Showing 9 results for Safari
F.ghassemi and R.safari,
Volume 14, Issue 2 (1-1996)
Abstract
Distance relays are used to protect EHV and HV Transmission lines. Over the past decades many algorithms have emerged for digital distance relays. These are based on the calculation of the transmission line impedance from the relaying to fault points. In this paper a novel method for digital distance relaying is proposed. In the method the tracking procedure is implemented. The method uses the calculus of variations for optimization of functionals. The method tracks the fundamental component of the waveforms and at the same time calculates the fault loop impedance. This eliminates the need for a pre-algorithm filtering which in turn improves the speed of the relay. Comparison with other algorithms has shown that the proposed method has a faster response and improved accuracy, in particular when a long line is considered.
A, Saidi, M. H. Abbasi and J. Safarian,
Volume 19, Issue 1 (7-2000)
Abstract
Sponge iron (DRI) due to the high surface area, often shows a high tendency to re-oxidation and at some cases spontaneous combustion (autoignition). In this work, re-oxidation behavior and autoignition of sponge iron, produced from different types of iron ore has been investigated. Isothermal and non-isothermal re-oxidation experiments were carried out on each type of DRI and their autoignition temperature was determined. Microscopic examination and porosimetric measurements also were used to elucidate the relationship between the DRI specification and its re-oxidation behavior. The type and chemical analysis of the iron ore, used for the production of DRI, had a strong influence on the microstructure of sponge iron and, in turn, on its sensitivity to re-oxidation and autoignition.
J. Safarian-Dastjerdi and A. Saidi, ,
Volume 24, Issue 1 (7-2005)
Abstract
A higher bustle temperature in midrex direct reduction process is always desirable due to its positive effect on the productivity and DRI quality. The limit of the bustle temperature is related to the sticking or clustering behaviour of oxide pellets during the reduction in the reactor. It has been well estabilished that coating of oxide pellets by a refractory material decreases its
tendency to clustering. In this study, the clustering behaviour of oxide pellets (produced from Golegohar-Chadormalu iron ore) during redution at different temperatures was investigated. The effect of coating with different amounts of hydrated lime on the clustering behaviour was also examined. Microscopic examination of coated pellets shows a porous, non-continious layer of Ca(OH)2 being fromed on the surface of the pellets. The clustering tendency of coated pellets, measured by the standard sticking test at pilot scale, was much lower, compared with normal (uncoated) pellets, while their reducibility was the same.
A. R. Safari, M. Ghayour, and A. Kabiri,
Volume 25, Issue 1 (7-2006)
Abstract
It is empirically established that, due to a number of factors involved, a classical (linear) analysis of buckling pressure is impossible. Nonlinear theories of buckling are, therefore, required that involve effective factors such as imperfections and welding effects. In this study, models are developed which are as close to allowable standard deviations as possible. In the next stage, their buckling behavior is investigated both experimentally and numerically using finite element packages ADINA, ANSYS, COSMOS, and MARC based on specific capabilities of each. Results show that reasonable estimates of real buckling pressure will become possible when material and geometrical nonlinearities and initial imperfections are introduced into the analytical system. Finally, in the light of the results obtained, a submarine pressure hull is analyzed.
M.a. Yousefpour, F. Safari Kooshali, B. Khoshandam,
Volume 34, Issue 3 (Journal of Advanced Materials-fall 2015)
Abstract
The purpose of this work was to study the hydrogen adsorption on the surface of mesoporous materials based on silica (SBA-16) modified with palladium via temperature. Since mesoporous silica materials have a high specific surface area, and the ordered mesoporous size of 2-10nm, they are suitable for adsorption and storage of hydrogen. SBA-16 is suitable for this purpose due to its cubic crystalstructure and open pores. Single-stage sol-gel method was used to produce nanostructure composite from salt of palladium (PdCl3) and mesoporous silica precursor. The aging time was selected as 12 hr at 80˚C. Furthermore, the obtained materials were heated at 550˚C for 6 hr to remove surfactant and to form pores. Then the materials were characterized by large angle and small angle x-ray diffraction analysis, and hydrogen absorption analysis at upto 200kPa pressure at three different temperatures of -196˚C (77 K), -123˚C (150 K) and 30˚C (303 K). Furthermore, adsorption-desorption of nitrogen gas was studied. The surface morphology was observed by field emission scanning electron microscope (FESEM). In addition, the amount of palladium, oxygen, and silicon were measured by using energy dispersive spectroscopy) EDS ). Finally, the functional groups on the surface of mesoporous silica materials were evaluated using Fourier transform infrared spectroscopy (FTIR). The results of XRD and EDS analyses confirmed the presence of palladium and palladium oxide in mesoporous amorphous silica. In addition, BET results showed that addition of palladium in SBA-16 decreased the surface area, and produced 791 and 538m2/g for SBA-16 and SBA-16/Pd, respectively. Hydrogen absorption in nano structure composite was decreasing with temperatur in comparison with SAB-16. On the other hand, the maximum hydrogen absorption in the nano structure composite containing palladium was obtained at -196˚C (77 K).
