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Oxide-ceramic based all-solid-state lithium batteries (ASSLB) can provide high intrinsic safety, extended operational temperature range, and high energy density. As the first two are intrinsic to the materials system, one prerequisite to obtain high energy densities with such ASSLBs is the manufacturing of composite cathodes. Preferably, cathode active material (CAM) and electrolyte should form an intertwined 3D-network with an intimate extended contact between two phases. The interface between the CAM and the electrolyte should feature high total surface area with a low impedance to enable an efficient charge transfer and transport and minimize the resistance losses in a battery. Composite solid cathode microstructures can be formed via a co-sintering of solid electrolyte and CAM powders. However, many CAMs such as Li[Ni1-x-yCoxMny]O2 (NMC), Li[Ni1-x-yCoxAly]O2 (NCA) or Li2NiMn3O8 (LMO) cannot withstand sintering temperatures required, for oxide class solid electrolytes as Li7La3Zr2O12 (LLZ) or Li1+xAlxTi2-x(PO4)3, to obtain sintered composite cathodes. Furthermore, the thermodynamic stability of CAMs significantly decreases in the presence of solid electrolytes. Still, several groups have demonstrated that thermodynamic limitations can be significantly lessened via a kinetic control of the process such as reduction of reaction times and a careful control of powder morphology during ceramic sintering process. Following this work, we now demonstrate that FAST/SPS enables fabrication of different solid-state battery components within minutes such as a dense LLZ separator layer with a high ionic conductivity, a dense dual LiCoCO2 (LCO)/LLZ composite cathode without any interfacial reactions, and an integrated cathode half-cell consisting of a composite cathode and a LLZ separator layer at temperatures as low as 675 – 800 °C. Analyzing the structure, morphology, and electrochemical performance of the obtained components, we conclude that the impurities (carbonates) on the surface of LLZ powder play a decisive role in the formation of high-quality interfaces and the minimization of porosity. Furthermore, these impurities decrease the ionic conductivity at low sintering temperature and deteriorate the cycling stability of an ASSLB. High areal capacity of up to 4.0 mA h/cm2 at 80 °C with a constant current of 50 µA/cm2 and a good utilization of LCO was achieved for ASSLB with LLZ powders free of surface impurities. FAST/SPS can therefore open new processing windows for ceramic-based ASSLBs to alleviate the problem of interphase formation.

Inhibition of dendrite growth in all-solid-state lithium batteries (ASSLBs) has long been a challenge to the field. In the present study, the conditions for dendrite growth for a similar but less mature technology, all-solid-state sodium batteries (ASSNBs), are investigated. By simply sticking sodium metal to Na3.4Zr2(SiO4)2.4(PO4)0.6 (NZSP) ceramic pellets and without applying external pressure during operation, the critical current density of Na/NZSP/Na symmetric ASSNBs reaches 9 mA cm−2 at 25 °C. The cells can be stably operated at an areal capacity of 5 mAh cm−2 (per half cycle, with 1.0 mA cm−2) at 25 °C for 300 h in a galvanostatic cycling measurement without any dendrite formation. The results outperform the existing ASSLBs and ASSNBs, and also go beyond satisfying the requirements for practical applications. The influence of the high metal self-diffusion coefficient on the dendritic plating/stripping is regarded as the most likely reason for the high dendrite tolerance of ASSNBs. A mathematical model based on Fick's second law was applied as a first approximation to illustrate this influence. Full ASSNBs were fabricated with infiltrated Na3V2(PO4)3 (NVP) as the cathode and can be stably operated with a capacity of 0.60 mAh cm−2 at high rate of 0.5 mA cm−2 at room temperature.

Gadolinium zirconate (Gd2Zr2O7, GZO) as an advanced thermal barrier coating (TBC) material, has lower thermal conductivity, better phase stability, sintering resistance, and calcium‐magnesium‐alumino‐silicates (CMAS) attack resistance than yttria‐stabilized zirconia (YSZ, 6‐8 wt%) at temperatures above 1200°C. However, the drawbacks of GZO, such as the low fracture toughness and the formation of deleterious interphases with thermally grown alumina have to be considered for the application as TBC. Using atmospheric plasma spraying (APS) and suspension plasma spraying (SPS), double‐layered YSZ/GZO TBCs, and triple‐layered YSZ/GZO TBCs were manufactured. In thermal cycling tests, both multilayered TBCs showed a significant longer lifetime than conventional single‐layered APS YSZ TBCs. The failure mechanism of TBCs in thermal cycling test was investigated. In addition, the CMAS attack resistance of both TBCs was also investigated in a modified burner rig facility. The triple‐layered TBCs had an extremely long lifetime under CMAS attack. The failure mechanism of TBCs under CMAS attack and the CMAS infiltration mechanism were investigated and discussed.

In this chapter, after having introduced the basics of electrochemical storage and types of secondary batteries, detailed focus is given on: (i) anode ceramic materials, (ii) cathode active materials, and (iii) separators and solid electrolytes. Chemistries of interest are based on lithium and sodium, covering both current commercial applications as well as technologies under development such as solid-state batteries.

Journal of the American Ceramic Society 103(10), 5952-5965 (2020). doi:10.1111/jace.17323 special issue: "Special Issue: Special section: Honoring the Legacy of Dr. Eric "Lou" Vance", Published by Wiley-Blackwell, Oxford [u.a.]

