Constrained sintering kinetics of 3YSZ films

3YSZ green layers approximately 10 μm thick were screen-printed onto 3YSZ substrates and their constrained sintering kinetics were measured at 1100-1350 °C using an optical dilatometer. The densification rates of the same powder in the form of pellets and free-standing films were also measured. The constrained densification rate was greatly retarded compared with the free densification rate at a given temperature and density. The retardation increased with increasing density and temperature and could not be properly accounted for by existing theories of constrained sintering. As a result the apparent activation energy is much lower for constrained sintering (135 ± 20 kJ mol⁻¹) than for free sintering (660 ± 30 kJ mol⁻¹). It is proposed that this is because the constrained microstructure exhibits larger and more widely separated pores at the higher temperatures.     

Impact of antioxidant additives on the oxidation stability of biodiesel produced from Croton Megalocarpus oil

The increase in crude petroleum prices, limited resources of fossil fuels and environmental concerns have led to the search of alternative fuels, which promise a harmonious correlation with sustainable development, energy conservation, efficiency and environmental preservation. Biodiesel is well positioned to replace petroleum-based diesel. Biodiesel is a non-toxic, biodegradable and renewable biofuel. But the outstanding technical problem with biodiesel is that, it is more susceptible to oxidation owing to its exposure to oxygen present in the air and high temperature. This happens mainly due to the presence of varying numbers of double bonds in the free fatty acid molecules. This study evaluates oxidation stability of biodiesel produced from Croton megalocarpus oil. Thermal and Oxidation stability of Croton Oil Methyl Ester (COME) were determined by Rancimat and Thermogravimetry Analysis methods respectively. It was found that oxidation stability of COME did not meet the specifications of EN 14214 (6 h). This study also investigated the effectiveness of three antioxidants: 1,2,3 tri-hydroxy benzene (Pyrogallol, PY), 3,4,5-tri hydroxy benzoic acid (Propyl Gallate, PG) and 2-tert butyl-4-methoxy phenol (Butylated Hydroxyanisole, BHA) on oxidation stability of COME. The result showed that the effectiveness of these antioxidants was in the order of PY > PG > BHA.     

Preparation and characterization of graded SSC-SDC MIEC cathode for low-temperature solid oxide fuel cells

Mixed ionic/electronic conductor (MIEC) cathodes with graded composition and microstructures have been fabricated using improved spin-coating technique. Two components, Sm_0.2Ce_0.8O_1.9 (SDC) and Sm_0.5Sr_0.5CoO₃ (SSC), were utilized to prepare the graded MIEC cathode. Graded microstructures, i.e., a SSC-rich outer layer with large interconnected pores and a SDC-rich inner layer with small interconnected pores, were observed. The corresponding single cell had an increase of 13.3% in maximum power density at operating temperature of 600 °C. The present work suggests that the graded MIEC cathode has great potential in improving performance of solid oxide fuel cells operated at lower temperature.     

Studies on slip casting behavior of lanthanum strontium manganite

Dispersion conditions for slip (slurry) formulation of a powder mixture of lanthanum strontium manganite (La_0.84Sr_0.16MnO₃ - LSM) and carbon (pore former) in water was studied through detailed zeta-potential and rheological measurements. The zeta potential variation with pH for the aqueous suspensions of only LSM or carbon exhibited a maximum value in alkaline medium (−40 mV to −50 mV at a pH of 10-11), establishing the pH window for their co-dispersion for slurry formulation. A study of the viscosity variation with shear rate for the slurries with varying solid content (in the range of 45-65 wt.%) exhibited pseudo-plastic flow behavior, indicating presence of flocculates in them. The yield stress values obtained from the Casson equation reduced with decreasing solid content, indicating reduction in the flocculate strength. The slip with solid content of 50 wt.% exhibited optimum flow characteristics to form long tubes with uniform wall thickness (wall thickness 2-4 mm and length of 150-200 mm). The tubular specimens formed after controlled carbon burn out and sintering at 1400 °C for 1 h possessed about 35% open porosity. The porosity remained the same upon further sintering at 1400 °C for 8 h.     

Effect of metal oxide nanostructures on the explosive property of metastable intermolecular composite particles

The fineness of reactants, degree of intermixing and interfacial contact area between fuel and oxidizer comprising of metastable intermolecular composite (MIC) particles are important factors to determine their overall kinetics of burning process. Here, we demonstrate a viable method for enhancing the explosive property of MICs by tailoring the nanostructures of oxidizer located in close proximity to fuel nanoparticles. The measured pressurization rate for a specific sample of solid Al nanoparticle (fuel)-porous CuO nanowire (oxidizer) MICs exploded in a closed vessel was found to be increased by a factor of ~ 10 compared with that for solid Al nanoparticle-solid CuO nanoparticle MICs. In addition, with the assistance of intensive sonication energy, the fabricated porous oxidizer nanowires were disintegrated into oxidizer nanoparticles, which considerably reduced the pressurization rate when they were ignited with fuel nanoparticles. This suggests that the morphology of oxidizer nanostructures from solid nanoparticles (i.e. 0-D) to porous nanowires (i.e. 1-D) play a key role in significantly changing the interfacial contact area with fuel nanoparticles so that nascent oxygen can be produced effectively for promoting the explosive property of the fuel nanoparticles.     

