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Zusammenfassung Die kontinuierliche Weiterentwicklung induktiver Näherungsschalter erweitert zunehmend deren Anwendungsbereiche. Gleichzeitig erlauben der stetige Fortschritt der Mikroelektronik und die höhere Integration von Rechen- und Speicherelementen in Mikrokontrollern komplexere Datenverarbeitung in kompakten Sensorsystemen. In diesem Beitrag wird ein neues Messverfahren vorgeschlagen, das zusätzlich zur eigentlichen Funktion der Präsenzerkennung bzw. Abstandsmessung die Unterscheidung verschiedener Target-Materialien ermöglicht. Das Prinzip dieses Verfahrens wird zunächst vorgestellt und mithilfe eines automatisierten Messaufbaus demonstriert. Im Anschluss werden der Einfluss des Materials, der Einbauumgebung und unterschiedlicher Targets dargestellt und diskutiert. Hierfür werden verschieden geformte Targets und verschiedene Targetgrößen der bereits vorgestellten Materialien eingesetzt. Es werden Potentiale dieses Verfahrens in Bezug auf die Unterscheidbarkeit der Targetmaterialien, der Einbauumgebung und Targetform diskutiert und die weitere Übertragbarkeit des Verfahrens bewertet. Abschließend wird die industrielle Verwertbarkeit beurteilt.

In hot forming and machining process chains heat treatment of steels is controlled by temperature and time. The process parameters significantly influence the material microstructure, which is important for the final component properties. The dependence between the predominant microstructure and the magnetic properties can be determined by means of Magnetic Induction Spectroscopy (MIS). In this paper, we propose to use the induction coil as an in-process sensor element to implement MIS in induction heating processes with subsequent cooling of steel sheets. This novel approach enables contactless, continuous in-process measurement of complex inductance and allows a non-destructive determination of steel microstructure. The novel measurement method can differentiate discrete microstructural states and determine phase transformation points during continuous heating and cooling, by analysing the inductance curve. The realized combination of sensor and actuator features enables both process monitoring and closed-loop control of production processes with integrated heat treatment.

BaTiO 3 is one of the well-known ferroelectric and piezoelectric materials, which has been widely used in various devices. However, the microscopic mechanism of the ferroelectric domain growth is not understood well. We investigated the effects of point defects, mono- and di-vacancies of Ba, Ti, and O, on the domain growth of BaTiO 3 using molecular dynamics simulation with the core-shell inter-atomic potential. We found the following: s (1) One kind of monovacancy, V O1 , located on the TiO plane perpendicular to the applied electric field direction, acts to hinder the polarization inversion induced by the applied electric field. The monopole electric field produced by V O1 either hinders or assists the local polarization inversion in accordance with the local intensity of the total electric field. (2) The 1st-neighbor divacancies V Ba -V O and V Ti -V O as compared to the 2nd-neighbor divacancies asymmetrically affect the domain growth with respect to the applied electric field, making the hysteresis behavior of applied electric field vs. polarization relation. The domain grows even at a small electric field when the directions of the applied electric field and the divacancy dipole are mutually the same. (3) The domain growth speed towards the applied electric field direction is about 2 orders of magnitude higher than that towards the perpendicular direction.

Modern production equipment is based on the results of quality control as well as process parameters. The magnetic anisotropy of materials is closely connected to internal mechanical stress by the Villari effect, and also to hardening effects due to plastic deformations, and could therefore provide an interesting basis for process control. Nevertheless, the analysis of anisotropic properties is extremely sensitive to sensor and workpiece misalignments, such as tilting. In this work, a novel eddy current sensor system is introduced, performing a non-contact measurement of the magnetic anisotropy of a workpiece and realizing a separation and correction of tilting effects. The measurement principle is demonstrated with the example of two samples with different magnetic anisotropy values induced by cold forming. Both samples are analyzed under different tilt angles between the sensor axis and the surface of the workpiece. In this work, digital signal processing is demonstrated on the acquired raw data in order to differentiate the effects of tilt and of anisotropy, with the use of preliminary results as an example of two prepared samples.

This paper presents the design, fabrication and performance of origami-based folding microactuators based on a cold-rolled NiTi foil of 20 µm thickness showing the one-way shape memory effect. Origami refers to a variety of techniques of transforming planar sheets into three-dimensional (3D) structures by folding, which has been introduced in science and engineering for, e.g., assembly and robotics. Here, NiTi microactuators are interconnected to rigid sections (tiles) forming an initial planar system that self-folds into a set of predetermined 3D shapes upon heating. While this concept has been demonstrated at the macro scale, we intend to transfer this concept into microtechnology by combining state-of-the art methods of micromachining. NiTi foils are micromachined by laser cutting or photolithography to achieve double-beam structures allowing for direct Joule heating with an electrical current. A thermo-mechanical treatment is used for shape setting of as-received specimens to reach a maximum folding angle of 180°. The bending moments, bending radii and load-dependent folding angles upon Joule heating are evaluated. The shape setting process is particularly effective for small bending radii, which, however generates residual plastic strain. After shape setting, unloaded beam structures show recoverable bending deflection between 0° and 140° for a maximum heating power of 900 mW. By introducing additional loads to account for the effect of the tiles, the smooth folding characteristic evolves into a sharp transition, whereby full deflection up to 180° is reached. The achieved results are an important step towards the development of cooperative multistable microactuator systems for 3D self-assembly.

