LaBaCuFeO5+δ-Ce0.8Sm0.2O1.9 as composite cathode for solid oxide fuel cells

The performance of the LaBaCuFeO_5+δ-Ce_0.8Sm_0.2O_1.9 (LBCF-SDC) composite cathodes was studied in this paper. Electrical conductivity, thermal expansion and electrochemical properties were investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. The thermal expansion coefficients of the LBCF-SDC were between (16.3 and 13.4) × 10⁻⁶ K⁻¹ from 30 to 850 °C, which was lower value than LBCF (17.0 × 10⁻⁶ K⁻¹). AC Impedance spectroscopy measurements of LBCF-SDC/SDC/LBCF-SDC test cell were carried out. Polarization resistance values for the LBCF-SDC10 cathode was as low as 0.097 Ω cm² at 750 °C.     

Effects of liquid phases on densification of TiO2-doped Al2O3–ZrO2 composite ceramics

This study investigated the densification behaviors and microstructural evolution of Al₂O₃–ZrO₂ (3Y) composite ceramics doped with four different amounts of TiO₂ (0, 1, 4, and 8 wt%; denoted as 0T, 1T, 4T, and 8T, respectively) to clarify the effect of TiO₂ dopants on densification. The shrinkage rate during densification increased with the increase in the amount of TiO₂. The development of grain boundary feature was also examined. The undoped ceramic showed clean grain boundaries. Thin liquid grain boundary phases were observed in 1T, whereas large liquid phases were found on the grain boundary and at the junction pockets in 4T and 8T. The results were discussed in terms of the relationship between densification and grain boundary feature.     

Compressive creep behavior of spark plasma sintered La2O3–YSZ composite

The present paper describes compressive creep behavior of cubic 8 mol% yttria stabilized zirconia+10 mol% La₂O₃ (fabricated by Spark Plasma Sintering) in the temperature range of 1300–1330 °C at a stress level of 45–78 MPa in vacuum. The pre- and post-creep microstructures, relative magnitudes of the stress exponent (n=1.7–2.1) and the activation energy (540–580 kJ/mol) suggest that grain boundary sliding aided by inter-diffusion of La and Zr leading to the formation of pyrochlore La_1.6Y_0.4Zr₂O₇ phase at the grain boundaries during creep is the active creep mechanism in this composite.     

Comparative study of magnetoelectric composite system Ba0.95Sr0.05TiO3–Ni0.8Co0.2Fe2O4 with ferrite prepared by different methods

In this paper, effect of addition of Ni_0.8Co_0.2Fe₂O₄ (NCF), prepared by three different methods namely solid state reaction method, sol–gel and co-precipitation, has been studied on microstructural, magnetic, dielectric, ferroelectric and magnetoelectric properties of multiferroic composite system 0.95 Ba_0.95Sr_0.05TiO₃–0.05 Ni_0.8Co_0.2Fe₂O₄. Ba_0.95Sr_0.05TiO₃ (BST) has been prepared by solid state reaction method. Titular representation of NCF samples prepared by sol–gel, co-precipitation, solid state reaction method is N–SG, N–CP, N–SS respectively and that of corresponding magnetoelectric composite is C–SG, C–CP, C–SS. X–ray diffraction analysis of the composite samples (C–SG, C–SS, C–CP) indicated the presence of both NCF and BST phases. Rietveld analysis of XRD pattern further confirmed the proper phase formation in the composite samples. Sol–gel and co-precipitation processes result in finer NCF particles as confirmed by Transmission electron microscopy (TEM). Sample N–SG possesses uniform particle size and shape. Magnetization versus magnetic field (M–H) loops of samples C–SS and C–CP possess respectively highest value of remanant magnetization and magnetic coercive field. Dielectric properties of BST, NCF and composite samples have been measured in the frequency range of 20 Hz–1 MHz and temperature range of 50–170 °C. The composite sample C–CP results in highest value of dielectric constant in comparison to samples C–SS and C–SG. Polarization versus electric field (P – E) measurements pointed that composite sample C–SG possesses highest value of remanant and saturation polarization and C–SS possesses lowest value of coercive electric field. The composite sample C–SS possesses highest value of magnetoelectric coefficient.     