Selective CO oxidation over promoted Au/γ-Al2O3 catalysts in the presence of CO2 and H2O in the feed

In this work, the effect of promoter type (Mg, Mn, Ce, Co, Fe and Ni) on selective CO oxidation performance of Au/γ-Al₂O₃ was studied with the realistic feed stream containing CO₂ and H₂O. The effects of Au loading, promoter loading, reaction temperature and the feed composition were also investigated. It was found that MgO was the best promoter in the presence of CO₂ and H₂O, and 1.25 wt.% Mg was sufficient for promotion. The CO conversion decreased with the addition of CO₂ while the presence of H₂O had some positive effects.     

Preparation of BaZr0.1Ce0.7Y0.2O3–δ Based Solid Oxide Fuel Cells with Anode Functional Layers by Tape Casting

Solid oxide fuel cells (SOFCs) based on the proton conducting BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY) electrolyte were prepared and tested in 500–700 °C using humidified H₂ as fuel (100 cm³ min^–1 with 3% H₂O) and dry O₂ (50 cm³ min^–1) as oxidant. Thin NiO‐BZCY anode functional layers (AFL) with 0, 5, 10 and 15 wt.% carbon pore former were inserted between the NiO‐BZCY anode and BZCY electrolyte to enhance the cell performance. The anode/AFL/BZCY half cells were prepared by tape casting and co‐sintering (1,300 °C/8 h), while the Sm_0.5Sr_0.5CoO_3–δ (SSC) cathodes were prepared by thermal spray deposition. Well adhered planar SOFCs were obtained and the test results indicated that the SOFC with an AFL containing 10 wt.% pore former content showed the best performance: area specific resistance as low as 0.39 Ω cm² and peak power density as high as 0.863 W cm^–2 were obtained at 700 °C. High open circuit voltages ranging from 1.00 to 1.12 V in 700–500 °C also indicated negligible leakage of fuel gas through the electrolyte.     

制备工艺对微乳化柴油稳定性能的影响

为了考察制备工艺对微乳化柴油稳定性能的影响,采用单因素变化试验和正交试验设计安排试验,系统分析了制备微乳化柴油时的温度、搅拌速度、搅拌方式、试剂的添加顺序以及各工序搅拌时间对其稳定性能的影响。结果表明:温度为25～35℃,搅拌速度为300～500r/m in,添加顺序为乳化剂和柴油先混合,再加入水,最后加入助乳剂,各工序搅拌时间均为5m in时所制备的微乳化柴油稳定性好。结论为制备微乳化柴油时温度、搅拌速度、搅拌时间以及添加顺序对其稳定性能影响较大,搅拌方式对其稳定性能影响较小。     

Aging effects of nanoscale ceria in ceria–platinum composite electrodes for direct alcohol electro-oxidation

Nanocrystalline Pt/CeO₂ composite electrodes were fabricated to study the electrochemical oxidation of methanol and ethanol. The performance of the electrodes was tested as the ceria solutions aged over time. It was observed that the performance oscillated with time, suggesting that the catalytic behavior towards alcohol oxidation was greatly dependent on the aging of the particles. These results point to a great dependence of the catalytic effect on the redox state of the ceria particles.     

Enhanced high-temperature polymer electrolyte membrane for fuel cells based on polybenzimidazole and ionic liquids

Polybenzimidazole (PBI)/ionic liquid (IL) composite membranes were prepared from an organosoluble, fluorine-containing PBI with ionic liquid, 1-hexyl-3-methylimidazolium tri?uoromethanesulfonate (HMI-Tf). PBI/HMI-Tf composite membranes with different HMI-Tf concentrations have been prepared. The ionic conductivity of the PBI/HMI-Tf composite membranes increased with both the temperature and the HMI-Tf content. The composite membranes achieve high ionic conductivity (1.6 × 10⁻² S/cm) at 250 °C under anhydrous conditions. Although the addition of HMI-Tf resulted in a slight decrease in the methanol barrier ability and mechanical properties of the PBI membranes, the PBI/HMI-Tf composite membranes have demonstrated high thermal stability up to 300 °C, which is attractive for high-temperature (>200 °C) polymer electrolyte membrane fuel cells.