In this paper, a portable and low-cost potentiostat based on an ARM Cortex M4 microcontroller is developed. The expansion of impedance analyzer functionality in terms of frequency range was explored. A potentiostat was developed using only a single microcontroller STM32F303 to generate a signal fed to the DUT using the two onboard digital-to-analog converters (DACs) and the output was measured using the onboard analog-to-digital converter (ADC). The prototype realizes a frequency range from 0.1 Hz up to 100 kHz with an excitation signal from -165 mV to 165 mV and a DC offset from -1.65 V to 1.65 V. The system consists of a potentiostat circuit, a current-to-voltage converter and ADC drivers. In addition, the software configuration utilizes a timer and Direct Memory Access (DMA) to run and deliver correct and precise values of the signals. The circuit was tested with dummy cells of different ranges as well as with electrochemical cells to measure the electrochemical impedance. The results were compared with standard lab instruments and deviations have been calculated and found to be acceptable in certain measurements. The circuit can serve in applications of a point of care in health monitoring, food quality, or other electrochemical applications.

This paper presents a simulation model for the coupled dynamic properties of thermomagnetic generators based on magnetic shape memory alloy (MSMA) films. MSMA thermomagnetic generators exploit the large abrupt temperature-induced change of magnetization at the first- or second-order magnetic transition as well as the short heat transfer times due to the large surface-to-volume ratio of films. These properties allow for resonant self-actuation of freely movable MSMA cantilever devices showing thermomagnetic duty cycles in the order of 10 ms duration, which matches with the period of oscillatory motion. We present a numerical analysis of the energy conversion processes to understand the effect of design parameters on efficiency and power output. A lumped element model is chosen to describe the time dependence of MSMA cantilever deflection and of temperature profiles as well as the magnitude and phase dependency of magnetization change. The simulation model quantitatively describes experimentally observed oscillatory motion and resulting power output in the order of 100 mW cm−3. Furthermore, it predicts a power output of 490 mW cm−3 for advanced film materials with temperature-dependent change of magnetization ∆M/∆T of 4 A m2 (kg K)−1, which challenges state-of-the-art thermoelectric devices.

The aim of this paper is to analyze the relation between magnetic and mechanical properties during and after forming processes. For this purpose, several tensile tests were carried out on sheet metal samples up to a defined plastic strain. The specimens were left in the clamping device in order to relieve the force in several steps until the specimen was completely relieved. As a consequence, the gradual relief leads to a reduction of internal stress states. During the forming process, the initial magnetic relative permeability and magnetic anisotropy of the sample were measured several times. Both properties are related to the mechanical states in the material through the effects of magnetic embrittlement and magneto-elasticity. The plastic strain of the specimens was determined by optical measurements and the stresses in the measurement range during the tensile test was determined with the help of a subsequent numerical simulation. This made it possible for the first time to measure the magnetic properties of samples with different plastic strain and different stress states. The evaluation shows that there is a strong correlation between permeability and plastic strain as well as anisotropy and stress. Based on these findings, it has been confirmed, that the determination of the plastic strain by a soft sensor is possible.

A model for the evolution of the mechanical and thermal properties of shape memory alloy (SMA) films during elastocaloric cycling is developed and compared with experiments. The focus is on Ti-Ni-Cu-Co films of 20 μm thickness showing ultra-low fatigue properties. The films undergo a highly localized pseudoelastic transformation under tensile load cycling featuring strain and temperature band patterns that depend on the loading conditions. The corresponding temperature change is of special interest for film-based elastocaloric cooling applications. Starting from a thermodynamics-based Gibbs free energy model comprising mechanical and chemical contributions, we include a martensite-austenite interface free energy term, for which formulations from a phase-field model are adapted. A 3D continuum mechanics description is modified to treat plane stress conditions appropriate for polycrystalline thin films. The nucleation mechanism of strain bands under dynamic loading is described by introducing a spatial random distribution of the transformation stress barriers reflecting the degree of material inhomogeneity. Heat transfer due to conduction and convection is taken into account. The simulations predict the correlated mechanical and thermal local response of the films including band formation and evolution, tilt angle as well as strain-rate dependence. Macroscopic stress-strain characteristics and thermal evolution curves well represent the experimental results.

