فصلنامه مواد پیشرفته در مهندسی
سال چهلم شماره 1 (بهار 1400)

In this research, a kind of environmentally-friendly inorganic-organic hybrid nanocomposite coating based on silica containing titania/silica core/shell nanoparticles was synthesized and characterized for conservation of facade tiles in historical buildings. The matrix of the composite was prepared by sol-gel process via two methods of ultrasonic and reflux stirring. Tetraethyl orthosilicate (TEOS) and poly-dimethyl siloxane hydroxy-terminated (PDMS-OH) were used for the formation of silica network and creation of flexibility and hydrophobicity, respectively. Titania nanoparticles were used in the form of titania/silica core/shell as ultraviolet absorber. The synthesized nanocomposite was applied on the microscope slides and tiles by dip coating technique. The properties of nanoparticles and coatings were characterized by Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and water contact angle measurement. The results revealed that formation of titania/silica core/shell structure was successful. The investigation of PDMS content effect on transparency, cohesion and hydrophobicity of the coating confirmed that the optimum content of this siloxane was around 20 wt.%. In general, the results showed that the silica-based hybrid nanocomposite reinforced with TiO2/SiO2 core/shell nanoparticles could produce a transparent and hydrophobic coating for tile and glass protection.

Silver nanowires (AgNWs) are considered as one-dimensional nanostructures, which have received much attention due to their nanoscale size, high aspect ratio, high electrical and thermal conductivity, optical transparency and high mechanical stability. Preparation of AgNWs by polyol process is remarkably sensitive to the interactions between synthesis parameters. In this study, the effect of the simultaneous change of four synthetic parameters, namely the reaction temperature, the molecular weight of polyvinylpyrrolidone (PVP) stabilizer, the amount of sodium chloride, as well as, the solution mixing rate by the polyol process was reported. The results of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) confirmed that the synthesized AgNWs were below 100 nm. X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analysis, as well as, Fourier transform infrared spectroscopy (FT-IR) confirmed that the formed AgNWs were free of impurities. It was also found that temperature, molecular weight of PVP, salt concentration and solution mixing rate caused a significant change in the morphology of AgNWs. More importantly, a strong interaction was created in the preparation process of AgNWs by adjusting the parameters.

In this research, microstructure and mechanical properties of laser welded joints between 2304 duplex stainless steel and Inconel 718 nickel-based super alloy were investigated. Microstructural evolution in the various areas of welded joints and also the effect of welding parameters on the mechanical properties of dissimilar joints were studied. Response surface methodology based on the central composite design was used in order to find the optimum welding parameters. Effective parameters of the welding process including laser power, travel speed and defocusing distance were set in the range of 1000 to 1900 W, 1 to 5 mm/s and -1 to 1 mm, respectively. Uniaxial tensile test was used to evaluate the fracture force of weld joints. The microstructural observations and phase evolutions were studied using optical microscope. It was found that the fracture force of the weld joints firstly increased by travel speed and defocusing distance and then decreased by further increase. The maximum fracture force was obtained when laser power, travel speed and defocusing distance were 1900 W, 3 mm/s and 0 mm, respectively. The center line of weld metal was mainly consisted of equiaxed grains where, columnar grains were formed in the fusion line. The obtained results from the hardness measurement showed that the hardness of Inconel 718 was decreased due to dissolution of TiC and NbC particles.

Mn0.8Zn0.2Fe2-xDyxO4 (where x= 0, 0.025, 0.05, 0.075, 0.1) ferrite nanoparticles were synthesized by auto- combustion sol-gel method for the first time in this study. The effect of Dy-doping on the structural and magnetic properties of the produced specimens was examined using the X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometery (VSM), and field emission scanning electron microscope (FE-SEM). The results showed that a cubic spinel structure was formed in all of the synthesized specimens. It was also found that the addition of Dy increased the lattice parameter while decreased the average of crystallites size. Furthermore, the FE-SEM micrographs showed that Dy not only plays an effective role in reducing the agglomeration of nanoparticles and their distribution, but also reduces the average of particle size. It was also observed that the addition of Dy had no effect on the morphology of the synthesized nanoparticles. Investigation of the magnetic properties revealed a clear decrease in the saturation magnetization and coercivity by the Dy addition. So that the saturation magnetization of the samples decreased from 66.3 to 58.4 emu/g and the coercivity decreased from 78.5 to 71.9 Oe.

