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• TiNb alloys were solution heat treated using a molten KCl as protective atmosphere. • Molten salt shield prevents oxidation of Ti-Nb alloys during heat treatment. • Martensitic phases were formed in the heat-treated Ti-Nb alloys. • Lowest elastic modulus was found after solution treatment followed by quenching. Ti-Nb alloys have attracted growing attention for biomedical implant application due its low elastic modulus. Nb is a β-stabilizer in Ti alloys and retains its high biocompatibility. Thermal treatment plays a key role for optimization of mechanical properties and microstructure of Ti-Nb alloys. However, high oxygen affinity of Ti alloys requires the use of a protective atmosphere during their processing at high temperatures. In this context, we propose the use of molten salt as novel atmosphere protection during solution heat treatment of Ti-Nb alloys avoiding elaborated encapsulation. For that, Ti-Nb parts were solution treated in molten KCl followed by water quenching. Microstructure and phase transformation were evaluated by SEM, EDS, X-ray Diffraction, Elastic Modulus and Vickers microhardness measurements. No evidence of oxidation of Ti-Nb parts was found, which suggested that molten salt was an effective measure to protect Ti alloys from oxidation. After treatment, a martensitic microstructure was achieved. A martensitic structure enables to decrease elastic modulus to ca. 35 GPa, which can avoid stress shield in the case of bone implant application. [ABSTRACT FROM AUTHOR]

Iron-air rechargeable oxide batteries (ROB) comprising solid oxide cells (SOC) as energy converters and Fe/metal-oxide redox couples were characterized using planar SOC stacks. The charge and discharge of the battery correspond to the operations in the electrolysis and fuel cell modes, respectively, but with a stagnant atmosphere consisting of hydrogen and steam. A novel method was employed to establish the stagnant atmosphere for battery testing during normal SOC operation without complicated modification to the test bench and stack/battery concept. Manipulation of the gas compositions during battery operation was not necessary, but the influence of the leakage current from the testing system had to be considered. Batteries incorporating Fe 2 O 3 /8YSZ, Fe 2 O 3 /CaO and Fe 2 O 3 /ZrO 2 storage materials were characterized at 800 °C. A maximum charge capacity of 30.4 Ah per layer (with an 80 cm 2 active cell area) with ∼0.5 mol Fe was reached with a current of 12 A. The charge capacity lost 11% after ∼130 ROB cycles due to the increased agglomeration of active materials and formation of a dense oxide layer on the surface. The round trip efficiencies of the tested batteries were ≤84% due to the large internal resistance. With state-of-the-art cells, the round trip efficiency can be further improved. [ABSTRACT FROM AUTHOR]

All-oxide model-composite electrodes were established consisting of a thin, micropatterned, electronically conducting oxide, which acts as a current collector, and a thin film of gadolinia-doped ceria, which is an electrochemically highly active mixed conductor under reducing atmospheres. The choice of the current collecting oxides was based on their electronic conductivity assessed by measurements of thin films using the van der Pauw method. Lanthanum and niobium doped strontium titanate as well as alumina doped zinc oxide, were investigated this way in a humid hydrogen atmosphere. Promising materials were incorporated as a current collector into model-composite microelectrodes and tested for their stability and efficiency in electrochemically activating the microelectrode. Alumina doped zinc oxide, while being an excellent electron conductor, showed severe stability problems at temperatures above 600 °C. However, a microelectrode with a current collector of niobium doped strontium titanate (Sr 0·9 Ti 0.8 Nb 0·2 O 3 ) performed comparable to an electrode with a Pt current collector and, additionally, showed an improved tolerance to sulphur poisoning in a humid hydrogen atmosphere with 10 ppm of hydrogen sulphide. [ABSTRACT FROM AUTHOR]

Protonic ceramic conductors based on the solid solution BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ (BZCY72) have great potential as electrolytes in various energy conversion devices. However, their refractory nature requires very high sintering temperatures to achieve sufficient densification for gas tightness. In this study, we present a novel processing route using the cold sintering process (CSP) to consolidate BZCY72 powders at 350°C using 400 MPa and deionized water as a sintering aid. Through a systematic variation of the calcination pretreatment, we demonstrated that the cold sintering ability of BZCY can be tuned through the phase composition of the starting powder. The cold sintering process of BZCY bases on a decomposition reaction of a Ce-rich BZCY phase, which plays a major role for low temperature densification. A subsequent post thermal treatment (PTT) at 1300°C is sufficient to regain the BZCY phase resulting in total conductivities of 1*10−3 Scm−1 at 500°C in air. [Display omitted] [ABSTRACT FROM AUTHOR]