In situ high‐temperature powder X‐ray diffraction analysis (HT‐XRD) was carried out in the temperature range from 25°C‐1430°C to investigate the crystal structure of double perovskites, La2(Al1/2MgTa1/2)O6 (LAMT) and its phase transitions. This complex perovskite is a promising candidate for application in thermal barrier coating systems. Rietveld analysis shows a rock‐salt type ordering of the B‐site cations in the monoclinic space group symmetry, P21/n at room temperature. Upon heating, a structural phase transition occurs at ~855°C, and the crystal structure becomes rhombohedral with the space group symmetry urn:x-wiley:00027820:media:jace16740:jace16740-math-0001. On further heating, LAMT transforms to the ideal cubic phase at ~1390°C with the space group symmetry urn:x-wiley:00027820:media:jace16740:jace16740-math-0002. Both of the structural phase transitions are completely reversible, and were confirmed through complementary differential scanning calorimetry and thermogravimetry measurements. With increasing temperature, the degree of the octahedral tilting decreases and the variance of the different B–O bond lengths is reduced, until in the cubic phase, no tilting is present, and almost equal B–O bond lengths are obtained.

Free-standing Li1.5Al0.5Ti1.5P3O12 electrolyte sheets with a thickness of 50–150 μm were prepared by tape casting followed by sintering at 850–1000 °C in air. While a sintering temperature of 850 °C was too low to achieve appreciable densification and grain growth, a peak relative density of 95% was obtained at 920 °C. At higher sintering temperatures, the microstructure changed from a bimodal grain size distribution towards exclusively large grains (> 10 μm), accompanied by a decrease in relative density (down to 86% at 1000 °C). In contrast, ionic conductivity increased with increasing sintering temperature, from 0.1 mS/cm at 920 °C to 0.3 mS/cm at 1000 °C. Sintering behavior was improved by adding 1.5% of amorphous silica to the slurry. In this way, almost full densification (99.8%) and an ionic conductivity of 0.2 mS/cm was achieved at 920 °C. Mechanical characterization was carried out on the almost fully densified material, yielding elastic modulus and hardness values of 109 and 8.7 GPa, respectively. The fracture strength and Weibull modulus were also characterized. The results confirm that densification and reduction of grain size improve the mechanical properties.

In high‐temperature combustion atmospheres, well‐adhering environmental barrier coatings (EBCs) are required to protect the underlying ceramic matrix composites (CMCs) from corrosion. Herein the adhesion mechanisms of three different coatings produced by atmospheric plasma spraying (APS) on an Al2O3/Al2O3‐CMC are investigated. In particular, the influence of surface structuring by laser ablation prior to coating production is investigated. Y2O3, yttria‐stabilized zirconia (YSZ), and Gd2Zr2O7 are chosen as potential EBCs. The coating adhesion on CMC‐substrates with and without surface structuring is analyzed by furnace cycling, pull‐adhesion tests, and burner‐rig tests with gradient. Special interest is paid to the interactions at the coating–substrate interface before and after heat treatment and their effect on the coating adhesion and lifetime. Two different adhesion mechanisms are found: adhesion promoted by chemical reaction and adhesion promoted by mechanical interlocking.

Applying atmospherically plasma-sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) protective coatings on interconnector steels minimized the chromium-related degradation within solid oxide fuel cell stack-tests successfully. Post-test characterization of the coatings disclosed a severe microstructural and phase evolution. A self-healing of micro-cracks, the formation and agglomeration of small pores, the occurrence of a dense spinel layer at the surface and a strong elemental de-mixing were reported in ex situ experiments. In the present publication, we prove for the first time these mechanisms by tracking the microstructure in situ at a single APS coating using synchrotron X-ray nano-tomography at the European Synchrotron Radiation Facility. Therefore, a 100-µm-long cylindrical sample with a diameter of 123 µm was cut from an APS-MCF free-standing layer and measured within a high-temperature furnace. All microstructural changes mentioned above could be verified. Porosity measurements reveal a decrease in the porosity from 9 to 3% during the annealing, which is in good accordance with the literature. Additionally, a partial detachment of an approximately 5-µm-thick layer at the sample surface is observed. The layer is dense and does not exhibit any cracks which are penetrating the layer. This kind of shell is assumed to be gastight and thus protecting the bulk from further oxidation.

Gadolinium-Doped Ceria (GDC) is a prospective material for application in electrochemical devices. Free sintering in air of GDC powder usually requires temperatures in the range of 1400 to 1600 &deg, C and dwell time of several hours. Recently, it was demonstrated that sintering temperature can be significantly decreased, when sintering was performed in reducing atmosphere. Following re-oxidation at elevated temperatures was found to be a helpful measure to avoid sample failure. Sintering temperature and dwell time can be also decreased by use of Spark Plasma Sintering, also known as Field-Assisted Sintering Technique (FAST/SPS). In the present work, we combined for the first time the advantages of FAST/SPS technology and re-oxidation for sintering of GDC parts. However, GDC samples sintered by FAST/SPS were highly sensitive to fragmentation. Therefore, we investigated the factors responsible for this effect. Based on understanding of these factors, a special tool was designed enabling pressureless FAST/SPS sintering in controlled atmosphere. For proof of concept, a commercial GDC powder was sintered in this tool in reducing atmosphere (Ar-2.9%H2), followed by re-oxidation. The fragmentation of GDC samples was avoided and the number of micro-cracks was reduced to a minimum. Prospects of GDC sintering by FAST/SPS were discussed.

Gas turbine components are often operated in harsh conditions, which can lead to severe damage. As it is highly desirable from both an economical and an ecological point of view to restore these worn areas instead of manufacturing new components, repair technologies are of huge interest for companies supplying maintenance and overhaul of gas turbines. In this article, two thermal techniques are described that can be used for this application: cold gas spraying (CGS) and vacuum plasma spraying (VPS). The CGS process allows the deposition of metallic coatings with excellent mechanical properties; several examples including γ‐TiAl, Inconel (IN) 718, and IN 738 are given. Essential for the deposition of high‐performance coatings in CGS is to exceed the so‐called critical velocity. This is discussed also with experimental findings. As a final topic, experiments that use VPS for the repair of single‐crystal alloys are described.

