مجله مواد نوین
سال ششم شماره 2 (پیاپی 22، زمستان 1394)

In this study, the effects of adding of alumina particles and carbon monoxide gas bubbles through the runner system on graphite morphology and microstructure of gray cast iron was studied. To add alumina particles, thermite reaction of aluminum and iron oxide powders in runner was used and for production of carbon monoxide gas bubbles in runner, reduction reaction of iron oxide by carbon was carried out. Light microscopy, scanning electron microscopy and XRD were investigated. The burning of sand in chamber of powders provided that reactions were performed in according with the expected and their heat caused the sand burning of Microscopic evaluation showed that the addition of alumina particles has great influence on the graphite morphology. The presence of these particles in the liquid was cased heterogeneous nucleation of graphite and as a result, B type of graphite and Kish-graphite were produced. Alumina particles have no affected microstructure. Bubbles of carbon monoxide have no effect on the graphite morphology and microstructure.

Aluminium and aluminium base composite foam core sandwich panels are good energy absorbers for impact protection applications, such as light-weight structural panels, packing materials and energy absorbing devices. In this study, quasi-static perforation tests were carried out on sandwich structures with Al A356/SiCpcomposite foam core andAl 1100 aluminium face-sheets, face-sheets without foam core and aluminium foam without face-sheets. For these tests a 10 mm diameter 60oconical nosed indenter with very low displacement velocity (0.02 mm/sec) was used. The results showed significant increase on energy absorption of sandwich structures in comparison with witness samples. Also increasing foam core and face-sheet thickness leaded to gain higher piercing force and more absorbed energy. Further, explicit finite element (FE) analyses of quasi-static perforation on panels were performed using ABAQUS 6.12. The stress distribution, force-displacement curve, peak piercing fore and energy absorption of different structures were presented. The numerical prediction was found to be in good agreement with the experiments.

Attempt to significant decreasing of permeability of polymeric material in versus liquid and gases for production of inert polymeric products in engineering applications have special situation in research. The purpose of this research is to study the permeability behavior of Acrylonitril-Butadiene copolymerre inforced by calcium carbonate nanoparticles in the temperature range 25–45°Cand using the solvent permeability tests to microstructure evaluation of the polymer nanocomposites. Results show the concentration of nano particle plays an important role in the diffusion, sorption and permeation coefficients and by increasing the amount ofnano-CaCO3up to optimum content (10-15%) decrease in the secoefficients (22% decrease in diffusion coefficient)is observed, whereas for higher concentrations, especially at higher temperature increasing trend were obtained for the secoefficients. By increase temperature, diffusion mechanism is more close to Ficki an mechanism. Increase of nano particle concentration in nanocomposite decrease ultimate swelling and diffusion rate of solvent and also activation energy (up to two fold).The micro structure and the dispersion of nano-CaCO3in the polymer matrix was evaluated using SEM micrographs and an appropriate relationship was established between the micro structure and the experimental results(permeability and mechanical properties).In general, swelling test and mechanical analysis an delectron micro scope images were presented similar behavior for prepared nanocomposites and can be recommended that swelling and permeability test scan be used as an inexpensive and simple method to characterization and evaluation of the properties of polymer nanocomposites.

Magnesia–carbon (MgO–C) refractories are widely used in basic oxygen furnaces, electric arc furnaces and steel ladles. These refractories have excellent slag resistance and thermal shock resistance due to the good properties of carbon such as low wettability, high thermal conductivity and low thermal expansion. In this context, main problems are erosion of the refractories of slag line, carbon oxidation, chemical corrosion and mechanical wear of refractories by slag and need to repair and replace them with other refractories. In this study, the effect of using sodium hexametaphosphate(SHMP) as a bonding agent was investigated in the presece of water and spent magnesia-carbon refractory aggregates. For this purpose, different compounds composed of 0, 3 and 5 wt. % SHMP are prepared and some parameters such as bulk density, percent of apparent porosity (%AP) and cold crushing strenght (CCS) were measured at different temperatures (200, 500 and 1100 °C) and phase and microstructure studies were performed by XRD and SEM. Results indicated that using of 5% SHMP at different temperature, specially at low temperature causes some phosphate bonds with needle-shape morphology like MgP2O7, Mg3(PO4)2 and AlPO4 and improve physical and mechanical properties, so these monolithic refractories can be used for the cold repairing of ladles.

Among different strengthening mechanisms, grain refinement has been accepted as an effective and law cost method. So far, ferrite grains in plain low carbon steels were refined to grain sizes equal or less than one micrometer. Severe plastic deformation is one of the grain refinement methods which was successfully used and implemented in recent years. In the present research, severe plastic deformation was conducted using integrated extrusion equal channel angular pressing (ECAP) on a plain low carbon steel to refine ferrite grains and produce ultra-fine and Nano size grains. Results showed that integrated extrusion and equal channel angular pressing is an effective method that can be used for processing of Nano structured low carbon steels. In the present study a nanostructured low carbon steel was produced with crystallite sizes of 125 nanometer and yield strength tree times higher than initial coarse grained one.

