Proton electrolyte membrane properties and direct methanol fuel cell performance: I. Characterization of hybrid sulfonated poly(ether ether ketone)/zirconium oxide membranes

This paper presents an evaluation of the zirconium oxide effects in sulfonated poly(ether ether ketone) (sPEEK) with sulfonation degree (SD) of 87%. A series of inorganic–organic hybrid membranes were prepared with a systematic variation of the zirconium oxide content via in situ zirconia formation (2.5, 5.0, 7.5, 10, 12.5 wt.%). This procedure enabled the preparation of proton electrolyte membranes (PEM) with a wide range of properties, which can be useful for evaluating the relationship between the PEM properties and the direct methanol fuel cell (DMFC) performance. The investigated properties are the proton conductivity, proton transport resistance, water uptake, water, methanol, oxygen, carbon dioxide and nitrogen permeability coefficients, morphology and elemental analysis. The results obtained show that the inorganic oxide network decreases the proton conductivity and water swelling. It is found that it leads also to a decrease of the water, methanol, carbon dioxide and oxygen permeability coefficients, an increase of the water/methanol selectivity and a decrease of the carbon dioxide/nitrogen and oxygen/nitrogen selectivities. In terms of morphology, it is found that in situ zirconium alkoxide hydrolysis enables the preparation of homogeneous membranes that present a good adhesion between inorganic domains and the polymer matrix.     

Fabrication and electrochemical characterization of a vertical array of MnO2 nanowires grown on silicon substrates as a cathode material for lithium rechargeable batteries

A complementary metal-oxide-semiconductor (CMOS) compatible process for fabricating on-chip microbatteries based on nanostructures has been developed by growing manganese dioxide nanowires on silicon dioxide (SiO₂)/silicon (Si) substrate as a cathode material for lithium rechargeable batteries. High aspect-ratio anodized aluminum oxide (AAO) template integrated on SiO₂/Si substrates can be exploited for fabrication of a vertical array of nanowires having high surface area. The electrolytic manganese dioxide (EMD) nanowires are galvanostatically synthesized by direct current (dc) electrodeposition. The microstructure of these nanowire arrays is investigated by scanning electron microscopy and X-ray diffraction. Their electrochemical tests show that the discharge capacity of about 150 mAh g⁻¹ is maintained during a few cycles at the high discharge/charge rate of 300 mA g⁻¹.     

Combustion of activated aluminum

Combustion of activated aluminum was studied by four different methods: microscopic imaging of the preignition process, digital imaging of the combustion process at pressures up to 64 bar in air, nitrogen, and carbon dioxide, TGA, and DSC. Activation by three fundamentally different methods was found effective in enhancing both the ignitability and the burn rate. The complex fluoride coating prevented agglomeration completely in all stages of combustion, while the nickel and cobalt coatings promoted agglomeration of aluminum oxide at combustion, but prevented the agglomeration of the aluminum metal before combustion. Nickel coating catalyzed aluminum nitride formation, accelerating burn rate more than other coatings in air and in nitrogen, while complex fluoride coating was most effective in carbon dioxide. Carbon coagulation in carbon dioxide quenched burning in many cases at higher pressures than 8 bar. The complex fluoride activation accelerated combustion in CO₂ extremely effectively, but did not prevent carbon shell formation and subsequent quenching at high pressures. Ni coating negated the effects of carbon coagulation in CO₂, but enhanced the burn rate only slightly. Co coating reduced the carbon shell formation, but did not accelerate combustion in CO₂. Only the Ni coating applied in large amounts promoted combustion in nitrogen.     

Influence of the protective strip properties on distribution of the temperature at transient frictional heating

The analytical solution of a boundary-value problem of heat conduction for tribosystem, consisting of the homogeneous semi-space, sliding uniformly on a surface of the strip deposited on a semi-infinite substrate, is obtained. For materials of frictional systems: steel–aluminum–steel and steel–zirconium dioxide–steel, the evolution and distribution on depth from a surface of friction for temperatures and thermal fluxes, is studied.     