Magnetic properties of hard (CoFe2O4)–soft (Fe3O4) composite ceramics

Composite ceramics of CoFe₂O₄/Fe₃O₄ with different weight ratios were synthesized by Spark Plasma Sintering (SPS) at a sintering temperature of 500 °C. The X-ray diffraction patterns demonstrate that all samples are composed of CoFe₂O₄ and Fe₃O₄ phases. The magnetization curves for all the composite ceramic are single-step loops indicating the existence of exchange spring effect. Due to the competition between the exchange interaction and the dipolar interaction, magnetic properties like coercivity (H_c) and remanence (M_r) are sensitive to the weight ratio of the soft phase.     

Electrochemical properties of LaBaCo2O5+δ-Sm0.2Ce0.8O1.9 composite cathodes for intermediate-temperature solid oxide fuel cells

The electrochemical properties of LaBaCo₂O_5+δ-xSm_0.2Ce_0.8O_1.9 (LBCO-xSDC, x = 20, 30, 40, 50, 60, wt%) were investigated for the potential application in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The LBCO-50SDC composite cathode exhibited the best electrochemical performance in the LBCO-xSDC cathodes. With x = 50 wt%, the ASR was 1.308 Ω cm² at 500 °C (0.267 Ω cm² at 600 °C and 0.052 Ω cm² at 700 °C). The maximum of exchange current density i₀ was 0.5630 A cm⁻² at 700 °C. The improved electrochemical properties of LBCO-50SDC were ascribed to the porous structures of the cathode and more cathode/electrolyte/gas triple phase boundary (TPB) areas.     

Carbon–Al2O3–Ag composite molecular sieve membranes for gas separation

Phenolic resins loaded with two different inorganic fillers (boehmite (γ-AlO(OH)) and silver (Ag)) were used to prepare composite carbon membranes. Polymer solutions containing γ-AlO(OH) and AgNO₃ were prepared and the effect of Ag on the transport properties of the composite membrane was evaluated. The polymer solutions were coated on α-Al₂O₃ tubes and carbonized in a single dipping-drying-pyrolysis step. After pyrolysis at 550 °C, γ-AlO(OH) yielded γ-Al₂O₃, and Ag agglomerated forming spherical nanoparticles of 30 nm in diameter. Ag loading enhanced the carbon membrane performance for several gas pairs of interest, especially for C₃H₆/C₃H₈ separation, where the C₃H₆/C₃H₈ permselectivity increased from a maximum of 15 to 38.     

Characterizations of composite cathodes with La0.6Sr0.4Co0.2Fe0.8O3?δ and Ce0.9Gd0.1O1.95 for solid oxide fuel cells

Composite cathodes with La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) and Ce_0.9Gd_0.1O_1.95 (GDC) are investigated to assess for solid oxide fuel cell (SOFC) applications at relatively low operating temperatures (650–800 °C). LSCF with a high surface area of 55 m²g⁻¹ is synthesized via a complex method involving inorganic nano-dispersants. The fuel cell performances of anode-supported SOFCs are characterized as a function of compositions of GDC with a surface area of 5 m²g⁻¹. The SOFCs consist of the following: LSCF-GDC composites as a cathode, GDC as an interlayer, yttrium stabilized zirconia (YSZ) as an electrolyte, Ni-YSZ (50: 50 wt%) as an anode functional layer, and Ni-YSZ (50: 50 wt%) for support. The cathodes are prepared for 6LSCF-4GDC (60: 40 wt%), 5LSCF-5GDC (50: 50 wt%), and 4LSCF-6GDC (40: 60 wt%). The 5LSCF-5GDC cathode shows 1.29 Wcm⁻², 0.97 Wcm⁻², and 0.47 Wcm⁻² at 780 °C, 730 °C, and 680 °C, respectively. The 6LSCF-4GDC shows 0.92 Wcm⁻², 0.71 Wcm⁻², and 0.54 Wcm⁻² at 780 °C, 730 °C, and 680 °C, respectively. At 780 °C, the highest fuel cell performance is achieved by the 5LSCF-5GDC, while at 680 °C the 6LSCF-4GDC shows the highest performance. The best composition of the porous composite cathodes with LSCF (55 m²g⁻¹) and GDC (5 m²g⁻¹) needs to be considered with a function of temperature.     

