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Showing 16 results for Ahmadi

A. Ahmadi,, H. Sarpoolaky,, A. Mirhabibi, F. Golestani-Fard,
Volume 4, Issue 3 (Summer &Autumn 2007 2007)

Abstract: Dolomite based refractories are widely used in Iranian steelmaking plants. In the present research, wear and corrosion of refractories used in steel-making converter lining in Esfahan Steel Company was studied. Post-mortem analysis of refractories clarified that the wear started with oxidation of carbon followed by chemical corrosion. Iron oxide from slag reacted with calcia, resulting in formation of low melting phase, and subsequent washout process, caused the refractory corrosion onset from the hot face. In addition, the effect of aluminum as an anti-oxidant and graphite on the corrosion resistance of refractory was investigated. Tar-dolomite samples containing different amount of graphite (0, 4, 7, and 10 wt. %) were prepared in order to study their physical properties, before and after coking. SEM micrographs employed to analyze the microstructures to determine the effect of graphite and antioxidant on corrosion behavior of the refractory. Results showed that oxidation process of carbon in the system was hindered and improved corrosion resistance by introducing graphite and antioxidant into the refractory composition.
A. Shokuhfar, S. Ahmadi, H. Arabi, S. Nouri,
Volume 6, Issue 3 (Summer 2009 2009)

Abstract: Guinier-Preston (GP) zone formation and precipitation behavior of T1 (Al2CuLi) phase during the ageingof an Al-Cu-Li-Zr alloy was studied by differential scanning calorimetry (DSC) technique and electrical resistancemeasurement of the samples. Results show that endothermic effects in the thermograms of the alloy between 180°Cand 240°C can be related to the enthalpy of GPzones dissolution. Formation of GPzones in the structure increasedhardness, tensile strength and electrical resistance of the Al-Cu-Li-Zr alloy. Furthermore, precipitation of T1 phaseoccurred in temperature range of 250ºC to 300ºC whereas its dissolution occurred within the temperature of 450-530ºC. Activation energies for precipitation and dissolution of T1 phase which were determined for the first time inthis research, were 122.1(kJ/mol) and 130.3(kJ/mol) respectively. Results of electrical resistance measurementsshowed that an increase in the aging time resulted in the reduction of electrical resistance of the aged samples.
S. Ahmadi,, H. R. Shahverdi*, S. S. Saremi,
Volume 7, Issue 4 (Autumn 2010 2010)

Abstract: In this research work, crystallization kinetics of Fe55Cr18Mo7B16C4 alloy was evaluated by X-ray diffraction, TEM observations and differential scanning calorimetric tests. In practice, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates. Results showed that a two -step crystallization process occurred in the alloy in which - Fe phase was crystallized in the first step after annealing treatments. Activation energy for the first step of crystallization i.e. - Fe was measured to be 276 (kj/mol) according to Kissinger model. Further, avrami exponent calculated from DSC curves was 2 and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline á – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.

M. Sh. Bafghi, A. Yarahmadi, A. Ahmadi, H. Mehrjoo,
Volume 8, Issue 3 (september 2011 2011)


the reduction agent. Pellets of barite ore containing about 95% BaSO

temperature, time, ore grain size and the type and grain size of the carbon materials. Graphite, coke and charcoal have

been used as the reducing agent and the reduction experiments have been performed in the temperature range of 925-

1150 °C. Apart from conducting the experiments using pellets made of ore powder, kinetic analysis of the experimental

data by use of the reduced (dimensionless) time method has been another unique feature of the present study.

Experimental results show that grain size of either carbon material or barite ore has not appreciable effect on the

reaction rate. Kinetic analysis of the experimental data revealed the rate is strongly controlled by the chemical reaction

of carbon gasification (Boudouard reaction). The reaction rate is very considerably related to the type of carbon

material so that the activation energy varies from 15.6 kcal.mol



The present study deals with the reduction of barium sulfate (Barite) to barium sulfide by use of carbon as4 has been reduced under different conditions of-1 for charcoal to 26.3 kcal.mol-1 for graphite and 20.8-1 for coke. This behavior provides further support for the postulated reaction mechanism, i.e., carbon
S. Ahmadi, H. R. Shahverdi,
Volume 10, Issue 4 (december 2013)

