Elaboration, by tape casting, and thermal characterization of a solid oxide fuel half-cell for low temperature applications

In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cell (SOFC) down to about 700 °C. In this respect, materials with a high ionic conduction at intermediate temperature have to be found and the processes to elaborate fuel cells, using these new materials, have to be developed.Apatite materials (La_10−xSr_x(SiO₄)₆O_2±δ) are attractive candidates for solid electrolyte working at intermediate temperature. The ceramic powder was produced by solid state reaction and was tape cast to obtain green sheets.Concerning the cathode, a perovskite oxide (La_1−xSr_xMn_1−yCo_yO_3−δ) has been chosen. The perovskite powder was also shaped by tape casting with the introduction of a pore forming agent (corn-starch) to obtain the required porosity in the sintered cathode.The co-firing of the electrolyte/cathode half-cell in air at 1400 °C-2 h gives a flat sample with a dense apatite (98.2%), a 42.7% porous cathode and neither delamination nor chemical reactivity between electrolyte and cathode materials.The dimensional behaviour of the electrolyte material is stable for an oxygen partial pressure ranging from 10⁻¹⁰ to 0.21 atmosphere, from room temperature to 700 °C. The thermal expansion coefficients of the electrolyte and cathode materials are rather close (Δα = 2.8 × 10⁻⁶ K⁻¹) under air.     

Influence of SiO2 fillers on microwave absorption properties of carbonyl iron/carbon black double-layer coatings

Epoxy resin (ER) based double-layer composite coatings were prepared with the thickness of 1.2 mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively. Especially, SiO₂ was introduced into the matching layer as wave-transmission material to improve the matching impendence. The complex permittivity, complex permeability and absorption properties were investigated in 2–18 GHz. With increasing SiO₂ content in the matching layer, the reflection loss (RL) was enhanced in the range 2–18 GHz. When the coating with the optimized SiO₂ and CI weight concentration (SiO₂:CI:ER) of 2:5:1, the optimal RL got to −17.3 dB and the effective absorption band (RL better than −4 dB) reached 5.7 GHz. In comparison, the minimum RL value was only −5.9 dB and the bandwidth (RL better than −4 dB) was just 4.1 GHz for the SiO₂-free composite coating.     

Solution growth of KDP single crystals doped with titanium dioxide nanoparticles

Pure KDP single crystals and KDP crystals doped with TiO₂ nanocrystals were grown by the method of temperature reduction from aqueous solutions. Adsorption of the phosphate-ions on the surface of TiO₂ particles was studied by FTIR spectroscopy. It was shown that the nanoparticles with adsorbed H₂PO₄^– and (H₂PO₄)₂^2–anions were incorporated predominantly into the positively charged face (1 0 1) of the pyramidal sector of KDP. High-resolution X-ray three-crystal diffractometry (TCD) investigation of the as grown samples of KDP + TiO₂ revealed the presence of the turns of the growth layer “stacks” up to 3 arcsec in the growth sectors {1 0 0} and {1 0 1}. The observed thickness of these “stacks” was of the order of 20–30 μm. For KDP + TiO₂ crystals there was found a relative change of the crystal lattice parameter (Δd/d) caused by incorporation of TiO₂ nanoparticles into the boundaries of the growth layers. This gave rise to the formation of a semicoherent binding on the interface between the captured TiO₂ and the matrix. No essential influence of the nanoparticles on the laser damage threshold of KDP with 10⁻⁵ wt.% of TiO₂ was established.     

Microstructure and martensitic transformation in Si-coated TiNi powders prepared by ball milling

Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO₂ occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powders were recovered and Ti₄Ni₄Si₇ was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.     

Structural, electrical and optical studies of SILAR deposited cadmium oxide thin films: Annealing effect

Successive ionic layer adsorption and reaction (SILAR) method has been successfully employed for the deposition of cadmium oxide (CdO) thin films. The films were annealed at 623 K for 2 h in an air and changes in the structural, electrical and optical properties were studied. From the X-ray diffraction patterns, it was found that after annealing, H₂O vapors from as-deposited Cd(O₂)_0.88(OH)_0.24 were removed and pure cubic cadmium oxide was obtained. The as-deposited film consists of nanocrystalline grains of average diameter about 20-30 nm with uniform coverage of the substrate surface, whereas for the annealed film randomly oriented morphology with slight increase in the crystallite size has been observed. The electrical resistivity showed the semiconducting nature with room temperature electrical resistivity decreased from 10⁻² to 10⁻³ Ω cm after annealing. The decrease in the band gap energy from 3.3 to 2.7 eV was observed after the annealing.     

