Moderate Thermal Expansion Coefficient Research Articles

SrTiO3-SrVO3 Ceramics for Solid Oxide Fuel Cell Anodes: A Route from Oxidized Precursors.

Perovskite-type Sr(Ti,V)O3-δ ceramics are promising anode materials for natural gas- and biogas-fueled solid oxide fuel cells, but the instability of these phases under oxidizing conditions complicates their practical application. The present work explores approaches to the fabrication of strontium titanate-vanadate electrodes from oxidized precursors. Porous ceramics with the nominal composition SrTi1-yVyOz (y = 0.1-0.3) were prepared in air via a solid state reaction route. Thermal processing at temperatures not exceeding 1100 °C yielded composite ceramics comprising perovskite-type SrTiO3, pyrovanadate Sr2V2O7 and orthovanadate Sr3(VO4)2 phases, while increasing firing temperatures to 1250-1440 °C enabled the formation of SrTi1-yVyO3 perovskites. Vanadium was found to substitute into the titanium sublattice predominantly as V4+, even under oxidizing conditions at elevated temperatures. Both perovskite and composite oxidized ceramics exhibit moderate thermal expansion coefficients in air, 11.1-12.1 ppm/K at 30-1000 °C, and insignificant dimensional changes induced by reduction in a 10%H2-N2 atmosphere. The electrical conductivity of reduced perovskite samples remains comparatively low, ~10-1 S/cm at 900 °C, whereas the transformation of oxidized vanadate phases into high-conducting SrVO3-δ perovskites upon reduction results in enhancement in conductivity, which reaches ~3 S/cm at 900 °C in porous composite ceramics with nominal composition SrTi0.7V0.3Oz. The electrical performance of the composite is expected to be further improved by optimization of the processing route and microstructure to facilitate the reduction of the oxidized precursor and attain better percolation of the SrVO3 phase.

Microstructural, electrical and thermal characterization of Dy3+, Sm3+, Er3+, Y3+ and Gd3+ multi-doped cerium dioxide as SOFCs solid electrolytes

The production of electrolytes with high ionic conductivity has been a key challenge in the progressive development of solid oxide fuel cells (SOFCs) for practical applications. Conventional approaches use ionic doping to develop electrolyte materials, such as yttria-stabilized zirconia (YSZ), but challenges remain. The doping systems discovered so far can confirm that co-doping/triple doping can introduce more oxygen vacancies to improve the electrical properties of ceria-based electrolytes compared to unitary doping. Therefore, In this work, we select the optimal dopant based on the criterion of optimal doping in cerium dioxide (effective average ionic radius close to 1.093 Å). And propose a novel multi-doped cerium-based Ce1−x(Dy1/5Sm1/5Er1/5Y1/5Gd1/5)xO2-δ (x = 0.10, 0.15, 0.20, 0.25, 0.30, abbreviated as DSEYG1, DSEYG2, DSEYG3, DSEYG4, DSEYG5) electrolytes to study its microstructure, electrical properties and thermal properties. Dy3+, Sm3+, Er3+, Y3+, and Gd3+ multi-doped electrolyte materials. Over 95% of the relative density values were obtained by sintering DSEYG series samples at 1400 °C. The single-phase cubic fluorite structure, high-density surface microstructure, elemental confirmation, and oxygen vacancy concentration were confirmed using X-ray diffraction, scanning electron microscope, energy dispersive spectrum, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electrical analysis by impedance spectroscopy confirmed the highest value of total ionic conductivity (σ800 °C= 4.04 ×10−2 S/cm) and the lowest value of activation energy (Ea= 0.834 eV) for the DSEYG3 composition. Thermal expansion analysis confirmed the moderate thermal expansion coefficient values for all compositions (TEC =11.12 ×10−6 K−1) in the range of RT-800 °C) and was found to be in good agreement with recently developed materials. The enhanced total ionic conductivity and moderate thermal expansion coefficient of DSEYG3 make it a potential electrolyte material for medium-temperature fuel cells.