Material issues pose a significant challenge for the design of future fusion reactors. Recently progress has been made towards fully dense multi short-fibre powder metallurgical production of tungsten-fibre reinforced tungsten (Wf /W) as well as optimizing the process understanding for the routes using chemical vapour deposition (CVD). For CVD-Wf /W weaves and textile preforms are being used to facilitate large scale production. Classically 150 μm tungsten fibres supplied by OSRAM GmbH have been used. In order to facilitate the better use of textile processes less stiff 16 μm filaments are being evaluated. The strength of the 16 μm filament is at 4500 MPa and thus significantly higher than the strength of the 150 μm fibre (~2500 MPa) (in the as-fabricated state). Better weavability allows a more flexible use of fibre preforms Two main yarn production routes have been investigated: covered yarns where a set of tungsten filaments is held together by a PVA (Polyvinyl alcohol) cover and braided yarns. In order to allow a comparison to the previously used single fibres, yarns with ~140 μm effective diameter were produced. Braided yarns with tensile strength of 2500 MPa and 6% strain at fracture and twisted yarns with tensile strength of 4500 MPa and 3% strain at fracture. For both yarns single fibre CVD samples have been produced to investigate the infiltration properties of the yarns and thus their applicability for the CVD route. A dense infiltration is observed for all yarns under investigation

The mobility of Na+ ions in Na3+xSc2(SiO4)x(PO4)3−x (0.1 < x < 0.8) was investigated by temperature-dependent 23Na NMR spectroscopy and relaxometry. These measurements are probing the local motion of the Na+ ions and give information about the average hopping rate of the ions and the activation barriers these ions have to overcome for single jumps. The results are compared with those obtained by impedance spectroscopy that is probing the long-range transport of the Na+ ions. A consistent picture is obtained with the fastest motion of the Na+ ions observed for the sample with x = 0.4.

Journal of the Electrochemical Society 169(2), 020556 (2022). doi:10.1149/1945-7111/ac5348, Published by IOP Publishing, Bristol

Sintering is one of the key issues in the high temperature service of thermal barrier coatings (TBCs), considering the continuously increasing operation temperature of gas-turbine for higher energy efficiency. Based on the conventional processing method of air plasma spraying (APS), suspension plasma spraying (SPS) technique has been developed recently, in order to improve the strain tolerance of TBCs. This strain tolerance of plasma-sprayed TBCs is largely effected by the sintering behavior, which is presently not fully understood. In this work, evolution of mechanical properties, in terms of Young’s modulus and viscosity, is systematically investigated by in-situ three-point bending test at 1200 °C on free-standing coatings, including micro-cracked APS, segmented APS, vertically cracked SPS and columnar structured SPS TBCs and correlated to the microstructural evolution. Based on experimental results, power law relations are proposed for the sintering induced mechanical evolution, which deepen the understanding of the sintering behavior of plasma-sprayed TBCs.

© 2018 Elsevier B.V. The influence of advanced thermal insulation on energy consumption and temperature distribution during electric field assisted sintering of conductive stainless steel powder and non-conductive zirconia powder was investigated. Four types of tool setup were considered: i) without insulation, ii) with die wall insulation, iii) with additional insulation of die faces and iv) with spacers manufactured from carbon fiber reinforced carbon composite (CFRC). The influence of thermal insulation on energy consumption was experimentally studied for samples with diameter of 17 mm. The temperature distribution in samples with diameters of 17 mm, 50 mm and 150 mm was modeled using the Finite Element Method. The power consumed during dwell was almost half the value when die wall insulation was used. The additional insulation of die faces and the application of CFRC spacers provide a threefold decrease in power during sintering of steel powder and a fivefold reduction during sintering of zirconia powder. The advanced thermal insulation significantly homogenizes the temperature distribution within samples of small and medium size. The advanced thermal insulation provides a strong decrease in the temperature gradient inside large conductive sample with a diameter of 150 mm. However, insulation apparently cannot ensure acceptable temperature homogeneity within non-conductive parts of such diameter. The reason for this is the specific current path and related heat concentration near the sample edge. ispartof: JOURNAL OF MATERIALS PROCESSING TECHNOLOGY vol:262 pages:326-339 status: published

Considering the challenging conditions imposed by application of membranes in an asymmetric design, in particular creep resistance of the substrate material is an important parameter for the stability in long-term operation. As promising material, in terms of chemical stability, the perovskite SrTi0.75Fe0.25O3-δ has been identified in previous works. Porous supports with different microstructures have been produced using different manufacturing methods and compared to the material in its fully dense state regarding creep behaviour. The creep deformation of pressed, porous tape-cast and freeze-dried SrTi0.75Fe0.25O3-δ specimens has been investigated in the application relevant temperature range of 850–1000 °C under compressive stresses of 15, 30 and 45 MPa. A global fitting method considering all experimental data was used to derive stress exponent and activation energy of SrTi0.75Fe0.25O3-δ, which are 2.9 ± 0.4 and 402 ± 25 kJ/mol, respectively. Thus, it is suggested that the mechanism controlling creep is mainly related to dislocation climb/glide.

Perovskite-structured powders of SrTi1-xCoxO3-δ (STC-x) with nominal stoichiometry of x = 0–0.75 as well as SrTi0.75Co0.25-yFeyO3-δ (STCF-y) where y = 0–0.25 were synthesized using the Pechini method. Thermal/chemical expansion behaviour, total electrical conductivities, and oxygen permeation rates were investigated. The substitution of Ti with Co leads to an increase in both electronic and ionic conductivities and, therefore, oxygen permeability. Thermal and chemical expansions also increase slightly. The optimum Co content was found to be 25–35% due to the trade-off between phase stability and permeability. The oxygen permeation rate of STC35 is comparable to that of state-of-the-art (La,Sr)(Co,Fe)O3-δ, whereas the expansion coefficients are lower. Co-doping in STCF-y did not produce any significant differences in oxygen permeability at both high temperature and sample thickness (1.0 mm), i.e. in a solid-state diffusion-limited regime. At lower temperatures (

