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Showing 20 results for Sem

Kaviani S., Marashi S. P. H.,
Volume 1, Issue 3 (9-2004)
Abstract

The surface condition and microstructure of near stoichiometric (Fe823Ndll.8B5.9) Nd-Fe-B alloy ribbons and the effect of melt spinning parameters were investigated using optical, scanning and transmission electron microscopes (SEM, TEM). The formation of gas pockets on the roll surface of the ribbons during melt spinning can prevent heat transform and result in local coarse grains. The local thickness would also be less in these places and thus perforates preferentially during ion beam milling. Therefore different areas of the sample should be carefully observed in the TEM. Reducing inert gas pressure in the chamber will eliminate the gas pockets. As a general trend, decrease in the ribbon thickness and mean Nd2 Fe14B grain size were observed on increasing the roll speed. By careful adjustment of the melt spinning parameters, the nanostructure will develop. An orientation relationship was found between Nd2 Fe14B and α-Fe precipitates for coarse grain samples melt spun at low roll speed. Dark field image of such grain also shows that some of these α-Fe precipitates have the same orientation. X-ray diffraction evident the development of texture by decreasing the roll speed.
M. Ghalambaz,, M. Shahmiri, Y. H. K Kharazi,
Volume 4, Issue 1 (6-2007)
Abstract

Abstract: Problems such as the difficulty of the selection of processing parameters and the large quantity of experimental work exist in the morphological evolutions of Semisolid Metal (SSM) processing. In order to deal with these existing problems, and to identify the effect of the processing parameters, (i.e. shearing rate-time-temperature) combinations on particle size and shape factor, based on experimental investigation, the Artificial Neural Network (ANN) was applied to predict particle size and shape factor SSM processed Aluminum A.356.0 alloy. The results clearly demonstrated that, the ANN with 2 hidden layers and topology (4, 2) can predict the shape factor and the particle size with high accuracy of 94%.The sensivity analysis also revealed that shear rate and solid fraction had the largest effect on shape factor and particle size, respectively. The shear rate had a reverse effect on particle size.
A. Nemati, K. Pourazarang,
Volume 5, Issue 3 (9-2008)
Abstract

Abstract: The PZT-based ceramics with a composition of Pb1.1-xLax (Zr0.53Ti0.47)O3, were prepared by conventional mixed oxide followed by mechanical alloying and sol-gel methods in which x was chosen in the range of 0.02–0.06. The samples were calcined in the range of 450 °C - 750 °C for 4h. The physical and electrical properties of the samples were determined as a function of the calcination temperature. The obtained data from two methods were compared with conventional mixed oxide method. Microstructural and compositional analyses of the samples were carried out using XRD and SEM. Dielectric properties of the samples were measured with an impedance analyzer. The ferroelectric properties of the PZT and PLZT samples were measured using the frequencies applying equipment and d33 tester. The results indicated a complete tetragonal phase prepared from both methods. It was shown that the addition of La and reduction in calcination temperature improved both the dielectric and piezoelectric properties. The dielectric constant tended to increase with doping content, giving the maximum value of about 2000 at 3 mol% La3+. In addition, the mechanical coupling factor (Qm) of the doped samples showed a significant decrease. Finally, the value of planar coupling factor (kp) reached the maximum value of 0.47 at 1 mol% La3+.
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.
M .shahmiri, , H. Arabi ,
Volume 6, Issue 4 (12-2009)
Abstract

  Abstract:

  The aims of this research were to investigate the effects of semisolid metal (SSM) processing parameters (i.e., shear rates –times – temperatures combinations) on the primary solidification products and isothermal holding duration, subsequent to cessation of stirring on the secondary solidification of Al-Si (A356) alloy.