Optimizing the Copper Content in GdBa0.5Sr0.5Co2-XCuxO5+δ Double Perovskites as the High Performance Oxygen Electrodes for Reversible Solid Oxide Cells

Sustainable development and better protection of environment are among the top priority issues for human society. Seeking for cleaner and less greenhouse-emissive energy resources or solutions has been a dominating trend around the world, since daily functioning of the current society is still dependent on fossil energy sources, such as oil, coal, and also natural gas. Tremendous efforts have been made to develop alternative energy production technologies, among them, fuel cells have been found as very promising ones. Especially, reversible Solid Oxide Cells (rSOCs) have become famous for their all-solid structure, which consist of the porous fuel electrode, dense solid oxide electrolyte, porous oxygen electrode, and interconnects. Reversible SOCs can effectively work either in the fuel cell (e.g. H2 + 0.5O2 → H2O and heat) or electrolyzer modes, making them useful for grid balancing and utilization of surplus electrical energy. It is worth noting that the oxygen electrode has a decisive role regarding performance and long-term operation of the whole cell. Until now most of the widely-studied and also practically-implemented oxygen electrode materials are cobalt-based perovskite-type oxides or related compounds having the relatively high concentration of Co. This can be regarded as one of drawbacks, due to the toxicity, carcinogenicity, high costs, and poorly available resources of cobalt, despite impressive electrocatalytic activity and excellent electrochemical properties of such materials. Accordingly, numerous attempts have been carried out, which aim at replacing Co with other transition metal elements, such as Ni, Fe, Mn, and Cu, at least to some extent. For example, copper-doping into Co-based perovskites enabled to limit the excessive thermal expansion, as well as positively influenced redox stability.The A-site ordered double perovskites, REBaCo2O5+δ (RE: rare earth elements and Y), feature the layered structure with alternating configuration of REOδ and BaO layers along the c-axis, which generates fast diffusion channels for migration of oxygen anions, as well as the materials exhibit excellent electrical conductivity. In this work, an attempt has been made to further optimize the compounds, with the target compositions proposed as GdBa0.5Sr0.5Co2-xCuxO5+δ (0 ≤ x ≤ 2). Intermediate-size Gd3+ facilitates layered structure formation, while introducing Sr at Ba sites is beneficial to electrical conductivity, due to alleviated lattice distortion. Comprehensive studies have been directed to optimize the copper content in the selected oxides. After synthesis by a self-combustion sol-gel method, the samples were systematically characterized, including identification of the phase composition and crystal structure, thermal stability and chemical reactivity with solid electrolytes, thermal expansion behavior, oxygen content, total electrical conductivity and electrochemical properties. The adopted characterization methods include the X-ray diffraction at room and high temperatures with Rietveld refinements, iodometric titration and thermogravimetric tests, dilatometric measurements, total electrical conductivity studies. Also, laboratory-scale symmetrical and full cells have been manufactured and characterized concerning morphology of the electrodes, electrode-electrolyte interface, electrode polarization resistance with distribution of relaxation times method, as well as power output. High copper content (x > 1.15) was found as hindering factor for synthesis of pure samples. Bearing in mind a need to reduce cobalt content, GdBa0.5Sr0.5Co2-xCuxO5+δ compositions with x = 1, 1.05, 1.1, and 1.15 were selected for further evaluation. The oxides could be synthesized as practically phase-pure, revealing the desired P/4mmm tetragonal symmetry. All of them maintain stable lattice structure up to 1000 °C in air. They are chemically compatible with La0.8Sr0.2Ga0.8Mg0.2O3-δ and Ce0.9Gd0.1O2-δ electrolytes up to at least 900 °C. A moderate thermal expansion coefficients were measured, which decrease with the increasing Cu-doping content, from 15.8·10-6 K-1 (x = 1) to 14.5·10-6 K-1 (x = 1.15) in the temperature range of 300-900 °C. The equilibrated oxygen content in the considered samples ranges from 5.69 (x = 1) to 5.49 (x = 1.15). All oxides exhibit a sufficiently high total conductivity, above 10 S cm-1 in the working temperature range of 600-900 °C. The recorded electrochemical impedance spectra indicate that the lowest polarization resistance (0.017 Ω cm2 at 850 °C) can be obtained for the electrode with GdBa0.5Sr0.5Co0.9Cu1.1O5+δ composition (on La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte), which is lower than for the higher cobalt-content GdBa0.5Sr0.5CoCuO5+δ, 0.025 Ω cm2 at the same temperature. The developed GdBa0.5Sr0.5Co0.9Cu1.1O5+δ material used as the oxygen electrode in the La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte-supported full cell enabled to achieve power density output exceeding 1.2 W cm-2 at 850 °C, and 0.57 A cm-2 current density at 1.5 V in electrolysis mode at 700 °C. All the evidence prove that Cu-doping is an effective approach, since it allows for limiting the Co content and obtaining the desirable performance at the same time.