As structural materials for future fusion power plants, reduced activation ferritic martensitic steels as EUROFER97 can be used. Unfortunately, the interaction of the plasma with the steel would result in a limited lifetime, so protective layers are investigated. An excellent protective material is tungsten, as it shows unique properties with respect to low sputtering, high melting points and low activation. However, the mismatch of thermo-physical properties between tungsten and EUROFER97 can lead to large stress levels and even failure. A possible way to overcome this problem is the use of functionally graded material (FGM). The paper will describe the manufacture of these FGMs by vacuum plasma spraying and their characterization. First of all, two different feeding lines have been used to produce the coatings. A major problem lies in different melting points of tungsten and steel. So the particle size distribution has to be adjusted to achieve sufficient melting of both materials during the spray process. In a second step, the feeding rates were optimized to obtain the wanted amount of tungsten and steel phases in the graded structures. In a thermal spray process, the gradient cannot be made continuously, however it has to be applied in a step-wise manner. In this investigation, samples with 3 and 5 different concentrations (excluding the pure steel and tungsten part) have been produced. The microstructures of these layers have been investigated. In addition, hardness was measured and the residual stress state was determined by the hole drilling method.

Garnet Li6.4La3Zr1.6Ta0.4O12 thin films prepared by magnetron sputtering were analysed by secondary ion mass spectrometry, nuclear reaction analysis and Rutherford backscattering to identify, localize and quantify the reactions associated with the presence of low amounts of water and carbon dioxide. Samples in a pristine state and after storage in an Argon-filled glove box for months were compared. Both, lithium hydroxide and lithium carbonate were detected, with carbon-containing species and hydrogen-containing having surprisingly different depth profiles.

The thermal stability of LiCoMnO4 and LiCoMnO4 with 1 wt.-% LiF as an additive was compared upon heating in air. The stoichiometries of samples heat-treated at 700, 800, 900 and 1000 °C were analyzed by means of inductively coupled plasma optical emission spectroscopy for cation contents, inert gas fusion analysis for oxygen, and nuclear reaction analysis for fluorine contents, revealing that the sample chemistries remain constant except for oxygen. The oxygen content of the samples correlates with the Li2MnO3 secondary phase fraction, which forms upon heating, as is shown by X-ray powder diffraction. For each temperature, a greater amount of Li2MnO3 is formed in the samples with LiF addition than in the single LiCoMnO4 samples. In situ high-temperature X-ray powder diffraction between 650 and 950 °C demonstrates that LiCoMnO4 with LiF addition exhibits the same kind of decomposition reactions upon heating and cooling as the sample without LiF addition. However, for the samples with LiF addition, the formation of the decomposition product, Li2MnO3, is accelerated due to the excess Li through LiF addition, i.e. the stability of the spinel phase decreases due to the supply of lithium. Since lithium is consumed by Li2MnO3 formation and fluorine remains in the samples, we can also conclude that the fluorine anion is incorporated into the spinel or Li2MnO3 phase upon heating LiCoMnO4 and LiF together.

Hierarchically porous SrTi 0.75 Fe 0.25 O 3-δ specimens were produced through a freeze drying procedure, which yielded a channel-like porosity, reaching a value of 32%. Compressive testing was used to determine apparent elastic modulus and fracture stresses in the transverse (out-of-plane) and longitudinal (in-plane) direction, revealing a strong dependence onto pore orientation. The lower mechanical stability in the in-plane direction appears to be associated with bending mode of the pore walls, being a result of a lower resistance to crack initiation. Acoustic emissions recorded during compressive tests indicated continuous damage of the pore walls before complete failure of the specimen, which could be also confirmed by complementary in-situ compressive tests in a scanning electronic microscope.

An equimolar substitution of Zr4+ with Al3+ and Y3+ was chosen to prepare two NASICON series, Na1+2xAlxYxZr2−2x(PO4)3 and Na3+2xAlxYxZr2−2x(SiO4)2(PO4)3, which were compared with previously investigated Sc3+-substituted NASICON materials. The common feature of all series is a mean effective ionic radius of the transition metal cations of 0.718 A 0.1). The average linear coefficient of thermal expansion of Na3+2xAlxYxZr2−2x(SiO4)2(PO4)3, obtained from high temperature X-ray diffraction, increased when x was raised from 4.1 · 10−6 K−1 to 8.1 · 10−6 K−1. The ionic conductivity of Na1+2xAlxYxZr2−2x(PO4)3 compositions was one to two orders of magnitude lower than the Na3+2xAlxYxZr2−2x(SiO4)2(PO4)3 series. For the latter series, conductivity decreased when the Al/Y substitution was increased, despite the number of charge carriers (Na+) increasing. Conductivity was 0.8 mS cm−1 when x = 0, and 0.08 mS cm−1 when x = 0.3. This demonstrates that the transport properties in NASICON materials are not only affected by the steric interactions (i.e. reff, mean width of conduction path) but also the electrostatic interactions (charge, bond strength, atomic orbitals) of the substituting cations.

In this work, we studied the deposition of garnet electrolyte thin films in order to realize an all-solid-state battery with high energy density. Therefore, in a first step we investigated the stability of the garnet Li5La3Ta2O12 with the spinel LiCoMnO4 in order to determine the temperature window for a successful thin film deposition on high-voltage spinels. A mixture of both materials showed a thermal stability up to 600 °C, so that all-solid-state batteries could be realized when the electrolyte is applied at a low deposition temperature. The second part of the work was the thin film deposition of Li5La3Ta2O12 by a sputter deposition process. When a stoichiometric Li5La3Ta2O12 sputter target was used, the surface of the target showed a depletion of lithium after several depositions, which leads to decreasing Li content in the thin films. In order to compensate the lithium loss we enriched the target with LiOH∙H2O. Depositions carried out with the lithium rich target showed the garnet structure on glass substrates after deposition at 500 °C. The garnet structure was observed on Au-coated EN 1.4767 substrates already at a substrate temperature of 400 °C, which is 300 K lower than comparable depositions of Li7La3Zr2O12. These results show that the combination of thin garnet-structured electrolytes and high-voltage spinels is possible.

