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991.
K.F. Khaled 《Electrochimica acta》2010,55(22):6523-436
The inhibitive action of some benzimidazole derivatives namely 2-(2-furanyl)-1H-benzimidazole (FB), 2-(2-pyridyl) benzimidazole (PB) and 2-(4-thiazolyl) benzimidazole (TB), against the corrosion of iron in solutions of nitric acid has been studied using density function theory calculations (DFT), weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The calculated electronic parameters involved in the activity of the benzimidazole derivatives confirmed that the position of the side chain in the benzimidazole moiety affects the pattern of activity. The effectiveness of the benzimidazole derivatives is following the order TB > PB > FB. The same order is supported by the experimental chemical and electrochemical measurements. The relationships between inhibition efficiency of iron in 1.0 M HNO3 and the molecular orbitals of the studied molecules as well as number of electrons transferred ΔN from the inhibitor molecules to the iron surface were calculated by DFT method. The inhibition efficiency increased with the increase in EHOMO and decrease in ELUMO-EHOMO. TB had the highest inhibition efficiency because it had the highest HOMO energy and ΔN values, and it was most capable of offering electrons. Molecular modeling was used to evaluate the structural, electronic and reactivity parameters of the selected benzimidazole derivatives in relation to their effectiveness as corrosion inhibitors. Results obtained from weight loss, dc polarization and ac impedance measurements are in reasonably good agreement and show increased inhibitor efficiency with increasing inhibitor concentration.Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. 相似文献
992.
993.
The primary problems in water quality and availability in Jordan stem from poor long-term planning. This paper looks at past and current policies related to water management, considers their weaknesses, and suggests means of improving the management and planning aspects and the need for desalination infrastructure. The major water issues in Jordan can be attributed to both policy implementation failure and a lack of on-the-ground application of regulations. This study indicates that desalination of Red Sea water can be a long-term viable option to meet the growing domestic water needs within Jordan. 相似文献
994.
Khaled Chahine Mark Ballico John Reizes Jafar Madadnia 《International Journal of Thermophysics》2008,29(1):386-394
Design modifications are presented for a 289-mm long, 25.4-mm inner diameter blackbody heater element of a 48 kW Thermogage
blackbody furnace, based on (i) cutting a small “heater zone” into the ends of the tube and (ii) using a mixture of He and
Ar or N2 to “tune” the heat losses and, hence, gradients in the furnace. A simple numerical model for the heater tube is used to model
and optimize these design changes, and experimental measurements of the modified temperature profile are presented. The convenience
of the Thermogage graphite-tube furnace, commonly used in many NMIs as a blackbody source for radiation–thermometer calibration
and as a spectral irradiance standard, is limited by its effective emissivity, typically between 99.5% and 99.9%. The design
simplicity of the furnace is that the blackbody cavity, heater, and electrical and mechanical connections are achieved through
a single piece of machined graphite. As the heater also performs a mechanical function, the required material thickness leads
to significant axial heat flux and resulting temperature gradients. For operation at a single temperature, changes to the
tube profile could be used to optimize the gradient. However, it is desired to use the furnace over a wide temperature range
(1,000–2,900°C), and the temperature-dependence of the electrical conductivity and thermal conductivity, and that of the insulation,
makes this approach much more complex; for example, insulation losses are proportional to T
4, whereas conduction losses are proportional to T. In the results presented here, a slightly thinner graphite region near each end of the tube was used to “inject heat” to
compensate for the axial conduction losses, and the depth, width, and position of this region was adjusted to achieve a compromise
in performance over a wide temperature range. To assist with this optimization, the insulation purging gas was changed from
N2 to He at the lower temperatures to change the thermal conductivity of the felt insulation, and the effectiveness of this
approach has been experimentally confirmed. 相似文献
995.
996.
Dynamical simulation of an abrasive wear process 总被引:3,自引:0,他引:3
A dynamic computer model was developed to simulate wear behavior of materials on micro-scales. In this model, a material system
is discretized and mapped onto a lattice or grid. Each lattice site represents a small volume of the material. During a wear
process, a lattice site may move under the influence of external force and the interaction between the site and its adjacent
sites. The site–site interaction is a function of mechanical properties of the material such as the elastic modulus, yield
strength, work hardening and the fracture strain. Newton's law of motion is used to determine the movement of lattice sites
during a wear process. The strain between a pair of sites is recoverable if it is within the elastic deformation range; otherwise
plastic deformation takes place. A bond between two adjacent sites is broken when its strain exceeds a critical value. A site
or a cluster of sites is worn away if all bonds connecting the site or the cluster to its nearest neighbors are broken. The
model well describes the strain distribution in a contact region, in consistence with a finite element analysis. This model
was applied to several metallic materials abraded under the ASTM G65 abrasion condition, and the results were compared to
experimental observations. Good agreement between the modeling and the experiment was found.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
Chitosan is a polysaccharide derived from chitin, which is commonly found in shellfish waste materials. The present work is concerned with the graft copolymerization of 2-hydroxyethylmethacrylate (HEMA) onto chitosan using thiocarbonation–potassium bromate for redox initiation. The combined effects of the principal reaction variables for the grafting reaction were studied systematically. This grafting reaction was studied with respect to percentages of graft yield (%G.Y.), homopolymer (%H.P.), and total conversion (%T.C.). A tentative polymerization mechanism is proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 683–702, 2001 相似文献
998.