Dielectric behaviors of PHBHHx–BaTiO3 multifunctional composite films

Multifunctional polymeric composites were investigated for potential use in high energy storage capacitors and tissue engineering. The polymeric composites were fabricated by employing biodegradable polyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), as the matrix. Ferroelectric BaTiO₃ ceramic powders were added to the composites as fillers. The dielectric spectroscopy of the composites was measured over a wide frequency range (10⁰–10⁷ Hz) from −100 to 60 °C. The composition dependent dielectric behavior was modeled by a self-consistent effective medium theory. A percolation threshold of 0.367 was observed in the composites. The glass transition relaxation of the composite was also discussed by comparing the popular Vögel–Fulcher–Tammann law with a new glass model. The composites show attractive ferroelectricity and piezoelectricity for biomedical applications.     

Synthesis of BaTiO3 nanoparticle/poly(2-hydroxyethyl methacrylate) hybrid nanofibers via electrospinning

BaTiO₃ nanoparticle/poly(2-hydroxyethyl methacrylate) (PHEMA) hybrid nanofibers were fabricated from an in situ synthesized BaTiO₃ nanoparticle/polymer hybrid by electrospinning. The bulk hybrid for nanofibers was synthesized through the in situ hydrolysis of Ba–Ti alkoxide modified with 2-vinyloxyethanol and subsequent copolymerization with HEMA monomer. IR and ¹³C NMR spectra showed the formation of polymer matrix. The molecular weights of BaTiO₃ nanoparticle/PHEMA hybrid for spinning were 1.3 × 10⁵ for 20 equiv. PHEMA and 5.7 × 10⁵ for 30 equiv. PHEMA. The crystallite size of BaTiO₃ particles in the hybrid was 4.5 nm according to the Scherrer equation. The diameter of BaTiO₃ nanoparticle/PHEMA hybrid nanofibers ranged from 500 nm to 1 μm. A field stress–strain curve was observed for the BaTiO₃ nanoparticle/PHEMA hybrid nanofiber.     

Ionic conductivity of a gel polymer electrolyte based on Mg(ClO4)2 and polyacrylonitrile (PAN)

Magnesium ion containing gel polymer electrolytes based on polyacrylonitrile (PAN) have been synthesized and characterized using ac impedance measurements. The electrolyte composition having the highest room temperature conductivity was found by varying the ratios propylene carbonate/ethylene carbonate (PC/EC) and PAN/Mg(ClO₄)₂. The corresponding composition was 18 mol% PAN:64 mol% EC:14 mol% PC:4 mol% Mg(ClO₄)₂. The ac conductivity measurements were carried out from room temperature upto 70 °C with blocking (stainless steel) electrodes. The room temperature conductivity is 3.2×10⁻³ S cm⁻¹ and the activation energy is 0.24 eV over the temperature range used. The high conductivity and the low activation energy of the material could possibly be due to the liquid electrolyte, Mg(ClO₄)₂ in EC/PC trapped in a matrix of PAN, as suggested by previous workers. According to dc polarization measurements, the gel electrolyte appears to be predominantly an anionic conductor.     

Preparation of porous magnetic nanocomposites using corncob powders as template and their applications for electromagnetic wave absorption

Strong absorption, low density, and thin matching thickness are important parameters for electromagnetic (EM) wave absorbers. In this study, we prepared novel porous magnetic nanocomposites using corncob powders as template. The presence of corncob will significantly decrease the bulk density of samples from more than 4.0 to about 0.55 g cm⁻³. The porous structures remarkably decreased the permittivity (ε) and permeability (μ) and enhanced the impendence matching between the absorber and air. The porous magnetic nanocomposites exhibit enhanced absorption for EM waves at thin matching thickness. The optimum thickness is only 1.0–1.4 mm, with bandwidth of RL < −5 dB of about 8 GHz, covering the half X-band and the whole K_u-band. The areal density of magnetic absorbers at this study is only about 0.7–1.0 kg m⁻² at thickness of 1.0–1.4 mm, much lower than the reported values of other magnetic absorbers. Due to the strong absorption at low density and thin matching thickness, the porous magnetic nanocomposites prepared using corncob powders as template are promising light-weight EM wave absorbers.     

