Showing 776 results for Type of Study: Research
A. H. Kianfar, N. Eskandari, M. A. Arayesh,
Volume 39, Issue 2 (8-2020)
Abstract
In this research the synthesis of [Co(Salen)(PPh3)(H2O)]4[Fe(CN)6] and [Co(Salophen)(PPh3)(H2O)]4[Fe(CN)6] schiff base complexes was reported. Co3O4/CoFe2O4 magnetic nanoparticles were prepared by calcination of these complexes at 500, 550 and 600°C. Precursor complexes were identified by FT-IR and UV-Vis spectroscopy and their thermal behavior was studied via TG/DTA. Nanomagnetic samples were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FT-IR). Magnetic properties of the synthesized nanoparticles were studied using Vibrating Sample Magnetometer (VSM). Magnetic parameters such as saturation magnetization (Ms), remanent magnetization (Mr), coercive field (Hc) and squareness ratio (SQ = Mr/Ms) were determined at room temperature. Stoichiometry and approximate composition of the prepared samples were studied by Electron Diffraction X-ray spectroscopy (EDX). The prepared nanocomposites could be useful in some practical applications due to their high magnetization, good chemical stability and dispersion.
S. Torabi, S. Khorshidi, A. Karkhaneh,
Volume 39, Issue 2 (8-2020)
Abstract
For many years, dexamethasone has been used as an anti-inflammatory drug and is still one of the safest glucocorticoids for treating various diseases. Due to the wide range of the side effects of this drug, it is essential to find a suitable delivering system for reduction in dosage with increased effectiveness. Electrospinning is one of the fiber fabrication methods which is widely used to develop drug carriers due to its ability to load various drugs and biological components and control their release. In this research, neat poly (lactic acid) electrospun fibers and dexamethasone loaded fibers were prepared. To evaluate the effect of polymer concentration on morphology, mechanical properties and drug release profile of the resulting fibers, three polymer concentrations of 10%, 14% and 18% w/v were processed. Thereafter, 5% w/v dexamethasone was added to solutions. The scanning electron microscopy images were investigated to obtain the average diameter of fibers and the average area of pores in each sample. In neat samples, by moving from 10% to 18% composition, the average diameter of the fibers increased by 63.21%. However, in drug loaded samples this increased by 51/19%. After evaluating mechanical properties, an increase of 81/34% in Elastic modulus by moving from 10% to 18% composition was observed. Moreover, the ultimate strength increased by 68/021% when increasing the polymer concentration from 10 to 18%. Drug release from the electrospun samples was continued up to 7 days. Linear release was observed in 10% and 14% compositions. The drug release pattern of these samples was of zero order. Considering the importance of zero order release in different applications of dexamethasone, these delivering systems could be useful. The maximum drug release rate belonged to 14% composition (0.044 1/h).
M. Farhadian, K. Raeissi, M. A. Golozar,
Volume 39, Issue 2 (8-2020)
Abstract
This work is focused on the effect of amorphous SiO2 addition on the phase transformation and microstructural evolution of ZrO2 particles. Considering the structural similarities between the amorphous ZrO2 and its tetragonal structure, XRD results showed initial nucleation of metastable tetragonal ZrO2 from its amorphous matrix upon heat treatment. This metastable phase is unstable in pure ZrO2 sample and transforms to a stable monoclinic phase at around 600 oC. However, addition of amorphous SiO2 to ZrO2 structure causes metastable tetragonal phase to remain stable up to around 1100 oC. The temperature range for stability of metastable tetragonal ZrO2 structure increased from about 150 oC in pure ZrO2 particles to around 500 oC in ZrO2-10 mol.% SiO2 composite powders. A further increase in SiO2 content up to 30 mol.% did not change the stabilization temperature range but the average particle size reduced around 1.6 times compared to pure ZrO2 particles. Stabilization of metastable tetragonal ZrO2 explained by constrained effect of SiO2 layer surrounding zirconia nuclei. The thickness of this SiO2 layer enhanced by increasing SiO2 content which limited the growth of ZrO2 nuclei resulting in finer particle sizes.