Mineral precipitations are a common feature and limitation of initially open, permeable rock fractures by forming sealing structures or secondary roughness in open voids. Hence, the objective of this numerical study is the evaluation of hydraulic properties of fractures sealed by hydrothermally induced needle and compact quartz growth. Phase-field models of progressive syntaxial and idiomorphic quartz growth are implemented into a fluid flow simulation solving the Navier–Stokes equation. Flow simulations for both quartz types indicate an obvious correlation between changes in permeability, fracture properties (e.g. aperture, relative roughness and porosity) and crystal growth behavior, which also forms distinct flow paths. Thus, at lower sealing stages initial fracture permeability significantly drops down for the ‘needle fracture’ forming highly tortuous flow paths, while the ‘compact fracture’ records a considerably smaller loss. Fluid flow in both sealing fractures most widely is governed by a “parallel plate”-like cubic law behavior. However, the ‘needle fracture’ also reveals flow characteristics of a porous media. A semi-theoretical equation is introduced that links geometrical ( a m ) with hydraulically effective apertures ( a h ) and the relative fracture roughness. For this purpose, a geometry factor α is introduced being α = 2.5 for needle quartz and α = 1.0 for compact quartz growth. In contrast to most common a h - a m -relationships this novel formulation not only reveals more precise predictions for the needle (RMSE = 1.5) and the compact fractures (RMSE = 3.2), but also exhibit a larger range of validity concerning the roughness of the ‘needle’ (σ/ a m = 0–2.4) and the ‘compact fractures’ (σ/ a m = 0–1.8).

In various reservoirs such as geothermal reservoirs or host rocks for nuclear waste, fractures and in particular fracture apertures play a crucial role in acting as conduits or even barriers, and therefore control fluid flow and solute transport in such reservoirs or host rocks. Often such reservoirs are simulated by discrete fracture network (DFN) models, whose performance however rely strongly on reliable input parameters such as fracture apertures under different conditions. Hence, in this study we examine various novel field and numerical methods, which are able to determine hydraulic, mechanical and even chemical apertures of natural fractures. First, we compare three different methods, (1) syringe air permeameter, (2) microscope camera and (3) laser scanner for determining hydraulic fracture apertures. Our results prove that the air permeameter allows direct and reliable measurements of hydraulic apertures in the laboratory and also in the field. Additionally, the novel air permeameter could be successfully validated by flow through experiments using various types of fractured core samples. In contrast, microscope camera and laser scanner only provide reliable mechanical apertures. In order to also simulate fracture closure under normal stresses, an innovative contact mechanical approach is introduced and validated using a granodiorite fracture. The simulations indicate the best performance for an elastic–plastic (EP) model, which fits almost perfectly the experimentally derived normal closure data. Finally, a phase-field model (PFM) for hydro­thermally induced quartz growth is used to understand the effect of sealing fractures on the flow behaviour. Our results demonstrate that flow behaviour and hydraulic properties of such chemically altered fractures, i.e. chemical fractures, significantly depend on the evolving crystal geometries. Consequently, a novel equation to estimate hydraulic apertures is derived, which includes a geometry factor α for dissimilar crystal geometries (α = 2.5 for needle quartz and α = 1.0 for compact quartz). Finally, the outcome of our studies clearly demonstrate that nowadays novel experimental and numerical methods exist to precisely determine various fracture apertures improving our understanding of coupled processes on the fluid flow behaviour in fractured media.Acknowledgements to Florian Amann, Christoph Butscher, Frieder Enzmann, Christoph Naab, Jens Oliver Schwarz and Daniel Vogler

When the metal undergoes the process of cold work and temperature treatment, the magnetic properties of the metal changes. The determination of metal hardness is vital in these processes. Thus, the need for non-destructive metallic material hardness analyzers is increasing.In this paper, we propose to design, test and evaluate an inductive sensor system, which can analyze the hardness level of metallic materials in relation to the lift-off between metal surface and coil sensor. In this work, we have used an eddy current inductive sensor, which can differentiate between unhardened and hardened metal surface on the basis of magnetic properties like ‘permeability’. The eddy current sensor was designed and tested with an impedance analyzer in the frequency range of 4 kHz to 4 MHz over the metallic surface and the inductance results were compared to the Dodd and Deeds model simulation on MATLAB. The system evaluation shows the different permeability values for unhardened and hardened metal surfaces thus, Dodd and Deeds model together with non-contact inductive sensor system design can be used for analysing hardness level of ferromagnetic materials.

Novel damping devices are presented and characterized that make use of energy dissipation due to the one-way shape memory effect in micromachined shape memory alloy (SMA) foil actuators of 30 µm thickness and lateral dimensions a few mm. The design of SMA foil actuators consists of free-standing planar suspensions with bridge, spiral and folded beam design for load control in-plane and out-of-plane. In contrast to SMA wire-based solutions, this new approach is compatible to MEMS batch fabrication technology. Under pulsed loading, a damping capacity of up to 0.92 is achieved, which compares favorably with the best viscoelastic damping concepts.

We present the design, fabrication, and characterization of single and antagonistic SMA microactuators allowing for uni- and bi-directional self-folding of origami-inspired devices, respectively. Test devices consist of two triangular tiles that are interconnected by double-beam-shaped SMA microactuators fabricated from thin SMA foils of 20 µm thickness with memory shapes set to a 180° folding angle. Bi-directional self-folding is achieved by combining two counteracting SMA microactuators. We present a macromodel to describe the engineering stress–strain characteristics of the SMA foil and to perform FEM simulations on the characteristics of self-folding and the corresponding local evolution of phase transformation. Experiments on single-SMA microactuators demonstrate the uni-directional self-folding and tunability of bending angles up to 180°. The finite element simulations qualitatively describe the main features of the observed torque-folding angle characteristics and provide further insights into the angular dependence of the local profiles of the stress and martensite phase fraction. The first antagonistic SMA microactuators reveal bi-directional self-folding in the range of −44° to +40°, which remains well below the predicted limit of ±100°.