Zied Djedidi Jihen Ben Khaled Ridha Ben Cheikh Jean-François Blais Guy Mercier Rajeshwar Dayal Tyagi 《Hydrometallurgy》2009,95(1-2):61-69
The sludge dewatering properties (settling, filtration and centrifugation) of metal precipitates generated during treatment of monometallic solutions (0.020 mol/L) have been evaluated in this research. The precipitation tests carried out on 15 different metals gave metal removal yields generally similar to those predicted by MINEQL+ software, with the exception that kinetic aspects should be considered during precipitation of metal sulphides and phosphates. Hydroxides precipitation at pH 10.0 was the most efficient technique for the removal of eight metallic ions (Al3+, Cd2+, Co2+, Fe2+, Fe3+, Mg2+, Mn2+, Ni2+), whereas phosphates precipitation (at pH 6.0 with an addition of 0.0133 mol PO43?/L) gave highest removal yields for Ba2+, Ca2+, Cr3+. Sulphides precipitation (at pH 7.0 and using, 0.020 mol S2?/L) has been found the most efficient technique only for Cu2+ and Sn2+ precipitation, whereas carbonates precipitation (at pH 8.0 and using 0.020 mol CO32?/L) gave better removal yield only for Pb2+. Results have also shown that metal phosphates have generally better dewatering characteristics (SVI, filtration capacity, SRF, sludge solids content) than metal carbonates, sulphides and hydroxides. In fact, considering only the sludge dewatering characteristics, phosphates precipitation appears the most appropriate technique for the precipitation of many metals (Al3+, Ba2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, Ni2+ and Zn2+). Metal hydroxides formation constitutes the best option for Ca2+, Cu2+, Mg2+ and Sn2+ removal, whereas precipitation of metal carbonates is particularly interesting for treatment of Mn2+ and Pb2+ containing solutions. 相似文献
999.
A.-R.A. Khaled 《International Journal of Heat and Mass Transfer》2005,48(11):2172-2185
Heat transfer enhancements are investigated inside channels by controlling thermal dispersion effects inside the fluid. Different distributions for the dispersive elements such as nanoparticles or flexible hairy fins extending from the channel plates are considered. Energy equations for different fluid regions are dimensionalized and solved analytically and numerically. The boundary arrangement and the exponential distribution for the dispersive elements are found to produce enhancements in heat transfer compared to the case with a uniform distribution for the dispersive elements. The presence of the dispersive elements in the core region does not affect the heat transfer rate. Moreover, the maximum Nusselt number for analyzed distributions of the dispersive elements are found to be 21% higher than that with uniformly distributed dispersive elements for a uniform flow. On the other hand, the parabolic velocity profile is found to produce a maximum Nusselt number that is 12% higher than that with uniformly distributed dispersive elements for the boundary arrangement. The distribution of the dispersive elements that maximizes the heat transfer is governed by the flow and thermal conditions plus the properties of the dispersive elements. Results in this work point towards preparation of super nanofluids or super dispersive media with enhanced cooling characteristics. 相似文献
1000.
This paper presents experimental results of reinforced concrete beams strengthened using near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) reinforcement. A total of nine beam specimens were tested under fatigue loads. In addition, two specimens were tested for monotonic capacity. The beams were 3,500 mm long with a cross section of 254 mm deep by 152 mm wide. Different load ranges were considered in the fatigue tests to construct the fatigue life curves. The test results showed that under monotonic loading, the beam strengthened with NSM CFRP rod exhibited increases of 26 and 50% in the yield and ultimate load over the control beam, respectively. Under cyclic loading, the fatigue life for the strengthened beams was 24% higher than that of the control unstrengthened beams. An analytical model using sectional analysis and strain-life approach was developed to estimate the fatigue life of the specimens at various cyclic load ranges. A good agreement between the experimental results and analytical prediction of the fatigue life was obtained. 相似文献