Journal of Advanced Materials in Engineering (Esteghlal)

The aim of this study was to fabricate carbon nanotube (CNT) and bioactive glass nanoparticles (BG) (at levels of
5 and 10 wt%) incorporated electrospun chitosan (CS)/polyvinyl alcohol (PVA) nanofibers for potential neural tissue engineering applications.The morphology, structure, and mechanical properties of the formed electrospun fibrous mats were characterized using scanning electron microscopy (SEM) and mechanical testing, respectively. In vitro cell culture of embryonal carcinoma stem cells (P19) were seeded onto the electrospun scaffolds. The results showed that the incorporation of CNTs and BG nanoparticles did not appreciably affect the morphology of the CS/PVA nanofibers. The maximum tensile strength (7.9 MPa) was observed in the composite sample with 5 %wt bioactive glass nanoparticles. The results suggest that BG and CNT-incorporated CS/PVA nanofibrous scaffolds with small diameters, high porosity, and promoted mechanical properties can potentially provide many possibilities for applications in the fields of neural tissue engineering and regenerative medicine.

Perovskite structures including oxygen vacancies are the most important group of the oxygen preamble membranes. These membranes have potentially attractive applications in the membrane reactors for partial oxidation of methane. Doping Perovskite phase in order to increase the oxygen vacancies and oxygen permeation, besides Perovskite structure stability, has been the main approach of the recent researches. In this research, tantalum was chosen as the appropriate dopant for Ba(Co_0.8Fe_0.2)O_{3−δ}  Perovskite phase, according to the tolerance factor calculations. The X ray patterns of synthesized Ba (Co_0.7Fe_0.2Ta_0.1)O_{3−δ} indicate that the Perovskite structure was formed. Powder density, thermal expansion coefficient measurements and bond strength studies using FT-IR analysis revealed that the chosen dopant not only increases the oxygen vacancies volume but also reduces the thermal expansion coefficient without significant changes of bond strength. Results showed that the novel Ba (Co_0.7Fe_0.2Ta_0.1) O3_{−δ} is a good choice for the membrane fabrication of methane partial reduction reactors.

Ternary (%mol) (64SiO₂-31CaO-5P₂O₅) system of sol-gel derived bioactive glass fibers was prepared by electrospinning method. X-ray Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and nitrogen adsorption test (BET) analyses were performed to investigate the phase and chemical group of the composition, morphology of the surface and specific surface area of the fibers, respectively. SEM observations confirmed that the fibers were nano size. The amorphous nature and the presence of silanol groups in the composition were confirmed by XRD and FTIR, respectively. Apatite formation and biodegradability of the fibers were studied using various analyses after different days of soaking in simulated body fluid (SBF). The results affirmed the presence of apatite layers on the surface of the fibers. Cell culture evaluation indicated that MG-64 human osteoblast-like cells were attached and spread well on the surface. Furthermore, cell viability and cell growth demonstrated that the cells were grown and reproduced well on the fibers.

In this study, Ni-Mo nanocrystalline alloys were prepared on steel substrates by electrodeposition method from citrate-ammonia bath by applying current densities 30, 60 and 100 mA/cm². Results indicated that the obtained coatings were uniform and compact. Moreover, molybdenum content in the alloy and current efficiency decreased with increasing electrodeposition current density. X-ray diffraction analyses indicated that all coatings were composed of face-centered cubic solid solution of molybdenum in nickel with grain size of 9-5 nanometer. Moreover, the most intensive plane in X-ray diffragtogram was (111). On the othe hand, roughness measurements indicated that surface roughness escalated with increasing current density. Corrosion behavior study showed decrease in corrosion current density of substrate with applying Ni-Mo alloy coatings. In addition, corrosion current density reduced with increasing molybdenum content of the coating and the minimum amount was related to the coating with 13 atomic percent molybdenum.

In this study, a three-dimensional finite element (FE) model for armchair, zigzag and chiral single-walled carbon nanotubes (SWCNTs) is proposed. To create the FE models, nodes are placed at the locations of carbon atoms and the bonds between them are modeled using three-dimensional elastic beam elements. The FE model is used to investigate the influence of chirality and Stone-Wales defects on the ultimate strength (Ultimate stress and ultimate strain) of SWCNTs. Results indicate that Stone-Wales defect significantly reduces the ultimate stress and strain of armchair CNTs. But this defect has a negligible effect on the ultimate strength of zigzag nanotubes. Based on the results, the crack growth path in zigzag and armchair nanotubes have 90 and 45 degree angle to the long axis of the nanotube, respectively.

