Journal of Advanced Materials in Engineering (Esteghlal)

In this research, stiffness of polymer-clay nanocomposites was simulated by Mori-Tanaka and two and three dimensional finite element models. Nanoclays were dispersed into polymer matrix in two ways, namely parallel and random orientations toward loading direction. Effects of microstructural parameters including volume fraction of nanoclays, elastic modulus of nanoclays and interphase, thickness of interphase, aspect ratio of nanoclays and random orientation of nanoclays on elastic modulus of the nanocomposite were investigated by finite element model. Comparing the simulation with experimental results showed that the Mori-Tanak simulation results were closer to the experimental results. Analysis of results showed that the volume fraction of nanoclay, elastic modulus of nanoclay, deviation of nanoclay layers with respect to loading direction, nanoclays aspect ratio, thickness of interphase and the elastic modulus of interphase had respectively the most to the least effect on elastic modulus of nanocomposite.

In this study, the effect of Al₂O₃ addition as a diluent during mechanically activated self-propagating high temperature synthesis (MASHS) of Al₂O₃-ZrB₂ composite was investigated. For this purpose, the thermite mixture of Al, ZrO₂, H₃BO₃ and different amounts of Al₂O₃ (0, 3, 6, 9 wt.%) were used as the raw materials and mechanically activated for 5 h, then furnace sintering was performed at 650 °C. The results showed that by increasing the Al₂O₃ content up to 6 wt.%, the intensity of exothermic peak in the DSC curves increases, but for higher additive contents it decreases. In this case, more homogenous distribution of ZrB₂ particles with finer grain size was observed.

In this research, TiAl/Al₂O₃ composite was synthesized from mechanically activated TiO₂-Al powder mixtures using microwave heating.The initial powder mixtures were mechanically activated and pressed into cylindrical tablets and then heated in a microwave oven. The effect of different amounts of excess Al and microwave susceptor material (SiC or graphite) on the ignition time and the resultant reaction products were evaluated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used for characterization of the synthesized samples. XRD patterns revealed that when there was no excess Al in the initial powder mixture, the main resulting intermetallic phase would be Ti₃Al with negligible amounts of TiAl, while with 10 wt% excess Al, TiAl phase could be formed in the composite product.The results also showed that microwave synthesis took place faster and more reproducible when samples were packed in the graphite powder than when placed between two SiC blocks.

In this study, NBG was successfully achieved through a sol-gel technique, and to further improve its dispersibility, a crylate coupling agent was coupled onto the surface of the NBG. The 3-(Trimethoxysilyl)Propylmethacrylate coupling agent was used to the surface modification of the synthesized NBG by a wet-chemical method in a dynamic inert nitrogen atmosphere. The surface properties of the biomaterials before and after modification were characterized and compared using FTIR and AFM techniques. The characteristic peaks in FTIR spectra indicated that –CH2, –CH3 and C=O groups appeared on the surface of modified NBG, and also, AFM analysis revealed that the dispersibility of surface modified NBG was improved, significantly. The above results proved that the desired groups of 3-(Trimethoxysilyl)Propyl methacrylate had been covalently bonded onto the surface of NBG. Besides, a nanocomposite scaffold was synthesized using the synthesized NBG and polyurethane foam as raw materials. The morphology of pores, porosity contents, compress strength and bioactivity of the scaffold were studied. The results showed that the biological scaffolds for use in bone tissue engineering with the basic requirements (90% porosity and 200-600 μm pore diameter) were successfully prepared. The polymer component had no effect on the relationship between the scaffold pores and bioactivity of bioglass nanoparticles. Improvement of compressive strength and proper bioactivity of the resulted scaffold showed that it is an acceptable candidate for biomaterials applications.

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.

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 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.

In this study, aluminium composite foams reinforced by different volume fractions of SiC particles as reinforcement and stabilizing agent were fabricated with the direct foaming route of melt using different contents of CaCO₃ as foaming agent. The density of produced foams were measured to be from 0.38 to 0.68 g/cm³. The microstructural features and compressive properties of the AA356/SiC_p composite foams were investigated. The relation between plateau stress, density and, weight percentage of CaCO₃ and SiC_p volume fraction with a given particle size was also investigated. The results showed that compressive stress-strain curves of the products were not smooth and exhibit some serrations. Also, it was shown that in the same density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiC particles and decreasing weight percentage of CaCO₃.

In this study, fabrication of an in-situ composite through aluminothermic combustion synthesis in An Al–V₂O₅-NiO system was investigated. Therefore, Al, V₂O₅ and NiO powders with stoichiometric ratio of 11:1:1, respectively, were milled for an  hour and finally the mixtures were compressed. In order to investigate the temperatures of phase transformations, Differential Thermal Analysis (DTA) was utilized. Heat treatment was applied on the raw samples according to their peak temperatures treated in DTA. X Ray Diffraction (XRD) analysis for the samples shows formation of phases such as Al₃V and Al₃Ni₂ at different sintering temperatures. Microstructure and phase analysis showed that during sintering of this sample, Al₃V phase was not formed below 700 °C, at 880 °C Al₃Ni₂ it was formed and after 950 °C, it was transformed to Al₄Ni₃ phase. In addition, after 950°C, Al₃V transformed into Al₂₃V₄ phase. Analysis of samples density and hardness showed that, due to increase of volume fraction percentages of reinforcing phase, these two parameters increase as well.