For optimization of ageing behavior, electrochemical performance, and sulfur tolerance of metal-supported solid oxide fuel cells a new anode concept is introduced, which is based on a Ni/GDC cermet replacing the established Ni/YSZ anodes. In the present work optimized processing parameters compatible with MSC substrates are specified by doing sintering studies on pressed bulk specimen and on real porous anode structures. The electrochemical performance of the Ni/GDC anodes was characterized by means of symmetrical electrolyte supported model-type cells. In this study, three main objectives are pursued. Firstly, the effective technical realization of the Ni/GDC concept is demonstrated. Secondly, the electrochemical behavior of Ni/GDC porous anodes is characterized by impedance spectroscopy and compared with the current standard Ni/YSZ anode. Further, a qualitative comparison of the sulfur poisoning behavior of both anode types is presented. Thirdly, preliminary results of a successful implementation of the Ni/GDC cermet into a metal-supported single cell are presented. [ABSTRACT FROM AUTHOR]

This work investigates the effects of the sintering conditions on the morphology and mechanical performance of stainless steel (SS) hollow fibres. It was found that the morphology of the green hollow fibre to a large extent predetermines the final morphology of the sintered hollow fibre. There is a set of conditions which produce hollow fibres with high mechanical strength over 1000 MPa such as using small SS particles (6 and 10 μm), PEI as the polymeric binder and minimal amounts of the viscosity modifier PVP (preferably close to 0 wt%), particle loadings higher than 50 wt%, and sintering temperatures between 1050 and 1100 °C. The ductility of the hollow fibres was not greatly affected by these parameters as flexural strain variations were very small, though sintering in argon resulted in the formation of a few larger pores which tended to propagate cracks, leading to lower flexural strain. The sintering process in inert gases resulted in mass transfer of residual carbon from the binder to the SS particle, leading to regions of rich and lean chromium carbides, though mechanical effects of these inclusions were not significant. Finally, the morphology played a major role as SS hollow fibres containing a higher volume of sponge-like region were mechanically stronger than the analogous fibres dominated by finger-like and macroporous regions. [ABSTRACT FROM AUTHOR]

Cavitation is a severe wear mechanism in technical applications where parts are in contact with rapidly flowing liquids. Examples are turbine blades in hydropower plants or pump components. Coating exposed surfaces with wear-resistant materials is an effective measure for extending lifetime in the case of cavitation attack. NiTi is an attractive material for such coatings considering its clearly pronounced damping behavior based on its pseudoelastic properties. A promising processing route for coating net-shaped components with NiTi is low-pressure plasma spraying (LPPS). In the present work, NiTi layers were produced by LPPS, starting from pre-alloyed NiTi powder. Cavitation resistance was investigated in relation to LPPS parameters, layer thickness and specific surface treatment. Increased cavitation resistance was demonstrated compared to UTP 730, an established cavitation protection material. The study was accompanied by comprehensive characterization of microstructure and phase transformation behavior of the NiTi coatings. [ABSTRACT FROM AUTHOR]

Ultrafast High-temperature Sintering (UHS) is a novel sintering process enabling extremely high heating rates by direct contact of sample to electrically heated thin carbon strips. Using strontium titanate as a model system, the densification behavior by UHS was investigated. Controlled experiments via maximum current limitation were used to study the influence of the applied current on the degree of densification and resulting final grain size. Simulations by Finite Element Modeling (FEM) allow estimating the sample temperature reached during UHS, which is in good agreement with the experimental data. Moreover, the FEM simulations show a self-stabilization of the sample temperature by thermal radiation. UHS results suggest that rapid densification can be achieved with an extremely high heating rate. The microstructure of the undoped strontium titanate samples shows exaggerated grain growth and pore-boundary separation, which results in pore entrapment inside grains. The addition of 2 mol% iron in strontium titanate is beneficial by limiting the grain growth during the UHS sintering cycle. Uniform densification and grain growth in the sample is consequently observed. Scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDS) is utilized to analyze grain boundary segregation. Measurement of the electrical conductivity of the UHS sintered samples by impedance spectroscopy suggest that rapid densification by UHS enables full access to the functional properties of strontium titanate as compared to the conventionally sintered material. [Display omitted] [ABSTRACT FROM AUTHOR]

