مجله مواد و فناوری های پیشرفته
سال هشتم شماره 3 (پاییز 1398)

In the present study, Al 6061/Gr nanocomposites with a nanocrystalline matrix structure containing different amounts of graphite micro-particles were synthesized via Powder Metallurgy (P/M) method through mechanical milling, cold pressing and hot extrusion. Due to the limited quantity of the produced nano-composites and impossibility of making standard tensile test specimens, a shear punch test setup was used for evaluation of the mechanical properties of these materials. The results of XRD and SEM studies revealed that Gr particles were uniformly distributed in the nanostructured Al matrix. Hardness measurements showed that increasing the volume fraction of Gr resulted in decreased hardness of Al/Gr nanocomposites. The results of shear punch tests at room temperature revealed significant higher shear yield stress and ultimate shear strength by decreasing the grain size of Al-6061. However, Gr addition deteriorated the shear strength and ductility of Al/Gr nanocomposites. These observations confirmed that the Hall-petch mechanism was the major strengthening mechanism for these nanocomposites.

Electrochemical deposition of manganese hexacyanoferrate nanoparticles on a graphite substrate for supercapacitor application Electrochemical deposition of manganese hexacyanoferrate nanoparticles on a graphite substrate for supercapacitor application In this research, manganese hexacyanoferrate nanoparticles were deposited on a graphite substrate via electrochemical deposition method at a pulse constant current of 100 μA (0.5 s on and 0.5 s off) and at room temperature. The as-prepared electrode was characterized using X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). Electrochemical performance of the binder-free MnHCF electrode as supercapacitor electrode was investigated using cyclic voltammetry and galvanostat charge /discharge measurements in solution of 0.5 M sodium sulfate. The results of electrochemical tests showed that the prepared electrode possessed a high specific capacitance of 367 F g-1 at a current density of 1 A g-1, an appropriate rate capability and good capacitance retention of 88.8% after 1,000 cycles, indicating its high energy storage performance.

Magnesium alloys, with suitable strength, human-like elastic modulus and density, have potential medical applications in the field of biodegradable implant materials. However, one of the most important barriers to clinical applications of magnesium alloys is the rapid corrosion of these alloys in human body fluids. Grain refinement is an effective way to increase the strength and ductility of magnesium alloys and may improve the corrosion resistance of them. Grain refinement due to the thermomechanical process is an effective way to increase the strength and ductility of magnesium alloys and may affect the corrosion resistance of magnesium alloys. Hence, in this study, the effect of thermomechanical process (including warm forging at 250 ˚C and then annealing for 1 hour at 300 ˚C) on the corrosion behaviour of AZ31 magnesium alloy after 1, 4 and 7 days of immersion in a simulated body fluid was investigated at 25 ˚C. To investigate the microstructure of the samples, an optical and scanning electron microscopes were used. The electrochemical polarization and impedance tests were used to evaluate corrosion rate and corrosion resistance, respectively. The microstructure analysis of the samples showed that the thermomechanical process refined the grain and caused the twins to appear. In fact, the recrystallization resulting from the thermomechanical process caused the grain to refine, increasing the grain boundaries, and reducing the dislocations density, which, in turn, prevented corrosion. The results of impedance and polarization tests also showed that the corrosion resistance of AZ31 sample under thermomechanical operation increased after 7 days of immersion and decreased its corrosion rate.

Metal composite reinforced with ceramic particles, due to the desired mechanical and physical properties, are widely used in various fields, including wear-resistant parts and cutting tools. In this study, Fe-TiC composite is made using ilmenite mineral and soot. In order to make the composite, the raw materials after homogenization and activation through mechanical alloying were synthesized and sintered simultaneously by spark plasma sintering. Samples were prepared at temperatures of 1250, 1300 and 1350°C, under pressure of 10 to 30 MPa for 30 to 120 minutes. X-ray diffraction analysis was used to identify phases. Measurements of crystalline size were performed using the Williamson-Hall and Scherrer methods. Morphology and microstructure of the samples were also examined by scanning electron microscopy. The results showed that the iron composite reinforced with carbide titanium particles was successfully produced and the synthesis mechanism was gradual and intrusive. Iron and titanium carbide grains have a uniform distribution throughout the sample, and despite the long synthesis time, the size of grain remain in the nanometric, which can lead to improved mechanical properties.