Characterization and photocatalytic activity of nanostructured indium tin oxide thin-film electrode for azo-dye degradation

Photocatalytically active indium tin oxide thin film electrodes were prepared by electron beam evaporation technique onto a glass substrate having thickness 120 nm. Degradation of reactive dye yellow direct 42 has been performed using photoeletrocatalysis. A biased potential is applied across indium tin oxide photoelectrode illuminated by UV light. The best experimental conditions were found to be dye concentration 1.0 × 10^− 5 mol L^− 1, pH 5.25 and 0.5 mol L^− 1 NaCl as supporting electrolyte when the photoelectrode was biased at + 0.5 V versus saturated calomel electrode. The effects of other electrolytes, dye concentration, pH solution, electrode annealing temperature and applied potentials have been also investigated and are discussed. Several common inorganic salts Na₂SO₄, Na₂CO₃, NaNO₃ and NaCl were chosen to act as supporting electrolytes, which was added into the dye solution. It is shown that the charge-transfer resistance of photoanode can be calculated by the analysis of its electrochemical impedance spectroscopy, and the photoelectrocatalytic degradation rate of yellow direct 42 was inversely proportional to the value of charge-transfer resistance of photoelectrodes at different pH. The value of charge-transfer resistance is smaller, the higher its photoelectro-activity is.     

Corrosion resistance enhancement of Ni–P electroless coatings by incorporation of nano-SiO2 particles

Composite coatings were prepared using hypophosphite reduced electroless nickel bath containing 7 g/L SiO₂ nano-particles at pH 4.6 ± 0.2 and temperature 90 ± 2 °C. Deposition rate for SiO₂ nano-composite coatings was 10–12 μm/h. The amount of SiO₂ nano-particles co-deposited in the Ni–P matrix was around 2 wt.%. The analyzes of coating compositions, carried out by Energy Dispersive Analysis of X-ray (EDAX), showed that plain Ni–P and Ni–P/nano-SiO₂ deposits contained around 8 wt.% phosphorus. The X-ray diffraction (XRD) pattern of Ni–P/nano-SiO₂ coating was very similar to that of plain electroless Ni–P coating, whose structure was also amorphous.     

Relaxor ferroelectric like giant permittivity in PrCrO3 semiconductor ceramics

The electrical behavior of PrCrO₃ ceramics prepared by citric acid route and sintered at 1200 °C has been characterized by a combination of permittivity measurements, and impedance spectroscopy (IS). The effective permittivity obtained in frequency range 100 Hz to 1 MHz and temperature range 80–300 K, exhibits giant permittivity value of 3 × 10⁴ near room temperature. The response is similar to that observed for relaxor ferroelectrics. IS data analysis revealed the ceramics to be electrically heterogeneous semiconductor with room temperature resistivity <10² Ω m consisting of semiconducting grains with permittivity ?′ ∼ 100 and more resistive grain boundaries with effective permittivity ?′ ∼ 10⁴. We conclude, therefore that grain boundary effect is the primary source for the high effective permittivity in PrCrO₃ ceramics.     

Adsorption and electropolymerization of toluidine blue on the nanostructured octakis(hydridodimethylsiloxy)octasilsesquioxane surface

Toluidine blue O (TBO) was adsorbed on the octakis(hydridodimethylsiloxy)octasilsesquioxane (Q₈M₈^H) surface. The characterization of the precursor (Q₈M₈^H) and resulting materials obtained by the reaction of Q₈M₈^H and toluidine blue (CTBO) were defined using Fourier transform infrared spectra, nuclear magnetic resonance solid-state ¹³C and Si²⁹ magic angle spinning. The electrochemical polymerization in a glassy carbon electrode was verified by means of a film silsesquioxane formation (FCTBO) using cyclic voltammetry in a potential range of −0.5 to 1.3 V (vs. saturated calomel electrode (SCE)) in a Britton Robinson (B-R) buffer solution (pH 2.0). The cyclic voltammogram of the film exhibits two redox couples with a formal potential of −0.15 and −0.02 V (B-R buffer pH 5). The formal potential shifts linearly in the cathodic direction by increasing the pH solution with a slope of 71 and 57 mV per unit for the first and second couple, respectively. The film was electrochemically very stable.     