  The dendrite fragmentation was found to be the governing mechanism of the primary dendritic to non-dendritic transformation, via rosette to final pseudo-spherical shapes during the primary solidification

The secondary solidification of the liquid in the slurry was not only a growth phenomenon but also promoted by 1) fresh heterogeneous nucleation and growth of dendrites and 2) the dendritic growth of the primary solidification products in the remaining liquid. Upon cessation of stirring and gradual disappearance of the prior shear force, the slurry relaxed, and the secondary solidification products pertained to conventional solidification condition
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

B. Mehrabi, M. Abdellatif, F. Masoudi,
Volume 8, Issue 2 (6-2011)
Abstract

Abstract: Ore mineral characterization and various experimental testwork were carried out on Asian Abe-Garm dolomite, Qazvin province, Iran. The testwork consisted of calcining, chemical characterization, LOI determination, and reduction tests on the calcined dolomite (doloma), using Semnan ferrosilicon. Calcining of dolomite sample was carried out at about 1400 ºC in order to remove the contained CO2, moisture, and other easily volatilised impurities. The doloma was milled, thoroughly mixed with 21% Semnan ferrosilicon and briquetted in hand press applying 30 MPa pressure. The briquettes were heated at 1125-1150 ºC and 500Pa in a Pidgeon-type tube reactor for 10-12 hours to extract the magnesium. Ferrosilicon addition, relative to doloma, was determined based on the chemical analyses of the two reactants using Mintek’s Pyrosim software package. Magnesium extraction calculated as 77.97% and Mg purity of 96.35%. The level of major impurities in the produced magnesium crown is similar to those in the crude metal production.
A. A. Hosseini, A. Sadigzadeh, S. Mohammadi,
Volume 8, Issue 3 (9-2011)
Abstract

Abstract: In this study, carbon nanotubes (CNTs) were grown directly in the pores of micro porous pyrex membranes
and consequently ceramic membranes with very fine pores and high porosity were achieved. Our experiment was done
in two stages. Initially cobalt powder with different percent was homogeneously mixed with pyrex powder. In order to
produce row membranes, each of these mixtures were compacted in the form of tablet by use of a uniaxial cold press
and in a stainless steel mould, and then the tablets were sintered at different temperature in an electric furnace. In
second stage chemical vapor deposition (CVD) method was used to grow CNTs within the pores of the membranes.
Argon and ammonia were used as carrier and reactive gas respectively and acetylene was used as the carbon
feedstock. Morphology of the membranes before and after CVD process was studied by scanning electron microscopy
(SEM). After CVD process CNTs were grown in the pores of membranes and the pores size was decreased but total
porosity of the membrane was not changed considerably. In this way membranes with high porosity and fine pores were
fabricated.
M. J. Tafreshi, B. Dibaie, M. Fazli,
Volume 9, Issue 1 (3-2012)
Abstract

Abstract: A thermodynamic model was used to find out the optimum temperature for the growth of ZnS single crystals in closed ampoules by chemical vapor transport technique. Based on this model 1002 °C was found to be optimum temperature for 2 mg/cm3 concentration of transporting agent (iodine). ZnS Crystals were grown in optimum (1002 °C) and non-optimum (902 °C and 1102 °C) temperatures. The composition structure and microstructure of the grown crystals were studied by Atomic absorption spectroscopy, X-ray diffraction and Scanning electron microscopy measurements. Properties of the grown crystals were correlated to the growth conditions especially a stability in mass transport along the closed tube length.
J. Jac Faripour Maybody, A. Nemati, E. Salahi,
Volume 10, Issue 2 (6-2013)
Abstract

In the present study, bioceramic composites based hydroxyapatite (HAp) reinforced with carbon nanotubes (CNTs) was synthesized via sol-gel technique. The dried gels were individually heated at a rate of 5°C/min up to 600°C for 2 h in a muffle furnace in order to obtain HAp-MWCNTs mixed powder. Composites were characterized by XRD, FT-IR, SEM, TEM/SAED/EDX and Raman spectroscopy techniques. Results showed the synthesis of HAp particles in the MWCNTs sol which was prepared in advance, leads to an excellent dispersion of MWCNTs in HAp matrix. Apparent average size of crystallites increased by increasing the percentage of MWCNTs. The average crystallite size of samples (at 600°C), estimated by Scherrer’s equation was found to be ~50-60 nm and was confirmed by TEM. MWCNTs kept their cylindrical graphitic structure in composites and pinned and fastened HAp by the formation of hooks and bridges.
H. Mohammadi, M. Ketabchi,
Volume 10, Issue 3 (9-2013)
Abstract

