Showing 18 results for Rahimi
Ghobeiti Hasab M., Seyyed Ebrahimi S.a., Badaee A.,
Volume 2, Issue 2 (Jan 2005)
Abstract
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)
Abstract
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.
A. Poladi, M. Zandrahimi,
Volume 5, Issue 3 (Summer 2008 2008)
Abstract
Abstract: Austenitic stainless steels exhibit a low hardness and weak tribological properties. The
wear behaviour of austenitic stainless steel AISI 316 was evaluated through the pin on disc
tribological method. For investigating the effect of wear on the changes in microstructure and
resistance to wear, optical microscopy and scanning electron microscope were used. The hardness
of the worn surfaces was measured with a micro-hardness tester. Worn surfaces were analyzed
through X-ray diffraction. Results showed that with increasing the sliding distance and applied
load, the austenite phase partially transformed to ά martensite, and there was no trace of ε phase
detected. Due to the formation of probably hard and strong martensite phase, as the sliding
distance and applied load increased, the hardness and the wear resistance of the material was
increased. Wear mechanism was on the base of delamination and abrasion.
S. A. Sajadi, R. Ebrahimi, M. M. Moshksar,
Volume 6, Issue 1 (winter 2009 2009)
Abstract
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. Pirhadi Tavandashti, M. Zandrahimi, B. Akbari,
Volume 6, Issue 1 (winter 2009 2009)
Abstract
Abstract: Nanoparticles exhibit a high reactivity and strong tendency towards agglomeration. In this study, aluminum
oxide (alumina) nanoparticles were characterized by gas adsorption (BET), transmition electron microscopy (TEM)
and photon correlation spectroscopy (PCS) techniques to assess the agglomeration of the particles. There is a good
correlation between the BET and TEM measurements but PCS was larger in the mean and median size and with a
degree of agglomerates being detected. Some agglomeration was evident, but most of the particles existed as discrete
objects as observed in the (HR) TEM images which were in good agreement with the agglomeration factor.
M. Ebrahimi-Basabi,, J. Javadpour,, H. Rezaie, M. Goodarzi,
Volume 6, Issue 1 (winter 2009 2009)
Abstract
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
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.
A. Rezvanifar, M. Zandrahimi,
Volume 7, Issue 1 (winter 2010 2010)
Abstract
Abstract:
powerful method for the characterization of microstructures of crystalline materials in terms of crystallite size and
dislocation structures. In this paper the effect of the sliding on the microstructure of A356 in the as-cast and heat
treated conditions are studied, The X-ray phase analysis shows that with increasing applied load, the dislocation
density is increased, whereas the crystallite size is decreased. It was found that heat treatment raised dislocation
density during wear. The screw or edge character of dislocations in worn specimens were determined by analyzing the
dislocation contrast factors, it was demonstrated that the character of the prevailing dislocations in high loads is
nearly pure screw.
Diffraction peak profile analysis has recently been developed to such an extent that it can be applied as a
B. Akbari, M. Pirhadi Tavandashti, M. Zandrahimi,
Volume 8, Issue 2 (spring 2011 2011)
Abstract
Abstract: Most properties of nanoparticles are size-dependent. In fact, the novel properties of nanoaprticles do not prevail until the size has been reduced to the nanometer scale. The particle size and size distribution of alumina nanoparticle, as a critical properties, have been determined by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), surface area analysis (BET) and x-ray diffraction peak broadening analysis. The particle size was found to be in the range of 5-95nm. Cumulative percentage frequency plot of the data extracted form TEM images indicates that particle size distribution obeys the log-normal function. The TEM images also reveal that particles are spherical in shape and loosely agglomerated. Comparing of the XRD and TEM results shows that the particles are single-crystal. The HRTEM images also verify that the particles have a single-crystal nature. In comparison, there is a good correlation between the BET, XRD and TEM measurements other than PCS that is sensitive to the presence of the agglomerates.