On the basis of previous studies of perovskites in the quasi-ternary system LaFeO3–LaCoO3–LaNiO3, LaNi0.5Co0.5O3 (LNC) is chosen as the most promising air-electrode material in the series for solid...

In the Plasma Spray-Physical Vapor Deposition (PS-PVD) process, columnar structured coatings are deposited mainly from the vapor phase due to the intensive evaporation of the feedstock powder. This paper highlights the application of electron backscatter diffraction (EBSD) for the characterization of columnar structured ceramic PS-PVD coatings. The growth processes of PS-PVD coatings could be elucidated, developing from small equiaxed crystals to large columnar crystals. Furthermore, the main effect of the torch swing on coating deposition could be the interruption of crystal growth and thus repeated nucleation. This may have a similar effect as slowly rotating the substrate in Electron Beam-Physical Vapor Deposition (EB-PVD).

The plasma spray-physical vapor deposition technique (PS-PVD) is used to deposit various types of ceramic coatings. Due to the low operating pressure and high enthalpy transfer to the feedstock, deposition from the vapor phase is very effective. The particular process conditions allow for the deposition of columnar microstructures when applying thermal barrier coatings (TBCs). These coatings show a high strain tolerance similar to those obtained by electron beam-physical vapor deposition (EB-PVD). But compared to EB-PVD, PS-PVD allows significantly reducing process time and costs. The application-related properties of PS-PVD TBCs have been investigated in earlier work, where the high potential of the process was described and where the good resistance to thermo-mechanical loading conditions was reported. But until now, the elementary mechanisms which govern the material deposition have not been fully understood and it is not clear, how the columnar structure is built up. Shadowing effects and diffusion processes are assumed to contribute to the formation of columnar microstructures in classical PVD processing routes. For such structures, crystallographic textures are characteristic. For PS-PVD, however, no crystallographic textures could initially be found using X-ray diffraction. In this work a more detailed TEM investigations and further XRD measurements of the columnar PS-PVD microstructure were performed. The smallest build units of the columnar TBC structure are referred to as sub-columns. The observed semi-single crystal structure of individual sub-columns was analyzed by means of diffraction experiments. The absence of texture in PS-PVD coatings is confirmed and elementary nucleation and growth mechanisms are discussed.

In the atmospheric plasma spray (APS) process, micro-sized ceramic powder is injected into a thermal plasma where it is rapidly heated and propelled toward the substrate. The coating formation is characterized by the subsequent impingement of a large number of more or less molten particles forming the so-called splats and eventually the coating. In this study, a systematic investigation on the influence of selected spray parameters on the coating microstructure and the coating properties was conducted. The investigation thereby comprised the coating porosity, the elastic modulus, and the residual stress evolution within the coating. The melting status of the particles at the impingement on the substrate in combination with the substrate surface condition is crucial for the coating formation. Single splats were collected on mirror-polished substrates for selected spray conditions and evaluated by identifying different types of splats (ideal, distorted, weakly bonded, and partially molten) and their relative fractions. In a previous study, these splat types were evaluated in terms of their effect on the above-mentioned coating properties. The particle melting status, which serves as a measure for the particle spreading behavior, was determined by in-flight particle temperature measurements and correlated to the coating properties. It was found that the gun power and the spray distance have a strong effect on the investigated coating properties, whereas the feed rate and the cooling show minor influence.

Fluorinated LiCoMnO4–yFy (y = 0, 0.05, 0.1) spinel electrodes, electrochemically active at 5–5.3 V versus Li/Li+, show enhanced phase purity and enhanced capacity with increasing y. We disclose the impact of fluorination on the phase purity and reversible capacity of LiCoMnO4 via joint Rietveld refinement of neutron and synchrotron powder diffraction data, combined with micro-Raman spectroscopy. It is found that fluorination stabilizes the spinel phase and hinders precipitation of Li2MnO3 as a secondary phase, which controls the cation distribution on tetrahedral and octahedral sites in spinel. That is to say, for higher fluorine content the cobalt occupancy at the tetrahedral site in spinel decreases, and the lithium occupancy increases. Accordingly, the number of lithium sites that are available for electrochemical extraction and insertion of lithium ions is raised so that the capacity is increased. Further investigation of the lithium ion diffusion by means of cyclic voltammetry at different scan rates...

A four-layer solid oxide fuel cell stack with planar anode-supported cells was operated galvanostatically at 700 °C and 0.5Acm−2 for nearly 35,000 h. One of the four planes started to degrade more rapidly after ∼28,000 h and finally more progressively after ∼33,000 h. The stack was then shut down and a post-test analysis was carefully performed. The cell was characterized with respect to cathodic impurities and clarification of the reason(s) for failure. Wet chemical analysis revealed very low chromium incorporation into the cathode. However, SEM and TEM observations on polished and fractured surfaces showed catastrophic failure in the degraded layer. The cathode–barrier–electrolyte cell layer system delaminated from the entire cell over large areas. The source of delamination was the formation of a porous, sponge-like secondary phase consisting of zirconia, yttria and manganese (oxide). Large secondary phase islands grew from the electrolyte–anode interface towards the anode and cracked the bonding between both layers. The manganese originated from the contact or protection layers used on the air side. This stack result shows that volatile species – in this case manganese – should be avoided, especially when long-term applications are envisaged.