In this research, the effect of graphene oxide (GO) and reduced graphene oxide (RGO) nanosheets on the mechanical and microstructural properties of AISI 304 stainless steel welded joints produced by the flux-cored arc welding (FCAW) method was investigated. Light microscope, field emission scanning electron microscope (FE-SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), Raman spectroscopy, and tensile strength test were used to characterize the samples. GO was synthesized by modified Hummers’ method and reduced by hydrazine. Accordingly, the pastes of GO and RGO in different concentrations of 1, 3, and 10 mg/ml were applied in the groove. The results demonstrated that increasing the RGO concentration up to 10 mg/ml improves the tensile strength and hardness values of welded joints up to 23% and 43%, respectively. It seems that RGO nanosheets have a significant effect on the mechanical properties of the welded joints by pinning of dislocations.

In this article, the effects of Pr and Nd were investigated on the microstructure and absorption/desorption characteristics of MmNi5 hydrogen storage alloy. The alloys were prepared in Vacuum induction furnace and the microstructures and phases were analyzed using scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDS) and X-ray diffraction (XRD). Hydrogen absorption/desorption characteristics was performed on Sievert apparatus. The results showed that the microstructure of the alloys consist of matrix, second phase as a result of Al segregation, porosities and cracks. The amount of second phases and Al in this phase in Mm(Pr,Nd)Ni4.7Al0.3  is less than MmNi4.7Al0.3. Al in Mm(Pr,Nd)Ni4.7Al0.3 were more homogenized. Pressure-Composition Isotherms of hydrogen absorption/desorption at 25˚C showed that for MmNi4.7Al0.3 and  Mm(Nd,Pr)Ni4.7Al0.3, absorption pressures were 14.52 and 9.90 bar,  desorption pressures were 5.53 and 5.49 bar, hydrogen storage capacities were 1.37 and 1.33 wt. % and hysteresis were 0.73 and 0.58, respectively. These results are useful in industrial applications, because of inconsiderable decrease in hydrogen storage capacity and the other positive variation in absorption/desorption characteristics, especially the hysteresis and absorption pressure.

In this research, the hot deformation behavior of W360 tool steel was investigated using hot compression test at 1000-1200°C and strain rates of 0.001, 0.01, 0.1, and 1 s-1. According to the results, dynamic recrystallization was found the most important restoration factor of this alloy during hot deformation. Recrystallization was enhanced with an increase in temperature and strain rate. Also, the hot working process was optimized by drawing the processing map of this steel. Microstructural images obtained from the hot compression test showed that recrystallization started at 1000°C and the strain rate of 0.01 s-1 and developed with increasing temperature and strain rate due to an increase in the stored energy and suitable regions for nucleation. The results of drawing the processing map showed that the best hot deformation region was the temperature range of 1050-1150°C and strain rates of 0.1-1 s-1.

This study aimed to compare the phase changes and morphology of yttria-stabilized zirconium oxide powders (YSZ) synthesized by co-precipitation and molten salt methods. Ammonia precipitating agent was used for the synthesis of YSZ powder by co-precipitation method and a mixture of sodium carbonate and potassium carbonate salts was used as a molten salt in the molten salt method. Samples were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC) analysis. The results showed that only the sample prepared with zirconium oxychloride and yttrium nitrate by co-precipitation method had a single phase of yttria-stabilized zirconium oxide with tetragonal crystal lattice and particle size distribution in the range of 30 to 55 nm. The powder synthesized by the molten salt method contained a mixture of zirconia with monoclinic crystal lattice and yttria stabilized zirconia with tetragonal crystal lattice and particle size of 200 nm.