Microblogging

Twitter & Co. sind ein aktuelles Trendthema im Web. Dieser Beitrag stellt das Ph?nomen Microblogging vor, beschreibt, warum das Thema ein gro?es Entwicklungspotenzial aufweist und nennt zukünftige Forschungsaufgaben.     

Optimised selection of new protective coatings for biofuel boiler applications

Using biofuels in power and CHP boilers can pose a challenge for materials performance. Formation of deposits containing e.g. potassium, sulphur, calcium, sodium, and chlorine can result in severe corrosion of conventional steels and alloys at relatively modest temperatures. Given suitable component design and fabrication facilities, coatings may be considered to protect the fireside surfaces. This paper aims to present a systematic approach to the design and selection criteria for protective coatings of boilers. The approach includes modelling of the process and surface conditions, optimisation of the coating process and structure, and performance validation in the laboratory and plant scales. The applied examples have included iron and nickel based HVOF and arc sprayed coatings subjected to verification field testing in boiler testing under aggressive biofuel conditions. The coatings have shown good corrosion resistance in both laboratory tests and long‐term harsh field tests. The paper discusses the used approach for finding a suitable and cost effective coating for biofuel boiler applications. The paper gives test results from microstructural, corrosion resistance and field testing experience for the selected coatings.     

Oxidation behaviour of a Mo(Si,Al)2 based composite at 1500 °C

The oxidation of a Mo(Si,Al)₂ composite is investigated at 1500 °C in dry air using exposure times from 1 to 1000 h. Cross sections are examined with Scanning Electron Microscopy (SEM) and the phase composition is analyzed by X-ray diffraction (XRD). The material forms a continuous and protective alumina layer, the growth of the alumina layer following parabolic kinetics. Immediately below the scale Mo(Si,Al)₂ is replaced by a Mo₅(Si,Al)₃ layer due to the flux of aluminum to the scale. The Al concentration in the Mo(Si,Al)₂ phase in the underlying substrate decreases from 27% before exposure to 16–17% after 1000 h. The continuous alumina layer becomes covered by a top layer consisting of alumina grains embedded in a viscous melt with approximate composition 7 Na₂O–15 Al₂O₃–78 SiO₂. With time, sodium is volatilized from the melt and the top scale layer transforms to a mixture of alumina, mullite and silica melt.     

Kommentar I zum Fall “Aus dem Hospiz in die Schweiz?”

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Timber-framed partition walls and their restraining effect on warp in built-in wall studs – Models for twist

The shape of timber changes due to variations in moisture content (MC). Analytical models, which explain how the cladding restrains the timber studs that are prone to twist, are presented. The models are used for parametric studies of various properties, such as longitudinal shrinkage, torsional modulus of elasticity and cross-sectional size of the timber stud and stiffness of the cladding. With respect to twist, the bending stiffness of the cladding is of great importance. Large bending stiffness increases the restraint in the twist-prone studs and results in a straighter wall. Low torsional stiffness in the studs makes it easier for the cladding to restrain twist.     

On path-independent integrals within the linear theory of elasticity

Conservation laws and associated path-independent integrals play a dominant role in field theories ranging from theoretical physics to applied engineering. Especially, material conservation laws are widely used to assess structural components with flaws like defects or cracks. Within the linear theory of elasticity, a complete set of conservation laws are derived by employing the so-called Neutral-Action method. An illustrative application is discussed.     

Properties of pumice aggregate concretes at elevated temperatures and comparison with ANN models

The mechanical properties and thermal conductivity of concretes including pumice aggregate (PA) exposed to elevated temperature were analyzed by thermal conductivity, compressive strength, flexure strength, dynamic elasticity modulus (DEM) and dry unit weight tests. PA concrete specimens were cast by replacing a varying part of the normal aggregate (0–2 mm) with the PA. All concrete samples were prepared and cured at 23 ± 10C lime saturated water for 28 days. Compressive strength of concretes including PA decreased that reductions were 14, 19, 25 and 34% for 25, 50, 75 and 100% PA, respectively. The maximum thermal conductivity of 1.9382 W/mK was observed with the control samples containing normal aggregate. The tests were carried out by subjecting the samples to a temperature of 0, 100, 200, 300, 400 500, 600 and 700 °C for 3 h, then cooling by air cooling or in water method. The results indicated that all concretes exposed to a temperature of 500 and 700 °C occurred a significant decrease in thermal conductivity, compressive strength, flexure strength and DEM. An artificial neural network (ANN) approach was used to model the thermal and mechanical properties of PA concretes. The predicted values of the ANN were in accordance with the experimental data. The results indicate that the model can predict the concrete properties after elevated temperatures with adequate accuracy. Copyright © 2016 John Wiley & Sons, Ltd.