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排序方式: 共有642条查询结果,搜索用时 15 毫秒
71.
采用改进的柠檬酸溶胶-凝胶法(即前驱体先在N2气氛下高温预处理)制备了高比表面积纳米Ce0.9Cu0.1O2-δ固溶体。采用XRD、TEM和Raman等对催化剂进行表征,并考察了它们的低温CO氧化性能。研究结果表明,改进的柠檬酸溶胶 凝胶法可以制得晶相比较完整的Ce0.9Cu0.1O2-δ 固溶体,晶粒小于10 nm,明显小于常规方法制得的样品。随着样品焙烧温度的提高,表征氧缺位的600 cm-1左右Raman峰的位置向高波数方向迁移。采用改进方法制得的Ce0.9Cu0.1O2-δ 固溶体具有更高的CO氧化活性,其原因归结为晶粒的减小,容易形成氧缺位和表面高分散CuO的增加,从而促进了CO的氧化。 相似文献
72.
Kyu-Nam Jung 《Electrochimica acta》2007,52(5):2009-2017
Lithium transport through the partially inactive fractal Li1 − δMn2O4 film electrode under the cell-impedance-controlled constraint was theoretically investigated by using the kinetic Monte Carlo method based upon random walk approach. Under the cell-impedance-controlled constraint, all the potentiostatic current transients calculated from the totally active and partially inactive fractal electrodes hardly exhibited the generalised Cottrell behaviour and they were significantly affected in shape by the interfacial charge-transfer kinetics. In the case of the linear sweep voltammogram determined from the totally active and partially inactive fractal electrodes, all the power dependence of the peak current on the scan rate above the characteristic scan rate deviated from the generalised Randles-Sev?ik behaviour. From the analyses of the current transients and the linear sweep voltammograms simulated with various values of the simulation parameters, it was further recognised that the cell-impedance-controlled lithium transport through the partially inactive fractal Li1 − δMn2O4 film electrode strongly deviates from the generalised diffusion-controlled transport behaviour of the electrode with the totally active surface, which is attributed to the impeded interfacial charge-transfer kinetics governed by the surface inhomogeneities including the fractal dimension of the surface and the surface coverage by active sites and by the kinetic parameters including the internal cell resistance. 相似文献
73.
74.
V. A. Gruzdev S. G. Komarov S. V. Stankus 《International Journal of Thermophysics》2008,29(2):557-567
The density (300–363 K, up to 3.5 MPa) and speed of sound (293–373 K, 7.5–480 kPa) in gaseous R-404a have been studied by
an isochoric piezometer method and an ultrasonic interferometer, respectively. The pressures of the saturated vapor along
the dew line were measured from 298 to 330 K. The experimental uncertainties of the temperature, pressure, density, and speed-of-sound
measurements were estimated to be within ±20 mK, ±1.5 kPa, ±0.15%, and ±(0.1–0.2)%, respectively. On the basis of the obtained
data, the isobaric molar heat capacity of R-404a was calculated for the ideal-gas state. An eight-coefficient Benedict–Webb–Rubin
equation of state has been developed for the gaseous phase of R-404a. 相似文献
75.
《钢铁研究学报(英文版)》2016,(9):988-996
The concept of microalloying was applied to the δ-TRIP(transformation-induced plasticity)steel to investigate the feasibility of increasing the mechanical properties and understanding the effect of microalloying on the morphology and structure of the steel.A hot rolled δ-TRIP steel with three different contents of Nb(0,0.03,0.07 mass%)was subjected to the microstructural and mechanical examination.The high Al and Si concentration in these steels guaranteed the presence of the considerable δ-ferrite phase in the microstructure after the casting and the subsequent hot rolling.The obtained results showed that Nb dramatically affects the microstructure,the dynamic recovery and recrystallization behavior,as well as the grain shape and thus the stability of austenite after the thermomechanical process of hot rolling.The results also revealed an unexpected effect of Nb on the mechanical properties.The addition of Nb to theδ-TRIP steel led to a significant decrease in the ultimate strength(from 1 144 to 917 MPa)and an increase in ductility(from 24% to 28%).These unconventional results could be explained by the change in the steel microstructure.The work-hardening behaviors of all samples exhibit three stages of the work-hardening rate evolution.At the stage 2,the work-hardening rate of the studied steels increased,being attributed to the TRIP effect and the transformation of austenite to martensite. 相似文献
76.
Yunho Hwang Dae-Hyun Jin Reinhard Radermacher 《International Journal of Refrigeration》2007,30(4):633-641
To help provide a clear understanding of the relative performance potential of HFCs (R-404A and R-410A) as compared to R-290 for walk-in refrigeration systems representing direct expansion commercial refrigeration systems with small charge, an experimental evaluation of the three refrigerants was investigated. To compare the environmental impact of refrigerants over the entire life cycle of fluid and equipment, including power consumption, the life cycle climate performance (LCCP) of the three refrigerants were evaluated based on measured data. The estimated LCCPs at various emission rates indicate that the LCCP of R-290 is always lower than that of R-404A. The LCCP of R-410A is lower than that of R-290 as long as the annual emission is kept below 10%. It was concluded that R-410A has less or equivalent environmental impact as compared to R-290 when safety (toxicity and flammability), environmental impact (climate change), cost and performance (capacity and COP) are considered. 相似文献
77.
N.F. Aljuwayhel D.T. Reindl S.A. Klein G.F. Nellis 《International Journal of Refrigeration》2007,30(8):1347-1357
This paper describes a theoretical model of a large-scale, ammonia-fed evaporator coil used in an industrial refrigeration system and operating under low temperature air and refrigerant conditions that are typically encountered in refrigerated storage spaces. The model is used to simulate the performance of counter-flow and parallel-flow circuited evaporator coil designs under frosting conditions. The counter-flow frost model is validated using in situ data obtained from a field-installed evaporator coil. The performance of an evaporator in a parallel-flow circuit arrangement is simulated and compared to counter-flow circuiting. The effects of coil circuiting are evaluated in terms of the frost distribution across the evaporator coil and the associated reduction in cooling capacity during operation. 相似文献
78.
Sandrine Marinhas Anthony Delahaye Laurence Fournaison 《International Journal of Refrigeration》2007,30(5):758-766
In the present paper, the suitability of hydrate slurries in secondary refrigeration was investigated by the means of a new hydrate solid-fraction model. Considering the high melting enthalpy of CO2-containing hydrates, slurries presenting high hydrate solid fractions can carry sufficient latent heat to be useful for a two-phase secondary-refrigerant application. The model presented in this paper allowed to calculate the solid fraction of CO2 and CO2–THF hydrate from thermodynamic conditions of pressure and temperature. Contrary to a previous work on single CO2 hydrates in a closed system, the present model can take into account hydrate mixture and is well adapted to additional CO2 injections (opened system). By relying on the hydrate-conversion model results, the study of hydrates in suspension in a carrying liquid was also studied in an experimental loop and was based on a formation process by CO2 injection in a cooled aqueous solution. 相似文献
79.
80.
STUDYOFPHASESINU-10wt%ZrALLOYBYNEUTRONDIFFRACTION¥XIEGuoqiang;YANGJijian;ZHANGBaisheng;LIWendan(ChinaInstituteofAtomicEnergy,... 相似文献