Scientia Iranica
Volume:26 Issue: 3, May-Jun 2019

Now a day preparation of special and effective nanocatalysts is a hot research topic. Obviously the size and structure of the active site of a catalyst plays the key role in catalytic activity. In this novel research the Pt nanocatalyst supported on γ-Al2O3 was prepared in two different microemulsion systems to clarify the effect of microemulsion essence on catalyst character and activity. Two types of microemulsion systems were constructed from Triton X-100/2-butanol as surfactant and co-surfactant, n-heptane as organic phase and H2O + H2PtCl6 (or HCl(aq) + H2PtCl6) as aqueous phase to investigate the effect of HCl on the shape and structure of the prepared nanocatalysts. Shape, size and size distribution of the Pt nanoparticles on the alumina were monitored by cyclic voltammetry and SEM analysis. Activity of the nanocatalysts was determined by reduction of p-nitrophenol as a reaction model.

Finite element method (FEM) is used to study the hydrothermal characteristics of the nano-fluid subjected to Brownian motion. For effective thermal conductivity and effective, viscosity Koo-Kleinstreuer-Li (KKL) model is used. It is observed that the dispersion of nano-particles in Newtonian liquid causes a significant increase in the effective thermal conductivity. This results based on the dispersion of nano-particles help engineers to design an efficient thermal system. A significant role of viscous dissipation on diffusion of momentum of wall into the fluid is observed. Therefore, dissipations effects cannot be ignored while designing thermal systems. The buoyant force is responsible for the effect of electromagnetic thermal radiations on the velocity of fluid convectively heated surface enhances the rate of generation of entropy. This study also recommends that nano-fluids are the best coolants as compare to the base fluids. Imposition of magnetic field causes more entropy generation.

Green alternatives prevail over the hazardous and expensive pathways of nanoparticles synthesis. Here we report eco-friendly manufacturing of gold nanoparticles by microwave assistance. The water soluble organic constituents of the tropical herb Elephantopus scaber functioned as the three electron donor and the aggregation preventer. XRD spectra certified fcc crystal lattice and the TEM images supported mixed spherical and triangular geometry to the nanoparticles with an average particle size of 18.97±5.86 nm. Ecological relevance of the gold nanoparticles lies in their ability to degrade methylene blue and methyl orange. The catalytic capacity of the gold nanoparticles is exploited in the reduction of 4-nitrophenol. Large scale production of gold nanoparticles in an easy manner using renewable sources improves the ‘green’ significance of the present synthesis.

This paper investigates on the structural stability and electronic properties of titanium dioxide (TiO2) nanowires of different novel shapes using first- principle based density functional approach. Out of linear, ladder, saw tooth, square, triangular, hexagonal, and octahedron shaped atomic configuration, the ladder shape atomic configuration is energetically most stable. After computation of lattice parameters as well as various mechanical properties of nanowire TiO2, it is seen that highest bulk moduli is obtained for triangular TiO2 nanowire which shows the highest mechanical strength for the structure whereas hexagonal configuration has lowest Bulk moduli which shows the lowest mechanical strength for the structure. Analysis of various electronic properties show that different configurations of TiO2 nanowires can have different utility as solid state materials.

SU8 is commercial epoxy-Novolac resin, a negative tone photoresist with outstanding mechanical properties. Its nanocomposites have also been considered as a research material. In order to obtain insights about the SU8 nanocomposites with graphene the present work was conducted to simulate the mechanical properties using multiscale simulation atomistic, meso and macro scales. This has started from molecular dynamics, then moved to coarse grain and finally reached to macroscale. Peridynamics is the methodology which is governed throughout the work. Top-down and bottom-up loop has to be employed in order to confirm the total results. A tensile deformation is applied to a 2D plane at the upmost scale to result in an internal pressure. This is transferred to the lower scale in the next step as the external pressure. The procedure continues down until the molecular scale is reached. However, bottom-up strategy requires a bridging model to link the molecular scale to upper scales. The check point is the deformation values which have to be in the same order independent of top-down or bottom-up movement. At 2.1 wt.% of graphene in SU8, increased Young’s, bulk and shear modulus were calculated (62, 200, and 82 % respectively) compared to the neat SU8.