The microstructure and mechanical properties of 7075 wrought aluminum alloy produced by strain induced melt activation (SIMA) route were investigated.Also liquid volume fraction measurement was studied by three procedures. Remelting process was carried out in the range of 560 to 610 °C for 20 min holding. The microstructure in the semi-solid state consists of fine spherical solid grains surrounded byliquid.The mechanical properties of the alloy vary with the grain size and weak mechanical properties of globular samples would appear if an alloy reheated at a high temperature. Thermodynamic simulation is a fast and efficient tool for the selection of alloys suitable for semi-solid processing
R. Sarjahani, M. Sheikhattar, S. Javadpour, B. Hashemi,
Volume 13, Issue 1 (3-2016)
Abstract

Surface smoothness of ceramic glazes is always an important characteristic of ceramic glazes as a point of surface engineering studies. Surface roughness affects chemical resistivity, glossiness and stainabiliy of glazes. In fact, less surface roughness improves cleanability of the surface by the least usage amount of detergents. In this investigation, surface topography of two common opaque glazes, zirconia and titania-based, has been investigated. Crystallinity of the surface has been studied from SEM images, and comparison of EDS elemental results with phase analysis results of XRD. Surface roughness profile measured by Marsurf M300, shows that titania-based glaze is almost 24% percentage more smooth than zirconia based glaze. Surface smoothness is in relation with crystallinity of glaze surface, crystal type and crystal distribution in amorphous matrix phase

AWT IMAGE


M. Shahmiri,
Volume 13, Issue 4 (12-2016)
Abstract

Over the last few decades, there have been many mechanisms proposed to describe the formation of the non-dendritic microstructures during Semisolid Metal (SSM) processing; including dendrite fragmentation, spherical growth, cellular growth and recalescence. Dendrite fragmentation is the most popular mechanism of all these hypotheses. It is the purpose of the present article to examine the morphological evolution of the non-dendritic microstructures, based on models proposed by Flemings, Vogel, Cantor, and Doherty during SSM processing of the Al-Si (A356) alloy. Based on new microstructural evidences, including (1) - plastic deformation at the side arms by slip lines formation as a result of the thermal fatigue mechanism, (2) - crack formation at the root of the side arms and (3) – the interaction of a rapidly sheared hot viscous medium with these regions, i.e. erosion; it propose and hereby discuss a new mechanism called "fatigue –erosion", for dendrites fragmentation of the experimental alloy. Optical and Scanning Electron Microscopy (SEM) with EBSD and EDS, TEM, and AFM was used for the microstructural characterizations. 


M. Shahraki, S. M. Habibi-Khorassani, M. Noroozifar, Z. Yavari, M. Darijani, M. Dehdab,
Volume 14, Issue 4 (12-2017)
Abstract

The inhibition performances of nafcillin (III), methicillin (II) and penicillin G (I) on the corrosion of copper in HCl was studied and tested by weight loss, Tafel polarization, SEM, UV-vis spectrophotometry, molecular dynamics method and quantum chemical calculations. Polarization curves indicated that the studied inhibitors act as mixed-type inhibitors. The values of inhibition efficiency and surface coverage were found to follow the order: Blank ads, indicated that the adsorption of three inhibitors was a spontaneous process. The SEM micrographs confirmed the protection of copper in a 1 M HCl solution by penicillin G, nafcillin, and methicillin. The shape of the UV/vis spectra of inhibitors in the presence of the immersion of Cu showed a strong support to the possibility of the chemisorbed layer formation on Cu surface by nafcillin (between nafcillin and Copper) and physisorption between penicillin and methicillin with copper. DFT calculations were performed to provide further insight into the inhibition efficiencies which were determined experimentally. Molecular dynamics (MD) simulations were applied to find the most stable configuration and adsorption energies of penicillin G, nafcillin and methicillin molecules on Cu (110) surface. The interaction energy followed the order: nafcillin (III)> methicillin (II)> penicillin G (I), which confirmed that nafcillin has the strongest interaction with the metal surface. The obtained results from experimental and theoretical methods were in reasonable agreement.
 