Synthesis of mesoporous TiO2/γ-Al2O3 composite granules with different sol composition and calcination temperature

Mesoporous TiO₂/γ-Al₂O₃ composite granules were prepared by combining sol-gel method and oil-drop method. After calcination at 450 °C, the composite granules showed anatase and γ-Al₂O₃ phases with the specific surface area of 240-310 m²/g. The phase composition and pore structure of the granules can be controlled by calcination temperature and the mixing ratio of boehmite sol and titania sol. The product granules can be used as a photocatalyst or adsorbent in moving or fluidized bed reactors.     

Simultaneous synthesis and consolidation of nanostructured TaSi2–Si3N4 composite by pulsed current activated combustion

Dense nanostructured 4TaSi₂–Si₃N₄ composite was synthesized by pulsed current activated combustion synthesis (PCACS) method within 3 min in one step from mechanically activated powders of TaN and Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense 4TaSi₂–Si₃N₄ composite with relative density of up to 98% was produced under simultaneous application of a 60 MPa pressure and the pulsed current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.     

Eggshell-membrane-templated synthesis of hierarchically-ordered NiO–Ce0.8Gd0.2O1.9 composite powders and their electrochemical performances as SOFC anodes

Hierarchically-ordered NiO-Ce_0.8Gd_0.2O_1.9 (GDC) composite anode powders were synthesized using eggshell membranes as biotemplates. The morphology of the as-synthesized powders depended on the kind of Ni precursor and the use of EDTA as a chelating agent. Hierarchically-ordered anode powders were obtained from Ni chloride and Ni acetate precursors with EDTA. The Ni–GDC anode synthesized from Ni chloride precursor with EDTA exhibited the lowest polarization resistance at 800 °C and an activation energy of 0.01 Ω cm² and 0.74 eV, respectively, in humidified H₂. In accordance with the polarization resistance results, the 0.5-mm thick GDC electrolyte-supported single cell with the Ni–GDC anode synthesized from Ni chloride precursor with EDTA showed a maximum power density of 0.34 W cm⁻² at 800 °C with humidified H₂ fuel.     

Effect of the B2O3 addition on the sintering behavior and microwave dielectric properties of Ba3(VO4)2–Zn1.87SiO3.87 composite ceramics

The effect of the B₂O₃ addition on the low-temperature sintering, microstructure and microwave dielectric properties of the Ba₃(VO₄)₂–Zn_1.87SiO_3.87 composite ceramics was investigated. The results indicate that the addition of B₂O₃ can effectively promote the densification and further improve the microwave dielectric properties of the composite. The low-temperature sintering mechanism was ascribed to the formation of the liquid phase owing to the reaction between the additive B₂O₃ and the residual SiO₂ in the composite. B₂O₃–SiO₂ liquid phases can not only lower the sintering temperature, but also speed up the grain growth of the composite ceramics. The rapid grain growth occurs as the B₂O₃ content is more than 6 wt%. The 3 wt% B₂O₃ doped 0.5Ba₃(VO₄)₂–0.5Zn_1.87SiO_3.87 ceramics can be well sintered at 925 °C and exhibit excellent microwave dielectric properties of Q×f∼40,800 GHz, ε_r∼10 and τ_f∼0.5 ppm/°C.     

