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991.
为有效提取红土矿中镍钴资源,研究了常压盐酸浸出工艺提取红土矿中的镍钴。结果表明,矿料粒度为-0.15 mm,初始酸浓度8 mol/L,浸出温度353 K,固液比S/L=1:4,搅拌速度300 r/min,反应时间2 h,镍、钴、锰、铁、镁的浸出率分别达到93.94%、60.5%、94%、56%9、4%。 相似文献
992.
993.
Jean-Michel Thomassin Christine Jérôme Thomas Pardoen Christian Bailly Isabelle Huynen Christophe Detrembleur 《Materials Science and Engineering: R: Reports》2013,74(7):211-232
The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation. 相似文献
994.
《Materials at High Temperatures》2013,30(3-4):269-281
AbstractA series of experimental austenitic alloys has been produced in which the nickel content ranges from 14 to 43%, with constant levels of 20%Cr, 1%Mn and 0.5%Si. A combination of isothermal, discontinuous and cyclic oxidation testing has been used to elucidate the performance in dry air and in air with 10%, 45% or 62% water vapour at 700°C and 1000°C. Evaluation was by means of thermogravimetry, surface analysis with glow discharge optical emission spectroscopy and scanning electron microscopy.Nickel is shown to have several roles: it accelerates the kinetics of chromia formation yet suppresses chromia spallation at 700°C. At 1000°C, it strongly decreases the breakaway oxidation and spalling associated with iron oxide formation. This effect is particularly marked in environments containing water vapour, where the material loss may be decreased 10-fold by an increase in the nickel content. Results correlate to thermodynamic and kinetic data which show nickel to increase the chromium activity and diffusivity in the alloy. 相似文献
995.
《Materials at High Temperatures》2013,30(4):639-648
AbstractThe effect of impurities on the oxidation mechanism of nickel and on mechanical characteristics of the NiO scale was studied on two industrial grades and one pure nickel.The oxidation mechanism at 800°C was clarified using kinetics approach, microstructure observations, EDX and XPS analyses, profilometry, oxygen isotopic exchange and SIMS.The mechanical characteristics were determined mainly by three point bending tests performed in a scanning microscope.Whatever the nickel grade, the oxide toughness varies with the scale thickness and tends towards the value of massive NiO. The main difference related to Ni purity consists in the fact that spalling occurs at an oxide/oxide interface for the industrial grades, while it appears at the metal/oxide interface for pure Ni.Indeed, due to the presence of impurities, internal oxidation, extrusion of metallic nickel along grain boundaries of the substrate and formation of an inner equiaxed oxide film are observed in industrial grades. This induces mechanical keying of the oxide, and therefore crack propagation in a mixed mode is easier at the oxide/oxide interface.With pure nickel, only a single oxide film is formed by outward diffusion of Ni and there is no internal oxidation. Thus crack propagation occurs along the metal/oxide interface. 相似文献
996.
《Materials at High Temperatures》2013,30(1):165-171
AbstractCross-sectional transmission electron microscopy was used to characterize the alumina scales formed on several Ni-base alumina-formers. The alumina scale microstructure of Ni–20at%Cr–19Al–0.05Y after 100, 1 h cycles at 1,100°C was compared to an isothermally-grown scale. Despite being near the onset of mass loss in cyclic testing, very few defects were noted in either scale microstructure. The more adherent scales that form on Hf-doped NiAl and Ni–49at%Al–2Cr were also characterized. With the addition of Cr, the formation of α-Cr precipitates at the metal–oxide interface coincided with increased long-term scale spallation. No similar precipitation mechanism was observed to be associated with scale spallation on NiCrAlY. 相似文献
997.