S. Torkian, A. Shafyei, M.r. Toroghinejad, M. Safari,
Volume 35, Issue 3 (Journal of Advanced Materials-Fall 2016)
Abstract
In this paper the effect of deep cryogenic treatment time on microstructure and tribological behavior of AISI 5120 case hardennig steel is studied. The disk shape samples were carburized at 920 ◦C for 6 hours and air cooled; after austenitizing, the samples were quenched in oil.Then immediately after quenching and sanding, the sample were kept in liquid nitrogen for 1, 24, 30 and 48 h and then tempered at 200 ◦C for 2 hours. The wear test was done by ball on disk method using of WC ball at 80 and 110 N load. For characterization of carbides, the etchant solution of CuCl2 (5 gr)+HCl (100 mL) + ethanol (100 mL) was used. The hardness of samples before and after of tempering was measured by vicers method at 300 N load.. The amount of retained austenite was measured by X Ray Diffraction method. For 1DCT and 24DCT samples it was about 8% and 4%; in the other samples, the retained austenite peal was so decreased that it was not visible. The result showed that the hardness increases by deep cryogenic treatment in all speciments. While wear resistance increases in 1DCT and 24DCT samples, it decreases for 30DCT and 48DCT samples in compare with Conventional heat treatment (CHT) sample in both applied loads, such that , 48DCT sample has the least wear resistance. The cause of increament of hardness is due to reduction in amount of retained austenite as a result of deep cryogenic treatment and decreasing in wear resistance after 24 hour, is due to carbide growth and nonhemogenuse distribution in microstructure and then weakening of matrix. So the 24 hour deep cryogenic treatment was the best optimal for AISI 5120 steel.
M. Hakimi, M. Safari,
Volume 38, Issue 1 (Journal of Advanced Materials-Spring 2019)
Abstract
In this study, the improvement of the magnetic properties of Co2FeSi Heusler compound was followed by the utilization of different experimental synthesizing procedures. Comparing the crystal structure showed that the milled samples had a higher crystalline order than the arc-melted ones. Annealing of the milled sample improved the crystalline order, resulting in the highest saturation magnetization (5/24 μB/F.u.). The difference in the saturation magnetization of the other samples was explained by the core-shell model. Comparison of the various coercivity mechanisms showed that the decrease in the size of crystallites played a key role in the higher value of the milled samples coercivity.
N. Safari, M. Toroghinejad, M. Kharaziha, V. Saeedi,
Volume 38, Issue 3 (Journal of Advanced Materials-Fall 2019)
Abstract
The aim of this study was to fabricate the Mg-1Al-Cu alloys with various amounts of Cu content (0, 0.25, 0.5 and 1 wt.%) using spark plasma sintering (SPS) approach and evaluation of their degradation rate and biological properties. The results indicated that Cu incorporation (0.25 wt.%) significantly diminish degradation rate from 0.039 cm/h in pure Mg to 0.00584 cm/h in Mg-1Al-0.25Cu alloy. In addition, Mg-1Al-0.25Cu alloy could noticeably (1.25 times) promote viability of MG63 cells compared to pure Mg, owing to the optimized ion release. Moreover, the antibacterial activity of Mg-1Al-0.25Cu was considerable. In summary, Mg-1Al-0.25Cu alloy with appropriate degradation rate, good biocompatibility and antibacterial properties can be introduced as a biodegradable orthopedic implant.
R. Moradi, M. Roshanaee, H. Mostaan, F. Nematzadeh, M. Safari,
Volume 40, Issue 1 (Journal of Advanced Materials-Spring 2021)
Abstract
In this research, microstructure and mechanical properties of laser welded joints between 2304 duplex stainless steel and Inconel 718 nickel-based super alloy were investigated. Microstructural evolution in the various areas of welded joints and also the effect of welding parameters on the mechanical properties of dissimilar joints were studied. Response surface methodology based on the central composite design was used in order to find the optimum welding parameters. Effective parameters of the welding process including laser power, travel speed and defocusing distance were set in the range of 1000 to 1900 W, 1 to 5 mm/s and -1 to 1 mm, respectively. Uniaxial tensile test was used to evaluate the fracture force of weld joints. The microstructural observations and phase evolutions were studied using optical microscope. It was found that the fracture force of the weld joints firstly increased by travel speed and defocusing distance and then decreased by further increase. The maximum fracture force was obtained when laser power, travel speed and defocusing distance were 1900 W, 3 mm/s and 0 mm, respectively. The center line of weld metal was mainly consisted of equiaxed grains where, columnar grains were formed in the fusion line. The obtained results from the hardness measurement showed that the hardness of Inconel 718 was decreased due to dissolution of TiC and NbC particles.
