Advanced Materials Research Vol. 829

Abstract: Aluminum matrix hybrid nanostructured composites containing 30vol.%TiB₂/SiC particles were manufactured by underwater shock consolidation method. Underwater shock consolidation is a one-stage densification process, which involves a very rapid and intense deposition of shock energy on powder particle surfaces. The interfacial microstructure and characterizations of this composite was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the interface is clean and no reaction zone generated along the interface between SiC/TiB₂ particles and Al matrix. Transmission electron microscopy reveals the development of nanostructures in the Al matrix after shock wave consolidation. Density, hardness and bending strength of the composites compacts were measured. The hybrid composite samples showed better improvement in the bending strength regard to Al-30 vol. %TiB₂ and also Al-30 vol.%SiC composites.

Abstract: Hydrazine is an interesting reducing agent which is used in considerable number of different industrial catalytic applications including gas generators, pure hydrogen production for electric fuel cells and monopropellant thrusters. Hydrazine is a highly reactive molecule that decomposes at low temperature on many metal surfaces e. g. iridium, rhodium and tungsten. But the standard commercial catalyst used for decomposition of hydrazine is shell 405 which contents from high metallic content of iridium supported on gamma alumina. In the present study, iridium nanocatalysts based on gamma alumina with metallic content of 20 wt% have been synthesized by the incipient wetness impregnation using H2IrCl6.xH2O as precursor. The pretreatment effects on the metallic accessibility on the Ir/γ-Al2O3 have been evaluated. After ionic exchange, impregnated supports were calcined in air flow and the n followed by reduction in hydrogen flow. The prepared nanocatalyst has been identified using specific surface measurement (BET), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The catalytic mechanism was also briefly discussed. The main goal of this work is prepare, characterize, and determine the nanocatalytic behavior of iridium supported on gamma alumina in decomposition of hydrazine process. The results of this study show that the performance of synthesizes nanocatalyst is suitable for decomposition of hydrazine; however it is need of further investigation. The results indicate that however our synthesized nanocatalyst demonstrates a good job in hydrazine decomposition; some promoters had yet to be tested due to enhancement of economic efficiency.

Abstract: Cu-Ti system with a terminal solution in the Cu-rich portion of equilibrium Cu-Ti phase diagram with a decreasing trend with temperature shows a potential to develop age hardenable alloys with suitable strength and thermal and electrical conductivities. In the present study, the mechanical alloy process has been employed to increase solubility of Ti in Cu matrix to make age hardenable Cu alloys. Cu-Ti powder mixtures with different rations of 1 and 6 wt% of Ti were milled in planetary ball mill for different milling times of 4, 12, 48, 96 and 192 hours. The milled powder mixtures were investigated and characterised by X-ray diffraction (XRD) technique. The results show increasing in lattice parameter of Cu, which indicates that Ti atoms are dissolved in the Cu matrix. Cu crystal sizes showed decreasing trend which were more obvious in the mixture with higher Ti contents. The final crystal sizes were in the range of 17-23 nm after 192 hours of milling.

Abstract: Here, nano and microstructures of silicon oxide layers grown on p-Si (111) wafer have synthesized by evaporating SnCl₂.2H₂O powder in a mixture of Ar and O₂ gas flow using chemical vapor deposition (CVD) technique. The growth temperature and the vacuum pressure were 950 °C and 10^-3 torr, respectively. Through this study, samples have characterized by SEM, XRD, EDS and PL methods. The grown sample while has a combination of porous and layered morphology, it has a polycrystalline nature including a mixture of SiO_2-x (002) and SnO₂ phases. The EDS elemental analysis confirmed the presence of Si, O and Sn atoms in the composition, which is consistent with the XRD data. The PL spectrum show a strong peak in violet region (424 nm) attributed to the crystal defects at the SiO_2-x and SnO₂ interfaces.