In this study, TIG welding was used to clad and repair the surface of cast AZ91C magnesium alloy. Then, friction stir processing and T6 heat treatment wrer applied on the welded region. Microhardness results showed an improvement in the mean hardness of welded zone and also FSPed zone. Increase in the mean microhardness of the welded zone after T6 heat treatment to the maximum value was also concluded. The results of wear test showed that the wear resistance of the welded area was improved. Further improvement in wear properties was obtained after friction stir processing and T6 heat treatment.

In the present research NdFeB thin films coupled with buffer and capping layer of W were formed on Si/SiO₂ substrate by means of RF magnetron sputtering. The system was annealed at vaccum at different temperatures of 450, 500, 550,. 600 and 650 °C Phase analysis was carried out by XRD and it was found that NdFeB was formed without the formation of any kind of secondary phase. The cross sectional and grain size of the thin films were measured by scanning electron microscopy. Morphological studies were performed by atomic force microscopy. Magnetic properties of thin films including coercivity, saturation of magnetization and hysteresis area were evcaluated by vibrating sample magnetometer. It was found that by annealing at 400 °C the amorphous layer was formed.The highest intensity of peaks was formed at 550 °C and with an increase in temperature the intensity was declined. The grain size was increased by temperature and had an impact on the coercivity. With an increase of temperature up to 600 °C, perpendicular coercivity was increased and then by further increase of temperatute, coercivity was reduced. Based on the obtained data the temperature of 600 °C was selected as the optimum annealing temperature for reaching enhanced structural and magnetic feature.

In this study, nine Nd-Fe-B and FeCe thin films with 10-50 nanometers width were prepared by RF magnetron sputtering on the Si/SiO₂ substrate. Then, the films were annealed at 800 ^oC for 5 sec in rapid thermal annealing furnace. X-ray diffractometry (XRD) was used to analyze the phase composition of layers and existance of Nd₂F₁₄ and Fe₆₅Co₃₅ phase was confirmed, without formation of any other secondary phase. The layers surfaces were investigated using Field Emission Scanning Electron Microscope (FESEM). The morphology of layers surfaces was investigated using Atomic Force Microscope (AFM). The magnetic properties of layers were evaluated by vibrating sample magnetometer with maximum applied field of 24kOe, in order to measure coercivity, saturation of magnetization, hysteresis area, rectangular ratio and (BH)max. It was found that all layers have vertical magnetic anisotropy. Increasing thickness of FeCo resulted in increasing saturation of magnetization,  coercivity and saturation magnetization. The results indicate that by an increase in thickness of FeCo up to 20nm, exchange interaction strength between hard and soft magnetic layers is enhanced and, consequently, maximum energy induced from this hetero-structure is increased.

In the present article, RRA, T73 and T6 heat treatments were carried out to improve mechanical properties of 7075 aluminum alloy and its hardness, tensile and bending strengths were evaluated. For this purpose, solution annealing was performed at 530 ºC for 16 h. For T6 treatment, aging was executed at 150 ºC for 24 h after solution annealing. In T73, aging treatment was done in two stages after solution annealin, at 120 and 180 ºC for 7 and 20 h, respectively. RRA treatment was performed in three stages. The first stage was the same as T6 treatment, the second stage constitutes tempering at 200 ºC for
20 min and in the third stage aging process was repeated like T6 treatment. Evaluation of the microstructures and fractured surfaces were performed with optical microscopes (OM) and scanning electron microscopes (SEM). Energy dispersive spectroscopy (EDS) was used to study the chemical composition of precipitates. Hardness, tensile and bending strength were evaluated according to ASTM E384-11e1, ASTM B557-06 and DIN 50121 standards. RRA treatment increased tensile strength from 466 to 485 MPa and hardness from 110 to 165 Vickers. After T6 treatment, tensile strength increased from 466 to 505 MPa and hardness from 110 to 160 Vickers. In T73 process, the tensile strength remained almost constant (465 MPa) but yield strength increased from 394 to 410 MPa and hardness decreased from 110 to 84 Vickers. The bending strength increased from 797 to 844, 920 and 1030 MPa in T73, RRA and T6 processes, respectively. By applying RRA process in optimized temperature and time, hardness, tensile and bending strengths of 7075 aluminum alloy were enhanced from 5 to 15% compared to that of T6 and T73 processes.