Industrial wastewater treatment and recycling the treated water are drawn to attention. In this study, the removal of heavy metal cations (e.g. Cu, Ni, Co) as an important pollutants, has been investigated by applying the Nylon6/zirconia nano-composite absorbent. Nano-composite membranes containing different amount of zirconia nano-particles (NPs) were synthesized via electrospinning method. To study the microstructure and functional molecule groups of nano-absorbent, SEM and FTIR techniques were used, respectively. The results showed that the average diameter size of fibers and surface porosity decreased from 387 to 105 nm and 83.1 to 65.6 % with increasing the zirconia content, respectively. Furthermore, zirconia NPs were distributed heterogeneously and also electrospinning defects such as zirconia agglomerates were observed in the mat. Adding the zirconia NPs did not affect the functional molecule groups of Nylon6. According to the homogenous distribution and also creation of active sites by zirconia NPs, the ratio of zirconia to Nylon6 equals to 0.88 (g/g) was selected as the optimized composition. Water contact angle variations on the surface of nano- absorbent indicated that the mentioned surface had hydrophobic behavior at the beginning time of contact and then it switched to the hydrophilic manner. Kinetic study on the adsorption of heavy metal cations showed that it was followed by first-pseudo order model. The maximum adsorption was recorded 9.6, 8.7 and 4.8 mg/cm2 respect to the Cu, Ni, and Co cations. It suggests that the Nylon6/zirconia nano-composite has high efficiency to adsorb heavy metal pollutants. Eventually, the water recycling will be achieved by development of polymer-ceramic nano-composite.

In this study, graphene oxide was prepared by a modified Hummers’ method and used as support for dispersing of nanoparticles. SrCoO3-δ nanoparticles were prepared and characterized by X-ray diffraction technique. They were used accompanied by Pt nanoparticles on the reduced graphene oxide (RGO) support for preparing of Pt-SrCoO3-δ-RGO catalyst. Transmission electron microscopy images were used to show the morphology and distribution of nanoparticles. The catalytic activity of the prepared catalyst was investigated for methanol electrooxidation by cyclic voltammetry and electrochemical impedance spectroscopy techniques and compared with the catalytic activity of Pt-RGO catalyst. The effects of some experimental parameters affecting on methanol oxidation such as methanol concentration, temperature and scan rate were investigated on Pt-SrCoO3-δ-RGO catalyst and the optimum conditions were suggested. Pt-SrCoO3-δ-RGO catalyst showed better catalytic activity for methanol oxidation compared with Pt-RGO catalyst indicating that Pt-SrCoO3-δ-RGO can be used as a promising catalyst for application in direct methanol fuel cells.

magnetic graphene nanocomposites are suggested for application in modern technology because of their controllability via external magnetic field and their electrical conductivity. Electrochemical deposition method has found great advantageous to manufacture graphene/metal nanocomposite because of being simple, one –step and cost-effective method. In this research, the effect of electrolyte pH on magnetic response of graphene/cobalt nanocomposite synthesized by electrochemical deposition technique is studied. Synthesized samples in neutral and basic environment are nonmagnetic. Whereas, synthesized samples in acidic solutions are magnetic. In an acidic environment with pH=5, graphene-cobalt nanocomposites are produced with high output mass of synthesized materials and high magnetization. Optimum magnetic sample produced with pH=5 is characterized via X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and magnetic properties is determined with vibration sample magnetometer (VSM). Morphology of samples is probed by electron microscopy (SEM). The composite consists of graphene sheets and cobalt crystals with a high saturation magnetization of about 119 emu/g which has a potential for application in targeted drug delivery, water remediation, magnetic bio sensors, etc.

As to the crisis of energy in the recent years, devices manufacturing industry must be go toward the optimizing of energy consumption and increment in the lifetime leading to reduce production cost. Organic light emitting diodes (OLED) are one of the modern generations in the lighting industry that have many advantages such as being light and thin, flexibility, ability to be transparent, and easy to fabricate. These devices consist of hole injecting layer/electron and emissive layer. The main role of hole/electron injection layers is injection of charge carriers to emissive layer where electrons and holes recombinate and create photons. In this work we focused on optimization of hole injection in order to increase lifetime of device. We used the different composition of molybdenum oxide (MoOx) and graphene oxide (GO) in hole injection layer. The maximum efficiency of the devices owned to the composite thin film with 1:1 value ratio (MoOx:GO) that it could be reached to 7.5 lm/W.  The lifetime of the optimization of composite was compared to the standard device fabricated with PEDOT:PSS so that the results showed a 30 times enhancement in lifetime.