Showing 10 results for Karimi
Baradari H., Amani Hamedani H., Karimi Khoygani S., Rezaei H.r., Javadpour J., Sar Poulaki H.,
Volume 3, Issue 1 (Oct 2006)
Abstract
Ultrafine hydroxyapatite (HAp) powders with crystallite size in the range of 10-90 nm were synthesized by chemical precipitation process using Ca(OH)2 and H3PO4 solutions as starting materials. Molar ratio of Ca/P=1.68 was kept constant throughout the process and alkaline condition for the reaction was maintained using ammonium hydroxide. The role of raw material concentration on HAp crystallite size and morphology were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The results revealed that variations in crystallite size and morphology of synthesized HAp are strongly affected by the concentration of acid solution. To study the sintering behavior of HAp particles, the powders were pressed at 200 MPa using a uniaxial press. Sintering experiments were carried out at temperatures of 1100, 1250 and 1300°C with various soaking times at maximum temperatures. XRD was also used in determining thephases present after sintering process. The results indicated the decomposition of HAp into a-tricalcium phosphate (TCP) and b-TCP phases at 1300°C. The microstructure of the sintered HAp ceramics was characterized by SEM.
A. Karimi Taheri, Kazeminezhad, A. Kiet Tieu,
Volume 4, Issue 1 (winter & spring 2007 2007)
Abstract
Abstract: The theoretical calculation of dislocation density in different regions of a deformed
workpiece of 99.99% pure copper has been carried out using different procedures consisting of
Finite Element Method (FEM) and hardness measurement. To assess the validity of the results
pertaining to these procedures, the dislocation density is experimentally measured utilizing the
Differential Scanning Calorimetry (DSC). Comparing the predicted and experimental results, it
was found that the average error in prediction of the dislocation density by the hardness
measurement and FEM is 12% and 2.5%, respectively. Also, for further confirmation of the
evaluated dislocation density of each region of the deformed workpiece, the annealing process was
carried out and in the region of higher dislocation density, a finer grain size was observed.
B. Tolaminejad, A. Karimi Taheri, H. Arabi, M. Shahmiri,
Volume 6, Issue 4 (Autumn 2009 2009)
Abstract
Abstract: Equal channel angular extrusion (ECAE) is a promising technique for production of ultra fine-grain (UFG) materials of few hundred nanometers size. In this research, the grain refinement of aluminium strip is accelerated by sandwiching it between two copper strips and then subjecting the three strips to ECAE process simultaneously. The loosely packed copper-aluminium-copper laminated billet was passed through ECAE die up to 8 passes using the Bc route. Then, tensile properties and some microstructural characteristics of the aluminium layer were evaluated. The scanning and transmission electron microscopes, and X-ray diffraction were used to characterize the microstructure. The results show that the yield stress of middle layer (Al) is increased significantly by about four times after application of ECAE throughout the four consecutive passes and then it is slightly decreased when more ECAE passes are applied. An ultra fine grain within the range of 500 to 600 nm was obtained in the Al layer by increasing the thickness of the copper layers. It was observed that the reduction of grain size in the aluminium layer is nearly 55% more than that of a ECA-extruded single layer aluminium billet, i.e. extruding a single aluminium strip or a billet without any clad for the same amount of deformation. This behaviour was attributed to the higher rates of dislocations interaction and cell formation and texture development during the ECAE of the laminated composite compared to those of a single billet
N. Anjabin, Karimi Taheri,
Volume 7, Issue 2 (Spring 2010 2010)
Abstract
Abstract:
properties of AA6082 aluminum alloy. Considering that aging phenomenon affects the distribution of alloying element
in matrix, and the fact that different distribution of alloying elements has different impediments to dislocation
movement, a material model based on microstructure, has been developed in this research. A relative volume fraction
or mean radius of precipitations is introduced into the flow stress by using the appropriate relationships. The GA-based
optimization technique is used to evaluate the material constants within the equations from the uni-axial tensile test
data of AA6082 alloy. Finally, using the proposed model with optimized constants, the flow behavior of the alloy at
different conditions of heat treatment is predicted. The results predicted by the model showed a good agreement with
experimental data, indicating the capability of the model in prediction of the material flow behavior after different heat
treatment cycles. Also, the calculated flow stress was used for determination of the material property in Abaqus
Software to analyze the uniaxial compression test. The force- displacement curves of the analysis were compared to
the experimental data obtained in the same condition, and a good agreement was found between the two sets of results.
A novel constitutive equation has been proposed to predict the effect of aging treatment on mechanical
P. Karimi, K. S. Hui, K. Komal,
Volume 7, Issue 3 (summer 2010 2010)
Abstract
Abstract:
(Y2O3) and ethyl acetate as a mineralizer by hydrothermal method at a low temperature (T=.230°C, and
P=100bars).The as-prepared powders were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared
Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), UV-V Spectroscopy and Chemical Oxygen Demand
(COD) of the sewage water, respectively. The results show that hydrothermal method can greatly promote the
crystallization and growth of YVO4 phase. XRD pattern clearly indicates the tetragonal structure and crystallanity. An
FTIR spectrum of the YVO4 shows the presence of Y-O and V-O bond, respectively. The presence of these two peaks
indicates that yttrum vanadate has been formed. UV-V is absorption spectra suggesting that YVO4 particles have
stronger UV absorption than natural sunlight and subsequent photocatalytic degradation data also confirmed their
higher photocatalytic activity.