M. Etminan, M. Morakabati, S. M. Qazi Mir Saeid,
Volume 39, Issue 2 (8-2020)
Abstract
The aim of this study was to investigate the effect of temperature and time of homogenization treatment on the microstructure, distribution of alloying elements and hardness of the novel Co-based superalloy Co-7Al-7W-4Ti-2Ta. For this purpose, the specimens were first homogenized at 1250 and 1300 °C for 2, 4, 6 and 8 hours and then water-cooled. Subsequently, the specimens were subjected to hardness testing and microstructural examinations by optical and electron microscopy. The results showed that by increasing the homogenization temperature to 1300 °C, the porosity created by Ti oxidation and local melting of the Co-Al-Ti eutectic compounds led to a decrease in hardness to 90 Vickers. This phenomenon was due to high segregation of alloying elements in the cast structure. The intensity and destructive effects of this segregation were reduced by remelting of alloy. However, by homogenization at 1250 °C, no local melting of eutectic zones or porosity were observed in the specimens and a more uniform structure was obtained with increasing time. Minimum and maximum hardness values after homogenization at 1250°C were 348 and 406 Vickers, respectively. Moreover, the microstructure became more homogenous by increasing the homogenization treatment time at this temperature.
M. Jafari, M. Rafiei, H. Mostaan,
Volume 39, Issue 2 (8-2020)
Abstract
In this research, the effect of temperature and time on the properties of AISI420/SAF2507 dissimilar joint produced by transient liquid phase bonding process was investigated. A BNi-2 interlayer with 25 μm thickness was inserted between two dissimilar steel samples. The bonding process was performed at 1050 oC and 1100 oC for different bonding times. The microstructures of the joints were studied using optical microscope, scanning electron microscope and energy dispersive X-ray spectroscopy. Microhardness and tensile shear strength of bonded samples were investigated. Isothermal solidification was completed for the joints bonded at 1050 oC and 1100 oC for 45 min and 30 min, respectively. ASZ and ISZ areas of the bonding zone at the bonding temperature of 1050 oC indicated the highest (520 HV) and the lowest (300 HV) microhardness values, respectively. Sample bonded at 1050 oC for 1 min indicated the lowest tensile strength (196 MPa) and sample bonded at 1100 oC for 60 min indicated the highest tensile strength (517 MPa).
T. Rajabi, M. Vahedi, S. K. Sadrnezhaad,
Volume 39, Issue 2 (8-2020)
Abstract
Zinc/zinc oxide nanoparticles are used in an increasing number of medical and industrial applications due to their attractive physical, chemical and antibacterial properties. Therefore, achieving a simple and beneficial way to produce them is an important aspect. In this study, zinc/zinc oxide nanopowders were synthesized by fast electric discharges between two electrodes of (a) a spark device in distilled water medium and (b) a handmade high-voltage ignition machine in argon gas medium. The resulting powders were characterized by x-ray diffraction (XRD), dynamic light scattering (DLS) and field emission electron microscopy (FESEM). Using the spark device in distilled water, a mixture of zinc crystals with an average diameter of 11.28 nm and zinc oxide crystals with an average diameter of 22.22 nm was produced. However, using the handmade device in argon, zinc crystals with an average diameter of 7.5 nm were obtained and subsequently oxidized due to their extremely high activity. The production rate of the high voltage discharge method was lower than other conventional methods. On the other hand, its ability in reducing the size and increasing the particle activity was higher than other methods.
