مجله مواد و فناوری های پیشرفته
سال هفتم شماره 1 (بهار 1397)

Abstract The aim of this work is to optimize the hardness of anodizing aluminum coating by design of experimental method. Various parameters affect the hardness of these coatings among which time, temperature and pulse current parameters (current density limit, frequency and duty cycle) were considered. According to this, mentioned parameters in different levels were considered as input variables. Also, the effect of parameters on the hardness of anodizing aluminum coating was obtained as a mathematical model. The final model was achieved by Analysis of variance which was used for attaining the best method to predict the maximum hardness of these coatings. The most effective variables and optimized hardness of anodizing aluminum coating were obtained by using the mathematical model. Experimental results showed that temperature and quadratic behavior of duty cycle were the most important terms on the hardness of these coatings. Furthermore, the maximum hardness of this coating was 491Hv, which was attained at the maximum and minimum current densities of 4.09, 1.23 A/dm2, frequency of 146.94 Hz, time of 29.50 min, duty cycle of 65.16% and the bath temperature of 3.13oC.

Cobalt ferrite (CoFe2O4) powders were successfully prepared by solution combustion synthesis using metal nitrates as oxidant and glycine as fuel at various fuel to oxidant molar ratios (?=0.5, 0.75, 1 and 1.25). The structure, morphology and specific surface area of as-combusted CoFe2O4 powders were characterized by X-ray diffraction, scanning electron microscopy and nitrogen adsorption-desorption techniques. By increasing of fuel content, the specific surface area and pore volume decreased from 285 to 35 m2/g and 1.38 to 0.17 cm3/g, respectively. The as-combusted magnetic CoFe2O4 powders were used as adsorbent for removal of Cd(II). The effect of the contact time showed the kinetics of adsorption process followed the pseudo-second-order model and was controlled by film diffusion process. The adsorption isotherms were also well fitted on the Freundlich model. The as-combusted CoFe2O4 powders at ?=0.75 exhibited excellent adsorption capacity (694 mg g?1) and high adsorption rate.

Tungsten carbides are used in cutting blades and other similar items because of their high hardness. In this study, tungsten carbide (WC) powder and cobalt (Co) powder in size of less than 10 microns and weight ratio of 94% tungsten carbide and 6% cobalt (WC-6% Co) were mixed together in a high-energy mechanical milling. Then they milled in various ratios of ball to powder and time. Milled samples were studied using scanning electron microscopy (SEM). The results obtained were compared by microscopy and EDX elemental analysis. Optimized powder for the production of powder metallurgy sample was selected and sintered. Metallography and hardness testing and SEM imaging was performed on sintered sample. The results showed a significant improvement in grain size to reach below 100 nm in the milled powders and in the sintered samples were reaching below 150 nm. Vickers hardness in the final sample reached in 1752.

In the present work, charged graphene oxide (GO) layers were synthesized using conventional modified Hummer?s method. A thin film of GO was deposited using electrophoretic deposition technique from stable aqueous colloidal suspension of GO layers on hydrophobic surface of crystalline silicon (c-Si) samples. Surface modification with Ag particles was performed in order to improve surface adhesion of graphene oxide layers on hydrophobic silicon surface. Reduction process of deposited GO layer was performed at a temperature of 400 C under argon gas flow. The x-ray diffraction pattern showed that graphite layers with oxygen functional groups and increased interlayer spacing were successfully obtained using improved Hummer?s technique. Scanning electron microscopy micrographs showed that non-uniform GO layers were formed on silicon hydrophobic surface. Enhanced surface adhesion and deposition of a uniform thin film of GO was achieved via surface modification using Ag particles. Raman spectra of deposited films proved the existence of GO layers which were reduced.

Effect of Cu addition (5 wt.%) on the microstructure, hardness and antibacterial properties of the martensitic stainless steel (AISI 410s ) was investigated by means of scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and hardness measurement. Antibacterial performance was evaluated according to JIS Z 2801:2000 against Escherichia coli (E. coli) bacteria, the common pathogen of human disease. After austenitization treatment at 1050 C in a salt bath and oil quenching, the AISI 410s steel showed dual phase martensite-ferrite microstructure. Addition of about 5 wt.% Cu eliminated ferrite and led to a fully martensitic microstructure in the quenched condition. The latter associated with primary Cu precipitates formed during austenitization treatment. Aging treatment of the quenched steels was carried out at 500-700 C for one hour in a salt bath. Transmission electron microscopy (TEM) revealed the formation of fine, Cu-rich precipitates in aged Cu-bearing stainless steel (AISI 410s-Cu). After aging for one hour at 500 C, hardness of AISI 410s steel increased for 30 HV while that of AISI410s-Cu steel increased for about 100 Hv. AISI 410s steel represented no antibacterial performance against the E. coli bacteria but hopefully AISI 410s-Cu stainless steel exhibited strong antibacterial performance. Both of the primary and aging Cu precipitates are thought to release Cu ions to biological environment which act toxically against the E. coli bacteria.

