Showing 472 results for Al
M. Adeli, M. Shekari, S. H. Seyedein, M. R. Aboutalebi,
Volume 7, Issue 2 (6-2010)
Abstract
Combustion synthesis is a special thermophysico-chemical process applied for production of intermetallic compounds. In the present work, a reaction–diffusion numerical model was developed to analyze the combustion synthesis of aluminide intermetallics by self-propagating high-temperature synthesis process. In order to verify the reliability of the numerical model, an experimental setup was designed and used to perform the combustion synthesis of nickel and titanium aluminides. The developed model was further used to determine the temperature history of a powder mixture compact during self-propagating high-temperature synthesis. The effect of compact relative density on combustion temperature and wave propagation velocity was also studied.
A.m. Rashidi, A. Amadeh,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
nanocrystalline nickel samples with the grain size of ~25 nm were prepared via direct current electrodeposition and
aluminized for different durations by pack cementation method at 500
means of SEM, EDS and XRD techniques. According to results, short time aluminizing resulted in the formation of a
single aluminide layer whereas at long duration two distinct aluminide layers were formed. The growth kinetics of the
coating was non-parabolic at short times while it obeyed the parabolic law at long duration. The parabolic growth
rate constant of single phase coating formed on electrodeposited samples was about 30 ìm / h1/2 approximately 3 times
greater than the data reported for coarse grained nickel (8.4 ìm / h1/2). Meanwhile, the overall growth rate constant
was decreased to 11.7 ìm / h1/2, when double aluminide layers formed on nanocrystalline nickel.
In this research, aluminizing behavior of ultra fine-grained nickel was investigated. For this purpose,oC. The aluminide layers were examined by
N. Anjabin, Karimi Taheri,
Volume 7, Issue 2 (6-2010)
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
A. Noorian, Sh. Kheirandish, H. Saghafian,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
mechanical properties of AISIH 13 hot-work tool steel have been studied. Cast samples made of the modified new steel were homogenized and austenitized at different conditions, followed by tempering at the specified temperature ranges. Hardness, red hardness, three point bending test and Charpy impact test were carried out to evaluate the mechanical properties together with characterizing the microstructure of the modified steel using scanning electron microscope. The results show that niobium addition modifies the cast structure of Nb–alloyed steel, and increases its maximum hardness. It was found that bending strength bending strain, impact strength, and red hardness of the modified cast steel are also higher than those of the cast H13 steel, and lower than those of the wrought H13 steel.
In this research, the effects of partially replacing of vanadium and molybdenum with niobium on the
M.sh. Bafghi, A.h. Emami, A. Zakeri, J. Vahdati Khaki,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
has been investigated. It has been shown that the mechanism of leaching reaction is diffusion through the product layer
and does not undergo any change as a result of mechanical activation in a wide range of experimental conditions.
Leaching rate is strongly influenced by milling intensity and the effect of ball to powder mass ratio is stronger than
milling time. Curve fitting of experimental data shows that leaching rate constant is approximately a linear function
of ball to powder mass ratio, while it obeys a power function with regard to the milling time.
The kinetics of chalcopyrite leaching in a ferric sulfate media for raw and mechanically activated samples
K. Christine Stella, A. Samson Nesaraj,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
as magnetic materials, semiconductors, pigments, catalysts, refractories and electronic ceramics. In this paper, we
reported the preparation of NiAl
The resulting powder was chracterized by XRD, particle size analysis and SEM. The XRD patterns show that the
combustion technique was excellent to prepare single – phased cubic NiAl
found to be around 14 nm. From the particle size analysis, it was found that the 50 % of the particles lie below 30
µm. The micrographs show the formation of fluffy agglomerates composed of fine particles.
Spinels constitute an advanced group of materials with great technologial appeal, being able to be applied2O4 spinels by low temperature combustion technique using glycine and urea as fuels.2O4 particles and the crystallite sizes were
M. Nusheh*, H. Yoozbashizadeh,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
the competition between the precipitation of cobalt ions and evolution of hydrogen gas on the cathode surface during
the reduction process in a sulfate bath, investigation on the mechanism of metal precipitation is of great importance.
