Showing 366 results for Co
B. A. Ganji, B. Yeop Majlis,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract: In this paper, a DRIE process for fabricating MEMS silicon trenches with a depth of more than 250 m is described. The DRIE was produced in oxygen-added sulfur hexafluoride (SF6) plasma, with sample cooling to cryogenic temperature using a Plasmalab System 100 ICP 180 at different RF powers. A series of experiments were performed to determine the etch rate and selectivity of the some masking materials such as resists, and metal (Al). Experiments show that different materials have different etch rates, but for the Al mask, an etch rate of 5.44x10-3 nm/min was achieved, that exhibits very stronger resistance against RIE than resists. By controlling the major parameters for plasma etch, an etch rate of 2.85 microns per minute for silicon and a high selectivity of 5.24x105 to the Al etch mask have been obtained. A 90 min etching experiments using etching gas SF6 of 60 standard cubic centimeters per minutes (sccm) with oxygen (13 sccm) were performed by supplying RF power of 5 W to an ICP of 600 watts, and silicon etching process with a depth of 257 m was demonstrated. Our experiments show that Al is the best mask material for very deep trenches in silicon.
M. Ardestani,, H. Razavizadeh,, H. Arabi, H. R. Rezaie,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract:
materials can be fabricated by sintering of W-Cu composite powders. In this research W-20%wt Cu composite powders
was synthesized via a co-precipitation method. Precipitate obtained from a mixture of copper nitrate and ammonium
paratungstate (APT) in distilled water contained W-Cu compounds. This precipitate was washed, dried and calcined
at 550
of dried precipitate powder was determined by thermogravimetry (TG), differential thermal analysis (DTA) and X-ray
diffraction (XRD). The sintering of the reduced powders was investigated as a function of temperature. Relative density
of more than 98% obtained for the powders sintered at 1200
close to theoretical calculations. The hardness of the sintered powders was 320 Vickers.
W-Cu composites are widely used as contacts, heat sinks and electro discharge electrodes. These kinds of°C in air and then reduced in H2 atmosphere in order to convert to W-Cu powders. The calcination temperature°C . The corresponding electrical conductivity was too
A. H. Emami, M. Sh. Bafghi, J. Vahdati Khaki, A. Zakeri,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract:
the changes of BET surface area of a mineral substance during intensive grinding process. Validity of the proposed
model was tested by the experiments performed using a natural chalcopyrite mineral as well as the published data. It
was shown that the model can predict the experimental results with a very good accuracy and can be used to predict
what may happen under the similar experimental conditions.
Based on experimental observations, a model has been developed to describe the effect of grinding time on
Ali. A. Hosseini,, F. Ghaharpour, H. Rajaei ,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: In this paper‚ the physical and mechanical properties of Al nanocomposite reinforced with CNTs wereinvestigated. High purity Al powder and Carbon Nanotubes (CNTs) with different percentage were mixed by ballmilling method and the composite was fabricated by cold pressing followed by sintering technique. The variation ofdensity and hardness of composite with CNTcontent was investigated. The microstructure of composite was evaluatedby SEM (Scanning Electron Microscope) and XRD (X -Ray Diffraction). The results show that the density and hardnessincrease with CNTpercentage.
S. Zavareh, F. Majedi,, M. Sh. Sharif, F. Golestanifard,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: Multiwalled carbon nanotubes (MWCNTs) were coated with MgO nano particles using simple precipitationmethod. The growth of Mg(OH)2particles was controlled by adjusting the alkaline concentration, salt concentrationand feed rate in simple precipitation method. The nanometer-sized Mg(OH)2particles were precipitated on the surfaceof functionalized MWCNTs by reaction between MgSO4 solution and NH4OH. The samples have been characterizedby scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction and thermal gravimetricanalysis. The results showed a nominally complete MgO coating over the entire outer surface of MWCNTs resulting inimprovement of their oxidation durability.
A. Davoodi, J. Pan,ch. Leygraf, Gh. R. Ebrahimi, M. Javidani,
Volume 6, Issue 3 (9-2009)
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.