Microstructure and thermal barrier coating properties of plasma sprayed SrCeO3

The trend to improve the efficiency of gas turbine engines leads to an increase in requirements for thermal barrier coating (TBC) materials. Strontium cerate (SrCeO3) is a promising perovskite-like type oxide with a low thermal conductivity and moderate thermal expansion coefficient (TEC) value. In this work, TBC was applied by atmospheric plasma spraying to a nickel superalloy ZhS 32 VI, and the change in its microstructure and phase composition after thermal cycles was investigated. It was found that during spraying, SrCeO3 crystals orientated along the most densely packed directions, which led to the structuring of the coating. In the process of thermal cycling, Sr diffuses to the top coat – bond coat boundary with the formation of strontium chromate. SrCrO4 together with NiO form a layer of thermally grown oxide (TGO). TBC failed after 44 ± 3 thermal cycles of rapid heating up to 1200 °C followed by air cooling with 5 min of holding time at each stage. The absence of direct reactions of the top coat and bond coat, the TGO formation from components of both layers as well as low TEC mismatch allows to resist onset of exfoliation for about 30 cycles. The thermal conductivity value of nickel superalloy covered by SrCeO3 is only 1.65 ± 0.05 W·m−1·K−1 in the temperature range of 25–100 °C and mainly determines by top coat properties. The new experimental data being obtained highlights the prospects of the considered TBC based on SrCeO3.

Electrospun Nanofiber Electrodes with in situ Exsolved Nanocatalysts for Symmetrical SOCs

In this work, A-site deficient Sm0.9Ba0.9Mn1.8−xFexCo0.1Ni0.1O6−δ (x = 0, 0.45 and 0.9) double perovskites with in situ exsolved nanoparticles were successfully obtained and evaluated as electrode materials for symmetrical Solid Oxide Cells (SOCs). All obtained oxides belong to the P4/nmm tetragonal system, and a phase transition from P4/nmm to P4/mmm was recorded by the HT-XRD in the air. The in situ exsolution of nanoparticles has been confirmed by the XRD and SEM analysis. The proposed materials present excellent redox stability and moderate thermal expansion coefficients. Electrospun nanofibers (with 150 nm diameter) were successfully fabricated, indicating an excellent potential application in the electrode. The results show the developed A-site deficient double perovskites with iron doping at Mn-site can be potentially applied as novel electrode materials for symmetrical SOCs.

Characterization of Ruddlesden-Popper La2−xBaxNiO4±δ Nickelates as Potential Electrocatalysts for Solid Oxide Cells

Ruddlesden-Popper La2-xBaxNiO4±δ (x = 0-1.1) nickelates were prepared by a glycine-nitrate combustion route combined with high-temperature processing and evaluated for potential application as electrocatalysts for solid oxide cells and electrochemical NOx elimination. The characterization included structural, microstructural and dilatometric studies, determination of oxygen nonstoichiometry, measurements of electrical conductivity and oxygen permeability, and assessment of chemical compatibility with other materials. The formation range of phase-pure solid solutions was found to be limited to x = 0.5. Exceeding this limit leads to the co-existence of the main nickelate phase with low-melting Ba- and Ni-based secondary phases responsible for a strong reactivity with Pt components in experimental cells. Acceptor-type substitution of lanthanum by barium in La2-xBaxNiO4+δ is charge-compensated by decreasing oxygen excess, from δ ≈ 0.1 for x = 0 to nearly oxygen-stoichiometric state for x = 0.5 at 800 °C in air, and generation of electron-holes (formation of Ni3+). This leads to an increase in p-type electronic conductivity (up to ~80 S/cm for highly porous La1.5Ba0.5NiO4+δ ceramics at 450-900 °C) and a decline of oxygen-ionic transport. La2-xBaxNiO4+δ (x = 0-0.5) ceramics exhibit moderate thermal expansion coefficients, 13.8-14.3 ppm/K at 25-1000 °C in air. These ceramic materials react with yttria-stabilized zirconia at 700 °C with the formation of an insulating La2Zr2O7 phase but show good chemical compatibility with BaZr0.85Y0.15O3-δ solid electrolyte.