Dense monolithic SiC/HfyTa1−yCxN1−x/C (y = 0, 0.2 and 0.7) ceramic nanocomposites were prepared upon spark plasma sintering of amorphous SiHfTaC(N) ceramic powders which were synthesized from single-source-precursors. The microstructural evolution of the ceramic powders was investigated using elemental analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). The results reveal that the powdered and dense monoliths of SiC/HfyTa1−yCxN1−x/C ceramic nanocomposites annealed at T ≥ 1700 °C and at 2200 °C, respectively, are characterized by the presence of a homogeneous dispersion of HfyTa1−yCxN1−x-carbon core–shell nanoparticles within a β-SiC matrix. Hf/Ta atomic ratios (or y values) of the in situ generated HfyTa1−yCxN1−x-carbon core–shell nanoparticles can be controlled precisely by molecular tailoring of the preceramic precursors, which further tunes the thickness of the in situ formed carbon shell. Interestingly, with increasing the value y the thickness of the carbon shell increases, while the electrical conductivity of the dense monolithic SiC/HfyTa1−yCxN1−x/C (y = 0, 0.2 and 0.7) nanocomposites significantly reduces. The unique HfyTa1−yCxN1−x-carbon core–shell nanostructure opens a new strategy towards tailoring the electrical conductivity of SiC/HfyTa1−yCxN1−x/C nanocomposites for potential electromagnetic applications in harsh environments.

The sintering behavior of ring-shaped alumina films on different types of substrates (polished sapphire and platinum coated sapphire) has been investigated. Variation of substrate material, layer thickness and heating schedule led to different interface properties which were quantified using the interfacial friction parameter as a measure of the slip distance of the free edge. This interfacial friction implies the compliance of the film-substrate interface, thus allowing the quantification of the ability of the free edges to slide along the substrate. Ring structures were made with outer radii of 100 –500 µm and the ratios of inner to outer radii were 0.1 (broad ring segment with small inner hole) and 0.4 (narrow ring segment with big inner hole). During sintering, the outer film edge was found to recede in all systems, whereas the behavior of the free edge located at the inner hole was strongly dependent on the interfacial friction. When sintering of alumina micro-rings were carried out on sapphire substrate, a high interfacial friction resulted in the positive displacement of the inner edge, causing the inner hole to open. Sapphire substrates coated with platinum offered a lower interfacial friction resulting in the opening of the hole in a more distinct manner as compared to the uncoated sapphire substrates. As the thickness of the film also affects the interfacial friction, a thicker film (27 µm) on platinum coated substrate had very low friction. This resulted in a negative displacement of the inner ring leading to closing of the hole. These effects are in qualitative agreement with the predicted analytical model for constrained sintering of annular ceramic films. A combination of film thickness, substrate material and aspect ratio of the ring either leading to constriction or dilation of the annular alumina film were carefully investigated.

Tungsten (W) has a unique combination of excellent thermal properties, low sputter yield, low hydrogen retention, and acceptable activation. Therefore, W is presently the main candidate for the first wall material in future fusion devices. However, its intrinsic brittleness and its further embrittlement during operation bears the risk of a sudden and catastrophic component failure. As a countermeasure, tungsten fiber-reinforced tungsten (W f /W) with extrinsic toughening is being developed. A possible synthesis route is chemical vapor deposition (CVD) using heated W fabrics as substrate. The challenge is that the growing CVD-W can isolate domains from precursor access leading to strength-reducing pores. To deepen the process understanding and to optimize the CVD parameters, models were developed with COMSOL Multiphysics and validated experimentally. W deposition rate equations as function of the temperature and the partial pressures of the precursors H 2 and W F 6 were experimentally validated in previous work. In the present article, these equations are applied to obtain partial pressures within the CVD reactor. The results are taken as input for transient simulations in the microscale, in which W coatings, growing onto multiple adjacent W fibers, were simulated via mesh deformation and remeshing. The surface-to-surface contact of the W coatings and the corresponding potential pore formation were simulated by implementing sophisticated deposition rate stop conditions. Within the measuring uncertainties of ≃ ± 1%, the models are validated successfully by experimental comparison regarding the deposition rate, pore structure, and relative densities ranging from 0.6 to 0.9.

The good oxidation resistance of MAX phases up to temperatures around 1200 °C can be compromised for long exposure due to the breakaway of the protective alumina layer. Herein, we unveil a mechanism of breakaway oxidation of the Ti2AlC MAX phase, identifying the main trigger and the solutions to avoid it. It is caused by excessive rumpling of the oxide scale on surfaces with arithmetical mean roughness (Ra) > 3 µm and constitutes a key factor in subsequent consumption of Ti2AlC. First, the oxide scale experienced rumpling due to significant radial stresses generated at the Ti2AlC/oxide interface. Second, scale blistering resulted from substantial buckling due to the evolution of in-plane stresses and lateral lengthening. Third, blister collapse and exposure of the underlying Al-depleted Ti2AlC surface led to rapid ingress of oxygen and oxide/substrate interface recession. The self-healing ability of Ti2AlC has been restrained and breakaway oxidation kinetics following a linear trend have been initiated. Similarly, breakaway oxidation was observed on micro-damaged surfaces. A mixed oxide layer with high porosity mainly composed of rutile titanium dioxide (TiO2) promptly formed on these surfaces, gradually consuming the base Ti2AlC material.