J. Ngoret, V. Kommula,
Volume 16, Issue 1 (3-2019)
Abstract

This paper investigates premature failure of High Pressure (HP) PT6A-114A Compressor Turbine (CT) blades used for short-haul aircraft fleet at 6378 hours, contrary to 10000 hours pre-set by the manufacturer. The CT blades were sectioned both transversely and longitudinally and subjected to several microstructural examinations; X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Energy Dispersive Spectroscopy-Scanning Electron Microscopy (EDS-SEM) of the tips, airfoils, as well as the bases. It was observed that from repeated elevated heating, incomplete solutioning and recrystallization of the substrate material, brittle carbides were initiated and developed. The tips were more affected, followed by the airfoils and least at the bases. Impingement of heat from the combustors on the CT blades led to rapid graining and rafting with eventual cracking upon cooling. The results further suggested that pores which are typically manufacturing defects were pronounced at the bases than either at the airfoils and the tips. However, contrary to the expectation that the bases would degrade more and rapider, a more near uniform distribution of the cuboidal phase was evident relative to the tips and airfoils, confirming that degradation of the CT blades originated from creep and fatigue.

M. Hamdi, H. Saghafian Larijani, S. G. Shabestari, N. Rahbari,
Volume 17, Issue 3 (9-2020)
Abstract

Aluminum matrix composites are candidate materials for aerospace and automotive industries owing to their specific properties such as high elastic modulus (E), improved strength and low wear rate. The effect of thixoforming process on the wear behavior of an Al-Mg2Si composite was studied in this paper. During applying thixoforming process, casting defects  such as macrosegration, shrinkage and porosity are being effectively reduced. These advantages are sufficient to attract more exploration works of thixoforming operation. Thermal analysis of the composite, as-cast microstructure, wear surface and subsurface area of the thixoformed alloy were  investigated. Wear behavior of  the specimens were examined using a pin-on-disk machine  based on ASTM-G99, at the applied loads of 25, 50 and 75 N and the constant sliding velocity of 0.25m/s. The worn surfaces and subsurfaces were examined by scanning electron microscopy (SEM). The experimental results indicated that the thixoformed specimens exhibited superior wear resistance than the as-cast alloy. Moreover, the dominant wear mechanism is an adhesive wear followed by the formation of a mechanical mixed layer (MML). However, a severer wear regime occurs in the as cast specimens compared with the thixoformed ones

S. Das, R. Ghadai, A. Krishna, A. Trivedi, R. Bhujel, S. Rai, Sh. Ishwer, K. Kalita,
Volume 17, Issue 4 (12-2020)
Abstract

Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 o to 9.63 o and 26.4 o to 26.3 o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO..Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 o to 9.63 o and 26.4 o to 26.3 o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO.
Najwa Gouitaa, Lamcharfi Taj-Dine, Bouayad Lamfaddal, Abdi Farid, Mohamed Ounacer, Mohammed Sajieddine,
Volume 18, Issue 2 (6-2021)
Abstract

    The structural and dielectric properties of iron and bismuth co-substituted BaTiO3 ceramic with the formula: B0.95Bi0.05Ti1-xFexO3 for x=0.00 to 1.00, synthesis with solid state route, were characterized.     The X-ray diffraction results show a tetragonal phase for x=0.00. While for x=0.40 to 0.80 we observed a coexistence of tree phase tetragonal, hexagonal and pseudo-cubic. And at x=1.00 only the pseudo-cubic phase is present and the other phase disappeared. The Raman results indicate the existence of tetragonal band for x≤0.40, and an appearance of characteristic bands of Fe3+ ions for more than 0.40 of Fe content. The SEM micrographs show an increase in grain size with the increase of Fe content and it reaches a maximum at x=0.40.  And the Mossbauer spectroscopy indicates that our samples is paramagnetic at room temperature and that the Fe is   oxidized under Fe3+ with no existence of Fe2+ and Fe4+ ions. The temperature dependence of dielectric permittivity was investigated in the frequency range from 20 Hz to 2MHz. The results show three dielectric relaxation phase transitions from a rhombohedral ferroelectric to orthorhombic ferroelectric (TR-O) then to a tetragonal ferroelectric phase (at TO-T), and finally to cubic paraelectric at the Curie temperature (TC).  In addition, the temperature of phase transition shifted to the lower temperature with the increase of Fe content for all the phase transitions. And the maximum of dielectric permittivity increases for TR-O while for TT-O and Tm phases transitions, it reaches a maximum at x=0.60 and x=0.80 respectively and then decreases.