Development of Ni-Sr(V,Ti)O3-δ Fuel Electrodes for Solid Oxide Fuel Cells.

A series of strontium titanates-vanadates (STVN) with nominal cation composition Sr1-xTi1-y-zVyNizO3-δ (x = 0–0.04, y = 0.20–0.40 and z = 0.02–0.12) were prepared by a solid-state reaction route in 10% H2–N2 atmosphere and characterized under reducing conditions as potential fuel electrode materials for solid oxide fuel cells. Detailed phase evolution studies using XRD and SEM/EDS demonstrated that firing at temperatures as high as 1200 °C is required to eliminate undesirable secondary phases. Under such conditions, nickel tends to segregate as a metallic phase and is unlikely to incorporate into the perovskite lattice. Ceramic samples sintered at 1500 °C exhibited temperature-activated electrical conductivity that showed a weak p(O2) dependence and increased with vanadium content, reaching a maximum of ~17 S/cm at 1000 °C. STVN ceramics showed moderate thermal expansion coefficients (12.5–14.3 ppm/K at 25–1100 °C) compatible with that of yttria-stabilized zirconia (8YSZ). Porous STVN electrodes on 8YSZ solid electrolytes were fabricated at 1100 °C and studied using electrochemical impedance spectroscopy at 700–900 °C in an atmosphere of diluted humidified H2 under zero DC conditions. As-prepared STVN electrodes demonstrated comparatively poor electrochemical performance, which was attributed to insufficient intrinsic electrocatalytic activity and agglomeration of metallic nickel during the high-temperature synthetic procedure. Incorporation of an oxygen-ion-conducting Ce0.9Gd0.1O2-δ phase (20–30 wt.%) and nano-sized Ni as electrocatalyst (≥1 wt.%) into the porous electrode structure via infiltration resulted in a substantial improvement in electrochemical activity and reduction of electrode polarization resistance by 6–8 times at 900 °C and ≥ one order of magnitude at 800 °C.

Study on Ce and Y co-doped BaFeO3-δ cubic perovskite as free-cobalt cathode for proton-conducting solid oxide fuel cells

The use of triple-conducting (electron, proton, oxide ion) cathodes is an effective strategy for significantly decreasing cathode polarization of proton-conducting SOFCs. In this study, a new triple-conducting BaFe0.8Ce0.1Y0.1O3-δ (BFCY) perovskite cathode is prepared by Pechini sol-gel process and its properties are evaluated comprehensively. High-temperature XRD measurement demonstrates that the codoping of Ce and Y can stabilize the cubic perovskite of BFCY in investigated temperature range from room temperature to 900 °C. BFCY material exhibits a moderate average thermal expansion coefficient of 22.08 × 10−6 K−1 smaller than cobalt-based cathode and good chemical compatibility with BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte after the calcining treatment at 1000 °C. XPS analysis indicates the existence of Ce3+/4+ and Fe3+/4+ ions and abundant oxygen vacancies in BFCY powder surface. Thermal gravimetric analysis reveals that a larger number of oxygen deficiencies -are generated at elevated temperatures, which favors the catalytic activity on oxygen reduction. The maximum value of BFCY electrical conductivity remains at 1.55 S cm−1 at 600 °C in humidified air. BCFY (BaCe0.8Fe0.1Y0.1O3-δ) material is introduced in order to construct BFCY-BCFY composite cathode with the good cathode/electrolyte interface adhesion. For the single cell with BFCY-BCFY composite cathode, the polarization resistance as low as 0.05 Ω cm2 and peak power density as high as 750 mW cm−2 are reached at 700 °C, respectively, demonstrating the great potential of BFCY oxides as proton-conducting SOFC cathode.

