The influence of activated carbon as an additive in anode materials for low temperature solid oxide fuel cells

The effects of activated carbon (AC) as an additive in multi-oxide nano composite LiNiCuZn–O for application as anode in solid oxide fuel cell (SOFC) is reported. The composite was synthesized using solid state reactions method with varying content of AC in range 0.1%–0.9% for use as anode in the cell. The cell was composed of the synthesized composite as anode, LiNiCuZn–O as cathode and Samaria doped ceria (SDC) as electrolyte. The prepared composites were characterized for morphology and crystal structure by scanning electron microscope (SEM) and x-ray diffraction (XRD) respectively. Furthermore, the crystallite sizes of LiNiCuZn–O and LiNiCuZn–O with AC as an additive have been found in the range from 50 nm to 70 nm. The prepared composite materials were observed porous and the porosity of the sample having 0.5% additive was found highest. The conductivity and power density of the SOFC were studied at temperature of 600 °C. The maximum value of conductivity was found as 4.79 S/cm for the composite containing 0.5% AC as measured by using 4-probe method. The maximum value of power density of the fuel cell with anode comprising of 0.5% AC along with the mentioned cathode and the electrolyte was 455 mW/cm². Therefore, out of the compositions studied, the composite comprising of LiNiCuZn–O with 0.5% AC offered best performance for anode in the cell. This oxide composite is reported as a potential candidate for use as anode in low temperature SOFCs.     

Synthesis method of novel Gd2O3@Fe3O4 nanocomposite modified by dextrose capping agent

In current study, gadolinium oxide was heterogeneously formed on the surface of iron oxide nanoparticles and further modified with dextrose capping agent to be used in biomedical applications, especially for contrast enhancement in MR images. First, two types of iron oxide nanoparticles were prepared at 25 and 80 ^°C via simple coprecipitaion method. Then, gadolinium oxide nanoparticles were synthesized through a consecutive precipitation process on previously formed iron oxide seeds in an aqueous media and subsequent annealing at 300 ^°C. Finally, dextrose was used as capping agent to stabilize nanocomposites in a colloidal suspension. X-ray diffraction (XRD), Scanning and Transmission electron microscopy, Dynamic Laser Scattering (DLS), Fourier-Transform Infrared Spectroscopy (FTIR), and Magnetometery (VSM) techniques were employed for nanocomposites investigation and MTT-assay method used for viability assessment of colloidal samples. Measurements based on Scherrer equation from XRD patterns showed that increasing coprecipitation temperature resulted bigger iron oxide crystallites. The iron oxide crystallite size was increased from 15.1 to 28.1 nm. Precipitation process led to gadolinium oxide formation with 30.7 and 38.8 nm crystallite sizes, respectively. TEM images revealed that iron oxide agglomerates were encapsulated in gadolinium oxide surroundings. Hydrodynamic size of the coated nanoparticles with dextrose was 208 and 247 nm. In VSM examinations, nanocomposites did not display coercive field and the saturation magnetization was 1.93 emu/g. MTT-assay results showed 80% viability in 285 μg nanocomposites containing 96.9 μg [Fe] and 11.4 μg [Gd].     

Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.     

Finite element optimization of sample geometry for measuring the torsional shear strength of glass/metal joints

Assessment of mechanical properties of glass/metal joints is a challenging process, especially when the application relevant conditions of the joints have to be considered in the test design. In this study, a finite element method (FEM) is implemented to analyze a torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cells application. Deviations from axial symmetry of the square flanges (ends) of respective hourglass-shaped specimens and also supporting and loading sockets of the test set-up are included in the model to simulate conditions close to reality. Undesirable tensile stress and also shear stress concentration appear at the outer edge of glass-ceramic layers, which are less for the hollow-full specimen. The simulation results show that for a specimen with either 9 mm thick square- or 6 mm thick triangular-flanges, locally enhanced tensile stresses almost disappear, resulting in a symmetric shear stress distribution. The difference between the analytically derived nominal shear strength and the real critical shear stress derived via simulation reduces with decreasing the fracture torque.     

Size-dependent separation of graphene oxide by deformation of packed-gel in a chromatographic column

ABSTRACT

A deformable gel-packed chromatographic column was used to separate as-synthesized graphite oxide with different sizes. The synthesized gel (56 µm) was deformed by pressure of the fluid flow and the gaps in the gels showed a range of sizes. A suspension of graphene oxide (0.1 g/L, 10 mL) was injected, and graphene oxide in the elution had a size at 0.56 μm and 0.14 μm, whereas in half upper and bottom domain of the gel layer graphene oxide had a size at 33 µm and 2.9 µm, respectively, demonstrating that graphene oxide suspension was separated by size through gel layer.     

Influence of the synthesis conditions on the microstructural,compositional and morphological properties of graphene oxide sheets

In this paper we report about the synthesis and characterization of graphene oxide (GO). We monitor the effects of the different synthetic processes on the morphological and structural properties of the materials. A modified Hummers' method is adopted to obtain GO powder; H₂SO₄ is employed as intercalating agent, to increase the distance between graphitic layers, while KMnO₄ is used as oxidizing reagent for introducing the oxygen functionalities in the graphitic structure. The oxidized graphite powder is treated in acid solution; different washing cycles are applied. The recovered powders are dispersed in aqueous solution and sonicated for 30 min or 60 min, respectively. Subsequently, these solutions are deposited on Si and SiO₂(317 nm)/Si substrates by means of dip coating. GO powders, GO solutions and GO on substrate are characterized through several analytical and spectroscopic techniques. These analyses reveal that the sonication time and the washing procedure of the samples can influence the structure and the morphology of the graphene oxide flakes. Moreover, when KOH is employed as alkaline agent in a chemical reducing treatment of the GO powder before sonication, a considerable alteration of the native structure of graphene oxide is observed. The detailed characterization indicates that the properties of the GO samples are strongly influenced by the chemical and physical treatments to which it is subjected.     