Graphene is a thin sheet with special properties and complicated mechanical behavior. It’s important to study graphene experimentally and theoretically. Stone–Wales defects, cracks and atom vacancy are popular defects in carbon allotropes especially in graphene. In this paper, residual strain in graphene was discussed. At first, stress-strain curve of non-defected graphene sheet was obtained using molecular dynamics simulation and effect of temperature on mechanical properties of graphene was obtained. Then, four different cracks were considered in center of graphene sheets. Stress-strain curves of defected graphene sheets with different tension strain rates were plotted. The results showed that cracks lead to the graphene to fracture sooner. Also, increasing temperature lead to the Young’s modulus of graphene decreases and graphene fractured at lower strain. On the other hand, residual strain of non-defected and cracked graphene increased by increasing temperature from 200 K to 1200 K. It means that graphene had more plasticity behavior by increasing temperature.

Calcium phosphate (Ca-P) based bioceramics has proved to be alluring materials for biomedical applications. Among these, particular attention has been given to hydroxyapatite (HA), Ca10(PO4)6(OH)2. Due to its favorable some physical, mechanical, chemical properties and biocompatibility, HA-coated Ti6Al4V alloy has been approved as one of the most interesting implant materials for orthopedic and dental applications. High Velocity Oxy Fuel (HVOF) is a method used to coat hydroxyapatite (HA) on metallic implants such as titanium (Ti) and its alloy (Ti6Al4V). In this work decreasing the crack occurrence and increasing adhesion strength were investigated. For this purpose, sol-gel synthesized nano sized HA, alumina (Al2O3) and Boron oxide (B2O3) powders were produced. First, a series of HA/Al2O3 HA/B2O3 coatings have been deposited on Ti6Al4V substrate by HVOF method. All specimens’ surfaces were used to characterize by using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM-EDS) and X-ray Diffraction (XRD). Adhesion strength of the samples was found to affect with increasing amount of Al2O3 and B2O3 in HA. Furthermore, water contact angles of coating layer were decreased with increasing amount of Al2O3 and B2O3 in HA. This coating surface was expected to combine the advantages of Ca-P (osseointegration) and adhesion strength.

Bismuth Titanate (Bi4Ti3O12) ceramics, so-called BiT, have many modern applications in microelectronics, sensors, and capacitors. In this study, the related solutions for fabricating BiT thin films were prepared and then coated on glass substrates by using the sol-gel technique and the spin coating instrument. The Xray diffraction patterns of our samples indicate that the crystalline phases of BiT are orthorhombic. Based on the transmission-spectra analysis, the samples are transparent in the visible spectrum, and their optical energy gaps are found to be 3.36 eV and 3.41 eV for the BiT thin films annealed at 600◦C and 650◦C, respectively. Other physical quantities such as refractive index, thickness, extinction coefficient and dielectric constant were estimated by swanepol’s method. The results show that as the annealing temperature rises the real part of the dielectric constant becomes larger indicating our samples are good dielectric materials

In this paper to include small scale effect, the augmented Love displacement potential functions (DPF) are developed for isotropic micro or Nano scales medium based on couple stress theory. By substituting the new DPF in equilibrium equations, governing equations are simplified to two linear partial differential equations of sixth and fourth order. Then the governing differential equations are solved for simply supported rectangular plate using the separation of variable method with satisfying exact boundary conditions without any simplification assumptions. Displacements, bending and torsional moments of rectangular plate are obtained for different length scale parameters, aspect and Poisson’s ratios. The obtained results are compared with other studies which show excellent agreement between them.

In this research, lead acetate as a source of Pb2+ and thiourea as a source of S2- have been used, and the eects of deposition time (tD < 90 min) and deposition temperature (TD: 28, 55C) on the prepared thin lms of Lead-Sulde have been investigated. In order to investigate the morphology of thin lms and crystalline nanostructure of the lms, atomic force microscopy and X-ray diraction have been utilized, respectively. Values of lattice constant for prepared PbS lms vary in the range of 0.5937- 0.5959 nm. Preferred growth orientation for prepared lms is 200. The thickening process of layers has declined after 60 min (t at 28C: 130-530 nm and t at 55C: 300-975 nm).