JOURNAL OF NEW MATERIALS
Year:2018 | Volume:8 | Issue:4 (32) |Papers Count:14

The magnetic photocatalyst Fe3O4/SiO2/ZnO was synthesized by sol-gel method. For this purpose, in the first stage, Fe3O4 particles were prepared as the magnetic core of this composite and using the carbon recovery method. In the second stage, the coating of the SiO2 shell was performed using the tetraethyl orthosilicate (TEOS) precursor. In the end, the zinc oxide shell was deposited using a zinc hydrate nitrate precursor on the Fe3O4/SiO2 composite. The as-prepared nanostructures were characterized by environmental scanning electron microscopy analysis (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Vibrating Sample Magnetometer (VSM) and Energy Dispersive X-ray (EDX). FESEM and TEM results confirmed the coating of silica and zinc oxide on core particles and the Fe3O4/SiO2/ZnO magnetic photocatalyst was successfully prepared. The particle size mean of Fe3O4 was 300 nm approximately. The silica shell thickness was 25 nm, and the thickness of the zinc oxide shell was about a few nanometers approximately. The VSM results showed that coating of silica and zinc oxide shells reduced the saturation magnetization (Ms) of Fe3O4 powder so that the saturation magnetization decreased from 80/8 emu/g to 48/8 emu/g, which It is suitable for Magnetic Recovery. Photocatalytic properties of Fe3O4/SiO2/ZnO composite were studied on methylene orange degradation under UV light irradiation. Destruction of orange methylene was achieved 70%.

Automotive industry has developed a variant of the Friction Stir Welding named Friction Stir Spot Welding (FSSW), to replace resistance spot welding (RSW) for aluminum sheets. It is claimed that the use of energy and the investment cost are decreased with using of friction stir spot welding in comparison with resistance spot welding. However, one of the disadvantages of FSSW technique is that a keyhole generally remains at the center of the stir zone. Keyhole defect can reduce the mechanical properties of FSSW joints. A novel friction stir spot welding technique was developed with the purpose to improve the mechanical property of the joints by removing the keyhole. This novel FSSW method was applied to 2024 Al alloy sheets, 1 mm in thickness, under different shoulder size and dwell times. The effect of shoulder size and dwell time on the mechanical properties of the spot joints has been studied. Studies show that this new spot welding technique can produce a defect-free metallurgical bond with a homogenous fine grain microstructure. The welding parameters variations change the bonding area, depth stir zone, upper sheet thickness, grain size and mechanical properties of the welds.

In this study, the effect of different amounts of Sr (0, 0. 05, 0. 5, 1 wt. %) was investigated on microstructure and mechanical properties of the AZ91 magnesium alloy. The microstructure and mechanical properties were investigated using optical microscope, scanning electron microscope (SEM), X-ray diffractometer (XRD) and tensile test. The results shown that by adding Sr, the volume fraction of the Mg17Al12 phase decreased. It was also found that the grain size decreased significantly by addition of Sr, after homogenization. In this case, the grain size decreased from 131 μ m in AZ91 to 43 μ m in AZ91 with 1 wt. % Sr. Furthermore, the optimum amount of UTS and elongation were observed by the addition of 1 wt. % Sr to AZ91 magnesium alloy. UTS and elongation increased from 129 MPa and 1. 1% to 177 MPa and 2%, respectively, when the 1 wt. % Sr was added to the AZ91 alloy. The fracture surface observations showed that fracture mode in these alloys were cleavage and the Sr addition does not change the fracture mode.

Undoped and In-doped SnS thin films have been prepared using an electrochemical deposition method. The bath temperature, deposition time, deposition potential, and pH kept constant at 60 ℃ , 30 minutes,-1 V and 2. 1, respectively. The synthesized un-and In-doped SnS thin films have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), room temperature photoluminescence (PL), and UV-vis spectroscopy. The XRD patterns showed that the crystalline quality and crystallite size has been decreased after In-doping. The morphology of un-and In-doped SnS thin films was grain-like. A new PL emission peak has been appeared after In-doping. The absorbance spectra of In-doped SnS thin films have been improved, compared with that of undoped SnS. In addition, the band gap energy of undoped SnS is decreased from 1. 5 eV to 1. 45 eV due to In-doping. Therefore, all results showed that the key role of indium dopant on the structural and optical properties of SnS thin films.

A rolled AA3003-H14 aluminum alloy sheet and Titanium metal powders were used to fabricate Al-surface composites reinforced by in-situ formed Al3Ti aluminide nanoparticles while applying friction stir processing (FSP). The titanium powder of particle sizes smaller than 45 microns was used as reinforcement. Tensile strength and the hardness of the surface composites were determined after applying 6 passes FSP. Its phase analysis was done by using an X-ray diffraction and the microstructural examinations were performed using an optical microscope and scanning electron microscopy. Microstructural examinations revealed that the large size and elongated grains of the base metal have transformed into a more homogeneous, equiaxed and smaller ones after applying FSP. It was also noticed that the reaction between the titanium powders and the aluminum matrix led to the formation of Al3Ti aluminide at the interface between the two elements. This aluminide formation was in the form of a spherical shell around the aluminum, wherein the later stage of processing fragmented into smaller particles and distributed throughout the matrix. Results showed that tensile strength and the hardness of the base metal were increased by about 30% after applying 6 passes FSP.