Catalytic oxidation of carbon monoxide over radiolytically prepared Pt nanoparticles supported on glass

Platinum nanoparticles have been prepared by radiolytic and chemical methods in the presence of stabilizer gelatin and SiO₂ nanoparticles. The formation of Pt nanoparticles was confirmed using UV-vis absorption spectroscopy and transmission electron microscopy (TEM). The prepared particles were coated on the inner walls of the tubular pyrex reactor and tested for their catalytic activity for oxidation of CO. It was observed that Pt nanoparticles prepared in the presence of a stabilizer (gelatin) showed a higher tendency to adhere to the inner walls of the pyrex reactor as compared to that prepared in the presence of silica nanoparticles. The catalyst was found to be active at ≥150 °C giving CO₂. Chemically reduced Pt nanoparticles stabilized on silica nanoparticles gave ∼7% CO conversion per hour. However, radiolytically prepared Pt nanoparticles stabilized by gelatin gave ∼10% conversion per hour. Catalytic activity of radiolytically prepared platinum catalyst, coated on the inner walls of the reactor, was evaluated as a function of CO concentration and reaction temperature. The rate of reaction increased with increase in reaction temperature and the activation energy for the reaction was found to be ∼108.8 kJ mol⁻¹. The rate of CO₂ formation was almost constant (∼1.5 × 10⁻⁴ mol dm⁻³ h⁻¹) at constant O₂ concentration (6.5 × 10⁻³ mol dm⁻³) with increase in CO concentration from 2 × 10⁻⁴ mol dm⁻³ to 3.25 × 10⁻³ mol dm⁻³. The data indicate that catalytic oxidation of CO takes place by Eley-Rideal mechanism.     

Preparation and electrochemical properties of lamellar MnO2 for supercapacitors

Lamellar birnessite-type MnO₂ materials were prepared by changing the pH of the initial reaction system via hydrothermal synthesis. The interlayer spacing of MnO₂ with a layered structure increased gradually when the initial pH value varied from 12.43 to 2.81, while the MnO₂, composed of α-MnO₂ and γ-MnO₂, had a rod-like structure at pH 0.63. Electrochemical studies indicated that the specific capacitance of birnessite-type MnO₂ was much higher than that of rod-like MnO₂ at high discharge current densities due to the lamellar structure with fast intercalation/deintercalation of protons and high utilization of MnO₂. The initial specific capacitance of MnO₂ prepared at pH 2.81 was 242.1 F g⁻¹ at 2 mA cm⁻² in 2 mol L⁻¹ (NH₄)₂SO₄ aqueous electrolyte. The capacitance increased by about 8.1% of initial capacitance after 200 cycles at a current density of 100 mA cm⁻².     

Room temperature deposited vanadium oxide thin films for uncooled infrared detectors

We demonstrate the room temperature deposition of vanadium oxide thin films by pulsed laser deposition (PLD) technique for application as the thermal sensing layer in uncooled infrared (IR) detectors. The films exhibit temperature coefficient of resistance (TCR) of 2.8%/K implies promising application in uncooled IR detectors. A 2-D array of 10-element test microbolometer is fabricated without thermal isolation structure. The IR response of the microbolometer is measured in the spectral range 8-13 μm. The detectivity and the responsivity are determined as ∼6×10⁵ cm Hz^1/2/W and 36 V/W, respectively, at 10 Hz of the chopper frequency with 50 μA bias current for a thermal conductance G∼10-3 W/K between the thermal sensing layer and the substrate. By extrapolating with the data of a typical thermally isolated microbolometer (G∼10⁻⁷ W/K), the projected responsivity is found to be around 10⁴ V/W, which well compares with the reported values.     