Crystallization kinetics of Fe52Cr18Mo7B16C4Nb3 alloy was evaluated using X-ray diffraction, differential scanning calorimetric (DSC) tests and TEM observations in this research work. In effect, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates (10, 20, 30, 40 K/min) and kinetic models (i.e. Kissinger- Starink, Ozawa, and Matusita methods). Results showed that a two -step crystallization process occurred in the alloy in which α - Fe and Fe3B phases were crystallized respectively in the structure after heat treatment. Activation energy for the first step of crystallization i.e., α - Fe was measured to be 421 (kj/mol) and 442 (kj/mol) according to both Kissinger- Starink and Ozawa models respectively. Further, Avrami exponent calculated from DSC curves was 1.6 and a two -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. TEM observations reveal that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology
S. Ahmadi, H.r. Shahverdi, H. Arabi,
Volume 11, Issue 3 (september 2014)

This study is focused on the effects of electroslag remelting by prefused slag (CaO, Al2O3, and CaF2) on macrostructure and reduction of inclusions in the medical grad of 316LC (316LVM) stainless steel. Results showed that in order to obtain uniform ingot structures during electroslag remelting, the shape and depth of the molten pool should be carefully controlled. High melting rates lead to deeper pool depths and interior radial solidification characteristics. Furthermore, decrease in the melting rate caused more reduction of non-metallic inclusions. In practice, large shrinkage cavities formed during the conventional casting process in the primary ingots were the cause of the fluctuation in the melting rate, pool depth and extension of equiaxal crystals zone
S Ahmadi, H. R. Shahverdi,
Volume 11, Issue 4 (December 2014)

Achieving extreme hardness in the newly synthetic steel formed by converting from initial amorphous state to subse-quent crystalline structure –named as devitrification process- was studied in this research work. Results of TEM observa-tions and XRD tests showed that crystallized microstructure were made up four different nano-scale phases i.e., α-Fe, Fe 36 Cr12 Mo10 , Fe 3 C and Fe3 B. More, Vickers hardness testing revealed a maximum hardness of 18.6 GPa which is signifi-cantly harder than existing hardmetals. Detailed kinetic and structural studies have been proof that two key factors were contributed to achieve this extreme hardness supersaturation of transition metal alloying elements (especially Nb) and also reduction in the structure to the nano-size crystals.
A. Ahmadi, A. A. Youzbashi, A. Nozad, A. Maghsoudipour, T Ebadzadeh,
Volume 11, Issue 4 (December 2014)

Synthesis of YSZ nanopowder by alkoxide sol-gel method, through two different hydrolysis routes, one under careful control by using acetyacetone as ligand, and the other through basic hydrolysis, was investigated. The synthesized powders were characterized by various analytical techniques such as, XRD, STA, PSA, BET, SEM, and TEM. The results showed that, the YSZ powders prepared through the basic hydrolysis route consist of weakly agglomerated nanosized spherical particles whereas the products obtained through the controlled hydrolysis route, consist of hard irregular shaped agglomerates. Sinterability of these powders was examined at 1480 °C, which showed that the powder synthesized through the basic hydrolysis route attains a density of 94%, against 60% for the other case. It was therefore concluded that, alkoxide sol-gel method through basic hydrolysis route, can be more suitable for the synthesis of YSZ nanopowder and its subsequent sintering.
S. Ahmadi, H. R. Shahverdi,
Volume 12, Issue 2 (June 2015)

Crystallization of α – Fe phase during annealing process of Fe55Cr18Mo7B16C4 bulk amorphous alloy has been evaluated by X- ray diffraction, differential scanning calorimetric tests and TEM observations in this research. In effect, crystallization mechanism and activation energy of crystallization were evaluated using DSC tests in four different heating rates (10, 20, 30, 40 K/min). A two -step crystallization process was observed in the alloy in which α–Fe phases was crystallized in the first step after annealing process. Activation energy for the first step of crystallization process (i.e. α – Fe phase) was measured to be 276 (Kj/mole) according to Kissinger kinetic model. Furthermore, Avrami exponent calculated from DSC curves was two and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology
K. Susilo, A. Ahmadi, O. S. Suharyo, P. Pratisna,
Volume 14, Issue 2 (June 2017)