Friction stir processing (FSP) was used to fabricate AZ31/Al2O3 nanocomposites for surface applications. The effects of probe profile, rotational speed and the number of FSP passes on nanoparticle distribution and matrix microstructure were studied. Three tool designs, non-threaded, threaded and three flutes were used. The grain refinement of matrix and improved distribution of nanoparticles were obtained after each FSP pass. By increasing the rotational speed, as a result of greater heat input, grain size of the base alloy increased and simultaneously more shattering effect of rotation, cause a better nanoparticle distribution. In the non-threaded and three flutes FSP tool due to absence of threads some voids was observed. XRD results show that the reinforcement volume is low. Also, the texture of FSPed samples changes significantly. Some fluctuations were measured in the hardness values which are due to banded structure of the stir zone. With increase of rotational speed a smoother hardness results was produced.

In this research the behavior of the steel AISI 422 has been investigated during the various continuous cycle of cooling in dilatometer and CCT diagram has been obtained. The standard test samples were prepared in accordance with the requirements of the standard Dilatometers SEP 1681 in cylinders with a diameter of 4 mm and length of 10 mm. In the dilatometer test, heating the samples were conducted in controlled vacuum atmosphere. The results showed that after reaching the austenitizing temperature of 1040°C, holding time of 15 minutes , cooling time of 5, 15, 30 minutes, 1, 3, 6, 12 and 18 hours, martensite was formed in range of 238-300 °C. Colling In 24, 36 and 48 hours, pearlite phase was formed. The start temperature range of this transformation was 472-621°C and the final temperature rang of perlite transformation was 367-504°C. The martensite transformation for this cooling times was 300-310°C. In the cooling time of 36 hours, the bainite phase was formed in the temperature rang of 402-451°C. The results of this steel's hardenability test showed high hardenability and the jominy curve showed constant line

The Si/Al ratio is one of the effective parameters on the physicochemical properties of nanostructured LaAPSO-34 catalysts. Utilization of optimum ratio of Si/Al could significantly enhance the efficiency of these molecular sieves in the methanol to olefins conversion. To this aim, a series of nanostructured LaAPSO-34 catalysts with different Si/Al ratios were synthesized via hydrothermal method and characterized by XRD, FESEM, EDX, BET and FTIR techniques. XRD results showed that the growth of crystalline network is not considerable in the low Si/Al ratio, while the crystallinity has increased by increasing of this ratio. FESEM images revealed that by increasing Si/Al ratio, cube-shaped chabazite particles completely were formed. However, rough on the surface of the catalyst particles was observed in the high ratio of Si/Al. EDX analysis confirmed the presence of elements of this zeolite and also showed a uniform distribution of components. BET results showed that by increasing of Si/Al ratio from 0.1 to 0.3, specific surface area of the nanostructured LaAPSO-34 catalysts increased. FTIR spectrums confirmed framework vibrations of chabazite in different Si/Al ratios. Catalytic performance tests showed that by increasing of reaction temperature, methanol conversion increased. Increasing the Si/Al ratio from 0.1 to 0.3 led to the enhancement of the LaAPSO-34 performance and catalyst stability.

The α–phase metal hydroxides are layered materials whose structure is similar to that of thebetter studied layered hydroxides, LDHsα.– LHs and their nanohybrids have been suitable precursors tomake undoped and doped nanostructured metal oxides, metal and metal alloys as well as carbonmaterials and metal oxide carbon composites.In this research with co-perception synthesis method, organic/inorganic nanohybridα–phase layered hydroxide by zinc hydroxide nitrate(Zn5(OH)8(NO3)2) was produced and The initial layered materials were doped with transition metals such as Ni, Co, Fe, Al ions and carbonic resource of gallic acid added among layers. Then obtained nanohybrids were heat-treated at 900 and 1000 °C under an inert atmosphere N2andresulting in the production of carbon materials and metal oxides.Finally, for remove the obtained metal oxides,acid etching was done.Application of produced carbon materials was investigated as elecrocatalysts in polymeric fuel cell cathode. At all electrodes due to existence of mesoporouscarbonand also nitrogenin carbon structure, excellent electron transition and faster Oxygen reduction reaction was done. Open circuit voltage that obtained from analysis of LSV showed values in range of 0/9-1/1 V for all non-precious metal catalysts. These values are very close to the theatrical amount for oxygen standard reduction potential (1.2 V). Exchange current density for all electrodes is multiple of 10-4 or 10-5 or 10-6 and also obtained tofel slope for major electrodes being in range of 100-140 mv/dec that is very close to pt.