In this paper, YVO4 powder was successfully synthesized from Vanadium Pentaoxide (V2O5), Yttrium Oxide
M. Sheikhshab Bafghi, M. Karimi, M. Adeli,
Volume 10, Issue 4 (december 2013)
Abstract
In the present study, reduction of zinc oxide from the pellets made of steelmaking electric arc furnace dust has been investigated. Effects of such parameters as the type of carbon material (graphite, coke and charcoal) as well as time and temperature on the reduction reaction have been examined. The reduced (dimensionless) time method was applied to perform a kinetic analysis of the system. Experimental results showed that increasing the temperature in the range of 925-1150°C results in a remarkable increase in the reduction rate. It was also shown that the reduction process is controlled by chemical reaction. Meaningful difference in the activation energy values calculated for reduction with graphite (24.75 kcal/mol), coke (18.13 kcal/mol) and charcoal (11.52 kcal/mol) indicate the predominant role of chemical reaction (carbon gasification) in the overall reaction rate and its rate-controlling mechanism. Carbothermal reduction of pelletized EAF dust proved to be an efficient reduction method, so that above 90% reduction was achieved in about one hour at temperatures around 1100°C.
M. Karimi Sahnesarayi, H. Sarpoolaky, S. Rastegari,
Volume 16, Issue 2 (June 2019)
Abstract
In this study nanosized TiO2coatings on the 316L stainless steel substrate were prepared by means of dip-coating technique in which thickness of the coating layer increased byrepeating the coating cycles in two different routes: (I) dipping and drying,respectively, were repeated one, three and five times and finally the dried coated sample was heat treated (single); (II) multiple heat treatment performed after each dipping and drying cycle, respectively.The structural, morphological and optical characterizations of coatings as well as thickness of coatings were systematically studied.The photocatalytic activity of the various TiO2 coatings was investigated based on the degradation of an aqueous solution of Methyl orange.Moreover, thecorrosion protective properties of coatings were evaluated in both dark and UV illumination conditions based on the obtained polarization curves. The results indicated 1.75 times improvement in photocatalytic reaction rate constant, a two orders of magnitude decrease in corrosion current density in dark condition and about 140 mV electrode potential reduction under UV illumination with optimum coating preparation procedure, repeating the cycle from dipping to heat treatment three times, than the sample prepared with one time coating and heat treatment since this procedure provided not only high thickness and defect-free coating but also transparent one.
M. Sadeghi, M. Hadi, O. Bayat, H. Karimi,
Volume 17, Issue 1 (March 2020)
Abstract
In this paper a constitutive equation was considered for the isothermal hot compression test of the Mn-Ni-Cr alloy. The hot compression test was performed in the strain rate range of 0.001-0.1 s-1 and deformation temperature was varied from 700 to 900 °C. A considerable reduction in flow stress was observed regardless of the strain rate when temperature was increased from 700 to 750 °C. DTA and XRD evaluation revealed that the removal of Mn3Cr phase and formation of the single solid solution phase were the reason for the flow stress reduction. At the low deformation temperature (700°C) and the high strain rate (0.1 s-1), a partially recrystallized microstructure was observed; this was such that with increasing the temperature and decreasing the strain rate, a recrystallized microstructure was completed. Also, the relationships between flow stress, strain rate and deformation temperature were addressed by the Zener-Holloman parameter in the exponent type with the hot deformation activation energy of 301.07 KJ/mol. Finally, the constitutive equation was proposed for predicting the flow stress at various strain rates and temperatures.
Saeid Karimi, Akbar Heidarpour, Samad Ghasemi,
Volume 18, Issue 2 (June 2021)
Abstract
In this research, expanded graphite (EG) was successfully fabricated using a simple ball milling process followed by hydrofluoric (HF, 10 wt. %) leaching. The effects of ball milling time (0-15 h) and leaching time (1-24 h) on the exfoliation of graphite were examined by XRD and Raman spectra. Furthermore, the morphological evaluation of the obtained expanded graphite samples was carried out by scanning electron microscopy (SEM). The XRD results of the ball-milled and HF treated samples showed a slight peak shift and broadening of (002) plane for expanded graphite compared to the precursor and HF-treated samples. Moreover, the intensity of the (002) planes remarkably decreased by the ball milling process but remained constant after HF treatment. Raman spectra of the samples confirmed the ordering process only in HF-treated specimens. Moreover, the intensity ratio of 2D1 to 2D2 band gradually increased with enhancing the HF treatment time up to 5 hours, indicating a decrement in the number of graphite layers by leaching in the HF solution.
Morteza Hadi, Omid Bayat, Hadi Karimi, Mohsen Sadeghi, Taghi Isfahani,
Volume 19, Issue 1 (March 2022)
Abstract
In this research, the effect of initial microstructure and solution treatment on rollability and crystallographic texture of a Cu-Mn-Ni-Sn alloy has been investigated. The initial tests indicated that the rolling of the alloy at different temperature conditions is not possible due to formation of second phases. Herein to eliminate the segregated phases, according to DTA analysis, proper temperature for solution treatment was selected as 750°C applied at different periods of time. The obtained results showed that after 15-hour solution treatment, the complete elimination of Sn, Mn, Ni, and Fe-rich phases can be achieved. Also, the peaks of XRD shifted to the higher angles indicating that the alloying elements are dissolved. Meanwhile, the intensity of the texture reduced and the dominant texture changed from Goss and Brass-texture to Copper-texture. Accordingly, the amount of maximum total reduction at the rolling process increased from 16.37 to 109.46 after solution treatment.
