Increasing Working Temperature Research Articles

Electrochemical Preparation of Cu-Mn Alloy Powder in Molten Salt for Methanol Synthesis

Cu-Mn alloy powder was prepared by electrochemical reduction of a CuO and MnO2 mixture in a eutectic CaCl2-NaCl molten salt. The reduction pathway was probed by examining the partially reduced samples for various durations. The influence of the working temperature on the reduction was discussed. The Cu-Mn powder obtained was applied as a catalyst for methanol synthesis. The products before and after catalysis were characterized to investigate the possibility of the alloy as a catalyst for methanol synthesis. The results show that the Cu-Mn alloys, including CuMn4 and CuMn were successfully synthesized. The alloys were made up of interconnected nodular particles with a three-dimensional framework structure. The particles provided more adequate locations for catalytic reactions than the particles produced from mechanical alloying. The increased working temperature promoted the alloying process of CuMn4 and Cu to form CuMn. The electrolytic products of CuMn and CuMn4 were beneficial to synthesize methanol. The CH3OH selectivity was maintained at greater than 93%, obviously better that of the reference catalysts. MnO was formed on the top surface of the alloy particles during catalysis, separating the Cu-Mn alloys from the feed gas. This phenomenon decreased the performance of the Cu-Mn alloys for methanol synthesis.

Effects of mechanical strength, working temperature and wax lubricant on tribological behavior of polystyrene

Abstract The tribological properties of polystyrene (PS) samples with different mechanical strengths were systematically investigated. The friction of the PS samples tested against a 6 mm steel ball significantly increased with increased working temperature from room temperature (RT) to glass transition temperature (Tg)+20°C, while their wear apparently decreased. The harder PS samples exhibited lower friction and wear for all working temperatures. Lubricating the PS samples with wax lubricant at RT resulted in much lower friction and wear compared to those of the ones tested dry, because the wax lubricant effectively lubricated the rubbing surfaces. Addition of soda lime glass microspheres into the wax lubricant slightly lowered the friction of the PS samples with lower hardness compared to that of the same ones lubricated without the microspheres, due to the reduced direct contact between two rubbing surfaces and the free-rolling effect of the microspheres.

Investigation of the effect of microstructural parameters on the initial yield surface of non-isothermal composites

AbstractIn this paper, the effects of microstructural parameters on the initial yield surface of non-isothermal composites were investigated. The fiber phase was assumed to be a linear elastic material, and the matrix was assumed to be a non-linear material. Incorporating the Bodner-Partom viscoplastic constitutive model into a high-fidelity generalized method of cells allowed the initial yield surfaces of non-isothermal composites with different microscopic arrays and fiber cross-section shapes to be studied. Moreover, working temperature effects on initial yield surface are also discussed. The results show that the initial yield stress in the σxx–σyyplane of unidirectional fiber-reinforced composites tends to decrease with increasing working temperature. Furthermore, the effects of fiber arrays and fiber off-axis angles on initial yield stress show similar variation at different working temperature conditions.

Ultra-refractory Diboride Ceramics for Solar Plant Receivers

Concentrating Solar Power (CSP) is considered to be one of the most promising and sustainable technologies for electricity production in the future, and as efficiency of solar thermal systems rapidly increases with increasing working temperature, the big challenge for future is to develop novel solutions for solar receivers. In this framework, Ultra-High Temperature Ceramics (UHTCs) are mainly studied as thermal protection materials for aerospace and military applications, but their peculiar properties (very high melting points and good thermo-mechanical properties at high temperatures) can be advantageously exploited to increase the operating temperature of thermodynamic solar plants in concentrating solar power systems. This work is devoted to the study and characterization of the spectral reflectance of hafnium and zirconium diborides containing MoSi2 as secondary phase in order to evaluate their potential as novel solar absorbers. To assess the spectral selectivity properties, room-temperature hemispherical reflectance spectra were measured from the UV wavelength region to the mid-infrared, considering different levels of porosity for each system, in order to understand how porosity affect spectral reflectance. Moreover, for zirconium diboride and hafnium diboride composites containing 10vol% of MoSi2 sintering aid, the thermal emittance was measured in the 1100–1400K temperature range in PROMES-CNRS solar furnace. Data obtained were compared with spectral characteristics and high temperature emittance of a monolithic silicon carbide.