A. Ghasemi, M. R. Loghman Estarki, S. Torkian, G. R. Gordani,
Volume 39, Issue 2 (8-2020)
Abstract
The purpose of this study was to evaluate phase changes and magnetic properties of neodymium doped Ni0.7Zn0.3NdxFe2-xO4 (x = 0, 0.01, 0.03, 0.05, 0.07, 0.10) nanoparticles synthesized by complexing sol-gel method. In this method, triethanolamine (TEA) acted as both a gelling agent and a chelating agent. Samples were characterized by X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). XRD patterns of all synthesized samples revealed the formation of a spinel ferrite phase. Magnetic evaluation of the specimens showed that the Nd0.01 doped sample with a quasi-spherical morphology and particle size of about 60 nm has the highest saturation magnetization of 50 emu/g and coercive force of 103 Oe.
A. Zolriasatein, S. Navazani, M. Rezaei Abdadchi, N. Riahi Noori ,
Volume 39, Issue 3 (12-2020)
Abstract
In this paper, the effect of adding aluminum trihydrate (ATH) on electrical (including dielectric constant, dielectric loss and strength, volume and surface resistivity) and hydrophobic properties of two-part room temperature volcanized (RTV) silicone rubber resin coatings were investigated. For this purpose, the RTV-ATH nanocomposite was made by physical mixing and its electrical and hydrophobic properties were compared with those of pure RTV. The results showed an increase in the dielectric constant (from 3.11 to 4.13), the dielectric loss (by ~ 0.06) and the dielectric strength (by ~ 4 KV/mm) of the RTV-ATH composite compared to the pure RTV. Moreover, ATH increased volume resistivity and reduced the surface resistivity of composite coatings. On the other hand, by spraying of coatings, no improvement in the hydrophobicity class of composite coating compared to pure RTV was observed and both samples were standardized in the HC2 standard class. Structural analysis of samples was performed by X-ray diffraction, optical microscopy and scanning electron microscopy and the presence of the main phases in them was confirmed.
S. Asghari, A. M. Eslami, A. Taheri Zadeh, N. Saeidi,
Volume 39, Issue 3 (12-2020)
Abstract
In this study, the effect of welding heat input on microstructure and mechanical properties of dissimilar joints of API-X42 and API-B pipeline steels was investigated. Evaluation of the microstructures showed that increasing the welding heat input decreased acicular ferrite in weld metal microstructure, while amount of Widmanstatten ferrite, polygonal ferrite and grain boundary ferrite increased. Also, results of microhardness test showed that by increasing the heat input, hardness of weld metal and the heat affected zone decreased. Tensile test results showed that as the heat input increased, fracture transferred from base metal of API-B to the heat affected zone. Impact test results also showed that increasing the welding heat input could sharply drop the impact energy of the heat affected zone for both base metals due to extensive grain growth.
S. Arjmand, M. Tavoosi,
Volume 39, Issue 3 (12-2020)
Abstract
The present work aims to modify surface properties of pure Ti by development of Ti-Al-N intermetallic composite coatings. In this regard, tungsten inert gas (TIG) cladding process was carried out using Al 1100 as filler rod with Ar and Ar+N2 as shielding gases. Phase and structure of the samples were investigated by X-ray diffraction (XRD) technique, optical microscopy (OM) and scanning electron microscopy (SEM). Hardness values and corrosion behavior of the obtained coatings were also compared using Vickers microhardness tester and potentiostat, respectively. The results showed that composite structure containing Al3Ti, Ti3Al2N2 and Ti3Al intermetallic compounds could be formed on the surface of pure Ti. Amounts of brittle phases and welding defects at the titanium-coating interface were least by welding under pure Ar shielding. Despite the increasing amount of structural defects such as porosity and non-uniformity under Ar+N2 shielding, the prepared coatings had higher hardness (more than 100 HV) and corrosion resistance (more than twice) compared with those obtained under Ar shielding.