Assessment on the mechanical,structural, and thermal attributes of green graphene-based water soluble polymer electrolyte composites

In the current study, graphene oxide (GO) was prepared using green chemistry with modified Hummer's method without incorporating sodium nitrate (NaNO₃). Solvent casting was employed to fabricate GO-doped poly(ethylene oxide) (PEO), that is, PEO/GO composites with various proportion of Na₂SO₄ and were then subjected to characterization via advanced spectroscopic techniques for different physicochemical aspects to estimate their potential applications as marketable products. XRD analysis explored that fabricated composites are more crystalline than neat PEO. PEO/GO/Na₂SO₄ composite films offered maximum crystallinity. SEM displayed the same trend. TG/DTA thermogram exposed better thermal stability than pristine polymer. FTIR studies confirmed complexation among hybrid's components. Elongation-at-break and Young's modulus displayed an enhancing behavior with an incremental loading of salt and filler. In terms of mechanical performance, composite of PEO with 0.37 wt % GO and 0.08 g salt was found to be an ideal composition during the course of study. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48376.     

MOF assisted synthesis of a Ho2O3/CNT nanocomposite photocatalyst for organic pollutants degradation

In this work, a holmium oxide (Ho₂O₃/CNT) photocatalysts were successfully synthesized through a MOF assisted route for the first time. The effects of the morphology and purity on the photocatalytic behavior of the products, were investigated by determining various physicochemical properties. The Ho₂O₃/CNT nanocomposite was systematically analyzed by powder X-ray diffraction (P-XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy studies. The Ho₂O₃ derived from a MOF assisted synthetic route using Ho(NO₃)₃·5H₂O and terephthalic acid with a 1:1 M ratio at a temperature of 750 °C for 3 h prove the most advantageous, 98% degradation of 20 mg/L aqueous tetracycline pollutant was observed within 60 min. The elevated photocatalytic activity was mainly attributable to the unique synthetic route, improved crystallinity, wide UV-light absorption rate and excellent adsorption capabilities of CNT, as well as enhanced oxygen deficiency. The photocatalytic results confirm that the Ho₂O₃/CNT nanocomposite is an efficient photocatalyst for the degradation of toxic tetracycline pollutant and is thus suitable for use in environmental remediation.     

Facile synthesis of Co0.5Zn0.5Fe2O4 nanoparticles decorated reduced graphene oxide hybrid nanocomposites with enhanced electromagnetic wave absorption properties

Herein, reduced graphene oxide/cobalt-zinc ferrite (RGO/Co_0.5Zn_0.5Fe₂O₄) hybrid nanocomposites were fabricated by a facile hydrothermal strategy. Results revealed that the contents of RGO could affect the micromorphology, electromagnetic parameters and electromagnetic wave absorption properties. As the contents of RGO increased in the as-synthesized hybrid nanocomposites, the dispersibility of the particles was improved. Meanwhile, numerously ferromagnetic Co_0.5Zn_0.5Fe₂O₄ particles were evenly anchored on the wrinkled surfaces of flaky RGO. Besides, the obtained hybrid nanocomposites exhibited superior electromagnetic absorption in both X and Ku bands, which was achieved by adjusting the RGO contents and matching thicknesses. Significantly, when the content of RGO was 7.4 wt%, the binary nanocomposites showed the optimal reflection loss of -73.9 dB at a thickness of 2.2 mm and broadest effective absorption bandwidth of 6.0 GHz (12.0–18.0 GHz) at a thin thickness of merely 2.0 mm. The enhanced electromagnetic absorption performance was primarily attributed to the multiple polarization effects, improved conduction loss caused by electron migration, and magnetic loss derived from ferromagnetic Co_0.5Zn_0.5Fe₂O₄ nanoparticles. Our results could provide inspiration for manufacturing graphene-based hybrid nanocomposites as high-efficient electromagnetic wave absorbers.     

1250°C liquidus for the CaO–MgO–SiO2–Al2O3–TiO2 system in air

Ti-bearing blast furnace slags have been regarded as an important secondary material in modern society, and the efficient recycling of Ti oxides from it is of key interest. For this reason, more thermodynamic data is needed regarding the phase relations in different composition ranges and sections. Therefore, the equilibrium phase relations of CaO–MgO–SiO₂–Al₂O₃–TiO₂ system in a low w(CaO)/w(SiO₂) ratio of 0.6–0.8 at 1250 °C in air and fixed concentrations of MgO and Al₂O₃, were investigated experimentally using a high temperature equilibration and quenching method followed by SEM-EDS (Scanning Electron Microscope and Energy Dispersive X-ray Spectrometer) analyses. The equilibrium solid phases of perovskite (CaO·TiO₂), a pseudo-brookite solid solution (MgO·2TiO₂, Al₂O₃·TiO₂)_ss, and anorthite (CaO·Al₂O₃·2SiO₂) were found to coexist with the liquid phase at 1250 °C. The calculated results of Factsage and MTDATA were used for comparisons, and significant discrepancies were found between predictions and the experimental results. The 1250 °C isotherm has been constructed and projected on the CaO–SiO₂–TiO₂-8 wt.% MgO-14 wt% Al₂O₃ quasi-ternary plane of the phase diagram. The obtained results provide new fundamental data for Ti-bearing slag recycling processes, and they add new experimental features for thermodynamic modeling of the high-order titanium oxide-containing systems.