This paper presents the design, fabrication and characterization of a linear actuator based on the magnetic shape memory (MSM) effect with intrinsic position sensing using the displacement-dependent change of electrical resistance. Active materials are Ni-Mn-Ga bulk single crystals with dimensions of 2.5 × 20 × 1 mm3 showing 10 M martensite with a dense parallel twin structure at room temperature. This structure gives rise to gradual strain characteristics when applying external stress or a magnetic field. In order to exploit this behavior for positioning applications, the correlation between magneto strain and electrical resistance is investigated as a function of external stress using either a compressive or tensile reset spring. Depending on spring constant, pre-stress as well as the modes of loading and sample fixation, reversible magneto strains up to 3.6% are achieved. The electrical resistance change shows linear correlation with magneto strain within 90% of actuation stroke allowing for position sensing with sensitivities of 2.1 and 2.7 μm/μΩ under compressive and tensile loading, respectively. This performance is simulated using a thermodynamics-based Gibbs free energy model taking into account a linear strain-resistance relationship. Near the end positions at large magnetic field, the magneto resistance effect gives rise to a nonlinear contribution to the magneto strain-resistance characteristics.

Non-destructive monitoring of metal hardness is important for process monitoring and product quality assessment. In this paper, a partially hardened metal sample is assessed in regards to physical effects using multi-frequency inductance spectroscopy. For this purpose, the influence of change of conductivity, permeability and stress on the inductance spectra are analyzed. To extract the numerical values of permeability, the measured inductance spectra are compared to the analytical inductance model. Statistical analysis with principal component analysis is conducted to fuse the spectral data into a single representative value. The results show the possibility to obtain information from different layers of the partially hardened sample, thus indicating a strong relationship between the measured inductance and restraint hardening.

This study reports a new chemical sensor based on ion-imprinted polymer matrix using copper nanoparticles-polyaniline nanocomposite (IIP-Cu-NPs/PANI). This sensor was prepared by electropolymerization using aniline as a functional monomer and nitrate as template onto the copper nanoparticles-modified glassy carbon (GC) electrode surface. Both ion-imprinted (IIP) and nonimprinted (NIP) electrochemical sensor surfaces were evaluated using UV-Visible spectrometry and scanning electron microscopy (SEM). The electrochemical analysis was made via cyclic voltammetry (CV), linear sweep voltammetry (LSV), and impedance spectroscopy (IS). Throughout this study various analytical parameters, such as scan rate, pH value, concentration of monomer and template, and electropolymerization cycles, were optimized. Under the optimum conditions, the peaks current of nitrate was linear to its concentration in the range of 1μM-0.1M with a detection limit of 31μM and 5μM by EIS and LSV. The developed imprinted nitrate sensor was successfully applied for nitrate determination in different real water samples with acceptable recovery rates.

Cross talking effects occur during measurements of sensor resistances in a two dimensional matrix. The cross talking current from neighborhood units influences measured values on the target sensor. This causes big systematic measurement deviations, especially for the piezoresistive sensors based on multi-walled carbon nanotube within Polydimethylsiloxane (PDMS). For this material, resistance value decreases significantly corresponding to the pressure value, which leads to large current increasing under the same excitation signal. In this paper, the cross talking effect is evaluated through the comparison between one usual data acquisition system and the data acquisition system equipped with voltage feedback circuit (VFC), which is suitable for the used nano-material. As result, it is demonstrated that voltage feedback method can eliminate the cross talking effect in the two-dimensional nano-composite sensor matrix. Meanwhile, the voltage feedback circuit cannot always remain high accuracy in extreme high resistance load range because of the non-ideal behavior of the hardware elements.

This paper presents a dynamic analysis of the free and forced vibration of a free-standing bridge of superelastic shape memory alloy TiNiCuCo film with ultra-low fatigue properties and evaluates its versatility for novel miniature scale damping applications. A thermodynamics-based finite element model is used to simulate the evolution of martensite phase fraction during load-induced martensitic phase transformation. The effects of pre-strain, strain rate and excitation load on the hysteresis of stress-strain characteristics are investigated in order to assess damping energies. The analysis is performed under non-isothermal conditions taking into account heat transfer and rate-dependence of release and absorption of latent heat. We show that damping energy can be maximized by applying an optimum pre-strain. A maximum damping capacity of 0.17 is determined for the case of complete stress-strain hysteresis loop during phase transformation.