A. Borouni, A. Kermanpur,
Volume 39, Issue 3 (12-2020)
Abstract
In this study, the effect of Ta/W ratio on the microstructure and stress rupture properties of Ni-based single crystal (SX) superalloy PWA1483 was investigated. For this purpose, single crystal (SX) superalloys with different Ta/W ratios (0.75, 1.0, 1.32 and 1.5 in wt.%) were fabricated. The alloys were directionally solidified by Bridgman method under the same solidification condition at withdrawal velocity of 3 mm/min and thermal gradient of about 7 K/mm followed by standard age hardening heat treatment. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM). The stress rupture properties were investigated at 982 °C and 248 MPa. The results showed that increasing the Ta/W ratio decreases the size and volume fraction of micro-pores together with the size of γ' precipitates. Hence, the stress rupture life increased. The superalloy with Ta/W ratio of 1.5 showed the minimum size of micro-porosity (18.2 μm) and the maximum stress rupture life (~34 h). The superalloy with Ta/W ratio of 1 showed the most uniform microstructure and creep behavior. It seems that the presence of topologically closed packed (TCP) η-phases is the main reason for stress rupture life decrease in SX superalloy as micro-pores initiated from TCP phases or the TCP/matrix interfaces.
M. Emami, S. Hayashi,
Volume 39, Issue 3 (12-2020)
Abstract
High-temperature erosion-oxidation behavior of nickel-based alloys containing 0-7 wt.% Mo in fluidized bed waste incineration conditions was studied. A stream of hot condensed air with a flow rate of 25 L/min caused hot silica sand (700 °C) mixed with 0.5 wt.% of chloride salts to hit the specimens for 250 h. By removing the erosive factor, the high-temperature oxidation behavior of the alloys in air and air-chlorine atmospheres was studied at 520 and 560 °C for 100 h. Mass gain measurement due to oxidation followed by thickness loss measurement in the erosion-oxidation tests showed that an increased Mo content led to improved oxidation resistance as a result of reduced scaling rate. However, under simultaneous oxidation and erosion conditions, the lower oxidation rate of the alloy with 7 wt.% Mo caused rapid removal of the protective scale and a reduction in erosion-oxidation resistance of the alloy. Under these conditions, the alloy with 3 wt.% Mo showed the smallest removal rate. Microscopic observations and XRD analysis confirmed formation of Cr2O3/NiCr2O4 scales on the surface. Mo-free alloy with lowest oxidation resistance showed a higher erosion-oxidation resistance. However, the high oxidation rate of this alloy led to a severe Cr-depletion and internal oxidation in subsurface region.
F. Mostafaee Heydarloo, M. Morakabati, H. Badri ,
Volume 39, Issue 3 (12-2020)
Abstract
The aim of this study was to investigate the suitable temperature range for hot deformation of three medium carbon Ni-Cr-Mo low alloy steels by hot tensile and hot torsion tests. Hot tensile tests were carried out in the te,prature range of 850-1150°C at a constant strain rate of 0.1 s-1 until fracture. Then, the tensile flow behavior, hot ductility and microstructural evolution of the steels were studied. Hot torsion tests were performed in the temperature range of 1200-780°C at strain of 0.1 with strain rate of 1s-1. The effect of titanium and niobium on the mean flow stress and the non-recrystallization temperature were investigated. The tensile test results showed that dynamic recrystallization was the dominant mechanism at temperatures above 950°C in the base steel and temperatures above 1050°C in the microalloyed steels. The results of hot torsion tests showed that the non-recrystallization temperatures of the base, Ti containing and Nb containing steels were 1070°C, 1069°C and 1116°C, respectively. Finally, the suitable hot deformation temperature range to achieve optimum mechanical properties in the base and Ti containing steels obtained as 950-1070°C and that of Nb containing steel obtained as 950-1100°C.
