نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 58 (پاییز 1400)

In this research, firstly amorphous Alumina powder was produced by co-precipitation method. Then YSZ/Al2O3 coatings were applied by plasma spraying process in two types of pyrolyzed and crystalline nano-alumina. High temperature oxidation and thermal shock resistance test were done at 1100˚C. Microstructure and phase analysis of coatings were studied by optical and electron microscopes and XRD method. Comparison of the microstructure of coatings showed that the use of crystalline nano-alumina powder in the YSZ/Alumina layer composite upgrades the thermal properties. High temperature oxidation and thermal shock resistance of plasma sprayed YSZ/Al2O3 with un-pyrolysed nano-alumina and coatings with same composition with crystalline nano-alumina to created by plasma spraying were studied. Findings showed that the use of un-pyrolyzed nano-alumina powder in YSZ/Al2O3 layer composite resulted in increased porosity and shrinkage cavities in the coating, which increased the diffusion of O2 that causes the TGO growth rate. Also, high density and proper contact between the splats made of crystalline nano-alumina powder results in higher resistance of thermal cycles.

In this study cadmium doped nickel copper ferrite Ni0.5Cu0.5Fe2O4 (cd doped) nanoparticles with spinel structure were synthesized using co-precipitation method. The nanoparticles were employed as a gas sensing material. X-ray diffraction (XRD), X-ray fluorescence (XRF) and transmission electron microscopy (TEM) techniques were used to characterize the nanoparticles structure. The sensing behavior of the nanoparticles was examined in the presence of different gases including. Acetone, acetonitrile, acrylonitrile, formamide, caron tetrachloride, vinyl acetate, ethanol, ammonia, and methanol. The characterization process was performed for a concentration of a 200 ppm and within a temperature interval from 50 ˚C to 300 ˚C and the best sensing behavior was found to be at 200 ˚C. Furthermore, various concentrations of acetonitrile gas at 200 ˚C within a concentration interval of 20 to 200 ppm were tested and it is found that the higher concentrations will result in a better response.

In this research, UNS S42000 martensitic stainless steel (SS) samples were subjected to tempering heat treatment at constant temperature of 550 oC for different time duration, ranging between 0.5 and 24 h, so as to assess the intergranular corrosion (IGC) behavior of the alloy. The microstructural characteristics and electrochemical properties of the alloys were evaluated using scanning electron microscopy (SEM) and anodic polarization method, respectively. The localized attack of the samples was investigated by potentiodynamic electrochemical impedance spectroscopy (PD-EIS) in the transpassive potential region. The results indicated that tempering up to 2 h would be followed by severe intergranular attack at martensite lath interfaces; however, the effect of tempering on corrosion performance of the alloys would be suppressed at prolonged tempering due to desensitization. Moreover, the PD-EIS results revealed that the charge transfer resistance (Rct) values of specimens at 1.10 V can be employed as a primary criterion in order to assess the localized attack of the martensitic SS. In this regard, the lower the Rct value at this DC bias potential, the lower the corrosion resistance to the IGC. These results were in good agreement with the SEM morphologies from the surfaces of corroded samples, indicating uniform corrosion, severe attack and desensitization for samples experiencing no-tempering, short tempering time and prolonged tempering, respectively.

In this study, welding of high strength low alloy steel, HSLA-100 was performed using three fillers metals, cut from base metal (HSLA-100), ER100S-G and ER120S-G by GTAW procedure. Microstructural studies were conducted using optical and scanning electron microscopes. Tensile, impact and hardness tests were also used to evaluate the mechanical properties of the joint. The results showed that the microstructure of HSLA-100 weld metal included granular bainite and polygonal ferrite, ER100S-G weld metal consisted of acicular, Widmannstatten and grain boundary ferrites and ER120S-G weld metal comprised of acicular, polygonal and quasi-polygonal ferrites. Furthermore, the formation of a secondary phase (constituent) of martensite / austenite (M / A) was observed in the microstructure of all weld metals. The predominant form of this phase in HSLA-100 and ER100S-G weld metals was blocky type and formed along the prior austenite grain boundries and in ER120S-G weld metal was in the form of stringer type. The results of mechanical tests demonstrated that among weld metals, ER120S-G weld metal had the highest tensile strength (859 MPa), percent elongation (22%), impact toughness (45 joule) and hardness (294.7 HV30). whilst, the ER100S-G weld metal had the lowest tensile strength (775 MPa) and hardness (268.4 HV30) and the HSLA-100 weld metal had the lowest impact toughness (25 Joule).