Flash sintering is a novel electric field and current assisted sintering technique which densify ceramics at moderate furnace temperature and in short time (few seconds) as compared to the conventional sintering techniques. The onset of flash encompasses three unique characteristics, (i) non-linear rise in conductivity, (ii) luminescence and (iii) rapid densification. the mechanism behind the flash phenomena is not fully understood yet. The present work experimentally demonstrated that the densification in flash sintering is primarily dominated by Joule heating. Herein, we distinguished the onset of flash and the degree of densification of cubic zirconia in sintering atmospheres with different oxygen partial pressures. In this study, we demonstrate that the flash onset temperature and densification are independently influenced by the sintering atmosphere during flash sintering. Furthermore, the extent of densification is not directly influenced by the current density rather, by the power dissipated in the sample. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this work we investigate the long-term effects of exposing an inorganic membrane for 1100h in a flue gas stream of a coal power plant. Of particular importance, from an industrial testing perspective, was the effect of fly ash deposition, water vapour and acid gases on the integrity of the membrane made of cobalt silica coated on a substrate of 316L steel, with interlayers of 310S steel, yttria-stabilized zirconia and γ-alumina. Subsequent to the flue gas testing, the membrane was characterized for single gas permeance, SEM and EDX spectroscopy. Diffusion of nickel and chromium during sintering was observed at the interface of the 316L/310S steels, resulting in a reduced capacity to withstand corrosion in this area. Single gas permeation testing following flue gas exposure revealed a maximum permeation of 1.85×10−8 molm−2 s−1 Pa−1 and 2.13×10−8 molm−2 s−1 Pa−1 for helium and hydrogen respectively, and selectivity of 5.1 and 5.2 for He/N2 and H2/CO2 respectively, was achieved at a pressure difference of 2×105 Pa (2bar) at 200°C. The permeation behavior of the membrane appeared to be altered as a result of flue gas exposure with the membrane displaying a reduced H2 flux in contrast to an unexposed but otherwise identical membrane which displayed fluxes an order of magnitude higher than the membrane used in the power plant. This change in permeation behavior was thought to be the result of densification of the silica matrix following long-term exposure to flue gas containing water vapour. Micro-fractures in the surface of the cobalt silica gas separation layer were also observed, possibly the result of expansion due to corrosion. However, bulk diffusion was not observed suggesting that the layer was not completely compromised. [Copyright &y& Elsevier]

Abstract: Frequently, the membrane employed in a traditional nano-filtration (NF) or gas separation (GS) membrane device consists of a polymeric material, having significant disadvantages including a restricted mechanical, chemical and thermal stability. As an alternative for the polymeric membranes, ceramic membranes with an improved stability have been introduced, but the current membranes still suffer from stability problems (e.g. brittle material, restricted chemical stability in water vapour). This paper reports the preparation of novel hybrid metallic–ceramic membranes, based on a porous 316L stainless-steel support material. The optimized membranes were made by deposition of a fine suspension with a particle size of ~180 nm, a colloidal sol with a particle size of ~30 nm and a nano-particle sol with a particle size of ~5 nm and show a comparable multilayer structure as current ceramic membranes for micro-, ultra- and nano-filtration and gas separation. The essential new features of the membranes include the use of an alternative metallic support material, which provides a high mechanical stability to the membrane, and the application of zirconia- and titania based functional membrane layers, which display a high chemical and thermal stability for potential filtration or gas separation applications. [Copyright &y& Elsevier]