In the present work, study on the kinetics of cobalt electrowinning and the mechanism of the involved reactions have
been carried out. The obtained results, confirm the mechanism of cobalt precipitation by depletion of hydroxides. The
effects of temperature and scan rate parameters were studied on electrowinning of cobalt by cyclic voltammetry
technique. The diffusion coefficient and rate constant of the reactions were measured and calculated by performed
experiments.
Nowadays cobalt is mostly produced through the electrowinning process of sulfate solutions. Regarding to
Mr Mohammadtaher Safarzadeh, Mr Seyed Mohammad Ali Boutorabi, Mr Asghar Arab,
Volume 7, Issue 3 (8-2010)
Abstract
The effects of anodizing condition and post treatment on the growth of nickel nanowires, were investigated. A two-step anodizing process was applied in phosphoric and oxalic acid solution. Nickel electrochemical plating was applied to fill Anodic Aluminum Oxide (AAO) pores. For pore filling enhancement, AAO surfaces were treated by silver predeposition. After electroplating, aluminum and oxide layer of some specimens were removed. The results showed that silver preplating increases the pore filling and as the applied voltage becomes higher, the pores diameter decreases.
Saber Khoshjavan, Mohammad Heidary, Dr Bahram Rezai,
Volume 7, Issue 3 (8-2010)
Abstract
Free swelling index (FSI) is an important parameter for cokeability and combustion of coals. In this research, the effects of chemical properties of coals on the coal free swelling index were studied by artificial neural network methods. The artificial neural networks (ANNs) method was used for 200 datasets to estimate the free swelling index value. In this investigation, ten input parameters such as moisture, volatile matter (dry), fixed carbon (dry), ash (dry), total sulfur (organic and pyretic)(dry), (British thermal unit (Btu)/lb) (dry), carbon (dry), hydrogen (dry), nitrogen (dry) as well as oxygen (dry) were used. For selecting the best model for this study the outputs of models were compared. A three-layer ANN was found to be optimum with architecture of ten and four neurons in first and second hidden layer, respectively, and one neuron in output layer. Results of artificial neural network shows that training, testing and validating data’s square correlation coefficients (R2) achieved 0.99, 0.92 and 0.96, respectively. The sensitivity analysis showed that the highest and lowest effects of coal chemical properties on the coal free swelling index were nitrogen (dry) and fixed carbon (dry), respectively.
Keywords: Coal Chemical Properties, Free Swelling Index, Artificial Neural Networks (ANNs), Cokeability and Back Propagation Neural Network (BPNN).
Mrs Somaye Alamolhoda, Dr Saeed Heshmati-Manesh, Dr Abolghasem Ataie,
Volume 7, Issue 3 (8-2010)
Abstract
In this research an ultra-fine grained composite structure consisting of an intermetallic matrix together with dispersed nano-sized Al2O3 obtained via mechanical activation of TiO2 and Al in a high energy ball mill and sintering of consolidated samples. Phase composition and morphology of the milled and sintered samples were evaluated by XRD and SEM techniques Thermal behavior of the powder sample milled for 8 hours was evaluated by DTA technique. DTA results showed that, the reaction happens in two steps. The first step is the aluminothermic reduction of TiO2 with Al. XRD observations reveals that minor amount of Ti3Al phase formed during reduction reaction together with TiAl and Al2O3 major phases. This intermetallic phase disappeared when sintering temperature was increased to 850 ºC. The second step in DTA is related to a reaction between residual Al in the system (partly dissolved in TiAl lattice) and the Ti3Al phase produced earlier at lower temperatures. SEM micrographs reveal that by completion of the reduction reaction more homogeneous and finer microstructure is observable in sintered samples.