Alkali decomposition with NaOH is the most commonly used method for extraction of zirconium from zircon mineral. This process includes alkali fusion, water leaching and acid leaching steps. In this study, Taguchi method was utilized to find the optimum operational conditions of alkali decomposition process. The results showed that under the optimal conditions of NaOH/ZrSiO4 mole ratio of 6:1, NaOH concentration of 30% and fusion temperature of 650 °C, 98.6% of the initial zircon was decomposed, as no pick of ZrSiO4 was observed in the XRD pattern of the alkali fusion product. The conditions of water leaching step were investigated as well, and under the optimal conditions of, liquid–solid ratio of 5:1, leaching temperature of 30 °C and leaching three times, 96.2% of sodium and 77.9% of silica content in the alkali fusion product were removed. The crystal phase structures of ZrO2 and SiO2 were observed in the residual solid after heat treatment. In the acid leaching step, leaching with 4 mol/L sulfuric acid with liquid/solid ratio of 20 at temperature of 60 °C, resulted in 92.73% recovery of zirconium and the silica content in the acid leaching solution was obtained 31 ppm. Results of this research suggest the optimal operational conditions of the facile, low price and proper industrial method for recovery of zirconium from zircon mineral.

In this research CuO and ZnO and CuO-ZnO nanocomposites were synthesized using sol- gel method. The samples were characterized by DRS-UV, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). The results of XRD showed that the CuO and ZnO and ZnO-CuO composite are crystalline. The results of the DRS-UV analysis showed that the CuO, ZnO, and ZnO-CuO composite, respectively, have a mean band gap of 1.27 and 3.21 and 2.43 eV. According to calculations CuO, ZnO and ZnO-CuO composite show 40, 10 and 68% of degradation efficiency against of rhodamine B dye, respectively. Therefore, the addition of CuO to ZnO increased the photocatalytic activity of the products. The mechanism of photocatalytic activity of synthetic products and copper oxide is discussed in the process of increasing the photocatalytic process intervals. ZnO-CuO nanocomposite has an antibacterial ability against Staphylococcus aureus as a positive bacterium and E. coli as a negative bacterium.

Bioactive glass (BG), is able to bind to body tissues, in this regard, it can be considered suitable material for applications such as bone tissue engineering. In this study, we first synthesized and studied the structural changes, biocompatibility, in vitro bioactivity, biological behavior and antibacterial properties of silicate-based BG containing with strontium. To evaluate the bioactivity, the BG powder was placed in a simulated body fluid (SBF) solution for 1, 3, 7 and 14 days and then before and after the mentioned time periods, the changes and the process of forming a hydroxyapatite (HA) layer on their surface was studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), release rates of various ions elements, pH changes and scanning electron microscopy (SEM). The results of X-ray diffraction tests and infrared spectroscopy studies confirmed the formation of crystalline HA layer on the BG surface. Moreover, the results of live/dead assay, nucleus microstructure and actin microfilaments of MC3T3-E1 osteoblast cells showed that 5% of strontium in silicate-based bioactive glass led to the growth, proliferation and activity of MC3T3-E1 osteoblast cells. The results of cytotoxicity test and evaluation of alkaline phosphate activity showed that substitution of strontium instead of calcium in silicate-based bioactive glass composition not only did not cause cytotoxicity but also caused significant proliferation and activity of MC3T3-E1 osteoblast cells. Meanwhile, improvements in the antibacterial properties of strontium-containing bioactive glass against MRSA bacteria were observed in comparison with strontium-free bioactive glass.