Fuel electrode-supported solid oxide cells (FE-SOC) offer the possibility of low operation temperatures and / or high power density through the incorporation of a thin, supported electrolyte between two highly active electrodes. However, integrating fuel electrodes with an ionic conductor that is different from that of the electrolyte into FE-SOC remains a challenge due to the interdiffusion phenomena during co-sintering of the half-cell. As a result, most FE-SOC use cermet fuel electrodes made from Ni and stabilized zirconia. Here, we present a FE-SOC based on a Ni-Gd0.1Ce0.9O2- d (GDC) fuel electrode, a three-layer GDC / zirconia / GDC electrolyte and an La0.58Sr0.4CoO3- d (LSC) air electrode. The electrolyte is fabricated by co-sintering a thin, screen-printed layer of GDC with the fuel electrode and support. Subsequent electrolyte layers are deposited via physical vapor deposition (PVD), and the air electrode is fabricated via screen printing. The total electrolyte thickness is less than 5 µm, enabling an area-specific ohmic resistance < 10 mΩ cm² at 700 °C. A current density of 1.6 Acm-² is achieved at a cell voltage of 800 mV and a temperature of 700 °C, using 10% H2O/H2 as fuel and air as oxidant. This performance is about twice as high as that of a conventional Jülich cell using Ni-YSZ and LSCF electrodes and a 10 µm YSZ electrolyte under similar conditions. An electrolysis current of 2 A cm-² was achieved at a cell voltage of 1.11 V, at a temperature of 800 °C and using 50% H2O/H2 and air. The conventional Jülich cell requires a cell voltage above 1.25 V under similar conditions. Under these conditions, the new cell achieves a cell efficiency of 84 %, compared to 73 % for the conventional cell. However, running high electrolysis currents at temperatures below 750 °C resulted in catastrophic cell failure, visible as large voltage jumps in the I-V curve. In addition, a decreasing OCV value with decreasing temperature indicated damage to the cell before the catastrophic failure. Post-test analysis found a large number of cracks in the electrolyte, nucleating at the fuel electrode / electrolyte interface and running toward the air electrode. We show that the likely cause for this failure is the electrochemical reduction and subsequent chemical expansion of the doped ceria electrolyte layer, necessitating a detailed study of the local mechanical stresses in the cell during operation.

We report on the materials interaction of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) in the context of high temperature sintering during manufacturing of anode supported solid oxide fuel cells (AS-SOFC). While ceria-based anodes are expected to show superior electrochemical performance and enhanced sulfur and coking tolerance in comparison to zirconia-based anodes, we demonstrate that the incorporation of a Ni-GDC anode into an ASC with YSZ electrolyte decreases the performance of the ASC by approximately 50% compared to the standard Ni-YSZ cell. The performance loss is attributed to interdiffusion of ceria and zirconia during cell fabrication, which is investigated using powder mixtures and demonstrated to be more severe in the presence of NiO. We examine the physical properties of a GDC-YSZ mixed phase under reducing conditions in detail regarding ionic and electronic conductivity as well as reducibility, and discuss the expected impact of cation intermixing between anode and electrolyte. This article is protected by copyright. All rights reserved.

In modern gas turbines, highly loaded components are internally cooled and furthermore covered with thermal barrier coatings (TBCs) to withstand the harsh operating conditions with temperatures exceeding the application limit of such coatings. Under realistic operating conditions, siliceous minerals, of a calcium-magnesium-aluminum-silicate (CMAS) composition, are ingested into the turbine and deposited on the TBCs. Besides erosion, this also leads to degradation by chemical interaction. The plasma spray-physical vapor deposition (PS-PVD) process is an advanced method for manufacturing TBCs, which fills the gap between traditional thermal spray processes and electron beam physical vapor deposition (EB-PVD). Due to the unique plasma conditions, coatings with columnar microstructures exhibiting high strain tolerance can be created. However, because of the high amount of open porosity the resistance of such structures to CMAS and erosion attack was expected to be low. In the present work, PS-PVD TBCs were investigated in a burner rig facility under thermal gradient cycling conditions and simultaneous CMAS attack. The interactions of the PS-PVD-deposited YSZ and the CMAS melt were studied by means of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS) and compared to EB-PVD coatings. Additionally, the resistance of PS-PVD TBCs to erosion is compared to APS TBCs by means of room temperature tests according to ASTM G76-13.

Beim „Plasma Spray-Physical Vapor Deposition“ (PS-PVD) Verfahren konnen grose Teile des pulverformigen Spritzwerkstoffs verdampft werden, so dass die Beschichtungen hauptsachlich aus der Gasphase abgeschieden werden. Diese Arbeit zeigt mittels numerischer Stromungssimulation (CFD), dass einerseits eine solche Verdampfung masgeblich in der Plasmabrennerduse stattfindet, und dass andererseits Keimbildung und Kondensation von Zirkondioxid an dieser Stelle moglich sind. Um die Eigenschaften der Deposite mittels PS-PVD zu untersuchen, wurden Experimente durchgefuhrt; insbesondere wurden Beschichtungen aus kondensierter Gasphase und aus Nano-Clustern, hergestellt mit den beiden Spritzabstanden 1000 mm und 400 mm untersucht. REM-Aufnahmen zeigen, dass beim grosem Spritzabstand viele kleine, nanoskalige Partikel (< 20 nm), welche deutlich kleiner sind als die Primarpartikel im ursprunglichen Spritzwerkstoff, die Spritzoberflache in der Mitte des Plasmastahls bestimmen. Beim kurzen Spritzabstand konnten diese nanoskaligen Partikel jedoch kaum beobachtet werden. Ferner zeigen die XRD-Spektren beim grosen Spritzabstand im mittleren Bereich des Plasmastrahls nur eine geringe bevorzugte Wachstumsrichtung, was eine Folge der geringen Beweglichkeit der abgeschiedenen Nano-Cluster sein konnte. Derweil zeigen die XRD-Spektren beim kurzen Spritzabstand deutlich bevorzugte Wachstumsorientierungen von (110) und (002). Die Ergebnisse dieser Arbeit liefern einen tieferen Einblick in die Entstehungsmechanismen von hochqualitativen, kolumnar strukturierten PS-PVD-Warmedammschichten, welche bei zyklischen Lebensdauertests eine hervorragende Leistungsfahigkeit aufweisen.

A novel sintering approach was developed in order to overcome the issue of insufficient adherence of (La,Sr)(Co,Fe)O3 type cathodes in metal-supported solid oxide fuel cells (MSCs). Investigation of the phase stability of the perovskite structure at high temperature in various atmospheres with low oxygen partial pressures provided the basis for the development of a sintering procedure applicable to full-cells. By investigating the layer adherence, time dependent mechanical integrity and reversibility of phase transformations, metal-supported cells with sintered cathodes could be produced reliably and were electrochemically characterized in single cell measurements. The novel sintering approach of such cathodes resulted in a significantly enhanced mechanical stability of the cathode layers. Extensive spallation of the cathode was prevented, which is a substantial improvement in comparison with state-of-the-art MSCs. Furthermore, the electrochemical measurements revealed a beneficial effect regarding the cell performance. Post-test characterization is assumed to provide further information regarding the quality of bonding between cathode and electrolyte. Further investigations cover the implementation of alternative high-performance cathode materials like LSC as well as the combination with optimized anode structures/compositions.