Khodamorad Abbaszadeh, Shahram Kheirandish, Hassan Saghafian,
Volume 7, Issue 3 (8-2010)
Abstract
The effects of lower bainite volume fraction on tensile and impact properties of D6AC ultrahigh strength steel were studied in the current work. To obtain mixed microstructures containing martensite and different volume fractions of the lower bainite, specimens were austenitized at 910° C, then quenched in a salt bath of 330°C for different holding times, finally quenched in oil. In order to obtain fully martensitic and bainitic microstructures, direct oil quenching and isothermal transformation heat treatment for 24 hours were used respectively. All specimens were double tempered at 200°C for 2 hours per tempered. Microstructures were examined by optical and scanning electron microscopes. Fracture morphologies were studied by scanning electron microscopy (SEM). Results showed that both yield and ultimate tensile strength generally decreased with an increase in volume fraction of lower bainite. However, a few exceptions were observed in the mixed microstructures containing 12% lower bainite, showing a higher strength than the fully martensitic microstructure. This can be explained on the basis of two factors. The first is an increase in the strength of martensite due to the partitioning of the prior austenite grains by lower bainite resulting in the refinement of martensite substructures. The second is a plastic constraint effect leading to an enhanced strength of lower bainite by the surrounding relatively rigid martensite. Charpy V-notch impact energy and ductility is improved with increasing the volume fraction of lower bainite.
A. Jafaria, S. H. Seyedeina, M. R. Aboutalebia, D. G. Eskinb, L. Katgermanb,
Volume 7, Issue 3 (8-2010)
Abstract
ABSTRACT Macrosegregation has been received high attention in the solidification modeling studies. In the present work, a numerical model was developed to predict the macrosegregation during the DC Casting of an Al-4.5wt%Cu billet. The mathematical model developed in this study consists of mass, momentum, energy and species conservation equations for a two-phase mixture of liquid and solid in an axisymmetric coordinates. The solution methodology is based on a standard Finite Volume Method. A new scheme called Semi-Implicit Method for Thermodynamically-Linked Equations (SIMTLE) was employed to link energy and species equations with phase diagram of the alloying system. The model was tested by experimental data extracted from an industrial scale DC caster and a relatively good agreement was obtained. It was concluded that a proper macrosegregation model needs two key features: a precise flow description in the two-phase regions and a capable efficient numerical scheme
P. Karimi, K. S. Hui, K. Komal,
Volume 7, Issue 3 (8-2010)
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
Z. Ghaferi, K. Raeissi, M. A. Golozar,, A. Saatchi, S. Kabi,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract:
current densities. Electrochemical impedance spectroscopy (EIS) results showed that the codeposition mechanism of
tungsten in Ni-W deposition is the reduction of tungsten oxide which changed to the reduction of tungsten-containing
ion complexes at higher current densities. In Co-W electrodeposition, the tungsten codeposition takes place via
reduction of tungsten oxide, although, the role of tungsten-containing complexes at higher current densities cannot be
ruled out. The surface morphology of Ni-W coatings was crack-free and was strongly dependent on deposition current
density. In addition, higher grain size and lower tungsten content were obtained by increasing the current density. In
Co-W coatings, no obvious variation in surface morphology was observed except for the fine cracks appeared at
higher current densities. In this system the grain size remained almost constant with increasing current density. The
microhardness values of Ni-W and Co-W coatings decreased due to the increase in the grain size and/or decrease in
tungsten content.
Ni-W and Co-W alloy nanocrystalline coatings were electrodeposited on copper substrate at different
H. Rafiee*,, S. Rastegari, H. Arabi, M. Mojaddami,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract:
activity gas diffusion process has been investigated in this research. Effects of coating temperature and aluminum
concentration in powder mixture on formation mechanism were studied using optical and scanning electron
microscopes, EDS and X-ray diffraction (XRD) techniques. For this purpose two different packs containing 1 and 2
wt% aluminum powder, were used for coating the samples at two temperatures, 850ºC and 1050ºC. The ratio of Al to
activator was kept constant in both packs. By increasing the Al content in high activity powder mixture, the
concentration of diffused Al increased in the coating layers, and the thickness of coating increased. At 1050ºC as the
rate of diffused Al to the interdiffusion zone increased, this zone gradually transformed to outer coating phases. At
850ºC coating formed by inward diffusion of Al, but at 1050ºC it was initially formed by inward diffusion of Al followed
by outward diffusion of Ni.