SDC‐SCFZ dual‐phase ceramics: Structure, electrical conductivity, thermal expansion, and O2 permeability

AbstractNew CO2‐resistant dual‐phase Sm0.2Ce0.8O1.925–SrCo0.4Fe0.55Zr0.05O3‐δ (SDC‐SCFZ) ceramics present a promising outlook for potential future applications in membrane reactors and solid oxide fuel cells. Their high oxygen permeation flux and stability in CO2 sweep gas also allow their integration in oxyfuel combustion. Here the structural characteristics, electrical conductivities, thermal expansion behaviors, and oxygen permeabilities of four different SDC‐SCFZ membranes with weight ratios of 10:90, 25:75, 50:50, and 75:25 (SDC:SCFZ) are systematically studied. Among these four SDC‐SCFZ compositions, 0.6 mm‐thick 25 wt% SDC‐75 wt% SCFZ displayed the highest oxygen permeation fluxes that reach 1.26 mL min−1 cm−2 at 950°C and retained its phase integrity under alternating He and CO2 sweep gas over 72 hours of operation. This composite also showed a moderate thermal expansion coefficient of 1.90 × 10−5 K−1 between 30°C and 1000°C and an electrical conductivity of at least 16 S cm−1 at 550°C and above. Modeling studies revealed that the oxygen permeation fluxes through 25SDC‐75SCFZ are limited by surface exchange reactions from 700°C to 800°C and mixed bulk diffusion and surface exchange reactions above 800°C.

Structure and transport properties of the novel (Dy,Er,Gd,Ho,Y)3Fe5O12 and (Dy,Gd,Ho,Sm,Y)3Fe5O12 high entropy garnets

High-entropy, iron-containing, garnet-structured oxides with (Dy,Er,Gd,Ho,Y)3Fe5O12 and (Dy,Gd,Ho,Sm,Y)3Fe5O12 compositions are synthesized for the first time. A modified Pechini method followed by calcination at 700 °C and sintering at 1300 °C enables obtaining single-phase, homogenous materials of cubic structure with Ia-3d symmetry. High-temperature in-situ X-ray diffraction studies show excellent phase stability of the garnets, as well as moderate thermal expansion coefficient, ca. 11·10−6 K-1 in 25−1000 °C temperature range. Raman spectroscopy measurements indicate the presence of local distortion of structural polyhedra, likely associated with the high-entropy effect. The collected Mossbauer spectra confirm distorted character of the lattice. Influenced by the presence of Fe3+ in locally distorted octahedra and tetrahedra, the electrical conduction at low temperatures of both oxides remains much lower comparing to Y3Fe5O12 (yttrium iron garnet - YIG), as well as to other rare-earth garnets up to 600 °C, where it reaches value similar to YIG.

Electrical conductivity and thermal expansion of Ln-substituted SrTiO3 for solid oxide cell electrodes and interconnects: The effect of rare-earth cation size

The present work aims to evaluate relevant effects of the size of substituting rare-earth cation on electrical conductivity and thermal expansion of donor-doped SrTiO3 as ceramic components of electrochemical solid electrolyte cells. A series of strontium titanate-based ceramics with a moderate doping level and different cation stoichiometry, Sr0.90Ln0.10TiO3±δ and Sr0.85Ln0.10TiO3±δ (Ln = La–Yb), are prepared under identical conditions with the final reductive treatment in 10%H2–N2 atmosphere at 1500 °C for 10 h. The solubility of rare-earth cations in the strontium sublattice of perovskite-type SrTiO3 is found to decrease with reducing ionic radius leading to a segregation of secondary pyrochlore-type Ln2Ti2O7 phase in the case of smaller rare-earth cations (Ln = Dy–Yb). The results of electrical, dilatometric and thermogravimetric studies suggest that the size of donor Ln3+ cation and cation stoichiometry have no evident impact on the electrical conductivity or thermal expansion behavior as long as the content of Ln3+ is within the solubility limits. All reduced donor-doped titanate ceramics (except Yb-doped) show a similar level of electrical conductivity, 100–155 S cm−1 at 800 °C, determined by the content of Ln3+ in the strontium sublattice, and moderate thermal expansion coefficients, 11.9–12.1 ppm K−1 at 25–1100 °C, compatible with that of conventional solid electrolytes.

