نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 47 (زمستان 1397)

Dispersion of nanotitan particles in polyurethane (PU) resin plays an important role to achievement better mechanical and physical properties. In this study nanocomposite coating was performed by incorporating nanotitania pigment with rutile and anatase phase in polyurethane to different loading level (0.1, 0.5, 1.0 and 2.0% by weight). Dispersion of nanoparticles in PU matrix was done by using ultrasonication mixing machine (2 h) and rotary mixer (3 h) and also again UT mixing machine (1 h) and finally gas removing. After addition of the appropriate amount of hardener, prepared nanocomposite coating was investigated by applying on steel and glass substrate and after 2weeks time for curing, exposing them to UV weathering, salt spray, scratch and hardness testing. The dispersion quality and surface morphology of nanocomposite coating was evaluated by using different analytical techniques. Dispersion quality of nanocomposite was investigated using optical microscopy. Dry film thickness (DFT) of samples was mostly in the range 90 µm. Roughness after exposing of naoncomposites on UV radiation and salt spray measurement by atomic force microscopy (AFM) topography and analysis by this apparatus and mechanical behavior also by using hardness and scratch test and also by colorimetry measurements, surface degradation of PU nanocomposite coatings was characterized by color changing, defined as the color measurement, after being exposed to accelerated weathering conditions.

In this study, the properties of the passive layer, formed on the surface of SAF 2205 duplex stainless steels in sulphuric acid solution, were investigated. The degree of sensitization of the samples sensitized for 1 h and 5 h were evaluated using double loop electrochemical potentiokinetic reactivation technique (DLEPR). The results were in good agreement with those of sodium hydroxide etch tests for classification of structures of duplex stainless steels. In addition, the potentiodynamic polarization test was performed to determine the passive potential range of the solution-annealed samples sensitized samples. Cyclic polarization in anodic branch revealed the beneficial effects of having less surface roughness on the protective properties of the passive layer. Mott-Schottky method was used to evaluate the density of point defects at the surface. The results showed that those samples with finer surface roughness, less degree of sensitization and more polarization cycles have less defects (up to 44%) in their passive layers. So, the more degree of sensitization and surface roughness lead to the formation of less intact passive layer due to the formation of sigma phase and less number of microcells at the surface.

This research aims to produce Ni-Vanadium Carbide composite nano powder, known as a hard metal, from oxide raw materials and magnesium as a reductant, using mechano-chemical method. With regard to the adiabatic temperature (T=3964 K), this reaction is a mechanically induced Self-sustaining (MSR) type. Raw materials were mixed according to stoichiometry reaction with a ratio of (1:1:6:2) for Nickel oxide, Vanadium oxide, Magnesium and graphite respectively. Milling was carried out in a planetary ball mill with a powder to ball ratio of 1:20 under argon gas atmosphere. After 40min of milling, combustion occurred out in the mill chamber. With regard to the results of X-ray difraction after the combustion, the intended products; that are, Nickel, Vanadium Carbide and Magnesium Oxide which is by-product of the reaction, were completely produced. HCl with a concentration of 9% was used to remove the magnesium oxide phase. The crystallite size and lattice strain were calculated using Williamson-Hall method, and the crystallite size and lattice strain of Ni and Vanadium Carbide were obtained 40nm, 0.00595, 54nm, 0.00615, respectively.

Metal bone plates are used to stabilize bone fractures in orthopedic surgical treatment for years. The differences between stiffness of Metal plates and bone lead to osteoporosis and increase the risk of again fractures in the area of the plate. In addition, wear and corrosion of metal plaques lead to release of unwanted corrosion products in the body. To fix this problem ceramic polymer degradable composites can be used. The purpose of this research was to fabricate non-degradable bone plate of Polycaprolactone-Baghdadite (Ca3ZrSi2O9) to stabilize and restore the bone tissue damages. Polycaprolactone (PCL) is semi-crystalline polymer with biocompatible body, but the degradation rate of PCL than other biocompatible polymer is lower and has higher fracture energy. Baghdadite is a bioceramic with high bioactivity properties, so the additions of baghdadite nanoparticles to PCL lead to increase the bioactive of PCL meanwhile improve the speed of degradation of the composites. In this study, Baghdadite powder was prepared by the sol-gel method and then values of 0, 10 and 20 wt% nano-powder added to PCL. In order to evaluate the biological properties, the test of immersion in (SBF) applied and assessment of particle shape and morphology of samples was done by scanning electron microscopy. Tensile test used to determine the mechanical properties. The results showed that the Baghdadite powder composed with average particle size of 30 nm, While have the proper distribution and uniformity in the polymer matrix; subjoin it to matrix phase lead to increased biological and strength properties of the composite.

