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91.
92.
The corrosion behaviour of nitrogen-containing austenitic stainless steel in methanol containing different concentrations
of H2SO4, HCl, LiCl and H2SO4 + HCl has been investigated using a potentiostatic polarization method. The cathodic reaction in the H2SO4, HCl and H2SO4 + HCl solutions was proton reduction whereas in the neutral LiCl solution, oxygen reduction was the predominant cathodic
reaction. Active, passive and transpassive behaviours were observed only for higher concentrations of H2SO4 (0.01–2.0 M) due to the inherent water content. A cathodic loop, characterized by measured negative current in the anodic
region, was also observed in solutions, in which the concentration of H2SO4 was 1.0 M or higher. The relative stability of the passive films decreased as the H2SO4 concentration increased, and thus the steel suffered from mild pitting corrosion. In the chloride environment, the rate of
corrosion increased as the Cl− ion concentration increased. The presence of acid along with Cl− ions enhanced corrosion, and the corrosion rate increased significantly. The steel suffered from mild intergranular corrosion
in acidic chloride solutions of methanol. In the H2SO4 + HCl solutions, passive films were only formed when the H2SO4 to HCl concentration ratio was greater than ∼10:1. 相似文献
93.
94.
The removal of Cu(II) by adsorption on fly ash has been found to be concentration, pH and temperature dependent. The kinetics of adsorption indicates the process to be diffusion controlled. The Langmuir constants have been calculated at different temperatures, and the adsorption has been found to be endothermic (ΔH = 15.652 kcal mol?1). The maximum removal is observed at pH 8.0, and variation in adsorption with pH has been explained on the basis of surface ionisation and complexation. 相似文献
95.
Using the symmetry reduction approach we have herein examined, under continuous groups of transformations, the invariance of Einstein exterior equations for stationary axisymmetric and rotating case, in conventional and nonconventional forms, that is a coupled system of nonlinear partial differential equations of second order. More specifically, the said technique yields the invariant transformation that reduces the given system of partial differential equations to a system of nonlinear ordinary differential equations (nlodes) which, in the case of conventional form, is reduced to a single nlode of second order. The first integral of the resulting nlode has been obtained via invariant-variational principle and Noether’s theorem and involves an integration constant. Depending upon the choice of the arbitrary constant two different forms of the exact solutions are indicated. The generalized forms of Weyl and Schwarzschild solutions for the case of no spin have also been deduced as particular cases. Investigation of nonconventional form of Einstein exterior equations has not only led to the recovery of solutions obtained through conventional form but it also yields physically important asymptotically flat solutions. In a particular case, a single third order nlode has been derived which evidently opens up the possibility of finding many further interesting solutions of the exterior field equations. 相似文献
96.
N. K. Acharya P. K. Yadav S. Wate Y. K. Vijay F. Singh D. Kavasthi 《Bulletin of Materials Science》2004,27(5):417-420
Ion irradiation of Si8+ ion beam of 100 MeV was scattered by a gold foil on a Mylar membrane of 25 Μm thickness in the form of film roll (width,
12.5 cm and length, 400 cm) at the Nuclear Science Centre, New Delhi. The characterization of etched nuclear tracks was carried
out by gas permeation measurements. The samples cut from the film roll of required size for permeability measurements were
etched in a controlled manner in a constant temperature bath of 6N NaOH solution. The opening of the conical etched tracks
was characterized by hydrogen gas permeation. 相似文献
97.
S Kaliyugavaradan 《电子设计技术》2003,10(12):84
基于电阻的传感器,如应力规和压阻器件,常用于测量多种物理参数.对于使用数字处理器或微控制器进行数据采集和信号处理的设备来说,传感器的响应必须表现为一种适合于转换成数字格式的形式.把这类传感器的电阻变化转换成一个与之成比例的频率或时间间隔是可取的,所以你就能用一个计数器或定时器来方便地得到数字形式的输出信号.图1所示电路把传感器的电阻RS线性地转换成与之成比例的时间间隔.这一电路实际上是一个张驰振荡器,由一个电流源、一个桥式放大器、一个比较器和一个触发器组成.电流IS分成两路,分别通过R1和R2,就如同这两个电阻并联在一起一样.假定运算放大器是理想放大器,则当RX(R4+RS)大于R1R3/R2时,该电路就起一个振荡器的作用. 相似文献
98.
The compositions (1 −x)Ag2SO4−(x)BaSO4, wherex=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba2+ in Ag2SO4 was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained
using a detailed impedance analysis. The partial substitution of Ba2+ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model
based on lattice distortion (expansion) due to partial substitution of Ag+ by the bigger Ba2+ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO4-dispersed Ag2SO4 conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the
light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO4 dispersed Ag2SO4 is due to percolation threshold. 相似文献
99.
Crystallization of Polymer-Derived Silicon Carbonitride at 1873 K under Nitrogen Overpressure 总被引:1,自引:0,他引:1
Martin Friess Joachim Bill Jerzy Golczewski re Zimmermann Fritz Aldinger Ralf Riedel Rishi Raj 《Journal of the American Ceramic Society》2002,85(10):2587-2589
The chemical stability of an amorphous silicon carbonitride ceramic, having the composition 0.57SiC·0.43Si3 N4 ·0.49C is studied as a function of nitrogen overpressure at 1873 K. The ceramic suffers a weight loss at p N2 < 3.5 bar (1 bar = 100 kPa), does not show a weight change from 3.5 to 11 bar, and gains weight above 11 bar. The structure of the ceramic changes with pressure: it is crystalline from 1 to 6 bar, amorphous at ∼10 bar, and is crystalline above ∼10 bar. The weight-loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, SiC, and Si3 N4 are set equal to those of the crystalline forms; this implies that the material crystallizes before decomposition. The amorphous to crystalline transition that occurs at ∼10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen is proposed as the likely mechanism. The supersaturation required to nucleate α-Si3 N4 crystals is calculated to be 30 kJ/mol. 相似文献
100.
Naber J.F. Singh H.P. Tanis W.J. Koshar A.J. Segalla G.L. 《Solid-State Circuits, IEEE Journal of》1992,27(10):1327-1331
An indirect, phase-locked-loop (PLL), GaAs-enhanced frequency synthesizer with 700 ns loop settling time has been developed. The two-chip GaAs insertion reduced the size of an existing synthesizer from 90 in3 to only 30 in3. The 6.0 in×5.5 in.×0.9 in module contains a 400 gate GaAs programmable divider and a sample and hold (S/H) which improved the settling time by 77% and reduced the size by 67% over the current state-of-the-art synthesizer. Furthermore, the divider reduced power dissipation by 9.7 W and the S/H reduced power dissipation by 1.3 W 相似文献