Copper matrix thermal conductive composites with low thermal expansion for electronic packaging

Reducing thermal expansion and improving thermal conductivity of copper based materials are particularly important for improving thermal stability of electronic packaging materials. Herein, Cu/Sc2W3O12/SiC composite with a moderate coefficient of thermal expansion (CTE) of 8.28 ppm/K and a high thermal conductivity of 287.2 W/m⋅K was successfully prepared by partial replacement of Sc2W3O12 by the nano SiC particles to compensate sacrificial thermal conductivity of the reported Cu/Sc2W3O12 composites using a hot-pressing method. Theoretical calculation and Ashby plot map suggests that this Cu/Sc2W3O12/SiC composite facilitate the best combination between tunable thermal expansion and high thermal conductivity, which may due to that SiC nanoparticles can strengthen the driving force of vacuum hot-pressing sintering and thus lead to more homogeneous microstructure accounting for improved thermal reliability. This work can provide useful insights into the design and synthesis of composites used as packaging material for various semiconductors.

Synthesis of PVZ glass and its improvement on mechanical and electrical properties of low temperature sintered silver paste

P2O5–V2O5–ZnO (PVZ) glass was prepared by the melt-quenching method and displayed its excellent properties including the low glass transition temperature (Tg = 387 °C), the moderate coefficient of thermal expansion of 6.48 × 10–6/°C and the excellent thermal stability (ΔT) of 198 °C. Both IR and Raman spectroscopy results indicated the units of VO2, VO3, (VO3)n chain structure increased with the increasing of V2O5 content, which resulting in the reduction of Tg and the increase of ΔT. A lead-free silver paste incorporated with different glass content was sintered on the Al2O3 ceramic substrate from 500 to 650 °C. The resistivity of the silver thick film increased with the increasing of the PVZ glass content, but the adhesion between the silver thick film and the Al2O3 substrates was obviously improved. The silver paste with 1 wt% glass showed a low resistivity (3.13 μΩ cm) and a high shear strength (40.47 MPa) after sintering at 650 °C for 10 min. The results suggested these improvements were attributed to the significant effect of PVZ glass on the densification of the silver thick film and the formation of the silver particles embedded in glass and AlPO4 reaction product. Hence, the PVZ glass exhibits tremendous potential application in nontoxic lead-free low temperature sintered silver paste for the Al2O3 ceramic metallization.

Investigation on micro-structural, structural, electrical and thermal properties of La3+, Sm3+ & Gd3+ triple-doped ceria as solid-electrolyte for intermediate temperature-solid oxide fuel cell applications

La3+, Sm3+, and Gd3+ triple-doped ceria Ce1−x(La1/3Sm1/3Gd1/3)xO2−δ (x = 0.06, 0.12, 0.18, 0.24, and 0.30) materials were synthesized by the sol-gel autocombustion method. The selections of dopants were made by an optimized-average atomic number in accordance with the criteria for optimal-doping in ceria. The higher values of relative-density were achieved above 95% by sintering the samples at 1300 °C. The single-phase cubic-fluorite structures, high-density surface-microstructure with uniformly distributed grains, elemental confirmations, and concentration of oxygen vacancies were confirmed using powder x-ray diffraction, scanning electron microscope with energy dispersive spectroscopy, and micro-Raman spectroscopy. Electrical analysis was carried out by impedance spectroscopy, which confirmed the highest value of total-ionic-conductivity, i.e., 0.0381 S/cm at 600 °C with a minimum activation-energy for the Ce0.82La0.06Sm0.06Gd0.06O2−δ (LSG6) composition. Thermal-expansion analyses confirmed the moderate coefficient of thermal-expansion values for all the compositions and were found to be in good agreement with the recently developed materials. The enhanced total-ionic-conductivity and the moderate coefficient of thermal expansion of LSG6 make it as a potential solid-electrolyte for intermediate temperature-solid oxide fuel cell applications.