Formation mechanism of an aluminide coating on a nickel base superalloy IN738LC via a single step high
Y. Fouad,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract: Rotating bending fatigue tests have been performed using smooth specimens of a rolled AZ31 magnesium alloy in laboratory air at ambient temperature. Fatigue strength and characteristic was evaluated and fracture mechanism was discussed on the basis fracture surface analysis. Electrical polishing (EP) as well as deep rolling (ball burnishing (BB)) U-notched specimens were performed on two groups of samples, to evaluate optimum conditions for fatigue life. The microstructure and tensile properties of roll cast (RC) Mg- 3% Al- 1% Zn (AZ31) was investigated. The fatigue strength of 107 cycles around 100 MPa for deep rolling while it was around 40 MPa for Electrical polishing. It was very important to understand the effect of (ball burnishing (BB)) conditions on the hardness of the surface through to the core. The two procedures improved the fatigue performance, but better improve in results were found in ball burnishing. The growth of small cracks initiated at the surface coincided with the FCP characteristic after allowing for crack closure for large cracks, but the operative fracture mechanisms were different between small and large cracks. At the subsurface crack initiation site, smooth facets were always present regardless of applied stress level.
M. Rezvani*,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract: In the present work, effect of the nucleating agent such as TiO2, ZrO2, P2O5, Ye2O3 and CeO2 in single, double, triple and fourth systems on the crystallization behavior of various compositions was studied. Using differential thermal analysis (DTA), the composition of Li2O-Al2O3-SiO2 (LAS) was optimized and the coefficient of thermal expansion (CTE), three point flexural strength, hardness, thermal shock resistance, and chemical resistance of the most favorable composition were evaluated. The crystalline phase was determined by the x-ray diffractometry. Moreover, the micro-structure of the samples was studied by SEM technique. According to the results, -Eucryptites (high quartz solid solution) was the main crystalline phase and the CTE values of the optimized sample were determined as 1.65-1.93 10-6 in the temperature range of 20-500 oC. Furthermore, three point bending strength ranged from 139 to 155 MPa.
S. Ahmadi,, H. R. Shahverdi*, S. S. Saremi,
Volume 7, Issue 4 (10-2010)
Abstract
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. Farzalipour Tabriz, M. Ghassemi Kakroudi*,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract: Cordierite-Mullite based kiln furnitures are widely used in fast-firing of ceramic products because of their low thermal expansion which confer them a very good ability to thermal shock resistance. Difference in CTE of constituent phase can develop damage during thermal cycling due to internal stresses. Increase in industrial competitiveness leads to the development of new means for extending refractory life and increasing reliability of industrial tools so investigations regarding the structuralmechanical behaviour of refractory systems are becoming essential. In this paper, Thermo-mechanical design of commercial Cordierite-Mullite based kiln furniture was investigated by using finite element method (FEM) and possible solutions for improvement of working life have been considered. The results indicated that the change of the kiln furniture geometry can decrease the maximum thermomechanical stress in study conditions which can prolong the refractory service life. Obtained results indicate the existence of an optimal thickness for the section under maximum thermo-mechanical stress. Increasing filet radius of ring region from 3 to 9 mm decreases thermo-mechanical stress value from 113 to 93 MPa.
M. Kazemimoghadam, and T. Mohammad,
Volume 8, Issue 1 (3-2011)
Abstract
Abstract: Nano pore Mordenite membranes were prepared on the outer surface of ceramic tubular tubes via hydrothermal synthesis and evaluated for dehydration pervaporation of water unsymmetrical dimethylhydrazine UDMH mixtures. Highly water-selective mordenite membranes were prepared and the optimum reaction condition was found to be 24 h crystallization time and 170 °C crystallization temperature. Effect of gel composition on separation factor and water flux of the water-UDMH mixtures was investigated. X-ray diffraction (XRD) patterns showed that mordenite is the only zeolite material which presents in the membrane. Morphology of the supports subjected to crystallization was characterized by Scanning electron microscopy (SEM). In PV of the water-UDMH mixtures, the membrane exhibits a hydrophilic behavior, with a high selectivity towards water and a good flux. The best membranes had a water flux of 2.67 kg/m2.h at 27 °C. The best PV selectivity was obtained to be 264.