Abstract: An ultrafine grained 304L stainless steel with average grain size of 650±100 nm was produced by a combination of cold rolling and annealing. Wear behavior of the steel was examined by dry sliding wear tests under different loads. Different microstructural characterizations were conducted on the ultrafine grained structure after thermomechanical processing and wear tests. The results demonstrated that the steel had yield strength of 720 MPa and total elongation of 47%, which is almost twice higher than typical coarse grained strength. Also, wear tests results showed a good linear relation between the cumulative wear loss and distance in each normal load. Wear rate was about 0.024, 0.043 and 0.093 mg/m for normal loads of 10, 20 and 30N, respectively. Wear mechanism was also recognized as delamination (in the early stage) and mixture of delamination and abrasion in higher distances.

Abstract: Three sets of novolac xerogel prepared with various solvents and the effect of solvent on drying shrinkage investigated. The results show that the polarity of solvent has profound effect on microstructure of gel. As the polarity of solvent increases, the ultimate particle size and pore size decrease and consequently, the higher capillary pressure exerts on gel and hence, more shrinkage observed.

Abstract: Copper oxide nanoparticles have been synthesized using micro reactors made of bis (2-ethylhexyle) sulfosuccinate (AOT)/water/n-Hexane microemulsions. The controls of particles size was achieved by varying water to surfactant molar ratio (W₀). At constant of surfactant concentration the increases in value of W₀ increased the population of micelles and resulted in lager particle size. Their sizes and appearance were characterized by TEM, SEM, Zetasizer, uv-visible methods. Scanning electron microscopy (SEM) showed the spherical morphology of as prepared CuO nanoparticles. The Transmission electron microscopy (TEM) showed 85 nm size of as prepared CuO particles.

Abstract: In this paper, a mode of nanostructured Pd anode of SOFCs is presented to calculate the effects of nanoparticles on the SOFCs' electrodes performance. Nanostructured electrodes of the SOFCs prepared by wet impregnation have attracted increasing attention as the most effective way to make highly active and advanced structures in the electrodes. The effects of infiltrated Pd-nanoparticles on the performance of Nickel/ Gadolinium doped Ceria (Ni/GDC) anode of SOFC are investigated. It is observed that a small amount of Pd catalyst has a significant decreasing effect on overpotential of anodes. One-dimensional analysis is carried out using a simplified geometry to calculate the effective polarization resistance by assuming the ionic conductor phase (GDC) as columns and the Pd phase mounted on these columns. The results of modeling are presented and compared with the experimental data as a function of temperature.

Abstract: Porous carbons are disordered materials with applications in many areas such as catalysis, molecular separation, and energy storage/conversion. Among porous materials, active carbons are the most popular materials in separation processes. They are non-crystalline materials with heterogeneous pore structures. This property does not permit accurate structural determinations by diffraction techniques. Thus only limited structural information can be extracted from experimental techniques. Consequently, a molecular model of nanoporous carbon can't be constructed that is based solely on experimental data. Computer simulation techniques provide an alternative way to tackle this problem. So, in this study, the synthesis process of an amorphous active carbon is investigated using molecular dynamics simulation. Simulations are carried out at constant temperature in the box containing specific numbers of pure carbon sheets. Two different types of ensembles have been used for simulation including NPT and NVT. Calculated results show that the final structure of porous carbons is in agreement with SEM images of some commercial active carbons. Also, results indicate that the final structure is consisted of three different pore size (r) zones: r<2 nm which produces micro pores,250 nm which named macro pores. These observations are exactly the same as what is observed in experiments. These various pore sizes especially micro and meso pores are observed in radial distribution function curve, too. At last, the temperature effect on the pore size is investigated. Three different temperatures of 973K, 1073 K and 1173 K are applied for the simulation. Calculated results show that increasing the temperature does not have any significant effects on the pore size and structure.

Abstract: The edge of graphene plays an important role in electronic and spintronic properties of graphene. As we know in many article zigzag edge used as stable edge but this edge cannot be true edge. When the graphene sheet is cut, bonds are broken along this line and electrons that participate in bond be free, so there is electron density gradient along the edge. Because of this the carbon atoms along the edge is moved till the stable structure be established. For achieving to this specific structure, density functional theory was used via Gaussian package. The result shows hexagons on the edge are going to deform to pentagon and heptagon by change the kind of bond in this chain. In the other zigzag chain behind the edge we have movement of electron density from one carbon atom to another carbon atom by help of carbon atom that placed between them. So we suggested new edge that can be replacement by zigzag edge in calculation with more less structure energy that identify in experiment method too.