A. Zamani, M. R. Loghman Estraki, S. R. Hosseini, M. Ramezani, A. Al-Haji,
Volume 39, Issue 3 (12-2020)
Abstract
The aim of the study was to investigate the effect of temperature, time, pH, capping agent concentration (mercaptoacetic acid), Zn to Se and Se to reducing agent (NaBH4) mole ratios on morphology, phase developments and size of zinc selenide nanoparticles prepared by hydrothermal method. Characterization of zinc selenide nanoparticles was performed by Field Emission Electron Microscopy (FESEM), Energy Dispersive X-ray Spectrometry (EDS), X-ray Diffraction (XRD), Induced Coupled Plasma Spectrometry (ICP), Fourier Transform Infrared spectroscopy (FTIR) and Simultaneous Thermal Analysis (STA). The results of EDS showed that the ratio of atomic percentage of Zn to Se in the optimized zinc selenide nanoparticles is 1: 1 and elements are evenly distributed in the nanoparticles. Based on the results of FTIR and STA thermal analyses, MAA as the stabilizing agent binds to and stabilizes zinc selenide nanoparticles. Finally, fine nanoparticles of zinc selenide with narrow size distribution, spherical shape and cubic crystal structure were obtained at the minimum temperature (130 °C) and processing time (15 hours) with the least amount of reducing and capping agents compared to previous researches.
M. T. Asadi Khanouki,
Volume 39, Issue 3 (12-2020)
Abstract
In this study, the influence of temperature and strain rate on plastic flow of a Zr-based bulk metallic glass (BMG) during the three-point bending test was studied to find a correlation between strain rate sensitivity (m) and flow behavior. The flexural stress-deflection curves revealed two distinct types of dynamics, serrated and non-serrated flow, related to temperature and strain rate. The serrated flow which appeared at temperatures higher than a critical value or strain rates lower than a critical value, was simultaneously due to activation of shear transformation zones (STZs) and time-dependent structural relaxations. Further results indicated negative and positive values of m at temperatures above and below 0.4 Tg, respectively. The main reason for negative strain rate sensitivity was insufficient time of structural relaxation at high strain rates which lead to generation of free volume inside shear bands making the BMG softer. Comparison of STZ activation energy with activation energy for the onset of serration indicated almost equal values and there was a close relationship between serrated flow and STZ operation.
S. S. Shafiei, M. Shavandi , Y. Nickakhtar ,
Volume 39, Issue 4 (2-2021)
Abstract
Tissue-engineering scaffolds provide biological and mechanical frameworks for cell adhesion, growth, and differentiation. Nanofibrous scaffolds mimic the native extracellular matrix (ECM) and play a significant role in formation and remodeling of tissues and/or organs . One way to mimic the desired properties of fibrous ECM is adding nanoparticles into the polymer matrix. In the current study, the uniform fibers of poly (ε-caprolactone) (PCL) enriched with different layered double hydroxide (LDH) contents (ranging from 0.1 wt.% to 10 wt.%) were successfully fabricated by electrospinning method. The LDH nano particles were randomly dispersed in the fibers, as confirmed by Energy Dispersive X-ray analysis (EDX). Scaffolds were analyzed from morphological, physical and mechanical view. Biological assessments of scaffolds in terms of cellular attachment and adipogenic differentiation of mouse adipose derived stem cells (mADSCs) were performed. The results showed that inclusion of LDH nanoparticles reduced the average fiber diameter and enhanced the tensile strength and elongation at break values of the PCL scaffold. The LDH-enriched electrospun PCL scaffolds had remarkable effects on cell adhesion. Moreover, a significant increase in adipogenic differentiation of mADSCs was observed. The PCL/LDH nanofibrous scaffolds showed great potential in application for soft tissue engineering.