Conditional extremum optimization analyses and calculation of the active thermal control system mass of manned spacecraft

The global lightweight optimization of the active thermal control system (ATCS) is of great importance to the manned spacecraft. The governing equations for the parameters that should be optimized for the minimum mass of the ATCS with dual liquid loops are established based on the energy conservation analyses, which makes the lightweight optimization become a conditional extremum problem. The ATCS mass equation is set up. The optimization equations are formulated by pursuing the extremum value of this mass equation and solved by the Newton iterative method. The optimization results for a typical ATCS in manned spacecraft are presented and the effects of the influencing parameters on the system mass are discussed. The results show that there is always an optimal value of the power consumption that leads to the minimum system mass, and the decrease in the specific mass of the power system leads to the reduction of the minimum system mass. The minimum system mass will reduce remarkably with decreasing total heat load or increasing working temperature of the thermal devices within a certain range.

Diode-pumped continuous-wave quasi-three-level Nd:GYSGG laser at 937 nm

A continuous-wave (cw) 937nm Nd:GYSGG laser based on the quasi-three-level transition 4F3/2 to 4I9/2 is reported. The output power of 0.80W at 937nm is achieved with the pump power of 8.2W, corresponding to the conversion efficiency of 9.8%. The variation of output power and pump threshold with increased working temperature is also studied, which demonstrates the deterioration operation because of the serious reabsorption in a quasi-three-level Nd3+ doped laser.

The strain and thermal induced tunable charging phenomenon in low power flexible memory arrays with a gold nanoparticle monolayer

The strain and temperature dependent memory effect of organic memory transistors on plastic substrates has been investigated under ambient conditions. The gold (Au) nanoparticle monolayer was prepared and embedded in an atomic layer deposited aluminum oxide (Al(2)O(3)) as the charge trapping layer. The devices exhibited low operation voltage, reliable memory characteristics and long data retention time. Experimental analysis of the programming and erasing behavior at various bending states showed the relationship between strain and charging capacity. Thermal-induced effects on these memory devices have also been analyzed. The mobility shows ~200% rise and the memory window increases from 1.48 V to 1.8 V when the temperature rises from 20 °C to 80 °C due to thermally activated transport. The retention capability of the devices decreases with the increased working temperature. Our findings provide a better understanding of flexible organic memory transistors under various operating temperatures and validate their applications in various areas such as temperature sensors, temperature memory or advanced electronic circuits. Furthermore, the low temperature processing procedures of the key elements (Au nanoparticle monolayer and Al(2)O(3) dielectric layer) could be potentially integrated with large area flexible electronics.

Effect of temperature on the antioxidant activity of phenolic acids

The effect of temperature on the antioxidant activity of phenolic acids (gallic, gentisic, protocatechuic, syringic, vanillic, ferulic, caffeic, and sinapic; 0.5 mmol/kg) was studied in pork lard, using an Oxipres apparatus, at a temperature range of 90°C to 150°C. The antioxidant activity of all studied compounds decreased with increasing working temperature, whereas a linear relationship (P < 0.01) existed between temperature and the antioxidant activity in all cases. However, the relative rate of the antioxidant activity decrease with increasing temperature (i.e. in comparison with the activity at 90°C) was not the same for all studied phenolic acids. Easily oxidisable phenolic acids (i.e. gallic, gentisic, protocatechuic, and caffeic) showed a slower decrease in antioxidant activity with increasing temperature (in comparison with their activity at 90°C) than the less oxidisable ones (i.e. syringic, ferulic and sinapic acids, and especially vanillic acid). Consequently, only gallic, gentisic, protocatechuic, and caffeic acids showed a significant antioxidant activity at 150°C and vanillic acid was active only at 90°C.  

Recrystallization of the hot isostatic pressed nickel-base superalloy FGH4096. II: Characterization and application

Abstract Recrystallization of the hot isostatic pressed nickel-base superalloy FGH4096 undergoes three characteristic periods, viz., incubation, nucleation and growth. Working temperature has a great effect on its boundary migration and nucleation. In recrystallization process, the nucleation rate is obviously accelerated with the increasing working temperature. To obtain fine grains, hot working should be carried out at the temperature of 1050–1080 °C. After two passes multiple forging, the grain size is significantly refined from 30.0 to 2.2 μm, and the refinement mechanism is found to be the repeated dynamic recrystallization (DRX) in the multiple forging process. Equiaxed-flatted gradient microstructure is obtained via the gradient temperature heat treatment (GTHT).

Effect of VOC on ozone detection using semiconducting sensor with SmFe1−xCoxO3 perovskite-type oxides

Fine particles of perovskite-type SmFe1−xCoxO3 oxides were synthesized by the thermal decomposition of the corresponding heteronuclear hexacyano complexes. The sensing characteristics of ozone, methylethylketone (MEK), ethanol and benzene were examined. These sensors responded to sub-ppm levels of ozone, and the sensitivity decreased with increasing working temperature. The response to 0.1ppm ozone was ca. 1000 at 250°C. The conductance of the sensors in ozone decreased due to the contamination of the same VOC levels. At around 200°C, the cross sensitivity of some VOCs to ozone was quite depressed. The partial substitution of Co for Fe resulted in an increased conductance in air and a decrease in the sensitivity to ozone.

