مجله مواد نوین
سال چهارم شماره 1 (پیاپی 13، پاییز 1392)

In this paper، the microstructural characteristics of ternary ceramic powders Al2O3-SiO2-ZnO system prepared by sol-gel method، in order to increase surface area of ZnO nanocrystals supported on silica-alumina matrix، have been studied. Values of 20، 50 and 70 weight percents of zinc oxide with an equal weight ratio of SiO2-Al2O3، using simultaneous reaction of zinc nitrate (Zn(NO3) 2. 6H2O)، tetraethyl orthosilicate، (TEOS) and aluminum nitrate (Al(NO3) 3. 9H2O) were synthesized. The nanostructure of prepared composites were characterized by X-ray diffraction، SEM/EDS and BET studies. The results showed that crystaline phase zinc oxide has been formed in amorphous silica-alumina matrix، which led to reducing zinc oxide particles size، preventaing of aglomeration and increasing specific surface.

Gray cast iron is one of the most important engineering materials in various applications in industries. According to the need to decrease the weights of industrial structures، application of cast irons decreases daily and it is expected that the use of this product increase when its lighter. In this work، 6. 2% aluminum was added in the crucible to rotary kiln molten iron. After dry sand casting، determination of the chemical composition، evaluation of microstructure by optical and scanning electron microscopes، hardness test، tensile test، compression test and XRD phase analysis was carried out. The results showed that adding aluminum to gray cast iron produced a secondary phase، resulting in a decrease in graphite contents. The examination confirmed that the secondary phase has higher carbon and aluminum contents than matrix and the matrix has higher ferrous and silicon contents than secondary phase. Secondary phase formation and reduction of graphite content increase hardness and decrease tensile and compression strength.

In this study، antibacterial behavior of nanoparticles of titania and nanoparticles of silver-doped titania were evaluated against Streptococcus mutans and were compared with three pathogen bacteria. Initially، the nanoparticles of titania and nanoparticles of silver-doped titania were synthesized by sol-gel method. The powders were characterized by X-ray diffraction (XRD)، Transmission Electron Microscopy (TEM) and Energy-Dispersive Spectroscopy (EDS) techniques. Then، Agar dilution was used to evaluate antibacterial properties of silver- doped titania nanoparticles against Streptococcus mutans and three types of pathogen bacteria. Phase structure evaluation showed anatase phase of titania in all silver-dopped titania nanoparticles. The particle size of titania and silver particles were determined 30 and 15 nanometers، respectively. The antibacterial results showed that Minimum Inhibition Concentration (MIC) of 3 mg/ml for silver-doped titania nanoparticles with different percentages of silver could inhibit bacteria growth، while nanoparticles of titania in fluorescent light indicated reducing growth of bacteria. Furthermore، MIC of 4 mg/ml was achieved for silver-doped titania nanoparticles with 5 mole percent sliver against the other pathogen bacteria and for other specimens observed growth of bacteria. These results showed that silver could increase antibacterial properties of titania. This is due to presence of silver nanoparticles and also the effect of silver on the photocatalyst properties increased antibacterial properties.

The objective of this work was to investigate the effect of initial pH، the adsorbent size and the contact time on the efficiency of adsorption of copper ions from copper sulfate solution with corncob particles. The surface morphology of adsorbent was observed using a scanning electron microscope، both before and after the adsorption. The porous and tubular structure of the corncob indicated the capability of corncob in adsorption of metal ions of the solution. In order to study the equilibrium sorption extent، Langmuir model and Freundlich model were used. The maximum Cu (II) binding capacity، qmax، calculated from Langmuir isotherm model was increased with increasing the initial pH and decreasing the adsorbent size. In addition، the results revealed that contact time is another important factor in sorption، the maximum adsorption occurred at the first 20 minutes and after that the sorption rate decreased and finally it reached a constant value after 2 hours.

The quality of parts in green sand mold casting mostly depends on the green sand properties such as compressive strength، permeability، mould hardness، etc. These parameters depend on input parameters like water، size and shape of the sand، percentage of bentonite and so on. The compressive strength of sand of different moisture contents which is required for modeling، obtained by experimental tests، and a research method، based on Artificial Neural Network (ANN). The predicted values of the compressive strength obtained by the ANN and new experiments found to be in good agreement with each other and showed that by using Artificial Neural Networks one can estimate the compressive strength of green sand precisely before molding.

Techniques of severe plastic deformation have been of continual interest in the production of novel metallic microstructures. Among these، accumulative roll bonding has been extensively used to produce multi-layered composites. In the present study، a new manufacturing process for Cu/MoSi2-1vol% and 1. 5vol% MoSi2 composites was developed by using Copper and nano sized MoSi2 particles as starting materials. After five ARB passes، it was showed the MoSi2 particles properly distributed in the copper matrix. With increasing strain during ARB passes strength and elongation of these composites increased. Structure and mechanical properties of these composites were studied within different stages of ARB process. Also، Electrical resistivity of the samples was measured by four point probe method

Adding some alloying elements such as copper and zinc into aluminium and appling precipitation hardening process، makes these alloys sensitive to different types of corrosion in marine atmospheric environments. Precipitates on the matrix and grain boundaries are the main factor for corrosion. In order to study the corrosion behavior of metals in marine atmospheric environments، simulated environmental conditions is required to provide severe atmospheric environments containing chloride ion. In this research، a new method is used to study the atmospheric corrosion. At first specially prepared samples were tasted in corrosion cells with different time periods that the salt crystals were placed on the surface of samples and end grain areas on sample thickness were investigated. In this situation 100% relative humidity condition was stable. The microscopic studies showed that the intergranular corrosion happened less than 72 hours in 7075 alloy because of presence of deposits in grain boundaries and after this time، intergranular corrosion transform to pitting and exfoliation corrosion. Uniform corrosion with small pits was stable for 2024 alloy and the corrosion rate for 6061 alloy was lower than 2024 and 7075 alloys. Finally In order to compare the corrosion behavior of surface، the alloys were placed into the salt spray test for 672 hours according to ASTM B117. In this situation، 2024 alloy had the highest rate of corrosion.

In this paper، bimodal Aluminum based nanocomposite prepared via mechanical alloying and hot extrusion. Mechanical alloying was used to synthesize Al2024 nanostructured powder in attrition mill under argon atmosphere up to 50 h. After mixing nanostructured aluminum and unmilled aluminum powders in low energy ball mill، the resulting composite powders were shaped through hot Pressing. Finally، the hot pressed powders were hot extruded. The microstructure and fracture surface were characterized by optical microscopy (OM)، scanning electron microscopy (SEM)، X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectrometry (EDS). In order to compare the mechanical properties of hot extruded samples، tensile، compression، and hardness tests were performed. Results showed that، with an increase in unmilled aluminum percentage، ductility of composite increased but strength and hardness decreased. The mechanisms for the simultaneously improved strength and ductility involves increased dislocation activity in the coarse-grained (i. e.، unmilled powder) regions as a result of the constraint of plastic deformation in these coarse-grained regions.