In this study, zinc oxide nanoparticles were synthesized with the addition of Ti (10% mol) and Si (10% mol) by sol-gel method. The properties of samples contaminated with metal cations (SZ, TZ, STZ) were compared with pure zinc oxide (ZnO = Z). XRD, SEM and UV-VIS methods are used to study crystalline phases, morphology and particle size, optical properties and photocatalytic properties of nanoparticles. Photocatalytic properties of the samples were studied under UV exposure for one hour using methylene blue (MB) as a color contaminant in the textile industry. X-ray diffraction results show that all samples are formed at 450 ° C from the crystalline phase of zinc oxide with a vortex composition. The particle size of the samples in the presence of titanium and silicon metal cations is smaller than that of the zinc oxide sample. Investigation of the optical properties of the samples shows an increase in the band gap of the samples relative to the pure zinc oxide sample. The photocatalytic efficiencies of the samples indicate a positive presence of metal contaminants to improve the photocatalytic properties of the samples, such that in the sample with the simultaneous contaminant (STZ), compared to the pure ZnO sample and the individual contaminants ( TZ and SZ) have a higher photocatalytic efficiency.

Bioactive glasses are widely used as coatings for bone remodeling and metal implants due to the ability to bind chemically and physically with the bone. Using of bioactive glass in composite coatings not only will increase chemical properties. The use of bioactive glass nanopowders in composite coatings, in addition to improving the chemical properties and increasing the biocompatibility of the extinctions in the body, due to the inherent hardness of the glass, also increases the strength of the coating. In this study, coatings containing bioactive glass were synthesized in Nano scale using a mixture of raw materials, and by dipping method one or more layers coated onto plates Titanium. On the other hand, in order to investigate more accurately the effect of vitreous glass and fluorapatite on the composition of the composite, various amounts of these materials were used in coating preparation. The chemical and mechanical properties of the coated specimens in body simulated solution (SBF) were investigated by XRD, SEM, PSA and FTIR. SEM images and X-ray diffraction analyzes (XRD) showed that the apatite layer is formed on the surface of the coating after immersion in the SBF. The formation of this layer increases with increasing immersion time in the SBF and increasing the amount of bioactive glass and fluorapatite. Finally, for the nanoparticles produced in this paper, the degree of hardness was studied in terms of the number of coated layers.

Nanocomposites are defined as systems that use engineered nano materials, like silica nanoparticles, which improve the final properties of the organic coatings. The main objective of this study is to fabricate a water based acrylic nanocomposite to achieve optimal weight percentage of silica nanoparticles as reinforcement. The organic coatings were prepared by a special formulation in which silica nano particles of 0. 5, 0. 75, 1. 0, and 1. 25 weight percent were incorporated into the organic coatings matrix. The adhesion, pencil hardness, microhardness (Vickers), wear, roughness measurement of the film surface, water resistance viscosity tests were performed to evaluate rheological, physical, mechanical and chemical properties of the nanocomposites. Moreover, scanning electron microscopy (SEM) and optical microscopy (OM) were employed to study the morphology and the time span for film's drying were measured. The results of SEM and OM showed that the silica nanoparticles were well dispersed up to 1. 0 wt% loading and the adhesion properties, between the matrix and reinforcement particles, will be enhanced. Besides, the paint properties were optimized as 1 wt% of nanoparticles were loaded.

Incremental Sheet forming (ISF) is one of the processes for producing sheet metal parts without the use of mold that has been developed to allow rapid prototyping and reduced time and cost of fabricating parts. In this process, as well as other forming processes, reducing of the forming force and improving of the mechanical properties of the created part are considered. For which purpose, various methods have been developed. One of these methods is the use of ultrasonic vibration and its application to the process. In this study, ultrasonic vibrations were used on the tool to improve the mechanical properties of the piece made in the incremental sheet forming process. The purpose of this study was to investigate the effect of ultrasonic vibration on the mechanical properties of parts made in the incremental forming process. So, suitable equipment for this process was designed and constructed. Then, pyramidal samples were produced under different conditions of horizontal and vertical feed rates under the influence of ultrasonic vibration and hardness and tensile testing were performed on the produced specimens. The results showed that hardness and tensile strength increased by 50% and 30% respectively, due to the applying ultrasonic vibration. Microstructural studies on the samples showed that due to the temperature increase of the samples as a result of the conversion of ultrasonic vibration into the heat, the continuous dynamic recrystallization (CDRX) process occurred in the microstructure of the samples, which resulted in the grain refinement and improvement in the mechanical properties.