Indonesian Navy (TNI AL) is the main component for Maritime Security and Defence. Because of that, TNI AL needs Indonesian Warship (KRI) to covered Maritime area. The main requirement from KRI is fulfilled by demand. To pock of fuel demand from KRI at Naval Base, it needs a new pipeline of fuel distribution network system. The pipeline network system used for maximum lifetime must be protected from corrosion. Basically, there are five methods of corrosion control such as change to a more suitable material, modification to the environment, use of protective coating, design modification to the system or component, and the application of cathodic or anodic protection. Cathodic protection for pipeline available in two kinds, namely Sacrifice Anode and Impressed Current Cathodic Protection (ICCP). This paper makes analysis from design of Impressed Current Cathodic Protection and total current requirement in the method. This paper showed both experimental from speciment test and theoritical calculation. The result showed that design of Impressed Current Cathodic Protection on fuel distribution pipeline network system requires voltage 33,759 V(DC), protection current 6,6035 A(DC) by theoritical calculation and 6,544 A(DC) from pipeline specimen test, with 0,25 mpy for corrosion rate. Transformer Rectifier design needs requirements 45 V with 10 A for current. This research result can be made as literature and standardization for Indonesian Navy in designing the Impressed Current Cathodic Protection for fuel distribution pipeline network system.

Hedayat Gholami, Hassan Koohestani, Mehdi Ahmadi,
Volume 18, Issue 1 (March 2021)

In this research, using impregnation method, spinel cobalt and copper ferrites nanoparticles are synthesized on the surface of hematite. Synthesized powders were characterized and examined by FTIR, XRF, XRD, FESEM, BET and EDS analysis and the dye degradation were investigated by UV-vis and AAS methods. Specific surface area increased especially in the sample containing cobalt, which indicates the precise of synthesis and the creation of high surface nano particles at hematite surface. The size of particles was in the nano scale and a good uniformity observed in the structure. The results indicated a significant increase in the catalytic ability of hematite nano composite after synthesis. Their catalytic capability investigated by the Fenton reaction with complete removal of methylene blue from the solution via UV-vis irradiation. The samples stability discovered to be excellent by the AAS method.
Reza Mirahmadi Babaheydari, Seyed Oveis Mirabootalebi, Gholam Hosein Akbari Fakhrabadi,
Volume 18, Issue 1 (March 2021)

Cu-based alloys have a wide range of applications in the electronics industry, communications industry, welding industries, etc. Regarding the type and percentage of the second phase, changing in the alloying elements has a significant effect on the mechanical and electrical properties of copper composites. The aim of the present work is to synthesize, investigate, and compare the micro-structure, micro-hardness, and electrical properties of different Cu-based nanocomposites. For this purpose, Cu-Al, Cu-Al2O3, Cu-Cr, and Cu-Ti were fabricated via ball milling of copper with 1, 3, and 6 weight percentages. The vial speed was 350 rpm and the ball-to-powder weight ratio was kept at 15:1. The milling process was performed at different times in Argon. Next, the prepared composites were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and dynamic light scattering (DLS). Based on XRD patterns, crystallite size, lattice strain, and lattice constant were calculated by Rietveld refinement using Maud software. The results show a decrease of crystallite size, and an increase of the internal strain and lattice constant by rising the alloying elements in all composites. Then, the produced powders compressed via the cold press and annealed at 650˚C. Finally; the micro-hardness and the electrical resistance of the manufactured tablets were measured. The results of these analyses show that micro-hardness is increased by enhancement of the reinforcement material, due to the rising of the work hardening. Cu-6wt%Ti with 312 Vickers and Cu-1wt%Al2O3 with 78 Vickers had the highest and lowest micro-hardness, respectively. Moreover, the results of the electrical resistance indicate a dramatic rise in the electrical resistance by increasing the amount of alloying material, which Cu-1wt%Al with 0.26 Ω had the highest electrical conductivity.
Sara Ahmadi, Bijan Eftekhari Yekta, Hossein Sarpoolaky, Alireza Aghaei,
Volume 18, Issue 4 (December 2021)

In the present work, monolithic gels were prepared through different drying procedures including
super critical, infrared wavelengths and traditional drying methods. Dense and transparent glasses
were obtained after controlled heat treatment of the dried porous xerogels in air atmosphere.
The chemical bonding as well as different properties of the prepared gels and the relevant glasses
were examined by means of Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmitt-
Teller (BET) and UV-Vis spectrometer. Based on the obtained results, different drying conditions
affect the average pore size and the total pore volume of the studied gels. The mean pore size was
found to be 8.7 nm, 2.4 nm and 3.2 nm for super critical, IR radiation and slow drying in air
atmosphere, respectively. The glass network structure was significantly changed by heat treatment  temperature so that the B-O-Si bonds were formed only after 450 °C. It was found that the gel dried under super critical condition was unable to reach to its full density all over the selected sintering temperature interval.