TiO2 coating was produced in single step and during a short time (10 min) by plasma Electrolytic Oxidation (PEO). In this study corrosion behavior of the CP-Ti and PEO coated sample were evaluated. Phase composition and surface morphology of the coating were studied by XRD and SEM respectively. X-ray diffraction result shows that the coating is consist of Anatase and the rutile is not formed under coating formation circumstances. Additionally, coatings demonstrate porous structure which contains micro-pores which are formed as a result of sparking process. Open circuit Potential and Cyclic potentio dynamic polarization tests were carried out in a de-aerated solution of 40 g l-1 H2SO4 and 40 g l-1NaCl. It is shown that thermodynamic stability of Titanium was enhanced which means that corrosion tendency was decreased. Furthermore corrosion rate was decreased more than eight times. The most important achievement of this study is improvement of the resistance against pitting corrosion.

β''-Alumina electrolyte as a sodium ion conductor is used in sodium sulfur batteries. To obtain the appropriate ionic conductivity, this electrolyte should gain high density and uniform microstructure during manufacturing process. For this purpose, in the present work, β''-alumina powder was synthesized and the parameters influencing the densification behavior of β''-alumina ceramic have been studied. β''- alumina powder synthesized by the zeta process and the raw samples were formed by uniaxial pressing and sintered at different temperatures and for different times. The phase identification of the synthesized powder and fabricated electrolyte was performed by X-ray diffraction (XRD), scanning electron microscopy and measuring of density were used to investigate the densification behavior. The results showed that the microstructure of the β''-alumina ceramics strongly depends on the sintering conditions.Decreasing in the density and the duplex microstructure occurred with increasing the time of the sintering. The optimum condition for the sinte ring of the β''- alumina electrolyte was determined to be at 1620 ºC for 15 min, which results in a dense sample with more than 99% of theoretical density, uniform microstructure, without excessive grain growth and the lack of duplex microstructure including more than 99 percent β''-Al2O3 phase.

Metal matrix composites (MMCs) are considered for their mechanical properties and wear resistance. In this study, the effect of milling time and sintering temperature on the microstructure and mechanical properties of Al/SiC composites was studied. Firstly, the powders with volume fraction of Al/20% SiC were mixed in a planetary ball mill under argon atmosphere for milling time of 0.5, 1, 2, 4 and 8 h. Then, the mixed powders were pressed by a cold pressure of 500 MPa into pellets and rods. With regard to the microstructure properties of the samples, the optimized milling time was determined. Then, the pressed samples were capsulated and sintered for 1 h at 400, 450, 500, 550 and 600 0C. Morphology, mechanical and tribological properties of the prepared composites was evaluated by scanning electron microscope (SEM), hardness and wear test. The result showed that the optimized milling time and sintering temperature are 8 h and 600 0C, respectively. Also, density, hardness and wear resistance increase with increasing sintering temperature.

In the current research, antibacterial properties of silver nanoparticles and polyethylene-silver nanocomposites against Staphyloccocus aureus (Gram-positive) and Escherichia coli (Gram-negative) bacteria were investigated by using disk diffusion method. For this purpose, silver nanoparticles were synthesized by chemical reduction method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). No additional peaks were observed in the XRD pattern and the mean particle size of nanoparticles was 21.7 nm. Then, polyethylene-silver nanocomposites containing 5, 10, 20 and 30 weight percent of silver nanoparticles were fabricated by mechanical milling and characterized by XRD, TEM and scanning electron microscopy (SEM). Results showed that the nanoparticles were well dispersed throughout the polyethylene matrix. Antibacterial investigation of samples showed that both nanoparticles and nanocomposites exhibit antibacterial properties against bacteria and this property increases with increasing weight percent of nanoparticles in the disk. Also sliver nanoparticles indicated stronger antibacterial properties against Staphyloccocus aureus than against Escherichia coli.

In thepresent research Zirconium diboride powder was synthesized by carbothermal activation (ZrO2+B2O3+C), borothermal activation (ZrO2+B4C), and a compound carbothermal- borothermal, i.e. borocarbothermal, activation (ZrO2+B4C+C) of different compositions at 1550°C for 3 h under argon atmosphere. XRD and SEM studies showed that the ZrB2 powder synthesized by carbothermal activation method has grown with a rod-like morphology. In addition, carbon impurity was observed in the ZrB2 powder. However, in the final product carbon appeared as an element which was omitted by heating at 500°C in an oxidation oven. The powder particles synthesized by this method are larger compared to those produced by other methods. Moreover, there is a lower possibility of sintering of the particles in this method. Synthesis by borothermal method, on the other hand, resulted in appearance of borate as impurity and the rod-like growth of ZrB2. The borate impurity was reduced by washing with ethanol. Synthesis by borocarbothermal route shows a lower amount of particles penetration compared to the borothermal method, which is due to the presence of carbon in the sample. Also, in borocarbothermal synthesis carbon was reduced from the system similar to the carbothermal method. A comparison between the abovementioned routes revealed that activation of borate carbide is a more appropriate method for synthesizing zirconium diboride powder compared to the other techniques.