Zusammenfassung Die analytische Modellierung von Spulenimpedanzen stellt die theoretische Grundlage vieler Wirbelstrommessverfahren dar. Wenn permeable Materialien untersucht werden, ist nicht nur die wirbelstrombedingte Impedanzänderung von Interesse, sondern auch die Relation dieser Änderung zu dem absoluten Wert. Feldmodelle auf der Grundlage des magnetischen Vektorpotentials wurden bereits zur Berechnung der wirbelstrombedingten Impedanzänderung benutzt. Durch Konvergenzprobleme bei der Integration lässt sich diese Berechnungsmethode nicht exakt auf den materialunabhängigen Impedanzanteil übertragen. In diesem Artikel wird die Ursache dieser Konvergenzprobleme gezeigt und über die Methode der Inneren und Äußeren Induktivität gelöst. So kann das bisherige Modellierungsverfahren um den materialunabhängigen Anteil auf eine ganzheitliche Impedanzbeschreibung erweitert werden. Eine ganzheitliche Modellierung umfasst alle betragsmäßig relevanten Impedanzanteile und liefert ein Maximum an Information aus den einzelnen Impedanzspektren. Die Leistungsfähigkeit dieses Verfahrens wird im anwendungsrelevanten Frequenzbereich von 10 kHz bis 10 MHz demonstriert, wobei berechneten Werten Versuchsdaten gegenübergestellt werden.

Ionic liquids (ILs) exhibit a far lower degradation potential compared to the established direct cellulose solvent N -methylmorpholine- N -oxide monohydrate used in the Lyocell process. Safety parameters such as onset temperature, pressure rise and heat release during exothermicity were measured in imidazolium ILs and solutions of cellulose in ILs by means of DSC, dynamic reaction calorimetry and UV/VIS spectroscopy with a special designed cuvette. Onset temperatures were determined using pressure rise measurement at a threshold value. Initial thermal activities in ILs occurred at much lower temperatures compared to DSC measurements and TGA literature data. For 1-ethyl-3-methylimidazolium acetate (EMIMAc) and 1-butyl-3-methylimidazolium acetate (BMIMAc) the onset temperatures 181 and 179 °C, respectively, were stated first time. Endothermic decomposition of pure EMIMAc is turned to an exothermic event by addition of cellulose accompanied by increased slope of pressure.

In this work we introduce and apply a diffuse interface model to the problem of polycrystalline evolution in zeolite thin film growth. The phase-field model is based on a Ginzburg–Landau free energy functional, where a set of non-conserved order parameters is used to capture geometry and temporal evolution of the solid grains and the liquid phase. Special attention is given to the modelling of anisotropic interface properties resulting in a growth shape which corresponds to experiments for hydrothermally grown MFI zeolites. The model parameters used in the simulations are determined from available physical data, taking into account the experimental length and energy scales. To produce sound results with a minimum of seed crystals, a method to cover the unit sphere in three dimensions with angularly equidistant grain orientations is developed. Simulations in 2D and 3D are carried out to study competitive growth of equisized seeds with randomly distributed orientations on a flat substrate. In each case, the evolution of the orientation distribution leads to a fibre texture, selecting the direction of fastest growth perpendicular to the substrate. The dynamics of front growth velocity and of the average grain diameter is evaluated and compares well to experimental and theoretical findings. No significant differences in the competitive growth process using either solid–liquid interface energy anisotropy or anisotropy in the kinetic coefficient were found. This allows the conclusion that under the imposed conditions no major effect of interface energy balances at triple junctions on structure evolution is present, as it is the case for grain growth. The simplifying assumptions imposed in the modelling of the process are discussed, and possible refinements of the phase-field model are proposed.

We use a thermodynamically consistent multi-phase, multi-component phase-field model, where the evolution equations for the different fields are derived from an entropy functional, for simulating peritectic growth structures in two and three dimensions. Different solidification morphologies are obtained in the computations and the characteristic properties of the growth forms are discussed. The phase-field method allows for a prediction of the surface energies in the three-phase system δ -ferrite, γ -austenite and liquid based on comparison between experimentally observed and simulated structures. Additionally an investigation of possible nucleation sites in evolving domains is presented and its dependence on the solid–solid surface energy is examined.

A diffuse interface description based on a multi-phase-field model for geological grain microstructures is introduced, especially useful in the treatment of partially molten structures. Each grain as well as different phases are represented by individual non-conserved order parameters, the phase fields @f"@a, which are defined on the complete simulation domain. The derivation of the model from a Ginzburg-Landau type free energy density functional is briefly shown and all occurring energy contributions are discussed. Also, the nondimensionalisation necessary to relate the simulation to real experiments and a brief overview of the numerical methods used in the simulations is given. To illustrate the applicability of the method to large grain systems a simulation of normal grain growth was carried out. The results on the dynamics of the process are in close agreement with theory. The extension of the phase-field model to incorporate phases with conserved volume is described next. This capacity is exploited for the liquid phase in a partially molten structure, where melt and a solid mineral phase are in equilibrium. Simulations with isolated melt inclusions within a grain structure in 2D and 3D are presented, resulting in the formation of the correct dihedral angles corresponding to the solid/solid and solid/liquid interface energies @c"S"S and @c"S"L. The case of complete wetting of the grain boundaries, if @c"S"L/@c"S"S

Functional cellulose shapes offer valuable properties for innovative application potentials in textile and medical products. Thereby excellent textile physiological properties of cellulose are allowed to be connected with novel application characteristics like bioactivity, electrical conductivity, heat storage or ability to adsorb liquids or gases. A very advantageous way to modify the properties of fibres, films or textile structures is to introduce particular additives via the Lyocell process. Regard to technical applications, functional additives will be able to incorporate themselves in the shape matrix and, in the case of using N-methylmorpholine-N-oxide monohydrate (NMMO) as solvent, implicate massive technological difficulties and deterioration of properties of the spinning dope. Beside a couple of limiting moments, ionic liquids (ILs) offer as direct solvents an excellent chance for physical modification of cellulose shapes. in contrast to NMMO, they exhibit a significantly higher thermal stability as well as a higher chemical resistance. ILs exhibit most widely a better dissolving capability for a number of different polymers. First results of the development of adsorber materials as well as novel bioactive fibres will be discussed and fibre characteristics will be given.