Working temperature dependence of metal-ferroelectric-insulator-semiconductor capacitors using a poly(vinylidene fluoride-trifluoroethylene) copolymer for nonvolatile memory applications

The working temperature dependence of organic ferroelectric capacitors using poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films was investigated for the nonvolatile memory operations. High-frequency C-V characteristics and memory operations, including the ferroelectric memory windows, for the Au/P(VDF-TrFE)/SiO2/Si capacitors were measured as a function of the measurement temperature from RT to 130 °C. In order to confirm the effect of the initial crystallinity of the P(VDF-TrFE), we prepared two types of capacitors by varying the temperature of the final heat treatment for the P(VDF-TrFE) to 70 and 140 °C. For the capacitor with the 70 °C-dried P(VDF-TrFE) film, the observed characteristics were affected by complex effects such as temperature-dependent ferroelectric properties, a temperature-induced crystallization process, and undesirable charge injection. On the contrary, for the capacitor with the 140 °C-annealed P(VDF-TrFE) film, the memory window decreased and finally vanished with increasing working temperature. The memory window width of 1.58 V was very stable even at 80 °C, and the C-V curve was almost recovered to the initial state after cooling from 130 °C to RT.

Highly sensitive H2S sensor based on template-synthesized CuO nanowires

A sensor device featuring massive aligned CuO nanowires has been fabricated for H2S detection. Metallic copper (Cu) nanowires were first synthesized by a template-assisted electrodeposition method. Dielectrophoresis (DEP) and thermal oxidation were then used to assemble and functionalize/oxidize the nanowires. Topology of the CuO nanowires showed rugged surfaces on the nanowires. H2S sensing properties were characterized by conducting experiments with varying influential factors, including concentration levels from 10 to 1000 ppb and working temperatures from 25 to 420 °C. The CuO nanowire sensor showed good response and repeatability upon H2S exposure with a detection limit of 2.5 ppb and a linear response ranging from 10 ppb to 100 ppb. In addition, the study of temperature influence revealed that the highest response was achieved at 180 °C. Furthermore, with increased working temperature, the CuO nanowire sensor had shorter response and recovery times. An interesting two-stage response was discovered for this CuO nanowire sensor responding to H2S exposure, indicating that two competing reactions existed on the CuO surface.

Influence of dispersant, storage time and temperature on the rheological properties of zirconia–paraffin feedstocks for LPIM

The dependence of the rheological properties of zirconia–paraffin feedstocks for low-pressure injection moulding (LPIM) on binder composition, storage time and temperature was investigated. Feedstocks with varying amounts of dispersant were fabricated to work out the required quantity for a monolayer of dispersant molecules on zirconia particles. Experimental results revealed that a shear rate dependent characteristic of the viscosity against the amount of dispersant exists. The observations were compared with calculated values according to an adsorption model, which overestimated the required quantity of dispersant to form a monolayer. Feedstocks stored at elevated temperature for several days exhibited a time-dependent decrease of the yield stress and viscosity, which is supposed to be caused by physical or chemical interactions among zirconia and the dispersant. Increasing working temperature and decreasing solids loading were found to significantly decrease the yield stress as well as the viscosity. Flow activation energies and flow indices were calculated and compared with literature. This study shows that the dispersant used in this investigation has a remarkable influence especially on the time-dependent flow behaviour of zirconia–paraffin feedstocks that affects further processing and reproducibility.

High temperature bending fatigue behavior of stainless steels for automotive exhaust

Abstract Continually increasing working temperatures and a growing need for greater efficiency and reliability of automotive exhaust system require immediate investigation into the high temperature fatigue properties of heat resisting stainless steels. In this study, evaluation method of high temperature bending fatigue life has been established and S–N curves for ferritic stainless steels, such as 409L, 436L and 429EM STS, produced by POSCO have been evaluated at the temperatures of 600 and 800 °C, which are typical temperatures of exhaust system exposed during operation of a vehicle. Endurance limit of 429EM was found to be higher than the other two stainless steels and significantly reduced with increasing temperature, from 150 MPa at 600 °C to 65 MPa at 800 °C. Thickness effect on the fatigue life has also been investigated by varying the thickness of specimen and was found insensitive within the thickness range from 1 to 2 mm.