M. Zandrahimi, A. Rezvanifar,
Volume 9, Issue 1 (march 2012 2012)
Abstract
Abstract: Cold working performed before an aging treatment has a significant effect on size and amount of precipitate produced. This could be caused by the increase in defect density, such as vacancies and dislocations. In this research, the Al-Cu-Si alloy was solution-treated, wear-tested and then artificially aged for a period of 1–5 h. Changes in the amount of precipitate, in the lattice parameter of the matrix, and in the precipitates are measured by X-ray diffraction and then calculated.It was observed that performing a wear test before the aging treatment was done significantly increased the amount of precipitate, while wear rate decreased.
A. R. Abbasian, M. R. Rahimipour, Z. Hamnabard,
Volume 10, Issue 3 (September 2013)
Abstract
In order to evaluate the sintering behavior of lithium meta titanate (Li2TiO3) powder, the shrinkage of powder compact was measured under constant rates of heating. Densification curves for Li2TiO3 have been constructed with the help of shrinkage powder measured at different heating rates. The activation energy at the initial stage of sintering was determined by analyzing the densification curves and the value of Q=377 kJ/mol was obtained. The diffusion mechanism at the initial sintering stage was determined by the analytical method applied to the constant rates of heating data. This analysis exhibited that the dominant mechanism for initial sintering stage of Li2TiO3 is volume diffusion from grain boundary and surfaces.
P. Amin, A. Nourbakhsh, P. Asgarian, R. Ebrahimi Kahrizsangi,
Volume 13, Issue 3 (September 2016)
Abstract
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)
Abstract
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)
Abstract
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)
Abstract
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.
A. Bahrami, M. R. Hosseini, F. Kazemi, S. Kheiri, M. Bakhshi, M. H. Rahimi,
Volume 16, Issue 1 (March 2019)
Abstract
Petroleum coke contains high amounts of carbon and is used in the manufacturing of anode electrodes for the aluminum extraction. In the process of aluminum production, some particles separate from anodes as waste which contain petroleum coke. Therefore, recycling and processing of these petroleum coke particles is the subject of this study. The ash content reduced to 31% and 13% in the jig and shaking table concentrate, respectively. These two steps were considered as the pre-processing methods and heavy media separation was used to decrease the ash content much more. Finally, flotation was performed in order to purify the particles with the size of less than one millimeter.
M. Akbarzadeh, M. Zandrahimi, E. Moradpur,
Volume 16, Issue 2 (June 2019)
Abstract
Molybdenum disulfide (MoS2) is one of the most widely used solid lubricants. In this work, composite MoSx/Ti coatings were deposited by direct-current magnetron sputter ion plating onto plain carbon steel substrates. The MoSx/Ti ratio in the coatings was controlled by sputtering the composite targets. The composition, microstructure, and mechanical properties of the coatings were explored using an energy dispersive analysis of X-ray (EDX), Xray diffraction (XRD), and nano indentation and scratch techniques. The tribological behavior of the coatings was investigated using the pin-on-disc test at room temperature. With the increase of doped titanium content, the crystallization degree of the MoSx/Ti composite coatings decreased. The MoSx/Ti coatings showed a maximum hardness of 13 GPa at a dopant content of 5 at% Ti and the MoSx/Ti composite films outperformed the MoSx films. Moreover, the films exhibited a steady state friction coefficient from 0.13 to 0.19 and the main wear mechanisms of the MoSx/Ti coating in air were abrasive, adhesive, and oxidation wear.
A. R. Abbasian, M. R. Rahimipour, Z. Hamnabard,
Volume 16, Issue 4 (December 2019)
Abstract
In this work, lithium meta titanate (Li2TiO3) nanocrystallites were synthesized by hydrothermal method and subsequent heat treatment. The shrinkage of the powder compact was measured under constant heating rate in order to study the sintering behavior of the synthesized powders. Densification curves of the synthesized powders were also constructed via the dilatometry analysis and evaluated at several heating rates. Two separate methods of analytical procedure and master curve sintering were employed to determine the activation energy of the initial sintering stage. The activation energy values were estimated based on these two distinct methods as 229±14 and 230 kJ/mol respectively, consistenting with each other. Moreover, surface diffusion was determined as the dominant mechanism of densification on initial sintering of Li2TiO3 nanocrystallites.