Mineral precipitation in an open fracture plays a crucial role in the evolution of fracture permeability in rocks, and the microstructural development and precipitation rates are closely linked to fluid composition, the kind of host rock as well as temperature and pressure. In this study, we develop a continuum thermodynamic model to understand polycrystalline growth of quartz aggregates from the rock surface. The adapted multiphase-field model takes into consideration both the absolute growth rate as a function of the driving force of the reaction (free energy differences between solid and liquid phases), and the equilibrium crystal shape (Wulff shape). In addition, we realize the anisotropic shape of the quartz crystal by introducing relative growth rates of the facets. The missing parameters of the model, including surface energy and relative growth rates, are determined by detailed analysis of the crystal shapes and crystallographic orientation of polycrystalline quartz aggregates in veins synthesized in previous hydrothermal experiments. The growth simulations were carried out for a single crystal and for grain aggregates from a rock surface. The single crystal simulation reveals the importance of crystal facetting on the growth rate; for example, growth velocity in the c-axis direction drops by a factor of ~9 when the faceting is complete. The textures produced by the polycrystal simulations are similar to those observed in the hydrothermal experiments, including the number of surviving grains and crystallographic preferred orientations as a function of the distance from the rock wall. Our model and the methods to define its parameters provide a basis for further investigation of fracture sealing under varying conditions.

The elastocaloric effect associated with the stress-induced first order phase transformation in pseudoelastic shape memory alloy (SMA) films and foils is of special interest for cooling applications on a miniature scale enabling fast heat transfer and high cycling frequencies as well as tunable transformation temperatures. The focus is on TiNi-based materials having the potential to meet the various challenges associated with elastocaloric cooling including large adiabatic temperature change and ultra-low fatigue. The evolution of strain and temperature bands during tensile load cycling is investigated with respect to strain and strain-rate by in situ digital image correlation and infrared thermography with a spatial resolution in the order of 25 µm. Major design issues and challenges in fabrication of SMA film-based elastocaloric cooling devices are discussed including the efficiency of heat transfer as well as force recovery to enhance the coefficient of performance (COP) on the system level. Advanced demonstrators show a temperature span of 13 °C after 30 s, while the COP of the overall device reaches almost 10% of Carnot efficiency.

The clean NiAl(1 1 0) surface and the Al2O3/NiAl(1 1 0) interface have been investigated by synchrotron X-ray diffraction experiments. In the case of the oxide surface the analysis of the NiAl(1 1 0) crystal truncation rods (CTR) provide information about the interface between the Al2O3 film and the NiAl substrate. The analysis of the CTR-data shows clearly a rippled Ni-Al topmost surface with an amplitude value of RNi/Al = 0.16 ± 0.01 A for the clean surface and RNi/Al = 0.18 ± 0.02 A for the oxide covered surface. On the clean surface the Al sites are expanded by +3.8\% (outwards) and the Ni sites are contracted by -3.2\% (inwards) respect to the unrelaxed interlayer separation. For the oxide covered surface an increase of the expansion of the outermost Al atoms (+7.3\%) relative to their bulk positions has been found, while the Ni atoms remain (-0.9\%) at the bulk position. On both cases, an ideal surface stoichiometry (1:1) was obtained. However, some intermixing (chemical disorder) of one specimen in the sites of the other and vice versa was present (less than 4\%). This chemical disorder was not enhanced by the presence of the Al2O3 overlayer. Neither rippling nor oscillatory relaxation in deeper layers was detectable.

By introducing smart materials in micro systems technologies, novel smart microactuators and sensors are currently being developed, e.g., for mobile, wearable, and implantable MEMS (Micro-electro-mechanical-system) devices. Magnetic shape memory alloys (MSMAs) are a promising material system as they show multiple coupling effects as well as large, abrupt changes in their physical properties, e.g., of strain and magnetization, due to a first order phase transformation. For the development of MSMA microactuators, considerable efforts are undertaken to fabricate MSMA foils and films showing similar and just as strong effects compared to their bulk counterparts. Novel MEMS-compatible technologies are being developed to enable their micromachining and integration. This review gives an overview of material properties, engineering issues and fabrication technologies. Selected demonstrators are presented illustrating the wide application potential.

A phase-field model is introduced to simulate the magnetic shape memory effect, i.e. the solid-state rearrangement of the boundaries of a martensitic microstructure using an external magnetic field, in the shape memory material Ni2MnGa. The model is derived from an existing phase-field model that has proven well in several applications in materials science, based on the interpolation of free energies. The micromagnetic and elastic energy contributions entering the constitutive free energy functional are given, and the coupled kinetic equations of motion for the phase fields that describe the microstructure geometry, the spontaneous magnetization and the elastic displacement field are derived from the principle of minimization of free energy. The concept of representative volume elements is applied for the microstructure simulations carried out to analyze the material behavior, and the relevant boundary conditions are discussed. Stress vs. strain and strain vs. applied magnetic field curves are shown for Ni2MnGa.