The Atmospheric Plasma Spray (APS) Process is a widely used technique for manufacturing ceramic coatings with unique properties for many applications, whereat the residual stresses within these coatings are an important factor affecting their performance. The coating formation is characterized by the subsequent impingement of a large number of more or less molten particles forming the so called splats. Understanding the mechanisms connecting these smallest structural elements with the overall coating properties enables the specific design of the coating process. In the present work, the correlation between coating porosity, Young's modulus, and residual stress with the particle melting was investigated. Therefore, single splats were collected on mirror-polished substrates and evaluated by identifying different types and their relative fractions under various spray conditions. Microscopic investigations were performed to obtain information on the spreading behavior of the different splat types to establish a relation to the coating properties. Furthermore, the particles were characterized by in-flight measurement of their temperature and the obtained results were evaluated in terms of their degree of melting. This was compared with the experimentally observed splat type amounts and finally correlated to the investigated coating properties.

The stability in ambient conditions of a scandium-based NASICON material, Na 3.4 Sc 2 Si 0.4 P 2.6 O 12 , was investigated using impedance spectroscopy, thermogravimetry/differential scanning calorimetry (TG/DSC) and multinuclear magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The presence of H 2 O and CO 2 in samples stored in ambient air could be evidenced as well as its impact on the ionic conductivity of the samples. The detected amounts of water and CO 2 in the samples had no influence on the measured conductivities at room temperature, which confirmed the absence of protonic conduction in hydrated samples. A loss of conductivity during heating of hydrated samples was due to a loss of contact between the ceramic and the electrode used for the conductivity measurement. The recommendation for handling of NASICON-type materials is therefore: samples require storage in an Ar-filled glove box or in a dry environment to avoid artefacts during high temperature measurements. Nevertheless, the stability of the NASICON-type materials is confirmed since their conductivity is not affected by the moisture.

Metal-supported solid oxide fuel cells (MSCs) have gained high attention as they offer a possibility to utilize solid oxide fuel cells (SOFCs) in mobile applications such as auxiliary power units in heavy duty vehicles. Cathode reliability is one of the main issues of MSC development, since cathodes tend to degrade rapidly after being in-situ activated during onset of the stack operation. In the present study, a novel sintering route for La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode material was developed. Sintering of the screen printed cathodes was performed before stack operation at 950 °C in reducing Ar atmosphere for 3 h. Under these conditions, severe oxidation of the metallic substrate and the Ni in the anode was avoided reliably. For proof of concept, phase stability and microstructure of the MSC cathodes were characterized. The results reveal that cathode layers sintered in Ar exhibit substantially improved adherence and mechanical stability compared to conventionally processed MSC cathodes, making them ready for systematic investigation of electrochemical performance.

Asymmetric membranes provide a low ionic resistance of the functional separation layer together with a high mechanical stability. However, the microstructure of the porous support in the membrane assembly affects the overall flux significantly. This effect was studied by applying the binary friction model (BFM) for the support together with a modified Wagner equation for the dense membrane using transport relevant parameters obtained from micro computed tomography data of a tape cast Ba0.5Sr0.5Co0.8Fe0.2O3–δ support. The influence of different pore diameters and thicknesses of the support were compared for different feed gases (oxygen and air) and flow configurations (3-end, 4-end, assembly orientation). The effect of the support at large pore diameters (>35 µm) for the 3-end mode transport process using oxygen as feed gas, was negligible. This was not the case for the 4-end mode irrespective of the feed gas, and for the 3-end mode using air as feed gas. This was attributed to the binary diffusion term in the BFM. Thin small-pored supports yield the same flux as thick large-pored supports considering a non-linear relationship between thickness and pore size. This can be used for the optimization of the support's microstructure with regards to mechanical strength and permeability.

A new class of ceramic matrix composites based on CrAlC MAX-phase containing 5 and 10 wt.% of SiC fibers was developed in this investigation. The CrAlC/SiC composites were performed through two consecutives steps: i) synthesis of the pure CrAlC phase from its elemental constituents by reactive method under argon atmosphere at 1400 °C and particle size refinement, and ii) processing of CrAlC powder and SiC fibers followed by densification using the field assisted sintering technology/spark plasma sintering. CrAlC/SiC composites presented high density (98.6%) with an excellent dispersion of the fibers within the matrix and a strong matrix/fiber interfase. Tribological behavior of the developed composites was studied under dry conditions to reveal the role played by the SiC fibers. Incorporation of the SiC fibers within the CrAlC matrix reduced the friction coefficient up to 20% for low testing loads, while the wear resistance increased up to 70–80% independently of the applied load., This work was supported by the Spanish Government under project MAT2012-32944.

With the aim of improving the electrochemical properties of the LiCoMnO4 high-voltage spinel for lithium ion battery applications, LiCoMnO4-yFy (y = 0, 0.05, 0.1) compounds were synthesized by a two-step solid-state reaction at 800 °C. The stoichiometry of the samples was verified by nuclear reaction analysis for the fluorine stoichiometry, inert gas fusion analysis for the oxygen stoichiometry, and inductively coupled plasma optical emission spectroscopy for the cation stoichiometry. X-ray diffraction analysis and scanning electron microscopy revealed increasing phase purity and changing microstructure upon fluorine incorporation. Electrochemical characterizations were carried out in battery test cells using a liquid electrolyte. The samples show poor coulombic efficiency, due to liquid electrolyte decomposition. However, fluorinated spinels demonstrated significantly improved capacities of up to 18% and improved cycling stability of up to 20%, compared to their non-fluorinated counterparts.