Due to the unique physicochemical properties of nanoparticles with the ability to inhibit the growth of bacteria, research has increased on nanoparticles and their applications as the antimicrobial agents. In this study, nanoparticles of copper-tin oxide were synthesized via electrical explosion in water between copper-tin electrodes. This method provides the possibility of producing oxide and metal nanoparticles with high production rates and high surface activity. Copper oxide and tin oxide nanoparticles are known as practical nanoparticles with antibacterial activity. Nanoparticles characterization was performed using the X-ray diffraction, scanning electron microscopy, UV-visible absorption recording and BET analysis. The results showed that by changing the intensity of the applied current, oxide copper-tin with an average size of about 19 to 37. 5 nm were formed by electrical explosion of wire. Antibacterial activity of nanoparticles against the E. coli bacteria was evaluated by determining the optical density of various samples with different concentrations of tin and copper oxide nanoparticles. The results showed that the copper-tin oxide nanoparticles possess antibacterial properties and this activity enhances by increasing the concentration of nanoparticles in the liquid medium and reduction the average grain size.

Thick tungsten coatings are used in diagnostic X-ray tube anode applications. Surface roughness has an important role in producing high quality diagnostic images, therefore it is crucial to develop and maintain a smooth anode surface. In order to improve the efficiency of such tubes, surface morphology of the plasma sprayed tungsten coatings was studied in the as-sprayed conditions, hydrogen annealed and top-coated with a chemically vapor deposited tungsten film. Hydrogen annealing was carried out in a wet hydrogen atmosphere at 1500 ° C for 90 minutes. Chemical vapor deposition was carried out in a bed of tungsten oxide at 1000 ° C. Surface morphology was evaluated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry and stylus-type roughness measurement instrument. The results showed that the suggested post treatments could alter the surface morphology from an oxidized and rough surface to a metallic and smooth morphology. The surface of the final coating was covered by a thin layer of fine tungsten crystals with average roughness of less than 1 micrometer.

In this study, the microstructures and mechanical properties of Al 7075 alloy obtained from conventional and modified SIMA have been investigated. In fact, the appropriate microstructure for the semi-solid forming is the non-dendritic microstructure with enough degree of spheroidity. In this research, a type of modified SIMA was used to make a comparison with the conventional SIMA. An annealed strip of Al 7075 alloy after rolling was soaked in an electrical furnace at 590 ° C for different periods and then was cooled to 500 ° C and quenched in cold water. After that, the mentioned procedure was repeated without rolling. The results showed noticeable improvement in the microstructure and the mechanical properties of the alloy processed by the modified SIMA. Not only was the globular structure finer and more homogenous but also, a more homogenous distribution of the secondary phase particles in a non-continuous manner was obtained at the grain boundaries and the eutectic structure was removed. These led to the improved mechanical properties such as ultimate tensile strength from 371 MPa to 442 MPa, elongation from 4. 2 % to 13. 1 %. In addition, although the maximum microhardness at grain boundaries decreased, the microhardness level within the grains improved and formability enhanced severely.

Grain growth is a challenge in AZ magnesium alloys casting. The purpose of this research was to develop a finer microstructure than the conventional sand casting. In this study, a new method ablation casting was used. In the ablation casting method the mold must be washed after pouring and before the part complete solidification. In this way the part solidification rate increases. The sand mold was washed by water pressure 30 seconds after pouring in order to remove the heat content of the piece only by water. Thermal analysis was done by thermocouples that were placed in certain positions in mold. Then the cooling rates of samples were measured by them. The cooling rates in mushy zone were 1. 27 and 0. 52° C/sec for ablated and conventional casting parts respectively. The Cooling rate of the ablated part was 2. 42 times further than the conventional CO2 sand casting. Size of dendrites decreased from 164. 5 to 46. 9µ m with increasing cooling rate. During the solidification temperature gradients between two points of the ablated part was measured to predict of dendritic solidification. The temperature gradient mean between these points was 1. 12° C/mm. In ablated sample, eutectic phase volume percent and precipitates were reduced. There was no change in shape of the pores in the ablated sample, but the volume percent of pores and maximum size was reduced. The average pore diameters were 82 and 42µ m in ablated and control sample respectively.

Co-based metallic glasses have attracted the attention of many researchers due to their excellent magnetic softness, as well as their high corrosion resistance. In the present research, Co-Fe-Ta-Hf-B glassy ribbon with a high thermal stability was prepared by melt-spinning and its isochronal crystallization kinetics at different heating rates was systematically investigated. The apparent and local activation energy of crystallization, the fraction of crystals at different temperatures and other kinetics parameters were calculated according to Ozawa method. In addition, the devitrification kinetics of the produced glass was studied based on the well-known Jahnson-Mehl-Avrami (JMA) and Sestak-Berggren (SB) models. The results indicated that the local activation energy increases with progress of crystallization. Furthermore, the average activation energy calculated based on the Kissinger model was 664 kJ/mol, which is larger than many other metallic glasses, and confirms a high thermal stability of this alloy. It was shown that the JMA model cannot be used for analysis of the crystallization behavior of the present alloy and due to a complex and autocatalytic nature of crystallization, the SB model gives more liable results for investigation of crystallization kinetics.