Preliminary results of a research on the effects of microstructure and surface roughness of a hypoeutectic cast iron on its wetting angle are presented in this article. For this purpose, molten cast iron was solidified at different cooling rates to produce two samples of the same composition, i.e. a gray cast iron with A type flake graphite and a white cast iron. Two samples were then prepared in polished, electroetched (four different stages) and mechanically abraded (four different stages) conditions and their wetting angles were measured after evaluating their roughness profile. Maximum and minimum wetting angles were observed on white cast iron surfaces roughened with 80 and 800 sand papers which were equal to 42 and 13 degrees, respectively.Wetting angles of electroetched white cast iron surfaces varied between 25 and 31 degrees by varying surface roughness. Maximum and minimum wetting angles on the surface of gray cast iron were obtained in stage one (40 degree) and stage three (25 degree) of electroetching, respectively. Wetting angles on mechanically abraded surfaces of this sample varied between 27 and 31 degrees. Then, the surface roughness factor and the solid fraction in contact with water were calculated using Wenzel equation and Cassie Baxter equation, respectively, and Wenzel and Cassie-Baxter wetting angles of the surfaces were calculated and were compared with their corresponding measured wetting angles. The results indicated that the surface microstructure and the type of constituents present at the surface, surface-roughening method and surface-roughness value influence the cast iron surface wettability, and it is possible to modify metal wetting angle by modification of its structure, surface-roughness method and surface-roughness value. It was also shown that in gray cast iron, the wetting behavior of the electroetched surfaces followed Cassie-Baxter equation in the first and second stages of electroetching and followed Wenzel equation at higher surface roughness (third and fourth stages of electroetching). In all stages of mechanically abrading, the surface of this sample followed Wenzel equation. The wetting behavior of the white cast iron followed Wenzel equation in all electroetching stages. In mechanically abraded conditions, the white cast iron wettability was variable and depended on the surface roughness.

In this study, electrical wire explosion has been used to produce aluminum carbon nanotube (Al-CNT) nanocomposite particles in acetone medium. In order to synthesize Al-CNT nanocomposites, initially, CNTs were ultrasonically dispersed. Then, aluminum wire was exploded in this medium. Synthesized samples were characterized by Fourier Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM) methods. The results exhibited formation of spherical nanoparticles in the medium. The average diameter of nanoparticles was 4 nm. Moreover, attained nanoparticles remained stable in acetone. Results revealed a good interaction between aluminum nanoparticles and CNTs in this medium. It is concluded that acetone is a suitable medium for synthesizing Al-CNT nanocomposite as appropriate dispersion of Al-CNT nanoparticles can be achieved in this medium.

In this paper, milling was investigated as a method for production of Mn-Ga binary alloys and the effect of milling process on phase formation of Mn:Ga samples with 2:1 and 3:1 ratio within 1, 2 and 5 hour milling times was studied. For Mn:Ga samples, according to the results, Mn_1.86Ga compound with tetragonal structure and I4/mmm space group was a stable phase. Also, some amounts of  Mn₃Ga compound with orthorhombic structure and Cmca space group was observed in the Mn:Ga solution. The effect of Ge addition, with the purpose of  replacing Ge with Ga was also studied in Mn:Ga:Ge (3:0.5:0.5) sample. Although improved magnetic properties is expected with the addition of Ge, but increasing the coercivity was occurred, and saturation magnetization did not change significantly in the studied sample. Ge addition caused elimination of the possibility of formation of asymmetric orthorhombic Mn₃Ga phase. In return, two new structures of Mn₁₁Ge₈ and MnGaGe were appeared. This phase change was confirmed by studying magnetic behaviour of samples. This behavior can be caused by unbalanced electrostatic forces resulting from Mn-Mn exchange interaction in Mn₃Ga orthorhombic structure and substitution of some Ge atoms with Ga.