Recent developments on Heusler alloys including Ni–Mn–X and Ni–Co–Mn–X (X = Ga, In, Sn,…) demonstrate multiferroic phase transformations with large abrupt changes in lattice parameters of several percent and corresponding abrupt changes in ferromagnetic ordering near the transition temperatures. These materials enable a new generation of thermomagnetic generators that convert heat to electricity within a small temperature difference below 5 K. While thermodynamic calculations on this energy conversion method predict a power density normalized to material volume of up to 300 mW cm−3, experimental results have been in the range of µW cm−3. Challenges are related to the development of materials with bulk-like single-crystal properties as well as geometries with large surface-to-volume ratio for rapid heat exchange. This study demonstrates efficient thermomagnetic generation via resonant actuation of freely movable thin-film devices of the Heusler alloy Ni–Mn–Ga with unprecedented power density of 118 mW cm−3 that compares favorably with the best thermoelectric generators. Due to the large temperature-dependent change of magnetization of the films, a periodic temperature change of only 3 K is required for operation. The duration of thermomagnetic duty cycle is only about 12 ms, which matches with the period of oscillatory motion.

Cooling and thermal management comprise a major part of global energy consumption. The by far most widespread cooling technology today is vapor compression, reaching rather high efficiencies, but promoting global warming due to the use of environmentally harmful refrigerants. For widespread emerging applications using microelectronics and micro-electro-mechanical systems, thermoelectrics is the most advanced technology, which however hardly reaches coefficients of performance (COP) above 2.0. Here, we introduce a new approach for energy-efficient heat pumping using the elastocaloric effect in shape memory alloys. This development is mainly targeted at applications on miniature scales, while larger scales are envisioned by massive parallelization. Base materials are cold-rolled textured Ti49.1Ni50.5Fe0.4 foils of 30 μm thickness showing an adiabatic temperature change of +20/−16 K upon superelastic loading/unloading. Different demonstrator layouts consisting of mechanically coupled bridge structures with large surface-to-volume ratios are developed allowing for control by a single actuator as well as work recovery. Heat transfer times are in the order of 1 s, being orders of magnitude faster than for bulk geometries. Thus, first demonstrators achieve values of specific heating and cooling power of 4.5 and 2.9 W g−1, respectively. A maximum temperature difference of 9.4 K between heat source and sink is reached within 2 min. Corresponding COP on the device level are 4.9 (heating) and 3.1 (cooling).

In this work, a method for the determination of the ion concentration and the diffusion coefficient of lithium ions in a phosphorus oxynitride will be presented. The reproducibility of the parameter extraction and the entire measurement process will be evaluated. The obtained results are in the value range of publications of similar sample properties.

International audience; It belongs to one of the oldest experiences of mankind to use fibrous materials of plant or animal origin with different fibre lengths and fineness as basic materials of human clothes. Cellulose forms linear macromolecules, preferentially useful for an application as textile fibres. Common used pulp fibres are too short for those applications and have to be transformed into staple fibres like wool or endless fibres like silk by means of solution shaping procedures. Dissolution of cellulose in common protic solvents like water or alcohol is hindered due to intra- and intermolecular hydrogen bonds. For that reason cellulose derivatives like cellulose nitrate, cellulose xanthogenate or cellulose acetate were used first in order to manufacture cellulose man-made fibres. Situation changes after investigation of direct dissolving liquids like cyclic amine oxides, especially N-methylmorpholine-N-oxide, and large-scale manufacturing of it became reality. In the late 1970s up to the late 1990s, direct dissolution technology, nowadays well known as Lyocell process, was developed up to technical scales. Dry-wet shaping has recently developed to a powerful tool for manufacturing of fibres, films, nonwoven or other shapes based on cellulose. The Lyocell process also offers new opportunities for chemical or physical functionalisation of cellulose shapes. Because of technological difficulties caused by the thermal and chemical sensitivity of the NMMO monohydrate and the strong fibrillation behaviour of dry-wet shaped fibres, alternatives are to be found to overcome these problems. CELSOL® and BIOCELSOL® processes are two approaches which investigated for substitution of Lyocell process. Native pulp fibres have to be pretreated before they could be used for direct dissolution in aqueous NaOH, the common solvent of CELSOL and BIOCELSOL processes. Development on direct dissolution in caustic soda is still under investigation and scaled up into semi-technical and technical scales. Besides fibres and films, the manufacture of highly porous materials is a very active field, offering the possibility to use them in a wide range of applications, from biomedical and cosmetics to insulation and electrochemistry. A review of the different processes able to manufacture fibres, films and porous objects is given here.