Mn-rich SmBaCo0.5Mn1.5O5+δ double perovskite cathode material for SOFCs

SmBaCo0.5Mn1.5O5+δ oxide with Sm-Ba cation-ordered perovskite-type structure is synthesized and examined in relation to whole RBaCo0.5Mn1.5O5+δ series (R: selected rare earth elements). Presence of Sm and 3:1 ratio of Mn to Co allows to balance physicochemical properties of the composition, with moderate thermal expansion coefficient value of 18.70(1)·10−6 K−1 in 300–900 °C range, high concentration of disordered oxygen vacancies in 600–900 °C range (δ = 0.16 at 900 °C), and good transport properties with electrical conductivity reaching 33 S cm−1 at 900 °C in air. Consequently, the compound enables to manufacture catalytically-active cathode, with good electrochemical performance measured for the electrolyte-supported laboratory-scale solid oxide fuel cell with Ni-Gd1.9Ce0.1O2-δ|La0.4Ce0.6O2-δ|La0.8Sr0.2Ga0.8Mg0.2O3-δ|SmBaCo0.5Mn1.5O5+δ configuration, for which 1060 mW cm−2 power density is observed at 900 °C. Furthermore, the tested symmetrical SmBaCo0.5Mn1.5O5+δ|La0.8Sr0.2Ga0.8Mg0.2O3-δ|SmBaCo0.5Mn1.5O5+δ cell delivers 377 mW cm−2 power density at 850 °C, which is a promising result.

Effects of electroless nickel plating method for low temperature joining ZnS ceramics

ZnS has been widely used as a material for windows in optical systems. This is because it has a good transmittance in both mid-infrared and far-infrared bands, a stable chemical performance, a moderate linear thermal expansion coefficient and an adequate mechanical strength. ZnS windows need the so-called splice technology implementation to satisfy the integrity of large size applications or special surface structures. Traditional ZnS light windows are mechanically assembled with metal frames. However, the strength of the large-size ZnS formed by mechanical assembly is low. Consequently, an adequate joining technology is needed to overcome the low splice strength and improve the mechanical strength of the assembly. In this paper, we proposed a pre-metallization method by using an electroless plating of Ni on ZnS surface. Subsequently, a low temperature joining by using a Sn63Pb37 solder was completed. By a study of the process and the corresponding mechanism of the electroless nickel plating, a Ni–P layer with a controllable P content and thickness has been formed, and a smooth surface and a good combination with ZnS has been obtained. The microstructure of the Sn63Pb37 and Ni–P/ZnS was analyzed, and the phase composition and element distribution within the joint were determined. The influences of process parameters on the microstructures of the joints have been explored, including the brazing temperature, the time of thermal energy preservation and the thickness of the coating. Finally, the shear strengths of joints under different imposed parameters were optimized leading to the peak soldering temperature of 250 °C and the dwell at the peak of 1 min. The fractures were along Ni–P/ZnS ceramic interface, therefore, a successfully low temperature joining process on ZnS ceramics using Ni–P plating and Sn63Pb37 solder had been performed.

Perovskite-like LaNiO3-δ as Oxygen Electrode Material for Solid Oxide Electrolysis Cells

Perovskite-like LaNiO3-δ was evaluated as potential oxygen electrode material for solid oxide electrolysis cells. Compared to the Ruddlesden-Popper Lan+1NinO3n+1 (n = 1,2,3) counterparts, LaNiO3-δ exhibits higher p-type metallic-like conductivity under oxidizing conditions (450 S×cm-1 at 800°C for highly porous ceramics) together with a moderate thermal expansion coefficient (13.7 ppm×K-1 in air at 25-800°C) compatible with common solid electrolytes. The measured electrode polarization resistance (Rη) in contact with YSZ, CGO and LSGM solid electrolytes was 1.4, 0.77 and 0.22 Ω×cm2 at 800°C, and 208, 123 and 7.1 Ω×cm2 at 600°C, respectively, under zero-current conditions in air. Surface modification of via PrO x infiltration resulted in lower values of Rη (0.024 Ω×cm2 at 800°C and 0.76 Ω×cm2 at 600°C) and low anodic overpotentials (20 mV at 800°C and 500 mA×cm-2) in contact with LSGM.