Understanding on the effect of morphology towards the hydrogen and carbon monoxide sensing characteristics of tin oxide sensing elements

Though the gas sensing properties of atmospheric plasma sprayed tungsten oxide, zinc oxide, titanium oxide, tin oxide and copper oxide coatings were well investigated, reports comparing sensing characteristics of plasma sprayed sensor thick film coating with its bulk counterpart are hardly found in the literature. This work attempts to compare hydrogen and carbon monoxide sensing characteristics, namely gas response, response time, recovery time of plasma sprayed tin dioxide thick film with tin dioxide bulk sensor. Gas response in the presence of hydrogen gas (23–81%) was superior to that of carbon monoxide gas (19–79%). An attempt was made to understand plausible reason behind superior hydrogen gas response. Thus, gas response as a function of temperature was simulated using a gas diffusion equation for hydrogen and carbon monoxide gases. Estimated parameters, namely, activation energy of transduction and first order kinetics were correlated with sensor microstructure and experimental gas response values. For hydrogen sensing, shorter response time (30–138 s) and recovery time (118–161 s) of thick film as compared to response time (64–234 s) and recovery time (183–196 s) of bulk sensor was correlated with microstructure of sensory elements. It was observed that tin dioxide thick film, owing to its porous morphology with small-sized particulates exhibited superior hydrogen gas response, short response time and recovery time as compared to its bulk counterpart.     

Microstructure and mechanical properties of aluminum back contact layers

The overall demand to reduce solar energy costs gives a continuous drive to reduce the thickness of silicon wafers. Handling and bowing problems associated with thinner wafers become more and more important, as these can lead to cells cracking and thus to high yield losses. In this paper the microstructure and mechanical properties of the aluminum on the rear side of a solar cell are discussed. It is shown that the aluminum back contact has a complex composite-like microstructure, consisting of five main components: (1) the back surface field layer; (2) a eutectic layer; (3) spherical (3-5 μm) hypereutectic Al-Si particles surrounded by a thin aluminum oxide layer (200 nm); (4) a bismuth-silicate glass matrix; and (5) pores (14 vol%). The Young’s modulus of the Al-Si particles is estimated by nanoindentation and the overall Young’s modulus is estimated on the basis of bowing measurements. These results are used as input parameters for the improved thermomechanical multiscale model of a solar cell.     

Angular solar absorptance and incident angle modifier of selective absorbers for solar thermal collectors

The solar absorptance of absorbers for thermal solar collectors is usually characterized at near normal angle of incidence. The solar absorptance is however a function of the angle of the incident light on the absorbers. In this paper the angular solar absorptance of commercial nickel pigmented aluminum oxide and sputtered nickel/nickel oxide solar selective absorbers are reported. The solar absorptance was calculated from experimental total reflectance spectra in the wavelength range 300–2500 nm for angles of incidence between 5 and 80°. It was found that the solar absorptance at higher angles of incidence is lower for the sputtered nickel/nickel oxide than for the nickel pigmented aluminum oxide coating. This could be understood from theoretical calculations based on microstructure models of the two types of coatings. The nickel pigmented aluminum oxide with a double-layer structure of its coating has an enhanced higher angle solar absorptance due to thin film interference effects which can not be achieved from a graded-index thin film coatings as is the case for the sputtered nickel/nickel oxide absorber. When the absorbers were covered by glass, as is common for most solar collectors, a negligible difference in optical performance at the higher angles of incidence has been obtained. These results were consistent with a theoretical calculation by use of an incident angle modifier model.     

不同方法制备的TBC涂层特性的研究

众所周知,热障涂层（TBC）主要包括粘接层和面层两部分。该文采用空气助燃超音速火焰喷涂（HVAF）和氧气助燃超音速火焰喷涂（HVOF）两种方法制备粘接层,大气等离子喷涂（APS）方法制备面层,来研究不同制备方法对TBC涂层微观结构和性能的影响。试验结果表明,HVAF和APS制备的TBC涂层,粘接层中氧化现象较少,热生长氧化物（TGO）生长相对致密均匀,以α-Al2O3为主,其它复合氧化物（NiO、CrNi、CoNi等）较少,表现出较好的高温性能。YSZ陶瓷面层隔热效果良好,是一种成本低廉的新型制备TBC涂层技术。     

A review and analysis on influence of temperature and concentration of nanofluids on thermophysical properties,heat transfer and pumping power

The Prandtl number, Reynolds number and Nusselt number are functions of thermophysical properties of nanofluids and these numbers strongly influence the convective heat transfer coefficient. The pressure loss and the required pumping power for a given amount of heat transfer depend on the Reynolds number of flow. The thermophysical properties vary with temperature and volumetric concentration of nanofluids. Therefore, a comprehensive analysis has been performed to evaluate the effects on the performance of nanofluids due to variations of density, specific heat, thermal conductivity and viscosity, which are functions of nanoparticle volume concentration and temperature. Two metallic oxides, aluminum oxide (Al₂O₃), copper oxide (CuO) and one nonmetallic oxide silicon dioxide (SiO₂), dispersed in an ethylene glycol and water mixture (60:40 by weight) as the base fluid have been studied.     