In this work crushed coconut coir was chemically modified by EDM method and its ?performance as adsorbent for removal of nitrate from aqueous solutions was investigated. In this regard, the effect of various parameters like time, adsorbent dosage, nitrate initial concentration, pH, and temperature on the adsorption process was studied. It was ?observed that the kinetic data followed the pseudo-first order kinetic model and the adsorption ?isotherms were properly fitted to Langmuir model. Thermodynamic analysis showed that the ?adsorption process was spontaneous, exothermic with decreased randomness at solid-liquid ?interface. Moreover, the adsorbent showed a superior performance at neutral pH and the adsorbed ?nitrate could easily be desorbed by adjusting pH of the solution suggesting the reusability of the ?adsorbent.?

In this study, curcumin/chitosan (Cs/Cr) nanocomplex with different weight percentages Cs/Cr (1:1) (sample A) and Cs/Cr (2:1) (sample B) by drug-poly saccharide complex method were fabricated and encapsulated into chitosan/alginate hydrogel and then the samples were evaluated. The morphology and functional group of the samples surface were evaluated via the scanning electron microscopy (SEM and FESEM) and fourier transform infrared spectroscopy (FTIR), respectively. The average hydrodynamic diameter of nancomplex A and B by the dynamic light scattering (DLS) were measured 80nm and 45 nm, respectively and their zeta potentials were obtained mV and mV, respectively. For characterization of Cs/Cr nano complex loaded hydrogel, the water vapour transmission rate (WVTR) and the swelling test in PBS were performed. The results indicated that hydrogel containing nanocomplex B with high absorbing fluids (2049%) and good WVTR (2300 g/m2/day) can be suitable for creating a wet environment for wound healing. Also, in vitro release studies by HPLC method was performed for evaluation of curcumin release from nano complex and the results showed a sustained release without initial burst release. To study the release mechanism of curcumin from nanocomplex, data obtained from release test were fitted to Korsmeyer-Peppas kinetics model. Also, the encapsulation efficiency of curcumin in nanocomplex was meseared 80% that the results indicated a high curcumin loading in nanocomplex. Finally, the viability and proliferation of fibroblast cell line (L929) on nano complex surface was evaluated by MTT assay and the results did not showed any cytotoxicity. Therefore, the hydrogel containing Cs/Cr nano complex can be a good choice as wound dressing for rapid healing.

Recently, nitrogen alloyed steels have attracted the attention of researchers and industrial specialists due to their combination of strength and elongation. The identification of mechanical properties of nitrogen alloyed steels is very important for using these alloys with high reliability in various applications. Meanwhile, the resistance of material to crack propagation is one of the important parameters. Nowadays, nanoscience and computer simulations at nanoscale are noticed as the most studied subjects in the world. Molecular Dynamics Simulation (MDS) is one of the numerical methods at nanoscale which is the most deterministic method among available methods for the solution of molecular systems. The aim of this study is to simulate the crack propagation in Iron-Nitrogen nanocrystalline. In this regard, Iron-Nitrogen nanocrystalline is modeled by applying Modi?ed Embedded Atom Method (MEAM) interatomic potential using the related parameters for Iron-Nitrogen alloy. The microstructure of crack growth in nanocrystalline with dimension are investigated under tensile loading with velocity magnitude of 0.8 /ps at temperature of 300K. The results show that crack velocity increases with the increase in crack length. The increase in the peak of radial distribution function curve during different time steps is as a result of change in the positions of particles during crack propagation. Also, the results indicates that the magnitudes of stress at three crystal directions has firstly nonlinear behavior and then changes to linear one which is due to the change of direction of crack growth during simulation time steps. Also, the track-growth direction and the track opening are investigated under simulation conditions.In this study, the OPLS all-atom model was developed for sulfur mustard in order to study the adsorption of this compound on graphene. Intramolecular bonding parameters and Lennard?Jones nonbonding parameters are taken from the OPLS all-atom force field database. Partial charges are determined by ab initio calculations at HF/6-31g(d) level. The results showed that the OPLS all-atom force field predicts the physical properties of sulfur mustard like density and heat of evaporation with the mean error of less than 1% and 5% respectively at temperatures of 298 K and 293 K compared to experimental data. The comparison of intramolecular bonding parameters obtained from molecular dynamics simulation and quantum mechanical calculations showed that these results are well consistent with each other. Also, the study of the interaction energy between sulfur mustard and graphene by molecular mechanics and quantum mechanics on coronene as a model of graphene indicated that OPLS force field can be used as an accurate and reliable model in the molecular dynamics simulation studies of this compound on the adsorbents based on graphene.In this study, Ce oxide and Ru-Ce mixed oxide were prepared by co-precipitation method in alkaline media. Also, the Ru-Ce mixed oxide nanoparticles were synthesized by a reverse micelle approach. All of the samples were characterized with XRD and BET methods and the size of nanoparticles synthesized in the reverse micelle was measured by the TEM technique. The catalytic activities of synthesized samples were investigated for oxidation of benzyl alcohol in the presence of molecular oxygen and solvent free condition. The obtained results show that the nano-catalyst is suitable candidates for the oxidation of benzyl alcohol to the benzaldehyde. In order to obtain maximum conversion of benzyl alcohol, the reaction parameters, like reaction temperature, amount of catalyst and reaction time, were optimized. Under the optimized conditions, a maximum of 99%benzyl alcohol conversion and 94 % selectivity for benzaldehyde was achieved with Ru-Ce nano mixed oxide as catalyst, at 80 oC and 3h.