Abstract Ultrahigh temperature ZrB2-SiC composites reinforced with different amount of nano-graphite (0, 2.5, 5, 7.5 and 10 wt%) were fabricated by spark plasma sintering process. The effect of graphite nano-flake on the densification behavior of the mentioned composites were investigated. Spark plasma sintering was carried out at a temperature of 1900 °C for a dwell time of 7 min under an applied pressure of 40 MPa. A fully dense ZrB2-SiC composite (with relative density of 100.6%) was obtained by the addition of 5 wt% nano-graphite. Elimination of oxide impurities through the chemical reactions with graphite as well as formation of sub-micron phases caused to an enhancement in the densification. In addition, the in-situ formed ZrC phase was one of the reasons behind the increasing of relative density. Keywords: spark plasma sintering, ultrahigh temperature composites, densification behavior, nano-graphite, ZrB2-SiC composites Keywords: spark plasma sintering, ultrahigh temperature composites, densification behavior, nano-graphite, ZrB2-SiC composites

Zinc oxide is a semiconductor which has photo-catalyst properties and could be used for degradation of organic materials. In this research silver doped zinc oxide nanoparticles were synthesized using Pechini sol-gel method in order to investigate its photo-catalyst properties. Nanoparticles show good photo-catalyst properties due to high surface area to volume ratio and adding of noble metals to semiconductor decreases recombination of electron-hole. Samples with different weight percentages of silver (0.6, 1.8, 3.1 and 6.2) were synthesized. Samples were characterized by UV-Visible spectroscopy, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Field Emission Scanning Electron Microscope (FESEM), Energy-Dispersive X-ray spectroscopy and Photo luminance Spectroscopy. Photo-catalyst properties of samples were analyzed by degradation of methylene blue. Results showed that Ag doping decreased the particle size of samples and the sample containing 1.8% Ag had maximum rate in degradation of methylene blue solution and this was coincidence with PL results. Adding of Ag to ZnO decreased recombination rate of electron-hole in oxide and therefore increased photo-catalyst properties of samples or degradation rate of solutions. To confirm the decolorization repeatability of the synthesized samples, three photocatalytic cycles were performed on the sample containing 1.8% wt% of silver. It was observed that the decolorization efficiency of sample was not significantly reduced, and it is indicate that the synthesized catalyst is stable and functional.

In this research, the tanks made of carbon steel, similar to the practical conditions and in the form of pilot, was investigated. The tank containing 98% and 72% sulfuric acid was evaluated by potentiodynamic polarization test, open circuit potentials and potentiostatic test. Also, electrochemical noise measurement was carried out before, during and after the anodic protection, and the results were analyzed by statistical analysis at time intervals. . By analyzing the frequency range, PSD curves were obtained and it was observed that the values of slope and current and potential skewness could be used to determine the deviation or non-deviation of the normal distribution of electrochemical noise data. It was also found that by using spectral density curves, it is possible to eliminate the negative effects of additional noise and obtain complete information about the corrosion process. Noise resistance was obtained, but the noise resistance could be applied qualitatively to determine the corrosion rate. In this study, it was concluded that the electrochemical noise method is an efficient method for studying corrosion phenomena, such as crevice corrosion and anodic protection system during protection of tanks and heat exchangers in sulfuric acid. It was found that for a mild steel tank in Sulfuric Acid 98%, during protection, the slope value of the ROLL-OFF region was 2.4 and for dilute sulfuric acid 4.4, and it was found that in this area, the anodic protection was considerably high for carbon steel so protection in the sulfuric acid solution 72% is more suitable.