The effect of temperature on the antioxidant activity of tocopherols

The effect of temperature on the antioxidant activity of α- and δ-tocopherol (at 100 mg/kg level) was studied in pork lard, using the Oxipres apparatus, in the temperature range from 80 to 150 °C. The antioxidant activity of δ-tocopherol decreased with increasing working temperature in the whole temperature range studied. The activity of α-tocopherol was practically constant in the temperature range from 80 to 110 °C and decreased with increasing temperature at temperatures higher than 110 °C. Both tocopherols were ineffective at 150 °C (p <0.05). Due to different temperature effects on the antioxidant activities of α- and δ-tocopherol, the δ-tocopherol activity was approximately two times higher than the α-tocopherol activity at 80 °C, but their activities were the same (p <0.05) at 130 °C.

Sprayed ZnO thin films for ethanol sensors

The electrical characteristics of ZnO thin films prepared by spray pyrolysis, have been studied for ethanol sensors. The sensitivities of the films are measured at various temperatures and concentrations of ethanol. It is observed that the sensitivity increases with increasing working temperature. At higher ethanol concentrations, the sensitivity increases more rapidly with increasing temperature. Further, the films show fast response and recovery times at higher working temperatures. The sensing mechanism of the films towards ethanol vapour has been explained.

New multicomponent solder alloys of low melting pointfor low-cost commercial electronic assembly

The requirements of the telecommunications, automobile, electronics and aircraft industries for non-toxic solders with melting points close to that of near-eutectic Pb–Sn alloys has led to the development of new Sn–Zn–In solder alloys. Differential thermal analysis (DTA) shows melting points of 198, 195, 190 and 185 ± 2 °C for the alloys Sn–9Zn, Sn–9Zn–2In, Sn–9Zn–4In and Sn–9Zn–6In, respectively. An equation that fits the data relating the melting point to the In content in the solders is derived. The X-ray diffraction patterns are analyzed to determine the phases that exist in each solder. The stress–strain curves are studied in the temperature range from 90 to 130 °C for all the solders except for those that contain 4 wt% of In, where the temperature range continues to 150 °C. The work-hardening parameters, σy (the yield stress), σf (the fracture stress), and the parabolic work-hardening coefficient X, increase with increasing indium content in the solders at all working temperatures. They decrease with increasing working temperature for each solder, and show two relaxation stages only for the Sn–9Zn–4In solder around a temperature of 120 °C. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation of nano-structured polymeric proton conducting membranes for use in fuel cells.

We briefly discuss the state of the art of polymer electrolyte membrane fuel cells and suggest that the main obstacles to the commercial development of these fuel cells are essentially the high costs and poor characteristics of present proton conducting membranes. A strategy for the preparation of improved nanocomposite membranes based on the introduction of proton conducting lamell? in the polymeric matrix of present ionomeric membranes is then discussed. Due to their high proton conductivity (in some cases even higher than 10(-1) S cm(-1)), tailor made lamellae obtained by exfoliation of superacid metal (IV) phosphonates are particularly suitable for the preparation of these hybrid membranes. The expected positive influence of the dispersed lamellae on important properties of proton conducting membranes, such as swelling, mechanical resistance, proton transport, and diffusion of methanol, are also discussed. The methods used to obtain good lamellar dispersions into ionomeric polymers and the preparation and main characteristics of some hybrid membranes are also briefly described. The presence of nanoparticles of metal phosphonates in the electrodic interfaces Nafion/Pt already considerably improves the electrochemical characteristics of fuel cells in the temperature range 80-130 degrees C. The increased working temperature of the fuel cell considerably reduces CO poisoning of the platinum electrodes and allows better control of the cooling system, thus overcoming important obstacles to the development of medium temperature PEM fuel cells.

Vanadium oxide films with improved characteristics for ir microbolometric matrices

Vanadium oxide (VOx) films intended for use in uncooled IR microbolometric matrices were deposited by reactive magnetron sputtering on silicon substrates. Optimum deposition conditions were determined, which provide for the obtaining of films possessing a current 1/f noise level 3–10 times lower, extended dynamic range, and increased working temperature interval. It was found that the 1/f noise level of the VOx films depends on the VO2 phase content and grain size. It is suggested that the observed 1/f noise is caused by the martensite transformation characteristic of the semiconductor-metal phase transition in VO2.

Working-life effects on the properties of plastic thermopipes

Mechanical properties and morphological studies of polypropylene thermopipes manufactured in Jordan and usually used in heating system networks, have been investigated. Samples were chosen to represent new and different working periods (1, 3.5 and 6 y). The flow resistance of water inside the pipes showed a slight decrease in the first year followed by an increase after the second year of use. A decrease in resistance was observed with increasing working temperature and Reynold's number. The stress–strain tests exhibit property changes towards brittleness and glassy behaviour, observed after 6 y working service. Evidence of deformation was seen by scanning electron microscopy (SEM). Deterioration and cracks on the internal surfaces of aged thermopipes were also noticed. © 1998 Kluwer Academic Publishers