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Showing 9 results for Ebrahimi

Ghobeiti Hasab M., Seyyed Ebrahimi S.a., Badaee A.,
Volume 2, Issue 2 (Jan 2005)

In this research the sol-gel auto-combustion method was used to prepare strontium hexaferrite nanopowder. A solution of distilled water, ferric and strontium nitrates, citric acid, trimethylamine, and n-decyltrimethylammonium bromide cationic surfactant, was heated to form a viscous gel. The gel was heated and then ignited automatically. As-burnt powder was calcined at temperatures from 700 to 900?C in air to obtain SrO.6Fe2O3 phase. The influence of the calcination temperature on the phase composition of the products has been investigated. X-ray diffraction confirmed the formation of single-phase strontium hexaferrite nanopowder at temperature of 800?C.
Ebrahimi A.r., Yadegari M., Khosroshahi R.a.,
Volume 3, Issue 3 (Jul 2006)

In this study, commercially pure titanium/304L stainless steel explosion bonded clads have been annealed under argon atmosphere over the temperature range of 700-900°C for 1h.Microstructure of the clads have been investigated before and after anealing. X-ray diffraction studies revealed that the annealing products in the form of intermetallic phases were gradually formed at the interface of the annealed clads. It was also found that, the bonding zone width increased with temperature according to an Arrhenius type equation. On the base of this equation, the activation energy of bonding zone growth was found equal to about 66.5 kJ/mol. The bond strength of the diffusion annealed clads were evaluated stress relieved. The maximum average tensile strength of ~350MPa was obtained for the as-welded clad. It was found that the bond strength decreased with annealing at 700°C due to an increase in the width of brittle intermetallic layer.
S. A. Sajadi, R. Ebrahimi, M. M. Moshksar,
Volume 6, Issue 1 (winter 2009 2009)

Abstract: In this paper, the forming process of a central hub by radial-forward extrusion is analyzed by using the finite element software, ABAQUS. Radial-forward extrusion is used to produce hollow parts that generally feature a central hub with radial protrusions. Effective design factors such as mandrel diameter, die corner radius, die fillet radius, mandrel corner radius, tube wall thickness and frictional conditions on the force required are investigated by simulation process. Commercially pure Aluminum AA1100 is selected as a model material for both experimental investigation and simulation analysis. Comparison is made and good agreement between the experimental result and that of finite element method is achieved.
M. Ebrahimi-Basabi,, J. Javadpour,, H. Rezaie, M. Goodarzi,
Volume 6, Issue 1 (winter 2009 2009)

Abstract: Nano- size alumina particles have been synthesized by mechanical activation of a dry powder mixture of AlCl3 and CaO. Mechanical milling of the above raw materials with the conditions adopted in this study resulted in the formation of a mixture consisting of crystalline CaO and amorphous aluminum chlorides phases. There was no sign of chemical reaction occurring during milling stage as evidenced by x-ray diffraction studies. Subsequent heat treatment of the milled powder at 350ºC resulted in the occurrence of displacement reaction and the formation of Al2O3 particles within a water soluble CaCl2 matrix. The effect of higher temperature calcinations on the phase development in this powder mixture was followed by X-ray diffraction (XRD) analysis and scanning electron microscope ( SEM). Differential thermal analysis (DTA) was used to compare the thermal behavior between the milled and unmilled powders. Perhaps the most important result in this study was the observation of á-Al2O3 phase at a very low temperature of 500ºC.
A. Davoodi, J. Pan,ch. Leygraf, Gh. R. Ebrahimi, M. Javidani,
Volume 6, Issue 3 (Summer 2009 2009)

Abstract: Localized corrosion of aluminum alloys is often triggered by intermetallic particles, IMP’s. To understandthe role of IMP’s in corrosion initiation of EN AW-3003, efforts were made to combine nano-scale ex-situ analysis ofthe IMP’s by SEM-EDS, SKPFM and in-situ AFM monitoring of the localized attack in chloride containing solution.The results showed that two distinct types of eutectically-formed constituent IMP’s exist the -Al(Mn,Fe)Si and theAl(Mn,Fe) phases. However, the exact chemical composition of the IMP’s varies with the particles size. Volta potentialdifference of surface constituents revealed that IMP’s have a higher Volta potential compared to the matrix, indicatingthe cathodic characteristic of the IMP’s. Noticeably, the boundary regions between the matrix and IMP’s exhibited aminimum Volta potential probably the sites for corrosion initiation. Localized corrosion attack monitored by in-situAFM clearly showed the trench formation occurrence around the large elongated IMP’s in the rolling direction.
P. Amin, A. Nourbakhsh, P. Asgarian, R. Ebrahimi Kahrizsangi,
Volume 13, Issue 3 (September 2016)