In this research, Glass Form Ability (GFA) has been investigated in the new class of Fe-based amorphous
alloys. Indeed, the main purpose is to evaluate the effects of alloying with niobium on glass form ability of Fe_55-xCr₁₈Mo₇B₁₆C₄Nb_x (X=0, 3, 4, 5) alloys. Vacuum induction melting (VIM) was utilized for production of primary ingots and melt spinning process was used for production of thin ribbons required for kinetic and structural investigations. Kinetic analysis was done using
the data obtained from Differential Scanning Calorimetry (DSC) tests. Results showed that GFA and viscosity were enhanced by Nb alloying. It was also determined that devitrification transformation was accomplished in alloys by nucleation and growth mechanisms.

In this study, centrifugal casting process was used for producing Al/Mg bimetal. Molten Mg was poured at 700 ^oC, with 1.5 and 3 melt-to-solid volume ratio (Vm/Vs) into the 450 ^oC preheated solid Al rotating at 800, 1200, 1600 and 2000 rpm. Castings were kept inside the centrifuged casting machine and cooled down to 150 ^oC. Investigating the effect of melt-to-solid volume ratio showed that increasing volume ratio from 1.5 to 3 results in diminishing metallurgical bonding in Al/Mg interface, because the force of contraction overcomes the resultant force acted on the interface. The results of study by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) showed that bimetal compounds of Al₃Mg₂, Al₁₂Mg₁₇ and δ+Al₁₂Mg₁₇ eutectic structure (δ is the solid solution of Mg in Al) are formed in the interface. Atomic force microscopy (AFM) image of Al surface showed that the surface was rough in atomic dimentions, which can result in the formation of gas pores in the interface.

This study has examined the properties of Crofer 22APU stainless steel produced by mechanical alloying for using as interconnect plates in solid oxide fuel cells.This alloy was produced by mixing the source powders and mechanical alloying for 40 hours. For creating a sample with high density, spark-plasma sintering was applied at 1100 °C and 50 Mpa stress for
10 minutes. To achieve the desired properties such as low electrical resistance and high oxidation resistance, a number of samples were coated by manganese-cobalt using electrodiposition technique at current density of 150 mA/cm ² for 40 minutes. Then, considering the properties required for an interconnect plate of solid oxide fuel cell, oxidation resistance and electrical resistance of the coated and uncoated samples were investigated. Oxidation behavior of the coated and uncoated samples, after 100 hours oxidation in air at 800°C did not follow any rule and its curve was a sinus type. The electrical resistance of uncoated samples was in the range of 0.1-0.2 mOhm.cm², but the electrical resistance of the coated samples after 100 h oxidation reached to a less ammount  than that of the corresponding uncoated ones. The alloy produced by mechanical alloying method, compared with commercial ones produced by casting methods, showed similar oxidation behavior after 100 h oxidation, but it had a surface electrical resistance far less than its commercial ones.

The purpose of this article is to study the formation of intermetallic compounds (IMCs) at the interface of Al/Cu bimetal produced by compound casting of molten Al in solid copper tubes. The mechanism of the intermetallic compounds formations at the interface, the effects of molten aluminum pouring temperature and solid copper tubes preheating tempreture, were investigated on the IMCs type and thickness and Al/Cu interface microstructures were characterized by optical microscope (OM) and electron probe micro-analyzer (EPMA). Results show that the interface consists of three main layers, where Layer (I) is α-Al/Al₂Cu eutectic structure, layer (II) is intermetal of Al₂Cu and layer (III) constituites several intermetallic compounds such as AlCu, Al₃Cu₄, Al₂Cu₃ and Al₄Cu₉. Considering the components of hypereutectic melt at the interface, initially layer (II) was formed by θ phase nucleation and growth mechanism, then layer (I) was formed by Al and Cu dissolving and solidification. Finally layer (III) was formed by solid-state phase diffusion. Raising molten Al temperature and preheating solid Cu leads to increase of the intermetallic compounds thickness at interface which consequently increases the specific electrical resistance and decreases the Al/Cu bond strength. From experimental results it seems that the bond strength is affected by the thicknesses of layer II and III.

