فصلنامه مواد پیشرفته در مهندسی
سال سی و هفتم شماره 2 (تابستان 1397)

Due to electrical properties (high electron mobility) and electrochemical characteristics (high electron transport rate), graphene-based materials have been widely applied for various scientific fields. However, due to their two-dimensional structures, these materials have low active sites for reaction. Therefore, changing from two-dimensional sheets dimensional to the three-dimensional ones could provide graphene-based materials with high specific surface and electron and mass transport particles. For these purpose, reduced graphene oxide (rGO) and polystyren (PS) aqueous solution were mixed with two different weight ratios kinetic. In this study, the three-dimensional graphene (3DG) was synthesized with graphene oxide using sacrificial PS particles. For this purpose, rGO and the PS aqueous solution were mixed with two different weight ratios of 95:5 and 85:15. Then, the 3DG-PS scaffolds were synthesized by controlling the pH value in the range of 6-8. Subsequently, PS particles were removed by immersing the synthesized scaffolds in toluene. In this research, the effect of filtering through the member filter and centrifuge on the morphology of the scaffolds was investigated. The scaffolds were characterized with X-ray diffraction and scanning electron microscopy. The results showed the formation of 3DG with a uniform distribution of porosities by using the centrifuge procedure. Moreover, the sacrificial PS particles were completely removed when the rGO to PS weight ratio was 95:5. So, 3DG with the uniform distribution of microscopy porosity could be synthesized through the sacrificial mold method and the centrifuge procedure; graphene oxide was also reduced with the PS weight ratio of 95:5. Further, based on the electrochemical evaluation of this optimized sample, as compared to the rGO , it was found that the 3DG had better electrochemical properties than the rGO. Therefore, 3DG with the optimized rGO to PS weight ratio of 95:5 could be an ideal substitute for rGO in electrochemical applications

NdFeB magnetic alloy is one of the hard magnets having the highest maximum energy in the world. The most popular methods of manufacturing magnetic alloys Nd2Fe14B are powder metallurgy and rapid quenching techniques. In this research, the effect of the hot press temperature on the magnetic properties of the hard magnet Nd2Fe14B was studied. Structural studies were carried out using X-ray diffraction, X-ray fluorescence spectrometer and Scanning Electron Microscope; Spectroscopic energy distribution of Nd2Fe14B bulk magnet and the magnetic tests were done using a vibrating magnetometer to investigate the structures and the magnetic properties of the produced samples. The results showed that in addition to the Nd2Fe14B phase, the α-Fe and Nd-rich phase also existed in the structure of the provided magnet. These secondary phases had effectively created exchange couplings with the main phase, improving the magnetic properties. The magnetic properties of the sintered magnets were improved by increasing the press temperature; finally, Nd2Fe14B magnet was made with the maximum energy, which was d higher than 290 kj/m3

This paper was concerned with the effect of Mg on the temperature mechanical behavior and evaluation of the microstructure. The results showed that with increasing Mg from 0 to 47 ppm, the grain size was reduced from 64 to 38 µm and the carbides volume fraction was raised from 2.2 to 4.6 vot%. Mg changed the morphology of the carbide from a coarse and continuous one to a separate one. Mg with the mechanisms of grain boundary and matrix/carbide boundary led to changing the carbide composition and also, the mechanical properties. Mg increment from 0 to 47 ppm caused the enhancement of yield strength and rupture life from 309 to 345 MPa and from 16h to 30h, respectively. Grain size and the amount of carbide were the main factors contributing to the rupture of life properties in this study. The increment of the carbide volume fraction was the main mechanism of rupture life enhancement

By using cathodic plasma electrolysis, a thin film of diamond-like carbon and carbyne was produced on the nickel surface. The ethanolic solution at different concentrations of 15, 30 and 50 vol% was used as the electrolyte; the produced carbon film was studied by using glow discharge optical emission spectroscopy, scanning electron microscopy, optical profilometer, and surface enhanced Raman scattering. The results proved the coating formation of 40-60 nm thick carbon materials on the nickel surface. The intensity ratio of carbyne band to the amorphous carbon structure band in the Raman spectroscopy was decreased from 1.o4 to 0.32 by an increase in ethanol concentration; this was related to the reduction at the carbyne and the increase of the diamond-like carbon content in the produced film. Also, the study of the samples surface showed an increase in the surface roughness from 520 to 750 nm by enhancing the ethanol concentration