• Thermal expansion of composites is close to its theoretical value expect for 75W. • Thermal conductivity of composites lies in the range between 15 and 25 Wm-1K-1. • W/FGM/steel joint manufactured using V filler at optimized parameter of 1000 °C, 30 min, 50 MPa. • Porosity of FGM inside the joint lies the range between 3 and 4 %. The differences in the thermophysical properties between tungsten and steel create thermal stress peaks at its interface when joined directly for the breeding blanket of a fusion reactor. In order to solve this problem, a graded interlayer made of several layers of W/steel-composites is considered to reduce these stress peaks. Plasma spraying under an argon shrouded chamber was employed as a cost efficient manufacturing technique for such composites and field assisted sintering technology/spark plasma sintering was used to diffusion bond them with bulk-W and bulk-steel. Firstly, thermophysical characterizations were performed on these composites. Secondly, two approaches have been investigated to join bulk-W and 75 vol% W composite: direct joining and using a vanadium foil. Only vanadium foil resulted in successful bond formation at all the three bonding temperatures of 800 °C, 900 °C and 1000 °C. Thirdly, investigation of diffusion bonding parameters (temperature and time) for the joining of 25 vol% W, 50 vol% W, 75 vol% W and bulk-steel were studied and optimum process parameter were identified. Finally, this optimized parameter (1000 °C; 30 min) was employed to manufacture a complete 12 mm x 12 mm W-steel joint consisting of this graded interlayer. [ABSTRACT FROM AUTHOR]

• Joining smart alloys to EUROFER without interface layer was achieved by FAST. • W–Fe diffusion zone formed at the interface during joining. • Hardness decrease with increasing grain size was shown experimentally. • Chromium-carbides were detected around Cr-rich phases using STEM. Tungsten test is currently the baseline first-wall armor material for a future DEMOnstration power plant. Smart alloys, containing tungsten (W), 11.4 weight (wt) % chromium (Cr), and 0.6 wt% yttrium (Y), aim at achieving passive safety in case of air ingress into the vacuum vessel and a loss-of-coolant accident causing a temperature rise above 1200 K for weeks. In such a case, smart alloys suppress oxidation and sublimation of radioactive W. This publication summarizes several important properties of smart alloys: the suppression of oxidation, the hardness as a function of the microstructure, and potential carbide formation in the presence of carbon (C) impurities. Further, first results on joining them to the EUROFER by field-assisted sintering technology (FAST) without interface layer are presented. In literature, FAST is also known as spark plasma sintering (SPS). A stable joint with an tungsten–iron (W–Fe) diffusion layer of 100 nm at the interface was achieved. The joint survived several heat cycles to 873 K. [ABSTRACT FROM AUTHOR]

One of the necessary prerequisites to advance the electrochemical performance of Li 7 La 3 Zr 2 O 12 (LLZ) based all-solid-state lithium batteries is the manufacturing of dense composite cathodes from cathode active material (CAM) and the LLZ ceramic solid electrolyte. However, free co-sintering of LLZ and CAM mixtures requires temperatures above 1000 °C which often leads to decomposition and secondary phase formation, especially for high energy CAMs. In our study we present a completely dry processing route which is fast, free of any sintering additives and coatings and suitable to fabricate dense mixed cathodes, pure LLZ separators and multilayers of the two. Through application of high mechanical pressure during Field-Assisted Sintering we were able to reduce the sintering temperature down to 675–750 °C with dwell times as low as 10 min, while still obtaining 95% theoretical density for LCO/LLZ mixtures. The low sintering temperature is suitable for high energy CAMs, but leads to a significant effect of surface impurities, especially from powder handling in air, and affects the crystallinity of the CAM/LLZ interface. In the present paper we investigate the impact of resulting interfaces on the ionic conductivity, the interfacial impedance and the cycling stability of produced cells and propose the optimization strategy. Image 1 • High-pressure spark plasma sintering enables low-T sintering of LLZ at 675 °C. • Surface impurities significantly decrease ionic conductivity of low-T sintered LLZ. • Amorphous grain boundaries between LCO and LLZ lead to high interface impedance. • Crystallization of interface reduces impedance and improves battery performance. • Low-T fabricated LLZ based all-solid-state batteries with high capacity. [ABSTRACT FROM AUTHOR]

During an accident with loss-of-coolant and air ingress in DEMO, the temperature of tungsten first wall cladding may exceed 1000 °C and remain for months leading to tungsten oxidation. The radioactive tungsten oxide can be mobilized to the environment at rates of 10–150 kg per hour. Smart tungsten-based alloys are under development to address this issue. Alloys are aimed to function as pure tungsten during regular plasma operation of DEMO. During an accident, alloying elements will create a protective layer, suppressing release of W oxide. Bulk smart alloys were developed by using mechanical alloying and field-assisted sintering technology. The mechanical alloying process was optimized leading to an increased powder production by at least 40 %. Smart alloys and tungsten were tested under a variety of DEMO-relevant plasma conditions. Both materials demonstrated similar sputtering resistance to deuterium plasma. Under accident conditions, alloys feature a 40-fold reduction of W release compared to that of pure tungsten. [ABSTRACT FROM AUTHOR]