In this research, the wear behavior of commercial grades of WC-10wt%Co (H10F), WC-40vol%Co and WC-40vol%FeAl-B composites with different amounts of boron from zero to 1000 ppm has been investigated by the pin on disk test  method at high temperature. The wear tests were done under load of 40 N, a distance of 100 m and at ambient temperature, 200 ̊C and 300 ̊C. Wear surfaces were examined by scanning electron microscopy. The results showed that the wear resistance of all composites decreased with increasing temperature. The boron free WC-40vol%FeAl composite showed the lowest wear resistance at all ranges of temperature. In the presence of boron up to 500 ppm in iron-aluminide matrix, the high temperature wear resistance of these composites improves and the wear mechanisms changes from particle pullout into abrasive state. The toughness enhancement of these composites and plasticity enhancement of iron aluminide in the presence of boron, leads to better link of the interface of FeAl matrix and tungsten carbide particles, and thus increases the wear resistance of these composites. WC-40vol% FeAl-500ppmB composite has a higher wear resistance at high temperature than WC-40vol% Co and commercial WC-10wt% Co.
 

Investigating the effect of Al₂O₃-TiB₂/Fe complex reinforcement (CCMR) on the mechanical properties of aluminum composites was the goal of this study. For this purpose, the Al₂O₃-TiB₂/Fe reinforcement powders were synthesized during milling and subsequent annealing. Different volume percentages of the produced reinforcement powders (1.25, 2.5 and 5 vol.%) were added to aluminum matrix, milled for 10 h and then hot extruded. The structural phasic and mechanical investigations of the specimens were carried out using X-ray diffraction, scanning electron microscopy and tensile test. The results showed that the metallic component (Fe rich phase) in this new type of reinforcement stuck the ceramic parts (Al₂O₃-TiB2) to aluminium matrix, and has an importance role in the flexibility of the product. The best volume percentage of CCMR in aluminium matrix was about 2.5%. This nanocomposite had a combination of strength and ductility of about 500 MPa and 6%, respectively.
 

In this paper, the optimization of the surface composite of Mg AZ31B-carbon nanotub(CNT) via friction stir processing was investigated. Then, the most effective process parameters such as transverse speed, rotational speed, CNT weight percent and welding passes were studied by Response Surface Methodology (RSM) design of experiment. The specimens were also characterized by micro-hardness, tensile, shear punch and pin on disk dry sliding wear tests. The optimization results of hardness and weight reduction responses showed that the best conditions would be achievable with a transverse speed of 24 mm/min, rotational speed of 660 rpm, 4wt.% CNT and 3 welding passes. Moreover, fracture analysis of the surfaces proved a uniform distribution of CNTs in the matrix resulted in higher tensile and shear strength.
 

In the present study, FeAl/Al₂O₃ nanocomposite coating was produced on the carbon steel plate using mechanical alloying (MA) technique via a mechanochemical reaction. Stoichiometric ratios of Fe, Al and Fe₂O₃ as well as a substrate were mixed and milled up to 22h in a vibrating high energy mill with a 4 mm ball. Samples prepared after 18h of MA were subjected to annealing at 773 K for 1-3 h. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and microhardness measurements were carried out to study mechanochemical reaction and coating formation characterization. The results showed that mechanochemical reactions were started after 10h of MA, which finally caused the slight formation of FeAl/Al₂O₃ nanocomposite. Increasing the milling time to 18 hours led to the continuous increase of the coating thickness up to 80 μm, while the coating layer fractured and began to peel by further milling. The microhardness of the coating after 18h milling was 1050 vickers. Annealing of the 18h milled powders at 773K for 3h led to the complete formation and synthesis of the FeAl/Al₂O₃ nanocomposite. The results showed that the annealing treatment had considerable effects on the hardness increase up to 1200 vickers as well as adhesion strength of the composite coating.
 

TiO₂/MWCNT nanocomposite thin films containing different percentages of multi-walled carbon nanotubes were coated on fluorinated tin oxide substrates by sol-gel dip coating method. Results of X-ray diffraction analysis indicated that the crystal structure of the coatings was anatase TiO₂. It was also understood that the size of crystallites reduced with CNT but structural properties and equilibrium phase remain intact. Field emission scanning electron microscope images showed that CNTs dispersed uniformly among 45 nm spherical TiO₂ particles of close relations. These images also showed that CNT promoted cracks on the coated surface. Results of the UV-Vis spectroscopy showed that the visible light range adsorption  increased with CNT and the absorption edge did not significantly differ with the pure TiO₂ layers.. Results of the photoluminescence spectroscopy revealed that the presence of CNT could reduce the pair electron–electron holes recombination which is considered totally undesirable.