感应加热在锆锭淬火中的应用

将感应加热方式应用在锆锭的加热淬火工艺中.对锆锭在加热过程中的温差控制及计算方法进行了实验验证,最后对锆锭在淬火液中的冷却过程进行了模拟分析,推算出有效淬火时间,并经试验验证.     

Effects of TiO2 and SDC addition on the properties of YSZ electrolyte

In this study, we investigate the effects of adding titanium dioxide (TiO₂) and samarium doped cerium oxide (SDC) on the properties of yttrium-stabilized zirconia (YSZ) electrolyte. The microstructure, mechanical, and electrochemical properties of the electrolyte are investigated. The performance in CO₂ electrolysis is measured by supplying carbon dioxide to Ni-YSZ electrode and nitrogen to LSM electrode. Results show that TiO₂ and SDC addition can reduce the sintering temperature and increase grain size. The ionic conductivity is 0.123 S cm⁻¹ at 1000 °C. In addition, the thermal expansion coefficient at 1000 °C is 8.25 × 10⁻⁶ K⁻¹. The current density of the cell is 439 mA cm⁻² at 1.3 V and 1000 °C in solid oxide electrolysis cell.     

Development of new correlations for convective heat transfer and friction factor in turbulent regime for nanofluids

This paper presents new correlations for the convective heat transfer and the friction factor developed from the experiments of nanoparticles comprised of aluminum oxide, copper oxide and silicon dioxide dispersed in 60% ethylene glycol and 40% water by mass. The experimental measurements were carried out in the fully developed turbulent regime for the aforementioned three different nanofluids at various particle volumetric concentrations. First, the rheological and the thermophysical properties such as viscosity, density, specific heat and thermal conductivity were measured at different temperatures for varying particle volume concentrations. Next, these properties were used to develop the heat transfer coefficient correlation from experiments, as a function of these properties and the particle volumetric concentration. The pressure loss was also measured and a new correlation was developed to represent the friction factor for nanofluids.     

Influence of nanofluids on parallel flow square microchannel heat exchanger performance

The effects of using various types of nanofluids and Reynolds numbers on heat transfer and fluid flow characteristics in a square shaped microchannel heat exchanger (MCHE) is numerically investigated in this study. The performance of an aluminum MCHE with four different types of nanofluids (aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), silver (Ag), and titanium dioxide (TiO₂)), with three different nanoparticle volume fractions of 2%, 5% and 10% using water as base fluid is comprehensively analyzed. The three-dimensional steady, laminar developing flow and conjugate heat transfer governing equations of a balanced MCHE are solved using the finite volume method. The MCHE performance is evaluated in terms of temperature profile, heat transfer rate, heat transfer coefficient, pressure drop, wall shear stress pumping power, effectiveness, and overall performance index. The results reveal that nanofluids can enhance the thermal properties and performance of the heat exchanger while having a slight increase in pressure drop. It was also found that increasing the Reynolds number causes the pumping power to increase and the effectiveness to decrease.     

Determination of interfacial heat transfer coefficient and analysis of influencing factors in warm forming the third-generation automotive medium-Mn steel

The third-generation automotive medium-Mn steel (TAMM steel) was newly developed. The medium-Mn steel holds the advantages of fine and even microstructure, low austenizing temperature and wide quenching rate range, and thereby it is possible to contribute to excellent properties, high efficiency and low cost in warm/hot forming. However, research on the forming of this TAMM steel has just started. It is necessary to understand the relation between forming process and heat transfer, and further apply the heat transfer characteristics to numerical simulation. Therefore, this paper explored the interfacial heat transfer rules during warm forming the TAMM steel and determined the interfacial heat transfer coefficient (IHTC) using a self-designed experimental platform and Beck's inverse estimation method. The results indicate that the IHTC is not constant but varies nonlinearly during quenching. Moreover, the influences of several factors, including stamping pressure, stamping temperature and surface coating, on the IHTC were investigated. The IHTC increases with the increase of stamping pressure and stamping temperature. However, it decreases greatly with the increase of coating thickness. It is also found that the microstructure and mechanical properties are not sensitive to the coating and quenching rate, which is beneficial to the achievement of even mechanical properties of the stamped TAMM part, and helpful to the flexible design of quenching method and coating application in actual warm stamping process.     

Novel thin film solar cell model with two antipolar MIS structures

In this article we introduce a new thin film solar cell model which uses the properties of two antipolar MIS structures. The active layer consists of unipolar polycrystalline silicon. We employed silicon dioxide as insulator. The back- and top electrode consist of indium tin oxide (ITO). The solar cell model was developed under consideration of the low-temperature chemical vapour deposition (i.e. PECVD). As oxide and ITO are optical transparent media and in compound with the planned process technology the solar cell concept would be very suitable for a stack arrangement which would increase the device conversion efficiency. Currently the preparation of silicon dioxide with a sufficiently large fixed negative charge seems to be out of technological facilities. Nevertheless, we consider the concept introduced herein as an important contribution to novel ways of efficient low-cost thin-film solar cells.     