The aim of the present study is to study the effects of adding  diopside (CaMgSi₂O₆) as well as silica sulfuric acid nanoparticles to ceramic part of glass ionomer cement (GIC) in order to improve its mechanical properties. To do this, firstly, diopside (DIO) nanoparticles with chemical formula of CaMgSi₂O₆ were synthesized using sol-gel process and then, the structural and morphological properties of synthesized diopside nanoparticles were investigated. The results of scanning electron microscopy (SEM) and particle size analyzing (PSA) confirmed that synthesized diopside are nanoparticles and agglomerated. Besides, the result of X-ray diffraction (XRD) analyses approved the purity of diopside nanoparticles compounds. Silica sulfuric acid (SSA) nanoparticles are also prepared by chemical modification of silica nanoparticles by means of chlorosulfonic acid. Fourier transform infrared spectroscopy (FTIR) technique was used to find about the presence of the (SO₃H) groups on the surface of silica sulfuric acid nanoparticles. Furthermore, various amounts (0.1, 3 and 5 wt.%) of diopside and silica sulfuric acid nanoparticles were added to the ceramic part of GIC (Fuji II GIC commercial type) to produce glass ionomer cement nanocomposites. The mechanical properties of the produced nanocomposites were measured using the compressive strength, three-point flexural strength and diametral tensile strength methods. Fourier transform infrared spectroscopy technique confirmed the presence of the (SO₃H) groups on the surface of silica nanoparticles. The compressive strength, three-point flexural strength and diametral tensile strength were 42.5, 15.4 and 6 MPa, respectively, without addition. Although adding 1% silica solfonic acid improved nanocomposite mchanical properties by almost 122%, but maximum increase in nanocomposite mechanical properties was observed in the nanocomposites with 3% diposid, in which 160% increase was seen in the mechanical properties.

Organic–inorganic hybrid coatings were prepared by sol–gel method and deposited on aluminum alloy 6061. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) were used for structural study of the hybrid coatings. Adhesive strength of sol–gel coatings to the substrate was evaluated quantitatively and qualitatively. Corrosion behavior of the samples was studied by cyclic potentiodynamic and linear polarization tests. Results showed that adhesion strength of the coatings to the substrates was increased with increasing tetrapropoxide of zirconium (TPOZ) and cerium content. Corrosion tests showed that corrosion current density of coated samples were decreased three to seven orders of magnitude in comparison with uncoated aluminum alloy 6061. Decreasing in corrosion current density and increasing in polarization resistance was observed by increasing zirconia and cerium content. Unlike the uncoated aluminum alloy 6061, the crack-free coatings did not show pitting tendency. 

In recent years the use of nanomaterials in bone tissue engineering scaffold has been considered due to its imitating the structure of natural bone tissue which contains a nanocomposite structure mixed with a three-dimensional matrix. In the meantime, Polycaprol actone has been used as a bio-polymer in bone tissue engineering applications as a scaffold. The aim of this study is to develop porous scaffolds made of polycaprol actone/layered double hydroxide biocomposite, with appropriate mechanical, bioactive and biological properties, for bone tissue engineering application. The nanocomposite scaffolds were fabricated by the particulate leaching method and freeze-drying method. In this study, MG63 cells (osteosarcoma) was investigated for cellular study. Energy dispersive X-ray analysis confirmed uniform distribution of ceramic phase in polycaprol actone matrix. The results of mechanical tests showed the increase in young’s modulus after addition of ceramic phase. The microscopic investigations demonstrated that the pores generated after addition of ceramic phase and the average size of pores was as large as 100-600μm. Also by the addition of LDH, the hydrophilicity of PCL increased but the rate of hydroxyapatite formation was delayed due to presence of magnesium ions. The cell culture experiments confirmed the attachment and proliferation of cells on the scaffolds. The results showed that the fabricated scaffolds have the potential to be used in cancellous bone tissue engineering.

Simultaneous application of mechanical pressure and electrical charge on powder samples in spark plasma sintering process, has resulted in a sample with a density close to the theory. In the present study, a thermal-electrical-mechanical coupled finite element model of spark plasma sintering system using multi-objective optimization algorithm is proposed to optimize the mold variable. The simulation performed for Si₃N₄-SiO₂ (1:1 mol) specimen has good agreement with the experimental results. Multi-objective genetic algorithms was used for optimization of mold design in order to maximize the temperature of sample core and minimize the mises stress in the mold. The results show that the optimized dimensions cause 8% increase in sample temperature and about 18% decrease in temperature difference between mold surface and sample core. This leads to better uniformity in the porosity distribution of final sample.