Production of hydrogen using photoelectrochemical water splitting is a promising method for production of clean and renewable energy source. Using positive and negative semiconductors respectively as photocathode and photoanode, water can be splitted into hydrogen and oxygen. In this study, hematite was synthesized using electrochemical deposition. The diffraction pattern obtained using x-ray diffraction showed hematite having rhombohedral crystal structure. Surface morphology obtained by scanning electron microscope showed a two-layer structure, lower layer with cracks and upper layer consisting of particles. Photocurrent density was obtained using linear sweep voltammetry under chopped illumination and it was obtained at 0.6V vs Ag/AgCl as 2.5 μA.cm-2. Nyquist plot of hematite at potentials of 0V and 0.6V was obtained using electrochemical impedance spectroscopy and an equivalent circuit was fitted to EIS data and the value of the parameters was obtained. Also, using Mott-schottky plot, the flat band potential and the carrier density were obtained to be -0.35V vs Ag/AgCl and 8.4×1018 cm-3.

In this study, the dielectric heating was performed by microwave irradition to synthesize polyurethane/silver nanocomposite, which was carried out by distributing and dissolving silver nitrate salt in the polyurethane and the reduction of silver cation retained in ethylene glycol micelles in the prepolymer solutions. Decreasing the time and number of synthesis processes and, consequently, reducing production costs is one of the advantages of this technique. During the chemical reactions, microwave waves with constant intensity and frequency at 30, 60, 90, 120 seconds were applied to solvent prepolymer by a microwave oven. By completion of the chemical reactions, silver nanoparticles were synthesized in a polyurethane matrix. The effect of microwave and insitu synthesis of and silver nanoparticles on chemical bonding of polyurethane in terms of structure, morphology, composition and particle size distribution were studied by using UV-Vis spectroscopy, X-ray diffraction (XRD), transmitted electron microscopy (TEM), X-ray diffraction spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR) analysis. Produced nanoparticles have spherical and semi spherical morphology with particle size distribution in the range of 10 to 80 nm, and the fcc crystalline structure and uniform dispersion in the polyurethane matrix. Meanwhile, Fourier transform infrared spectroscopy of nanocomposites showed synthesis of silver nanoparticles no negative effect on polyurethane chemical bonds by this method.

Among various techniques which have been used for degradation of chemical pollutants, advanced oxidation processes (such as photocatalytic process) have received attention due to their specific properties. In this investigation, ZnFe2O4-10wt% TiO2 composite film was elaborated using flame spraying process. Powders of titania (TiO2: 75vol. % anatase, 25vol. % rutile) and zinc ferrite (ZnFe2O4), which was synthesized by mechanical alloying process, were mixed together (weight ratio of 1:9) and deposited on stainless steel 316 substrate. In order to evaluate the structure, morphology, and photo-adsorption ability of the coating, X-ray diffractometer (XRD), scanning electron microscopy (SEM), and UV-VIS-NIR spectroscopy were used, respectively. Photocatalytic performance of the deposited film was studied by bleaching of aquatic methylene blue solution with the concentration of 5 mg/Lit. The results showed that the composite coating, which was elaborated by flame spraying, possesses relatively good photo-adsorption ability as well as photocatalytic activity for photodegradation of methylene blue (under visible light irradiation).

Abstract In this research, Fabrication of YSZ/Al composite coating on Incoloy 825 superalloy using electrophoretic deposition has been investigated. Dispersion of YSZ and Al particles suspension in acetone in presence of iodine, as dispersant, was studied by particle size and zeta potential measurement. According to the results, the suspension containing 1.2 g/l iodine has been chosen for electrophoretic co-deposition of YSZ and Al particles. Mean diameter of YSZ and Al particles in this suspension was measured 111.6 nm and 2.658 μm and zeta potential value of these particles was measured 50.2 and 16 mV, respectively. In order to investigate the influence of applied voltage and deposition time on quality of formed deposit, electrophoretic co-deposition has been carried out at different voltages and deposition times. Results revealed that the deposit formed at voltage of 6 V and deposition time of 3 min had uniform and crack-free surface. SEM image showed that this coating had thickness of 19.63 μm.