Thermo-mechanical aspects of the heterogeneous ignition of metals

During the heterogeneous oxidation of metallic particles in a gaseous oxidant, a film of oxide usually separates the metal and oxidant, with the reaction rate being governed to a great extent by the protective properties of the film. A theoretical and experimental study of the influence of the failure of the protective oxide film on the metal's heterogeneous ignition has been performed. The possible reasons for the fracture are analyzed; also the critical conditions of the oxide film are estimated. Experiments conducted with aluminum and titanium powders have shown that the fracture of the protective oxide film results in a significant increase in the metal's reactivity. The assumptions of a theoretical analysis are confirmed experimentally.     

Analysis of a solid oxide fuel cell and a molten carbonate fuel cell integrated system with different configurations

A solid oxide fuel cell with internal reforming operation is run at partial fuel utilization; thus, the remaining fuel can be further used for producing additional power. In addition, the exhaust gas of a solid oxide fuel cell still contains carbon dioxide, which is the primary greenhouse gas, and identifying a way to utilize this carbon dioxide is important. Integrating the solid oxide fuel cell with the molten carbonate fuel cell is a potential solution for carbon dioxide utilization. In this study, the performance of the integrated fuel cell system is analyzed. The solid oxide fuel cell is the main power generator, and the molten carbonate fuel cell is regarded as a carbon dioxide concentrator that produces electricity as a by-product. Modeling of the solid oxide fuel cell and the molten carbonate fuel cell is based on one-dimensional mass balance, considering all cell voltage losses. Primary operating conditions of the integrated fuel cell system that affect the system efficiencies in terms of power generation and carbon dioxide utilization are studied, and the optimal operating parameters are identified based on these criteria. Various configurations of the integrated fuel cell system are proposed and compared to determine the suitable design of the integrated fuel cell system.     

Catalytic properties of Sr2Ni0.75Mg0.25MoO6–δ based composites for application in hydrocarbon-fuelled solid oxide fuel cells

One of the key directions for the development of commercial solid oxide fuel cells fuelled by natural gases consists in the search for efficient fuel electrode materials operated under hydrocarbon-containing atmospheres. Within the present work, we synthesized and characterised novel composites based on a double-perovskite Sr₂Ni_0.75Mg_0.25MoO_6–δ phase and a second phase comprised of SrMoO₄ or NiO. For these composite materials, the reduction behaviour, tolerance to carbon dioxide and catalytic activity towards the partial oxidation of hydrocarbons mixture were comprehensively studied. It is shown that the target properties of the designed composites are affected not only by the type of catalysts but also by the method of their preparation. According to the presented results, the most appropriate materials are composites containing 20 wt% SrMoO₄ or 50 wt% NiO.     

Zirconium nitride based transparent heat mirror coatings —preparation and characterisation

Transparent heat mirror coatings based on thin zirconium nitride films have been prepared using reactive magnetron sputtering. The zirconium nitride films have been sandwiched between layers of zirconium oxide. It is shown that the multilayer configuration ZrO₂/ZrN/ZrO₂ can be used as solar control coatings on window glazings. A visible transmittance of around 60% and a thermal emittance lower than 0.2 can be obtained, and the ratio between visible transmittance and total solar transmittance can be as high as 1.7. The influence of substrate temperature on the optical quality of the films is evaluated and it is shown that the crystal structure of the first oxide layer is of importance for the optical quality of the nitride. The influence of preparation conditions and accelerated ageing has been modelled using the optical constants of thin films prepared under identical conditions as the films in the multilayer coatings.     

Modeling of a reacting nanofilm on a composite substrate

This article provides a detailed computational analysis of the reaction of dense nanofilms and the heat transfer characteristics on a composite substrate. Although traditional energetic compounds based on organic materials have similar energy per unit weight, non-organic material in nanofilm configuration offers much higher energy density and higher flame speed. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses. The numerical analysis of the thermal transport of the reacting film deposited on the substrate combined a hybrid approach in which a traditional two-dimensional black box theory was used in conjunction with the sandwich model to estimate the appropriate heat flux on the substrate accounting for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is provided. This work highlights two important findings. One is that there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon-silica. Secondly, with increase in substrate thickness, the quenching effect is progressively diminished at a given speed. These findings show that the composite substrate is effective and that the average speed and quenching of flames depend on the thickness of the silica substrate, and can be controlled by a careful choice of the substrate configuration.