor position in interior permanent magnet machines to produce position and velocity estimates both for field orientation and for all motion control of the drives. The technique functions in a manner similar to a resolver and resolver-to-digital converter (RTDC) sensing system, whereby in the proposed technique the motor acts as the electromagnetic resolver and the power converter applies carrier-frequency voltages to the stator which produce high-frequency currents that vary with position. The sensed currents are then processed with a heterodyning technique that produces a signal that is approximately proportional to the difference between the actual rotor position and an estimated rotor position. This position error signal and a torque estimate are then used as inputs to a Luenberger style observer to produce parameter insensitive, zero lag, position and velocity estimates     

Properties of CsI(TI) — Renaissance of an old scintillation material

CsI(TI) is an interesting material for calorimeters in high energy physics. Properties of this material are reported.     

Electrochemical impedance spectroscopy on porous electrodes

Electrochemical d.c. and a.c. measurements have been carried out on porous Raney nickel in H₂-saturated 0.1 M, 1 M, and 6 M NaOH solutions atT=303 K and 333 K using rotating-disc and static-plaar electrodes. For comparison, measurements were also performed on graphite-cloth and graphite-felt electrodes. From polarization curves and current transients obtained in the potential range of the hydrogen evolution and hydrogen oxidation reactions the dependence of the electrocatalytic activity of Raney nickel on the prepolarization conditions was studied. Impedance spectra in the frequency range 1 mHzf 10 kHz were used to determine the characteristic pore parameters and to identify the kinetic behaviour of the porous electrodes by application of transfer function analysis using non-linear fit routines.     

Oxidation limited life times of chromia forming ferritic steels

Long term, cyclic oxidation studies of three high – Cr, ferritic steels were carried out at 800°C and 900°C in air. It was found that with decreasing sample thickness the life time of the mentioned alloys decreases due to breakaway phenomena. This effect is caused by faster exhaustion of the chromium reservoir from the bulk alloy in case of thinner components. The observed life time limits can be predicted with reasonable accuracy by a theoretical model, using oxide growth rate parameters, initial alloy Cr content and critical Cr content required for protective chromia scale formation. In the calculation it has, however, to be taken into account that the oxidation rates of the steels increase with decreasing specimen thickness.     

Simple N‐Heterocyclic Carbenes as Ligands in Ullmann‐Type Ether and Thioether Formations

A simple N‐heterocyclic carbene (NHC) derived from 1‐methyl‐3‐ethylimidazolium tetrafluoroborate was found to be an efficient ligand for a range of copper‐catalyzed cross‐coupling reactions, leading to the formation of aromatic ethers and thioethers.

     

Nonlinear model predictive control for dividing wall columns

Dividing wall columns (DWCs) are practical, effective, and promising among distillation process intensification technologies. Nonlinear model predictive control (NMPC) schemes are developed in this study to control the three-product DWCs. As these systems are intensely interactive and highly nonlinear, NMPC may be more suitable than the traditional PI control. The model is established based on Python and Pyomo platforms. As the original mathematical model of the column section is ill-posed, index reduction is used to avoid a high-index differential-algebraic equation (DAE) system. The well-posed index-1 system after index reduction is employed for the steady-state simulation and dynamic control in this study. Case studies with three DWC configurations to separate the mixture of ethanol (A), n-propanol (B), and n-butanol (C) show that the NMPC performs very well with small maximum deviations and short settling times. This demonstrates that the NMPC is a feasible and very effective scheme to control three-product DWCs.