JOURNAL OF SCHOOL OF ENGINEERING
Year:2003 | Volume:15 | Issue:1|Papers Count:13

The major interest for development of chromium alloy deposits is the possible formation of a passive film of chromium oxide. This study, the corrosion behavior of Fe-Cr-Ni alloy electrodeposits is investigated by cyclic polarization in sulfuric acid solution. The localized corrosion susceptibility of alloy deposits at crack tip, is studied by potentiostatic experiments in above-mentioned solution. It is observed that with increasing the current density of electrodeposition, the chromium and nickel contents and microcracks dimensions in the alloy deposits are increased. Therefore, the enhancement in corrosion resistance is likely due to the passivation behavior due to increasing the chromium and nickel contents. The passivation behavior of alloy deposits is similar to stainless steels with same passive current density but lower passivation potential range. This effect is attributed to the presence of microcracks in microstructure of the alloy deposits.        

Mn-Te powder is prepared by SPEX milling method. Primary results of air-milled Mn-Te Mixture show that original crystallites are gradually broken and oxidized without any MnTe phase formation. X-ray pattern of argon-milled powders show MnTe crystallites after 120 min. Milling, accompanying with Mn-Te2 phase. Diffraction peaks of Mn Te phase are weakened for longer milling times and some unwanted iron impurity phases gradually appear. The percentage of MnTe phase in products decreases considerably for longer than 12 hours milling times, while MnTe2 phase remains stable even after 110 hours of milling.      

Ni and Al elemental powder mixture with composition Ni75Al25 were mechanically alloyed in a planetary ball mill under different conditions. The structural changes of powder particles were studied by x-ray diffractometry and scanning electron microscopy. Mechanical alloying for ≈ 10h resulted in a solid solution of Al in Ni which transformed to Ni3Al intermetallic compound with nanocrystalline structure after≈ 20h of milling time. Decreasing ball-to-powder weight ratio or rotation speed of mill, drastically retarded the formation of Ni3Al phase. However, decreasing size of balls, while the balls-to-powder weight ratio remained constant, did not change mechanical alloying process significantly.      

In this paper the relation of compressive strength of portland cement at 28 days with it's phases and fineness in completing of the Bogue's experimental formula have been contemplated. The laboratory results indicate that there is a direct relationship between phases and fineness of the cement with its compressive strength. In the proposed experimental formulas, the portion of each cement phase and its fineness has been given by coefficients. For any given value of the phases and fineness of cement, the compressive strength could be obtained with acceptable precision.        

One of the usual method for seismic retrofit of existing reinforced concrete buildings is steel bracing. The use of steel bracing and reinforced concrete shear wall for strengthening of existing reinforced concrete buildings usually leads to very complicated system and the study of this kind of structures is necessary. In this paper, the frame-shear wall and steel bracing interaction is investigated by the analysis of a then-story reinforced concrete building. The analytical results show that with an increase in the section area of steel bracing, the lateral displacement and earthquake shear absorption by the frame decreases. Increasing the section area of steel bracing improve the overall response of the structure, but it has a less significant effect on the results after a certain level. The behavior of steel bracing and frame and the amount of shear absorption by both of them is approximately the same in the lower part of structure. Application of steel bracing decreases the lateral displacement by about 50 percent.    

Non production of PFA and the non uniform quality of natural pozzolans is a potential obstical in production of concrete mixes for RCC dam construction in Iran. Another option that can be considered is utilization of a super pozzolan called silica fume, which is available in the country as a byproduct of ferrosilicon industries. A laboratory investigation to evaluate the effect of incorporating various dosages of silica fume on enhancing the quality of RCC mixes of low to medium pastes (80 and 110 Kg/m3 cementatious materials contents), was carried out. The results show that incorporation of silica fume causes significant improvements in compressive and tensile strength of RCC mixes. The improvements observed in strength, Ranged from 25 to 60 percent for 5 to 15 percent cement replacement by silica fume. Permeability tests carried out also show that, a significant reduction in permeability is achieved by utilization of silica fume in RCC mixes.      

In this study, Structure-Soil-Structure interaction effect on nonlinear response of high rise buildings using of dynamic nonlinear analysis by finite element method have been investigated. The structures used in this analysis are two 15 and 30 story steel structures which are categorized as mid-rise and j1igh-rise towers. These structures have been studied under two distinct conductors namely; 1/8 and 1/4 width of foundation in between located on two soft and hard soil profiles. The most important studied parameters include nonlinear lateral displacements and nonlinear interstory drifts. The outputs indicate that interaction of adjacent buildings can result in increase or decrease of level of damage, depending on dynamic specifications of soil, structure and frequency content of input motion.      

Anchored Geosynthetic Systems (ADS) is a method for stabilizing soil slopes by employing a geosynthetic fabric placed on the slope face and tensioned via anchorage to the ground. The required tension is achieved through frictional or pullout resistances of anchors that are fastened to the fabric and driven into the underlying soil mass. The developed tension and curvature of the fabric combine to compress the soil and favorably increase confining or normal stresses, i.e., shear strength, on potential failure surfaces. Unlike previous studies on AGS, the contributions of anchors on the stability are also considered in this study. The stability analysis examines Modified Bishop's method by incorporating the effects of AGS loads both at the slope face and the rupture surface, and the shear and bending moment strengths of anchors. A computer code is written in Visual Basic language to facilitate the analysis and also the presentation of results. The results for an example slope show that the shear and bending resistances of anchors cause small increase in the stability of AGS slope      

Because of proven enormous natural gas resources in the world, there is a strong incentive to study and develop processes that would convert methane into more valuable chemicals. Among various routes a subject receiving a great deal of interest is oxidative coupling of methane over appropriate catalysts. In this work, direct partial oxidation of methane was studied in fixed bed quartz reactor at atmospheric pressure condition. Catalysts were made with different percentage of La2O3 (0.2, 1, 5, 10, 20) on the TiO2 as support using impregnation method. Reaction feed included methane; oxygen and helium gases and reaction products contained CO2, CO, ethane, ethylene and unconsumed O2 and methane gases. The reaction is thought to proceed via production of methyl radical by a heterogeneous catalysis. Ethane is formed homogeneously and produces ethylene. Various parameters such as temperature, percentage of inert gas, methane to oxygen ratio in the feed, feed flow rate and appropriate catalyst were checked and the optimum conditions were determined. The experimental results reveal that maximum C2 selectivity and maximum methane conversion are 57% and 31%, respectively.      

Simple models of photochemical air quality are necessary to represent raw guesses for photochemical smog amount. Semiempirical models have constant parameters which must be determined by using of the mathematical methods and local experimental concentrations of pollutants. These parameters are determined for Mashhad in this paper. The results of three models are compared with the existing experimental data. With respect to this comparison, it can be concluded that the model containing temperature parameter is the best model because the number of its average bias and standard deviation is fewer than it of the other models, and also it predicts better the peak of ozone concentration arisen in midday.    

In this paper a planar parallel manipulator, for machine tools applications, is introduced. High stuffiness, nonexistence of singular cases in its workspace and relatively large workspace are its main advantages. Using the isotropy criterion, isotropic designs of the manipulator is given. Moreover, the global conditioning index (GCI) of the manipulator, throughout its workspace is happened to be pretty well which make it suitable for any high precision work such as machine tool applications.