H. Hadian, M. Haddad Sabzevar , M. Mazinani,
Volume 39, Issue 4 (2-2021)
Abstract
In this research, effect of swarf addition on the microstructure of die cast aluminum A380 alloy and the possibility of altering the alloy structure in the metallic die has been studied. The microstructure mainly consists of the α-phase, eutectic, intermetallic compounds and porosity. Since the alloy solidifies under non-equilibrium conditions, the Scheil equation with exact amount of equilibrium distribution, analyzed by SEM-Line scan around an intermetallic phase at different mixing times as well as governing equations of thermal analysis, was used to calculate the solid weight fraction. Finally, using the thermal flux analysis in the crucible, a scientific prediction on the optimal amount of swarf addition, mixing time and temperature, was made. The shape factor at an optimum temperature of 590 °C was measured as 0.643. According to the optical microscope images of the die cast samples, the addition method (adding it to the floor or to the surface) and increasing the injection temperature have a significant effect on the solid weight fraction, morphology of the α-phases and final microstructure of the alloy.
S. N. Hosseini, F. Karimzadeh, M. H. Enayati,
Volume 39, Issue 4 (2-2021)
Abstract
The bare and pre-oxidized AISI 430 pieces were screen printed by copper ferrite spinel coatings. Good bonding between the coating and the substrate was achieved by the reactive sintering process of the reduced coating. The energy dispersive X-ray spectroscopy (EDS) analysis revealed that the scale is a double layer consisting of a chromia-rich subscale and an outer Cu/Fe-rich spinel. The results showed that the spinel protection layer not only significantly decreased the area specific resistance (ASR), but also inhibited the subscale growth by acting as a barrier to the inward diffusion of oxygen. ASRs of 19.7 and 32.5 mΩ.cm2, much lower than that of the bare substrate (153.4 mΩ.cm2), at 800 °C after 400 h oxidation were achieved for the bare and pre-oxidized copper ferrite spinel coated samples, respectively. Excellent, stable ASR (20.5 mΩ.cm2) was obtained with copper ferrite coating after 600 h of exposure at 800 °C. The high electrical conductivity of CuFe2O4 and its doping by Mn, the growth reduction of Cr2O3 oxide scale and the good coating to substrate adherence are proposed to be responsible for substantial improvement in electrical conductivity.
S. Masoomi Ganjgah , M. Abbasi,
Volume 39, Issue 4 (2-2021)
Abstract
This study aims at investigating changes in microstructure and strength of W alloy and Cu bimetals with varying spark plasma sintering (SPS) temperature and percentage of copper in W-Cu-Ni alloy. After SPS of W (12 wt%)-Cu (14 wt%)-Ni (3 wt%) alloy powder into consolidated discs at 1350 ° C, they were spark plasma sintered to copper discs at various temperatures. Assessment of the interface microstructure and shear strength was performed by field emission scanning electron microscpe (FESEM) and shear strength test, respectively. Results indicated SPS is successful in forming a perfect metallic bond with monolithic interface and high shear strength of about 45 MPa in Cu/W-12Cu-3Ni bimetal that is extra high quality and not reported in previous investigations.
S. Arjmand, G. H. Akbari, G. R. Khayati,
Volume 39, Issue 4 (2-2021)
Abstract
The purpose of the present work is to investigate the influence of the number of weld-passes on microstructure, hardness and residual stresses of composite coatings composed of Ti-Al-Si intermetallic compounds. In this regard, surface coating of pure Ti was carried out using one and two passes of tungsten inert gas (TIG) welding with an Al filler alloy (grade 4043). Phase and structural evaluations of the coatings were investigated by X-ray diffraction, optical and scanning electron microscopies. microhardness and residual stress values of the coatings were measured using ASTM E384-HV device and the Sin2ψ method, respectively. The results showed that as the number of welding passes increased or the dilution ratio decreased, the volume fraction of Ti5Si3-Al3Ti intermetallic phases within the fusion zone increased and the volume fraction of martensite phase in the heat affected zone decreased. As a result, the average hardness value of the coating increased to be about 130 % compared to that of the pure Ti substrate. The tensile residual stresses at the center line of fusion zone were 165 ± 30 and 210 ± 35 MPa for the coatings prepared in one and two welding passes, respectively.