• Y content of 0.6 wt% Y optimum for oxidation resistance of bulk smart alloy. • Degradation of oxidation resistance due to oxygen impurities in the alloy shown. • Re introduced in the alloy to investigate the effect caused by neutron irradiation. • Spatially heterogeneous simulation of the exposure to 14 MeV neutrons. • Depth resolved simulation of Re, V, H, and He production due to neutron irradiation. Tungsten (W) is a prime candidate as first wall armor material of future fusion power plants as W withstands extreme particle, heat, and radiation loads without forming long-lived radioactive waste. The release of radioactive material from the reactor to the environment should be suppressed in case of an accident such as a loss of coolant (LOCA) with simultaneous air ingress into the vacuum vessel. W oxidizes and sublimates in case of a LOCA. Therefore, oxidation resistant tungsten, chromium, yttrium (W–Cr–Y) alloys are developed to provide intrinsic safety in case of such an accident. In this paper, the optimization of the yttrium (Y) concentration is presented on bulk samples compacted by field assisted sintering technology (FAST). W with 11.4 weight (wt)% Cr and 0.6 wt% Y appears to be an optimum regarding the oxidation resistance. Further, first preparations for industrial upscaling, which may increase the impurity level, are addressed. The oxygen (O) content is varied systematically. It is shown that a good oxidation resistance requires a low O level. The exposure of the material to fusion neutrons is another issue addressed on W–Cr–Y alloys. In a non-activated environment it is shown that 1 wt% rhenium (Re) dramatically changes the oxidation kinetics: at 1273 K the mass gain of W–Cr–Y–Re follows a cubic rate law while W–Cr–Y follows a linear rate law for two days. Further, the influence of the alloying elements on the neutron transport and transmutation of W is studied by simulating the exposure of spatially heterogeneous high-resolution models of the W–Cr–Y alloys to 14 MeV fusion neutrons. [ABSTRACT FROM AUTHOR]

Metal-supported fuel cells (MSCs) are promising candidates for not only stationary but also mobile applications. Their appeal is in their potential to withstand reoxidation of the anode, which might occur by an interruption of the fuel supply or an emergency shutdown of the fuel cell system. A novel nickel/gadolinium-doped ceria anode (Ni/GDC) was recently introduced in a MSC concept of Plansee, almost doubling power density compared to cells with a nickel/yttria-doped zirconia (Ni/YSZ) anode. In this study, both cell concepts are compared concerning their ability to tolerate harsh redox cycles. Therefore, controlled redox cycles of the anodes were conducted at different temperatures. The response of the cell's power output to the redox cycling experiments was continuously recorded. In the case of MSCs with a Ni/YSZ anode, strong degradation occurs after redox cycling. In contrast, cells with a Ni/GDC anode exhibit significantly improved redox tolerance and cell performance improves with the number of redox cycles. For understanding this behavior, microstructural investigations of the Ni/GDC anode and the adjacent electrolyte were performed by FIB-SEM. The long-term redox behavior of MSCs with a Ni/GDC anode was also investigated by conducting more comprehensive redox cycles at 400 °C, 500 °C, and 600 °C. • Metal-supported fuel cells with novel Ni/GDC anode show outstanding performance. • Ni/GDC anode is more tolerant against redox cycling than established Ni/YSZ anode. • Comparative study on cells with Ni/YSZ and Ni/GDC anodes was performed. • Performance testing was conducted including electrochemical impedance spectroscopy. • Microstructural changes could be evaluated by FIB-SEM 3D reconstruction technique. [ABSTRACT FROM AUTHOR]

Transparent polycrystalline ceramics have the potential to enable applications no other materials can, but to do so their strength and toughness must be improved. However, surface strengthening treatments like those used for glasses have so far remained elusive. Here for the first time, we report on engineering unprecedented surface compression, of the magnitude achieved for ion-exchange strengthened glasses (~750 MPa) in transparent ceramics. This was achieved by applying functional, low thermal-expansion yttria coatings onto yttria-stabilized zirconia substrates and thermally treating. In some instances, the treatment more than doubled the fracture toughness while simultaneously increasing light transmittance.