In this research, Ni-Mo-Al2O3 composite coatings were electro-deposited on the mild carbon steel in a citrate bath containing micro- sized Al2O3 particles. Afterward, the effect of the particle concentration in the electrolyte bath (ranging from 0 g/L to 30 g/L) on the microstructure, microhardness, and corrosion performance was evaluated. To investigate the microstructural changes and the surface morphology of the coatings, as well as the particle distribution in the deposits, optical and scanning electron microscopy coupled with the energy dispersive X-ray spectroscopy was utilized. The corrosion behavior of the prepared coatings was investigated in a 3.5 wt. % NaCl solution. The results showed that the presence of the Al2O3 particles in the Ni-Mo coatings changed the microstructure and also, increased the microhardness and corrosion resistance of them. It was also found that the desirable structure of the protruding crystallite morphology with no detectable pores could be achieved at the medium concentrations of reinforcement (e.g. 20 g/L). Further the optimum concentration of the particles in the electrolyte bath to attain the composite coating with the desirable microstructure and consequently, the desirable corrosion resistance was found to be 20 g/L

The purpose of this paper was modeling and mechanical analysis of the biodegradable biphasic calcium phosphate/silk (BCP/Silk) laminated composite bone plate for fractured tibia healing; to this aim,ABAQUS 6.13 was employed for modeling and mechanical analysis. First, the tibia bone was considered based on the anthropometric measurements of an average person as a two-layer cylinder; the inner part was the bone marrow and the outer one was the cortical bone. Then, the bone plate and screws were designed according to the defined standards and the properties of new composite in the ABAQUS software. The mesh of bone plate and other equipments were selected to be tetragonal and cubic, respectivelly. After that, the bone plate was placed on the bone while the bone was bounded along the Y axis and the force of around 400 N was loaded. The results showed that the biocompatible and biodegradable composite bone plate had the elastic modulus of about 21 GPa, which was close to the bone modulus

Rutile-phase titanium dioxide nanorod arrays were prepared by the hydrothermal method. Then, anatase-phase nanoleaves were successfully synthesized on the nanorod arrays via mild aqueous chemistry. Nanorod arrays scanning electron microscopy revealed that the thin film is uniform and crack free and the average diameter and height of the nanorods are 90 nm and 2 µm, respectively. Furthermore, nanorods are vertical to the substrate surface and have desired coverage density due to the predeposition of TiO2 seed layer which leaded to decrease the surface roughness of the substrate. Nanoleafed nanorods scanning electron microscopy indicated that the nanoleaves were grown uniformly on the entire surface of nanorods and the specific surface area and roughness factor of those are significantly improved. Energy dispersive spectrums suggested that F- and Cl- ions are partially doped into TiO2 crystals. Raman and X-ray spectra confirmed the formation of anatase-phase nanoleaves on the rutile-phase nanorods. X-ray diffraction also indicated that the nanorod arrays are highly oriented with respect to the substrate surface. The diffused reflectancetransmittance data revealed the incident light was more efficiently harvested by the nanoleafed nanorod thin film and the values of energy gap are 2.78 and 2.82 eV for rutile TiO2 nanorod and rutile橶굪 TiO2 nanoleafed nanorod thin films, respectively. Synthesized nanostructure, having improved charge separation and transfer (due to the presence of the surface anatase/rutile junctions), high specific surface area and light harvesting (due to the presence of the nanoleaves) and low band gap energy (due to the nonmetallic elements doping), is viable alternative to traditional single crystalline TiO2 nanorods for highly efficient photoelectrochemical applications

Nitride coatings with excellent hardness and wear resistance have been deposited by physical vapor deposition (PVD) in recent years. For most applications, the load bearing and adhesion of coatings are very important and can determine the life and performance of the final components. In this study, CrN/CrAlN nanostructured coatings with different thicknesses and numberes of layers were deposited on the stainless steel AISI 420 and hot-work tool steel by cathodic arc evaporation. Nanoindentation, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) were used for the structural characterization and estimation of stress in the coatings. Adhesion of coatings was evaluated by scratch adhesion and VDI 3198 Rockwell tests. The results revealed the high values of compressive residual stress in the physical vapor deposited coatings, in the range of 500 to 1800 MPa, with a detrimental effect on coating adhesion. Load bearing capacity was observed to be dependent on the thickness and adhesion of coating, reaching the maximum at an optimum thickness. Overall, the results proved that the type of steel substrate could have a significant influence on the coating adhesion