Surekha S. Jadhav, Amit A. Bagade, Tukaram J. Shinde, Kesu Y. Rajpure,
Volume 19, Issue 1 (3-2022)
Abstract

In present work Ni0.7Cd0.3NdxFe2-xO4 ferrite samples (0≤x≤0.03) were prepared by using oxalate co-precipitation technique. The different characterization techniques were achieved using X-ray diffraction (XRD), FT-infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), DC electrical resistivity and dielectric measurements. The crystallographic parameters such as crystal structure, crystallite size, lattice constant, unit cell volume and theoretical density have been systematically analysed. The XRD and FT-IR measurements confirmed the formation of single phase spinel ferrite structure. The cation distribution among the octahedral and tetrahedral sites has been proposed on the basis of analysis of XRD patterns by employing Rietveld refinement analysis. The samples exist as a mixed type spinel with cubic structure. The DC electrical resistivity confirms the semiconducting behaviour and the Curie temperature decreases with increase in Nd3+ content. The dielectric constant and loss tangent decreases with frequency and higher frequencies remain constant, which shows the usual dielectric dispersion due to space charge polarization. The AC conductivity reveals that the small type polarons responsible for conduction process.
Sandesh Jirage, Kishor Gaikwad, Prakash Chavan, Sadashiv Kamble,
Volume 21, Issue 1 (3-2024)
Abstract

The Cu2ZnSnS4 (CZTS) thin film is newly emerging semiconductor material in thin film solar cell industry. The CZTS composed of economical, common earth abundant elements. It has advantageous properties like high absorption coefficient and best band gap. Here we have applied low cost chemical bath deposition technique for synthesis of CZTS at low temperature, acidic medium and it’s characterization. The films were characterized by different techaniques like X-Ray diffraction, Raman, SEM, Optical absorbance, electrical conductivity and PEC study. The X-Ray diffraction, Raman scattering techniques utilized for structural study. The XRD revels kasterite phase and nanocrystalline nature of CZTS thin films. These results and its purity confirmed further by advanced Raman spectroscopy with 335 cm-1 major peak. The crystallite size which was found to be 50.19 nm. The optical absorbance study carried by use of UV-Visible spectroscopy analyses its band gap near about 1.5 eV and its direct type of absorption. The electrical conductivity technique gives p-type of conductivity. The scanning electron microscopy (SEM) study finds it’s rock like unique morphology. The EDS technique confirms its elemental composition and it’s fair stoichiometry. The analysis of PEC data revealed power conversion efficiency-PCE to 0.90%.
The Cu2ZnSnS4 (CZTS) thin film is newly emerging semiconductor material in thin film solar cell industry. The CZTS composed of economical, common earth abundant elements. It has advantageous properties like high absorption coefficient and best band gap. Here we have applied low cost chemical bath deposition technique for synthesis of CZTS at low temperature, acidic medium and it’s characterization. The films were characterized by different techaniques like X-Ray diffraction, Raman, SEM, Optical absorbance, electrical conductivity and PEC study. The X-Ray diffraction, Raman scattering techniques utilized for structural study. The XRD revels kasterite phase and nanocrystalline nature of CZTS thin films. These results and its purity confirmed further by advanced Raman spectroscopy with 335 cm-1 major peak. The crystallite size which was found to be 50.19 nm. The optical absorbance study carried by use of UV-Visible spectroscopy analyses its band gap near about 1.5 eV and its direct type of absorption. The electrical conductivity technique gives p-type of conductivity. The scanning electron microscopy (SEM) study finds it’s rock like unique morphology. The EDS technique confirms its elemental composition and it’s fair stoichiometry. The analysis of PEC data revealed power conversion efficiency-PCE to 0.90%.


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