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121.
122.
Indranil Roy Manish Chauhan Farghalli A. Mohamed Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2006,37(3):721-730
Thermal stability in bulk ultrafine-grained (UFG) 5083 Al that was processed by gas atomization followed by cryomilling, consolidation,
and extrusion, and that exhibited an average grain size of 305 nm, was investigated in the temperature range of 473 to 673
K (0.55 to 0.79 T
m
, where T
m
is the melting temperature of the material) for different annealing times. Appreciable grain growth was observed at temperatures
> 573 K, whereas there was limited grain growth at temperatures < 573 K even after long annealing times. The values of the
grain growth exponent, n, deduced from the grain growth data were higher than the value of 2 predicted from elementary grain growth theories. The
discrepancy was attributed to the operation of strong pinning forces on boundaries during the annealing treatment. An examination
of the microstructure of the alloy suggests that the origin of the pinning forces is most likely related to the presence of
dispersion particles, which are mostly introduced during cryomilling. Two-grain growth regimes were identified: the low-temperature
region (<573 K) and the high-temperature region (>573 K). For temperatures lower than 573 K, the activation energy of 25 ±
5 kJ/mol was determined. It is suggested that this low activation energy represents the energy for the reordering of grain
boundaries in the UFG material. For temperatures higher than 573 K, an activation energy of 124 ± 5 kJ/mol was measured. This
value of activation energy, 124 ± 5 kJ/mol, lies between that for grain boundary diffusion and lattice diffusion in analogous
aluminum polycrystalline systems. The results show that the strength and ductility of bulk UFG 5083 Al, as obtained from tensile
tests, correlate well with substructural changes introduced in the alloy by the annealing treatment. 相似文献
123.
Ali Hassanzadeh 《Corrosion Science》2007,49(4):1895-1906
In our previous works, the corrosion inhibition properties of propylamine (PA), iso-propylamine (i-PA), butylamine (BA), tert-butylamine (t-BA), hexylamine (HA), ethylenediamine (EDA), diethanolamine (DEA), 3-amino-1-propanol (3-AP), 2-dimethylethanolamine (2-DEA), cyclohexylamine (CHA), N-methylcyclohexylamine (N-MCA) and dicyclohexylamine (DCHA) have been investigated by means of electrochemical impedance spectroscopy (EIS) with a carbon steel rotating disc electrode in some petroleum/water corrosive mixtures containing acetic acid and NaCl at 25 °C. In this work, the Kramers-Kronig transformations (KKTs) were applied to evaluate the validity of the impedance data of these amine compounds in hydrodynamic condition. The results obtained showed that experimental impedance data did not satisfy in K-K relations completely viz. indicated some errors. These errors were related to stray capacitances, external transmission line effects, pits formation and change in interface during data acquisition at high and low frequencies regions. In addition, the selection of a suitable equivalent circuit strongly emphasized to better interpret of EIS data which in turn cause better resulted KKTs spectra. With considering obtained transformations, more effective inhibitor was selected with regard to its charge transfer resistance, the corrosion capacitance and well satisfying in K-K relations. 相似文献
124.
Koudymov A. Xuhong Hu Simin K. Simin G. Ali M. Yang J. Asif Khan M. 《Electron Device Letters, IEEE》2002,23(8):449-451
We demonstrate a novel RF switch based on a multifinger AlGaN/GaN MOSHFET. Record high saturation current and breakdown voltage, extremely low gate leakage current and low gate capacitance of the III-N MOSHFETs make them excellent active elements for RF switching. Using a single element test circuit with 1-mm wide multifinger MOSHFET we achieved 0.27 dB insertion loss and more than 40 dB isolation. These parameters can be further improved by impedance matching and by using submicron gate devices. The maximum switching power extrapolated from the results for 1A/mm 100 /spl mu/m wide device exceeds 40 W for a 1-mm wide 2-A/mm MOSHFET. 相似文献
125.
A variable friction model that relates the parameters of sheet metal drawing to the local lubrication conditions taking place during the deformation, has been integrated to a finite element program. Variable friction coefficients for the contacting surfaces are determined from the friction model, which uses the related parameters obtained at each time step of the finite element program as inputs. A number of numerical runs have been performed and the strains are compared with the experimental results for circular blanks. A good agreement is obtained between the numerical and experimental results for the variable friction model used. 相似文献
126.
Mohamed Salah Foda 《Journal of the science of food and agriculture》1981,32(11):1109-1114
A fermentation procedure using wheys from buffalo milk, sweet rennet and salted wheys containing up to 15% NaC1, and based on the selection of salt-tolerant fungal cultures for production of microbial proteins and some economically important enzymes, is described. Certain strains of Aspergillus flavus, A. niger, A. ochraceus and A. terreus gave yields of mycelium ranging between 1.5 and 30 g on a dry weight basis. Strong proteolytic activities were exhibited by A. ochraceus, A. flavus and, to a lesser extent, by A. niger in the presence of salt up to 10% as final concentration. Powerful milk-clotting activities were also detected in culture supernatants of A. flavus and A. ochraceus. Extracellular β-galactosidases were released in to the culture fluids of these fungal strains with variable activities, depending upon the salt content of the growth medium. The application of the procedure is discussed. 相似文献
127.
This article allows the determination of the induced perturbations at the ends of the coaxial line in wide frequency band enough. The perturbation source is a current direct point injection into the cable screen in any position. For this, we have applied the theory of the state variables, with foundation of the quasi-TEM approximation, in order to simulate the coaxial line above a ground level that has a finished conductivity. This allows us to supply the current and voltage expressions at the ends of the line as their analytic forms for any conditions of charge. Next, the elaborate objective is to verify experimentally on concrete applications if the test obtained results confirm the theoretical expectations supplied by calculation code finalizing. 相似文献
128.
Ali Bayram Agah Uguz Ali Durmus 《Journal of Materials Engineering and Performance》2002,11(5):571-576
Three types of material whose fracture toughness tests were previously performed by using circumferentially notched bars,
namely (1) a dual-phase steel with three different morphologies; (2) an Al-Zn-Mg-Cu-wrought alloy; and (3) Al-Si-cast alloys
with three different Si contents, were investigated in terms of accuracy and reliability of the testing method. Also, the
advantages of using circumferentially notched bars for fracture toughness determination of metallic materials were discussed.
With the help of stress concentration factors, which are associated with the bluntness of the notch, correction factors for
the fracture toughness calculations are derived. The corrected fracture toughness values are found to be close to the uncorrected
ones, implying that the testing procedure is reliable. 相似文献
129.
130.
The molecular weight of polyacrylic acid (PAA) was determined by a viscometric method using NaNO3 as solvent at 30°C. The specific electric conductivities (σ) of PAA as well as PAA doped with carbon black (CB), chromium oxide (Cr2O3), and cupferron with different concentrations (from 0.25 to 1 wt %) were measured at a temperature range 360–400 K. IR spectra of some polymers were determined and it was shown that when PAA was doped with 0.5 wt % CB, a C? O? C band appeared at 775–875 cm?1. The positron annihilation lifetime (PAL) spectra in PAA doped with the above‐mentioned dopants were measured as a function of their concentrations. It was observed that the short lifetime intensity I1 decreased, whereas the intermediate lifetime intensity I2, which is related to the conductivity of the material, increased with increasing the wt % of Cr2O3 and cupferron as well as at low concentrations of CB. These results are discussed in terms of the conducting island model. It was found that there were distinct positive relationships between σ and I2. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 877–883, 2002; DOI 10.1002/app.10381 相似文献