A study of phase evolution and crystal growth for nano-sized monoclinic Y4Al2O9 as a novel thermal barrier coatings

Nano-sized monoclinic Y4Al2O9 was produced by sol-gel process as a novel potential candidate material for thermal barrier coatings. The thermal behavior, structural evolution of the products and the morphological characteristics of the compacted bodies were investigated by Thermogravimetric analysis and differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Field emission scanning electron microscopy (FESEM). Qualitative analyses indicate that monoclinic Y4Al2O9 was formed at about 1000 °C, and exhibited good phase stability throughout the annealing temperature ranging from 1000 °C to 1400 °C. The thermophysical properties of Y4Al2O9 ceramics were also evaluated compared with 8YSZ and La2Zr2O7. The determined activation energy of crystal growth is about 72.71 ± 0.31 kJ mol−1. Meanwhile, Y4Al2O9 represents low thermal conductivity (1.71 W m−1 K−1), moderate thermal expansion coefficient (8.73 × 10−6 K−1), and high sintering-resistance ability. Such results reveal that nano-sized Y4Al2O9 is favorable for the application of TBCs.

Microstructures and Properties of Sm2(Zr0.7Ce0.3)2O7/8YSZ Double-Ceramic-Layer Thermal Barrier Coatings Deposited by Atmospheric Plasma Spraying

The properties of Sm2(Zr0.7Ce0.3)2O7 (SZ7C3) as a novel thermal barrier coating (TBC) candidate have been evaluated. There is no evidence for a phase transformation for SZ7C3 from room temperature to 1600 °C. SZ7C3 exhibits a higher sintering resistance than the conventional yttria-stabilized zirconia (YSZ). The Vickers hardness for the SZ7C3 bulk is ca. 9.6 GPa, and the fracture toughness lies in a range of 1.5-2.5 MPa m1/2. Single SZ7C3 coatings and SZ7C3/8YSZ double-ceramic-layer (DCL) coatings were prepared by plasma spraying. The thermal conductivities of SZ7C3 coatings range from 0.4 to 0.6 W m−1 K−1 (significantly lower than those of 8YSZ). SZ7C3 coatings also exhibit moderate thermal expansion coefficients (TECs), near 10.8 × 10−6 K−1 at 1200 °C. The values of thermal expansion coefficients and fracture toughness are higher than those of La2(Zr0.7Ce0.3)2O7 (LZ7C3), which has been proposed as a promising high-temperature (> 1250 °C) TBC candidate material. The thermal cycling lifetime of SZ7C3/8YSZ DCL coating is much longer than that of LZ7C3/8YSZ TBC as demonstrated by the furnace thermal cycling tests, further confirming that SZ7C3 coatings have great potential as high-temperature TBCs for use in the next generation of advanced engines.

Evaluation of the phase stability, and mechanical and thermal properties of Ba(Sr1/3Ta2/3)O3 as a potential ceramic material for thermal barrier coatings

Abstract Ba(Sr1/3Ta2/3)O3 (BST) ceramic was synthesized by a solid-state reaction method. The phase stability, microstructural evolution, and mechanical and thermal properties of the BST ceramic were investigated and characterized to evaluate the potential application of BST as a top coating material for thermal barrier coatings (TBCs). The results show that BST can maintain a stable hexagonal perovskite structure up to 1600 °C. Anisotropic growth of the grains above 1400 °C was observed. Its low elastic modulus and high fracture toughness suggest a high damage tolerance for the BST ceramic. In addition, the moderate coefficient of thermal expansion and superior heat insulation capability of the BST ceramic provide this ceramic the potential to serve as a top coating material of TBCs at higher temperature.