The aim of this study was to find newly structured biopolymer blends bearing those adjustable features able to produce innovative materials. Apart from cellulose derivatives (cellulose carbamate and carboxymethyl cellulose), mannans (guar gum, locust bean gum, and tragacanth gum), xylan, starch (cationized), ι-carrageenan, and xanthan were chosen as blend polysaccharides for cellulose as matrix. In order to study their integration into the cellulose skeleton, fibers were shaped from three different solvents: NaOH by a special wet-spinning process, as well as N-methylmorpholine-N-oxide (NMMO) and 1-ethyl-3-methylimidazolium acetate (EMIMac) via Lyocell technology. The structure and morphologies of the fibers were analyzed by X-ray wide-angle scattering and atomic force microscopy. Hydrophilic/hydrophobic properties were determined by means of a contact angle, as well as moisture content and water retention values, while the surface properties throughout zeta-potential measurements. Being very different processes, the wet spinning in NaOH solution and the dry–wet spinning are deeply impacted by the types of solvent and polysaccharide. The X-ray results for NMMO fibers revealed the highest orientation compared with EMIMac having the lowest orientation of NaOH fibrous types. AFM images also show the lowest surface roughnesses for NMMO and EMIMac fibers. The moisture content and water retention values support these trends, while the water contact angle results show insignificant differences between the samples from EMIMac and NaOH, even though the values calculated for NMMO fibers were the lowest.

We compare results from molecular dynamics simulations with those from phase-field modeling concerning the solidification and melting kinetics of a planar ${[{\text{Ni}}_{c}{\text{Zr}}_{1\ensuremath{-}c}]}_{\text{liquid}}{\text{-Zr}}_{\text{crystal}}$ interface. Our study is an illustration that both approaches may predict the same quantitative physical description when the key parameters calculated within the atomistic molecular dynamics approach are used to construct the mesoscopic phase-field model. We show in this way that a thermodynamic consistent phase-field model can be applied down to the range of atomic structure. At the same time, molecular dynamics simulation seems to be capable to treat correctly relaxation dynamics, driven by thermodynamic forces, in a nonequilibrium state of solidification and melting. We discuss, in particular, how the free energy from atomistic calculations is used to design the phase dependent free-energy density in the phase-field model. Bridging the gap between both simulation approaches contributes to a better understanding of the thermodynamic and kinetic processes underlying the solidification and melting processes in alloys out of chemical equilibrium. The effective thermodynamic enhancement of the diffusivity through the strong negative enthalpy of mixing in the NiZr solution is discussed.

We report on an interesting formulation of a phase-field model which incorporates a description of individual phases and particles with preserved volume evolving in a system of multiple phases such that the interfacial energy decreases. In our model, an antiforcing free energy density is defined to fulfill constraints on selected volume fractions by counterbalancing phase changes. Phases are defined as regions with energy bearing boundaries that may differ in their physical states, i.e., the regions may be distinguished in structure (crystal transformations), in composition (alloys, mixtures of fluids), or in the orientation of the crystal lattice (grains). The method allows one to simulate the formation of equilibrium crystal shapes and of the migration of inert particles and phases in microstructures. We show two- and three-dimensional simulations of bubble ensembles and foam textures and demonstrate the excellent agreement of crystal morphology configurations with analytical results.

In this article, we review the progress on phase-field modelling, sharp interface asymptotics, numerical simulations and applications to microstructure evolution and pattern formation in materials science. Model formulations and computations of pure substances and of binary alloys are discussed. Furthermore, a thermodynamically consistent class of non-isothermal phase-field models for crystal growth and solidification in complex alloy systems is presented. Explicit expressions for the different energy density contributions are proposed. Multicomponent diffusion in the bulk phases including interdiffusion coefficients as well as diffusion in the interfacial regions are discussed. Anisotropy of both, the surface energies and the kinetic coefficients is incorporated in the model formulation. A 3D parallel simulator based on a finite difference discretization is introduced illustrating the capability of the model to simultaneously describe the diffusion processes of multiple components, the phase transitions between multiple phases and the development of the temperature field. The numerical solving method contains parallelization and adaptive strategies for optimization of memory usage and computing time. Applying the computational methods, we show a variety of simulated microstructure formations in complex multicomponent alloy systems occuring on different time and length scales. In particular, we present 2D and 3D simulation results of dendritic and eutectic solidification in pure substances and binary and ternary alloys. Another field of application is the modelling of competing polycrystalline grain structure formation and grain growth.

The structure of the clean Ni3Al(111) surface has been studied using surface x-ray diffraction. Analysis of the crystal truncation rods reveals that the clean surface contains an unexpected disorder while the bulk remains ordered. This surface-induced disorder extends down to the sixth layer and it decreases gradually with depth. The surface is, on the whole, stoichiometric and the maximum deviation per layer from the ideal 3Ni:1Al composition is less than 8\%. There is a very small difference (0.02±0.01A) between the relaxations of the two different sites at the surface, and the interlayer distance between the outmost, second, and third layers is slightly reduced (0.02±0.01A) with respect to the bulk value.

Using ab initio thermodynamics we compile a phase diagram for the surface of Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto ignored polar termination with octahedral iron and oxygen forming a wavelike structure along the [110] direction is identified as the lowest energy configuration over a broad range of oxygen gas-phase conditions. This novel geometry is confirmed via x-ray diffraction analysis. The stabilization of the Fe3O4(001) surface goes together with dramatic changes in the electronic and magnetic properties, e.g., a half metal to metal transition.