Structure and thermal properties of La0.6Sr0.4Co0.2Fe0.8O3−δ-SDC carbonate composite cathodes for intermediate- to low-temperature solid oxide fuel cells

The structure and thermal properties of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ-SDC carbonate (LSCF-SDC carbonate) composite cathodes were investigated with respect to the calcination temperatures and the weight content of the samarium-doped ceria (SDC) carbonate electrolyte. The composite cathode powder has been prepared from La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ and SDC carbonate powders using the high-energy ball milling technique in air at room temperature. Different powder mixtures at 30 wt%, 40 wt% and 50 wt% of SDC carbonate were calcined at 750-900 °C. The findings indicated that the structure and thermal properties of the composite cathodes were responsive to the calcination temperature and the content of SDC carbonate. The absence of any new phases as confirmed via XRD analysis demonstrated the excellent compatibility between the cathode and electrolyte materials. The particle size of the composite cathode powder was ∼0.3-0.9 μm having a surface area of 4-15 m² g⁻¹. SEM investigation revealed the presence of large particles in the resultant powders resulting from the increased calcination temperature. The composite cathode containing 50 wt% SDC carbonate was found to exhibit the best thermal expansion compatibility with the electrolyte.     

Influence of Al2O3 whisker concentration on flexural strength of Al2O3(w)–ZrO2 (TZ-3Y) composite

On investigating the possibility of using alumina whisker reinforced 3 mol% Yttria stabilized Tetragonal Zirconia (TZ-3Y) composite for bioceramic applications, presented here is the influence of varying whisker concentration (2, 5, 10, 15 and 20 wt%) on flexural strength of the composite. Whiskers of hydrothermally synthesized Ammonium Aluminum Carbonate Hydroxide (AACH) were used for composite synthesis. These whiskers transformed in situ into alumina during sintering. It was found that with addition of alumina whiskers, strength was increased and reached a maximum value of 1212±60 MPa and 1325±65 MPa, in pure and 1 wt% CTAB added samples respectively, at a concentration of 10 wt% Al₂O₃ whiskers. The strength values of the synthesized composite can compete well with commercially available materials for dental applications.     

Microstructure evolution of Si3N4/Si3N4 joint brazed with Ag–Cu–Ti + SiCp composite filler

The Si₃N₄ ceramic was brazed by Ag–Cu–Ti + SiCp composite filler (p = particle) prepared by mechanical mixing. Effects of the content of Ti and SiC particles on microstructure of the joint were investigated. A reliable Si₃N₄/Si₃N₄ joint was achieved by using Ag–Cu–Ti + SiCp composite filler at 1173 K for 10 min. A continuous and compact reaction layer, with a suitable thickness, forms at the Si₃N₄/braze interface. The SiC particles react with Ti in the brazing layers, forming Ti₃SiC₂ thin layers around the SiC particles themselves and Ti₅Si₃ small particles in the Ag[Cu] and Cu[Ag] based solid solution. The higher content of SiC particles in the filler (≥10 vol%) depresses interfacial bonding strength between the Si₃N₄ substrate and composite brazing layer due to the thinner reaction layer and the bad fluidity of the filler. The Ti₃SiC₂ → TiC + Ti₅Si₃ reaction occurs when Ti concentration around SiC particles in the filler increases.     

In situ preparation of Si3N4–TiN composite by pyrolysis of polytitanosilazane (PTSZ)

Si₃N₄–TiN composite powders were obtained by in situ pyrolysis of polytitanosilazane. Dense Si₃N₄–TiN composites were prepared by hot-pressing at 1800 °C under 20 MPa for 2 h without sintering additive. Crystallization of amorphous PTSZ powders occurred between 1400 and 1500 °C with major phases, α-Si₃N₄, β-Si₃N₄, and small amount of phase TiN. Mechanical properties and microstructure of Si₃N₄–TiN composites were characterized. The results showed that the mechanical strength was 620 MPa, the fracture toughness was 7.8 MPa m^1/2 and the Vickers hardness was 8.5 GPa. SEM analysis indicated that Si₃N₄–TiN composite possessed excellent fracture toughness because TiN grains produced by in situ pyrolysis were well dispersed in Si₃N₄ matrix.     

