Electrical field assisted sintering of yttrium-doped ceria investigated by sinter-forging

The production of traditional and advanced ceramics is an energy-intensive activity, which requires high sintering temperatures and long holding times to activate diffusional processes necessary for densification. Electric field assisted processing has the potential to significantly reduce the sintering time and temperature which are not obtainable by other methods. The role of electric fields in the densification and coarsening of oxide ceramics is still under debate. By using a sinter-forging device equipped with a versatile power source and high-resolution laser scanners, it is possible to investigate in detail field assisted sintering process by quantifying uniaxial viscosity, viscous Poisson’s ratio and sintering stress of oxide ceramics. The macroscopic Joule heating effect was eliminated by using Finite-Element Simulations calibrated experimentally and by lowering the furnace temperature accordingly. In other words, the sample temperature was kept constant under the different testing conditions, enabling a correct estimation of a thermal electric field effects. The sintering parameters of the ceramic pellets were measured without / with alternating electrical field well below flash sintering conditions. Clear effect of the electrical field on both uniaxial viscosity and sintering stress were observed. Microstructures of the specimens were investigated by SEM and TEM, and correlated to the electrical properties of the samples measured by Electrochemical Impedance Spectroscopy in order to understand the interplay between grain boundaries and electric field

Modelling the effect of the porous support on the flux through asymmetric oxygen gas separation membranes

Oxygen Transport Membranes (OTM) represent a new technology for energy-efficient oxygen generation which can be used in low-pollutant power plants and oxygen generators or membrane reactors in the chemical industry and health care. The two competing demands of low ionic resistance of the functional separation membrane and high mechanical stability lead to an asymmetric design comprising of a thin membrane layer and a thicker porous support. However, the overall membrane performance is strongly affected by the microstructure of this support layer which prevented the use of the full potential of such a design in the past. Please download the full abstract below

Thermally sprayed protective coatings under demanding load conditions

Materials in turbines are facing increasingly demanding conditions under operation. This is due to their diversifying field of application as e.g. in interplay with renewable energy sources. Each set of loading conditions, in terms of e.g. operation temperature, start/stop-frequency or contaminants present in the combustion atmosphere, shows a specific footprint of degradation pathways. Understanding and performance data are available for many individual degradation footprints as to date materials and coatings are developed in respect to each one of that kind of loading scenarios. Less often, materials are assessed at a wider range of conditions where changes and interplay of degradation modes can be observed. Today’s demand for design of material systems for flexible or volatile conditions of operation requires to consider the wider range of operation regimes including complex sequences of loading phases adding up to the overall degradation. Performance and degradation modes of APS TBC systems (both single layer YSZ as well as a double layer of YSZ plus Gd2Zr2O7) were studied under various conditions in cyclic testing. This includes scenarios with isothermal and gradient testing as well as sequential vs simultaneous loading with CMAS. Results are evaluated with respect to changes of (coexisting) degradation modes and spallation lifetime. Applicability of some modeling tools is discussed for lifetime prediction. Complete affiliations: 1) Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, Materials Synthesis and Processing (IEK-1), 52425 Jülich, Germany 2) Jülich Aachen Research Alliance: JARA-Energ

Thermal runaway, dynamic stability and process control in flash sintering

Flash sintering is an innovative sintering method in which a critical combination of electrical field and temperature triggers a sudden densification in seconds. Due to the nature of the process, the flash sintering conditions lead to a non-linear conductivity surge followed by current control. This work tries to answer some questions related to process control during flash sintering by using a dynamic system model-based approach. An explicit solution for the folding points in the voltage control mode is presented (Figure 1). The analytical model uses a dynamic bifurcation approach which explains why the current control mode always leads to a steady state, due to the unicity of the solution to the equations, and why different modes of flash sintering such as current-controlled or power-controlled lead to a more uniform process. The model is validated with experiments in Cerium Oxide doped with Gadolinium and Yttrium. Please click Additional Files below to see the full abstract

Filamentous Biopolymers on Surfaces: Atomic Force Microscopy Images Compared with Brownian Dynamics Simulation of Filament Deposition

Nanomechanical properties of filamentous biopolymers, such as the persistence length, may be determined from two-dimensional images of molecules immobilized on surfaces. For a single filament in solution, two principal adsorption scenarios are possible. Both scenarios depend primarly on the interaction strength between the filament and the support: i) For interactions in the range of the thermal energy, the filament can freely equilibrate on the surface during adsorption; ii) For interactions much stronger than the thermal energy, the filament will be captured by the surface without having equilibrated. Such a ‘trapping’ mechanism leads to more condensed filament images and hence to a smaller value for the apparent persistence length. To understand the capture mechanism in more detail we have performed Brownian dynamics simulations of relatively short filaments by taking the two extreme scenarios into account. We then compared these ‘ideal’ adsorption scenarios with observed images of immobilized vimentin intermediate filaments on different surfaces. We found a good agreement between the contours of the deposited vimentin filaments on mica (‘ideal’ trapping) and on glass (‘ideal’ equilibrated) with our simulations. Based on these data, we have developed a strategy to reliably extract the persistence length of short worm-like chain fragments or network forming filaments with unknown polymer-surface interactions

Optimizing the Composite Cathode Microstructure in All-Solid-State Batteries by Structure-Resolved Simulations

All-solid-state batteries are considered as an enabler for applications requiring high energy and power density. However, they still fall short of their theoretical potential due to various limitations. One issue is poor charge transport kinetics resulting from both material inherit limitations and non-optimized design. Therefore, a better understanding of the relevant properties of the cathode microstructure is necessary to improve cell performance. In this article, we identify optimization potentials of the composite cathode by structure-resolved electrochemical 3D-simulations. In our simulation study, we investigate the influence of cathode active material fraction, density, particle size, and active material properties on cell performance. Special focus is set on the impact of grain boundaries on the cathode design. Based on our simulation results, we can predict target values for cell manufacturing and reveal promising optimization strategies for an improved cathode design

Pathophysiological role of prostanoids in coagulation of the portal venous system in liver cirrhosis

BACKGROUND: Prostanoids are important regulators of platelet aggregation and thrombotic arterial diseases. Their involvement in the development of portal vein thrombosis, frequent in decompensated liver cirrhosis, is still not investigated. METHODS: Therefore, we used pro-thrombotic venous milieu generation by bare metal stent transjugular intrahepatic portosystemic shunt insertion, to study the role of prostanoids in decompensated liver cirrhosis. Here, 89 patients receiving transjugular intrahepatic portosystemic shunt insertion were included in the study, and baseline levels of thromboxane B2, prostaglandin D2 and prostaglandin E2 were measured in the portal and the hepatic vein. RESULTS: While the hepatic vein contained higher levels of thromboxane B2 than the portal vein, levels of prostaglandin E2 and D2 were higher in the portal vein (all P<0.0001). Baseline concentrations of thromboxane B2 in the portal vein were independently associated with an increase of portal hepatic venous pressure gradient during short term follow-up, as an indirect sign of thrombogenic potential (multivariable P = 0.004). Moreover, severity of liver disease was inversely correlated with portal as well as hepatic vein levels of prostaglandin D2 and E2 (all P<0.0001). CONCLUSIONS: Elevated portal venous thromboxane B2 concentrations are possibly associated with the extent of thrombogenic potential in patients with decompensated liver cirrhosis. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03584204