Controllable growth of zinc oxide nanosheets and sunflower structures by anodization method

Large scale of ZnO nanosheets and sunflower structures were fabricated by anodization of zinc in (NH₄)₂SO₄ and NH₄Cl aqueous electrolytes. The products were characterized via scanning electron microscope, transmission electron microscope and X-ray diffraction analysis. Results show that the sheets are about 20–50 μm in dimension and 20 nm in thickness. The sunflower microstructures are about 400–500 μm in dimension. The possible growth mechanism is suggested on the basis of experimental results.     

High capacitive performance of nanostructured Mn-Ni-Co oxide composites for supercapacitor

Nanostructured Mn-Ni-Co oxide composites (MNCO) were prepared by thermal decomposition of the precursor obtained by chemical co-precipitation of Mn, Ni and Co salts. The chemical composition and morphology were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The electrochemical capacitance of MNCO electrode was examined by cyclic voltammetry, impedance and galvanostatic charge-discharge measurements. The results showed that MNCO electrode exhibited the good electrochemical characteristics. A maximum capacitance value of 1260 F g⁻¹ could be obtained within the potential range of −0.1 to 0.4 V versus saturated calomel electrode (SCE) in 6 mol L⁻¹ KOH electrolyte.     

Electrical resistivity of the hole doped La0.8Sr0.2MnO3 manganites: Role of electron–electron/phonon/magnon interactions

In this work, a quantitative analysis of reported metallic and insulating behaviour of resistivity in perovskite manganites La_0.8Sr_0.2MnO₃ is established. An effective inter-ionic interaction potential (EIoIP) with the long-range Coulomb, van der Waals (vdW) interaction and short-range repulsive interaction up to second-neighbour ions within the Hafemeister and Flygare approach was employed to estimate the Debye and Einstein temperature and was found to be consistent with the available experimental data. The electrical resistivity data in low temperature regime (T < T_MI) were theoretically analyzed within the framework of the classical electron–phonon model of resistivity, for example, the Bloch–Gruneisen (BG) model. The Bloch–Gruneisen (BG) model and terms T², T^4.5 simplify the electron–phonon, electron–electron and electron–magnon scattering processes. On the other hand, in high temperature regime (T > T_MI) the insulating nature is discussed with Mott's variable range hopping (VRH) model and small polaron conduction (SPC) model. For T > T_MI SPC model is more appropriate than the VRH model. The SPC model consistently retraces the higher temperature resistivity behaviour (T > θ_D/2). The metallic and semiconducting resistivity behaviours of La_0.8Sr_0.2MnO₃ manganites are analyzed, to the knowledge, for the first time highlighting the importance of electron–phonon, electron–electron, electron–magnon interactions and small polaron conduction.     

Interfacial control of uni-directional SiCf/SiC composites based on electrophoretic deposition and their mechanical properties

Interfacial control of uni-directional SiC_f/SiC composites were performed by EPD, and their mechanical properties at room temperature were evaluated. The effect of the thickness of carbon interphase on SiC fibers by EPD on mechanical properties of uni-directional SiC_f/SiC composites was also investigated. The average thickness of carbon coating on SiC fibers increased from 42 nm to 164 nm with an increase in the concentration of colloidal graphite suspension for EPD. Dense SiC_f/SiC composites were achieved and their fiber volume fraction was 47–51%. The SiC_f/SiC composites had a bending strength of 210–240 MPa. As the thickness of carbon coating was below 100 nm, the SiC_f/SiC composites (SC01 and SC02) fractured in almost brittle manner. In contrast, the SiC_f/SiC composites (SC03) showed a pseudo-ductile fracture behavior with a large number of fiber pullout as the thickness of carbon coating was above 100 nm. The fracture energy of SC03 was 3–4 times as high as those of SC01 and SC02 and the value was about 1.7 kJ/m². In consideration of the results of mechanical properties, the thickness of carbon coating on SiC fibers should be at least 100 nm to obtain high-performance SiC_f/SiC composites. The fabrication process based on EPD method is expected to be an effective way to control the interfaces of SiC_f/SiC composites and to obtain high-performance SiC_f/SiC composites.