Structural evolution of plasma sprayed amorphous Li4Ti5O12 electrode and ceramic/polymer composite electrolyte during electrochemical cycle of quasi-solid-state lithium battery

A quasi-solid-state lithium battery is assembled by plasma sprayed amorphous Li₄Ti₅O₁₂ to provide the outstanding electrochemical stability and better normal interface contact.Scanning Electron Microscope(SEM),Scanning Transmission Electron Microscopy(STEM),Transmission Electron Microscopy(TEM),and Energy Dispersive Spectrometer(EDS)were used to analyze the structural evolution and performance of plasma sprayed amorphous LTO electrode and ceramic/polymer composite electrolyte before and after electrochemical experiments.By comparing the electrochemical performance of the amorphous LTO electrode and the traditional LTO electrode,the electrochemical behavior of different electrodes is studied.The results show that plasma spraying can prepare an amorphous LTO electrode coating of about 8μm.After 200 electrochemical cycles,the structure of the electrode evolved,and the inside of the electrode fractured and cracks expanded,because of recrystallization at the interface between the rich fluorine compounds and the amorphous LTO electrode.Similarly,the ceramic/polymer composite electrolyte has undergone structural evolution after 200 test cycles.The electrochemical cycle results show that the cycle stability,capacity retention rate,coulomb efficiency,and internal impedance of amorphous LTO electrode are better than traditional LTO electrode.This innovative and facile quasi-solid-state strategy is aimed to promote the intrinsic safety and stability of working lithium battery,shedding light on the development of next-generation high-performance solid-state lithium batteries.     

Antibacterial and anti-flaming PA6 composite with metathetically prepared nano AgCl@BaSO4 co-precipitates

In this study,a facile and environmentally friendly method with low energy consumption for preparing nanoscale AgCl and BaSO4 co-precipitates(AgCl@BaSO₄ co-precipitates)was developed based on the metathetical reaction.Then,the dried co-precipitates were melt-compounded with polyamide 6(PA6)resins at a specified mass ratio in a twin-screw extruder.The results demonstrated that in the absence of any coating agent or carrier,the nanoparticles of AgCl@BaSO₄ co-precipitates were homogeneously dispersed in the PA6 matrix.Further analysis showed that after the addition of AgCl@BaSO₄ co-precipitates,the antibacterial performance,along with the flame-retardance and anti-dripping characteristics of PA6,was enhanced significantly.In addition,the PA6 composites possessed high spinnability in producing pre-oriented yarn.     

Structure and properties of nanostructured ceramic matrix composite coatings prepared in-situ by reactive plasma spraying micro-sized Al–Fe2O3–Cr2O3 powders

Nanostructured FeAl₂O₄-based ceramic matrix composite coatings were prepared in-situ by reactive plasma spraying micro-sized Al–Fe₂O₃ and Al–Fe₂O₃–Cr₂O₃ powders. The microstructure, toughness, Vickers hardness, and adhesive strength of these coatings were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and mechanical tests. The results indicated that both the coatings exhibited a nanostructured microstructure. The grains of coating AFC sprayed with Al–Fe₂O₃–Cr₂O₃ powders are finer than those of the coating AF sprayed with Al–Fe₂O₃ powders. The composite nano-coating sprayed with Al–Fe₂O₃–Cr₂O₃ powders exhibited higher hardness and better wear resistance compared with those of the composite nano-coating sprayed with Al–Fe₂O₃ powders. The adhesive strength, toughness, and wear resistance of the composite coating sprayed with Al–Fe₂O₃–Cr₂O₃ powders were significantly enhanced compared with those of the composite coating sprayed with Al–Fe₂O₃ powders, which were attributed to the Cr₂O₃ addition.