In this study, Boron carbide was synthesized using Mesoporous Carbon CMK-1, Boron oxide, and magnesiothermic reduction process. The Effects of temperature and magnesium grain size on the formation of boron carbide were studied using nano composite precurser containg mesoporous carbon. Samples were leached in 2M Hydrochloric acid to separate Mg, MgO and magnesium-borat phases. SEM, XRD and Xray map analysis were caried out on the leached samples to characterize the  boron carbide. results showed that the reaction efficiency developed in samples with weight ratio of B2O3:C:Mg = 11:1.5:12, by increasing the temperature from 550 to 650 °C and magnesium powder size from 0.3 m to 3 m.

T. Ebrahimi Sadrabadi, S.r. Allahkaram, N. Towhidi,
Volume 13, Issue 4 (December 2016)

Porous hollow glass microspheres have many uses, including encapsulation of active materials. In this paper a fast and facile method for fabricating porous hollow glass-microspheres was demonstrated by etching them using dilute hydrofluoric acid. Then, a highly reactive amine was infiltrated into the etched glass microspheres. Scanning electron microscopy was conducted for the hollow glass microspheres prior and post etching process. With regards to the porous hollow glass spherical sample, the spherical nature, morphology, pore diameter and the porosity were studied using scanning electron microscopy. Formation of the intact hollow glass microspheres with an open through wall porosities following phase separation and etching of the boron oxide rich phase was demonstrated using reciprocating shaker as the most suitable agitation method. The BET results indicated that the surface of the porous microspheres contained nano-pores. It is believed that the simplicity of the reported fabrication technique of micro/nano porous structure has the potential to scaling up for large scale production

M. Ebrahimi, S. A. Seyyed Ebrahimi, S. M. Masoudpanah,
Volume 14, Issue 1 (March 2017)

In this work, the effects of co-precipitation temperature and post calcination on the magnetic properties and photocatalytic activities of ZnFe2O4 nanoparticles were investigated. The structure, magnetic and optical properties of zinc ferrite nanoparticles were characterized by X-ray diffraction (XRD), vibrating sample magnetometry and UV–Vis spectrophotometry techniques.  The XRD results showed that the coprecipitated as well as calcined nanoparticles are single phase with partially inverse spinel structures. The magnetization and band gap decreased with the increasing of co-precipitation temperature through the increasing of the crystallite size. However, the post calcination at 500 °C was more effective on the decreasing of magnetization and band gap. Furthermore, photocatalytic activity of zinc ferrite nanoparticles was studied by the degradation of methyl orange under UV-light irradiation. Compare with the coprecipitated ZnFe2O4 nanoparticles with 5% degradation of methyl orange after 5 h UV-light light radiation, the calcined ZnFe2O4 nanoparticles exhibited a better photocatalytic activity with 20% degradation.

A. Kermanpur, H. Ebrahimiyan, A. Heydari, D. Heydari, M. Bahmani,
Volume 14, Issue 4 (December 2017)

Formation of stray grain defects particularly around re-entrant features of the turbine blade airfoils is one of the major problems in directional and single crystal solidification processes. In this work, directional solidification tests of the GTD-111 Ni-based superalloy were conducted at different withdrawal velocities of 3, 6 and 9 mm.min-1 using various stepped cylindrical and cubic designs. The process was also simulated using ProCAST finite element solver to characterize the crystal orientations. The phase transformation temperatures of the superalloy were estimated by the differential scanning calorimetry test. A process map was developed to predict the formation of stray grains in the platform regions of the stepped cylindrical and cubic specimens using the experimentally-validated simulation model. The process map shows critical values of the platform size, withdrawal velocity and initial sample size for the stray grain formation. The withdrawal velocity, platform size and initial sample size all had an inverse effect on the formation of stray grains.

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