《Materials at High Temperatures》2013,30(4):439-448
AbstractThe nickel base superalloys are extensively used in high temperature applications, so it is important to know their behaviour under conditions of high-temperature fatigue. This paper studies the influence of ΔK, loading frequency, stress ratio and temperature on the high temperature fatigue crack growth rate of nickel base superalloys. This study is based on fatigue tests carried out in corner crack specimens of Inconel 718 at 600°C and at room temperature. Three stress ratios (R = 0.05, 0.5 and 0.8) and loading frequencies ranging from 0.0017 to 15 Hz were considered in the tests. For frequencies below 0.25 Hz, the load wave shape was trapezoidal with different dwell times at maximum load. At relatively high frequencies the propagation is cycle dependent, while for lower frequencies it is time dependent. At intermediate frequencies a mixed crack growth occurs. The transition frequencies from cycle dependent to mixed regime and from mixed to time dependent regime were obtained for each R. The increase of R increases the transition frequencies, i.e., extends the time dependent crack growth to higher frequencies. The increase of R also produces an increase of cyclic crack growth rate for all regimes of crack growth. In the time dependent regime, a higher variation is observed, that can be explained by an acceleration of oxidation damage promoted by the increase of maximum stress. An approach for modelling the high-temperature fatigue crack growth in nickel base superalloys is presented. A good agreement was observed between time dependent fatigue results and mathematical models based on static load results. 相似文献
998.
AbstractThin films composed of MgAl2O4 and (Ni0.5Zn0.5)Fe2O4 ([MA(100-x)-NZFx] films) were grown on fused SiO2 substrates by pulsed laser deposition. X-ray diffraction measurements revealed that the films were polycrystalline, and that their lattice constant varied linearly with composition, indicating the formation of a solid solution. The film with x=60 was paramagnetic and those with x ≥ 70 were ferromagnetic. The films had a transparency above 75% in the visible range, but the transparency decreased with the x value. The optical band gaps were 2.95, 2.55, 2.30 and 1.89 eV for x=20, 40, 60, 80 and 100, respectively. The Faraday rotation angle increased with x in the visible range, and the film with x=70 exhibited a value of 2000 degrees cm-1 at 570 nm, which is comparable to the rotation angle of Y3Fe5O12. Owing to their high transparency, which extends into the visible range, the [MA(100-x)-NZFx] films can be used in novel magneto-optical devices. 相似文献
999.
Yuansheng Yang Qingsheng Zhang Youliang He Zhuangqi Hu 《Science and Technology of Advanced Materials》2013,14(1):271-275
The present paper investigates the segregation of copper and silicon in an Al–lwt%Cu–lwt%Si alloy solidified under the co-action of centrifugal and electromagnetic forces. The reasons for the solute segregation and the effect of electromagnetic force on segregation are discussed. Tubular samples cut from the solidified alloy are analyzed, the results showing that the segregation of copper and silicon occurs along the normal direction of the samples and that the electromagnetic field has a remarkable influence on the segregation of both copper and silicon. As the exciting current increases, the segregation of copper decreases, while the segregation of silicon first increases and then decreases. The migration of solute atoms in the melt depends not only on the density difference between the solute and aluminum atoms, but also on the strength of the electromagnetic force. The magnetic force changes the rotation velocity of the melt, reduces the migration velocity of copper and causes the reduction of copper segregation. Because of the difference of the electrical conductivity between the solute and the aluminum melt, the reductions of velocity are not equal. 相似文献
1000.
Jing Cai Jing Xu Jianming Wang Liying Zhang Huan Zhou Yuan Zhong Dan Chen Huiqing Fan Haibo Shao Jianqing Zhang Chu-nan Cao 《International Journal of Hydrogen Energy》2013
Three-dimensional (3D) nanoporous nickel films were fabricated by a novel and facile method. The fabrication process involved the heat treatment of the electrodeposited zinc layer on nickel substrate and the subsequent electrochemical dealloying. The mutual diffusion of Ni and Zn during the heat treatment resulted in the formation of the Ni2Zn11 alloy surface film. The 3D nanoporous nickel films with open pores and interconnected ligaments were obtained by the electrochemical dealloying of relatively active zinc from the alloy surface film. As the electrodeposited zinc amount increased, the thickness, pore diameter and pore density of the nanoporous nickel films became larger. In our experimental range, the thickest nanoporous nickel film presented a thickness of 8 μm and an average pore diameter of 700 nm. The as-prepared 3D nanoporous nickel films exhibited much higher electrocatalytic activity for hydrogen evolution reaction (HER) than smooth nickel foil, and their electrocatalytic activities for HER enhanced with increase in the porosity and thickness. It was concluded that the enhanced electrocatalytic activity and excellent electrochemical stability for HER of the as-prepared 3D nanoporous nickel films can be ascribed to their unique nanostructured characteristics. 相似文献