B. Tolaminejad, A. Karimi Taheri, H. Arabi, M. Shahmiri,
Volume 6, Issue 4 (12-2009)
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
Arash Yazdani, Mansour Soltanieh, Hossein Aghajani,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract: In this research plasma nitriding of pure aluminium and effect of iron elemental alloy on the formation and growth of aluminium nitride was investigated. Also corrosion properties of formed AlN were investigated. After preparation, the samples were plasma nitrided at 550oC, for 6, 9 and 12 h and a gas mixture of 25%H2-75%N2. The microstructure and phases analysis were investigated using scanning electron microscopy and X-ray diffraction analysis. Moreover corrosion resistance of samples was investigated using polarization techniques. The results showed that only a compound layer was formed on the surface of samples and no diffusion zone was detected. Dominant phase in compound layer was AlN. Scanning electron microscopy results showed that nitride layer has particulate structure. These nitrided particles have grown columnar and perpendicular to the surface. It was also observed that the existence of iron in the samples increases the nitrogen diffusion, thus growth rate of iron containing nitrides are higher than the others. Corrosion tests results showed that formation of an aluminium nitride layer on the surface of aluminium decreases the corrosion resistance of aluminium significantly. This is due to elimination of surface oxide layer and propagation of cracks in the formed nitride layer
A. Bahrami, M. R. Hosseini, M. Pazouki,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract:
point of view. In this study, a shaking-table was used for concentrating a manganese ore sample from the Ghasem Abad
area in Kerman, Iran. Experiments were designed by using L
The influence of each variable and their interactions on the operation of the device was studied. The variables under
investigation were: table slope, table frequency, water flowrate, feed rate, and particle size. The manganese
concentrate grade, recovery, and separation efficiency were used as response variables. It was shown that water
flowrate, table slope, feed rate, and particle size are the significant variable on concentrate grade while, all the
variables influence manganese recovery. Also, water flowrate, table slope, and table frequency have an important
effect on manganese separation efficiency. Finally, three mathematical models were presented to predict the values of
each response variables.
Among all gravity concentration methods, the shaking-table is the most effective one from the metallurgical8 Taguchi design with five variables, each in two levels.
M. Esmailian,
Volume 7, Issue 1 (3-2010)
Abstract
Abstract:
transformation temperature and different ferrite morphologies in one Nb-microalloyed (HSLA) steel has been
investigated. Three different austenite grain sizes were selected and cooled at two different cooling rates for obtaining
austenite to ferrite transformation temperature. Moreover, samples with specific austenite grain size have been
quenched, partially, for investigation on the microstructural evolution.
In order to assess the influence of austenite grain size on the ferrite transformation temperature, a temperature
differences method (TDM) is established and found to be a good way for detection of austenite to ferrite, pearlite and
sometimes other ferrite morphologies transformation temperatures.
The results obtained in this way show that increasing of austenite grain size and cooling rate has a significant influence
on decreasing of the ferrite transformation temperature.
Micrographs of different ferrite morphologies show that at high temperatures, where diffusion rates are higher, grain
boundary ferrite nucleates. As the temperature is lowered and the driving force for ferrite formation increases,
intragranular sites inside the austenite grains become operative as nucleation sites and suppress the grain boundary
ferrite growth. The results indicate that increasing the austenite grain size increases the rate and volume fraction of
intragranular ferrite in two different cooling rates. Moreover, by increasing of cooling rate, the austenite to ferrite
transformation temperature decreases and volume fraction of intragranular ferrite increases.
The effect of different austenite grain size and different cooling rates on the austenite to ferrite
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
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
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.
A. m. Hadian, B. Nazari,
Volume 7, Issue 3 (8-2010)
Abstract
ABSTRACT
Dolomite refractories have a good production potential in Iran
due to the existence of high-quality dolomite ore in many regions of the country, particularly in Isfahan and Hamedan. The basic problem associated with the production and use of this type of refractories is inherent tendency to hydration of calcined dolomite. One of the methods to overcome this problem is to increase the amount of magnesia in doloma. This study focuses on the use of Iranian dolomite to produce magnesia –doloma (mag-dol) refractory with high resistance to hydration and corrosion. It was found that addition of 20wt% magnesite to dolomite would result in capsulating of CaO by MgO that protects doloma from further hydration
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