Mohammad Molaahmadi, Majid Tavoosi, Ali Ghasemi, Gholam Reza Gordani,
Volume 20, Issue 2 (June 2023)

Investigation the structural and magnetic properties of nanocrystalline Co78Zr17B2Si1W2 alloy during melt spinning and annealing processes were the main goal of this study. In this regard, samples were prepared using vacuum induction melting, melt spinning and subsequent annealing. The specimens were evaluated using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM). Based on results, nanocrystalline Co5Zr single phase with hard magnetic properties (Ms=29.5 emu/g and Hc=2.7 kOe) successfully formed during melt spinning process (at wheel speed of 40 m.s-1). The coercivity value of rapid solidified sample increased to about 3.2 kOe during annealing process up to 400°C. However, more increasing in annealing temperature lead to the transformation of non-equilibrium magnetic Co5Zr phase to stable Zr2Co11 phase, which has distractive effects on final magnetic properties.
Leila Taghi-Akbari, Mohammad Reza Naimi-Jamal, Shervin Ahmadi,
Volume 20, Issue 4 (December 2023)

Two-dimensional molybdenum disulfide (MoS2) is used as a promising flame retardant and smoke suppressant nano additive in polymer composites due to its high thermal stability and layered structure. In this study, thermoplastic polyurethane (TPU) was melt-blended with MoS2 (1wt. %) and a halogen-free intumescent flame retardant (IFR) system. The IFR system consisted of ammonium polyphosphate (APP), Melamine polyphosphate (MPP), and pentaerythritol (PER), with a total amount of 25 wt. %. The TPU/IFR/MoS2 composite exhibited outstanding flame-retardant properties, achieving a UL-94 V-0 rating and a limiting oxygen index (LOI) value of 34%. Reaction-to-fire performance of the TPU/IFR/MoS2 composite was evaluated by cone calorimeter test (CCT). The CCT results indicated high flame-retardant efficiency and considerable smoke suppression performance, along with a significant decrease in the peak heat release rate (PHRR: 65.9%), peak smoke production rate (PSPR: 65.6%), and peak CO production (PCOP: 60.7%) compared to the neat TPU. The significant improvement in fire performance of TPU composite was mainly attributed to the effects of the physical barrier of MoS2 and catalytic carbonization of the IFR system. These resulted in forming an intumescent compact carbonized layer during the combustion, effectively restricting dripping. The continuous structure of the residual char was revealed by FESEM. Thermogravimetric analysis (TGA) indicated improved thermal behavior of the TPU composite in high temperatures. This work provides an effective method to improve the reaction to fire of TPU composites by incorporating traditional IFRs and MoS2, resulting in enhanced fire safety.

Sara Ahmadi, Reza Momeni,
Volume 20, Issue 4 (December 2023)

The polymer modified cementitious tile adhesives are very significant in construction sector. In order to considerably improve the bond qualities of the tile adhesive in polymer modified mortars, the proportions of constituent ingredients should be carefully selected. Consequently, to design high performance tile adhesives, interactions between all the components, such as the adhesion mechanisms between the polymers film and the substrate and the effect of various additives should be recognized. The effect of vinyl acetate ethylene (EVA), high alumina cement (HAC), and additives such as calcium formate and polycarboxylate on the adhesion qualities of ceramic tile adhesive was explored in this study. The findings indicated that these ingredients had an impact on the mortars' adhesive properties, and it is necessary to find their optimal amounts in order to achieve the maximum adherence. The results showed that the tensile strength of mortar was increased with increasing the polymer amounts. A microstructural analysis revealed that the polymer was distributed homogenously throughout the mortar.  The optimum amount of the used high alumina cement was determined 3 wt.%. Additionally, increasing the amount of accelerator and super plasticizer increased the tensile strength of ceramic tile adhesive by approximately 20-30%.

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