Sharif Digital Repository

Cubic MgO micro-particles with approximately 5-10 μm dimensions were synthesized indirectly from magnesium salt solutions through three consecutive steps, namely: wet chemical precipitation, hydrothermal and thermal dissociation. In wet chemical precipitation step Mg(OH)2 uniform lamellar hexagonal nano-structure with about 30 nm in thickness were synthesized from 0.2 M Mg(NO3)2 • 6H2O solution, subsequent hydrothermal processing of synthesized Mg(OH)2 lamellar hexagonal nano-structure in 10, 20, 30, 60, 120 and 180 min produced 5-10 μm MgCO3 micro-cubes which calcinations of these particles leads to production of the same size MgO micro-cubes. Most pure MgCO3 micro-cubes were synthesized... 

One of the most popular constitutive rules that correlate the continuum and atomic properties in multi-scale models is the Cauchy–Born (CB) hypothesis. Based on this constitutive law of continuum media, it assumes that all atoms follow the deformation subjected to the boundary of crystal. In this paper, the validity and failure of CB hypothesis are investigated for the silicon nano-structure by comparison of the continuum and atomic properties. In the atomistic level, the stresses and position of atoms are calculated using the molecular dynamics (MD) simulation based on the Tersoff inter-atomic potential. The stresses and strains are compared between the atomistic and continuous media to... 

In this paper, a novel coupling technique is developed in continuum–atomistic multi-scale analysis of temperature field problems. In this manner, a new thermostat is introduced based on the single-atom sub-system, where its capability to control the temperature and produce the canonical ensemble is investigated. Moreover, the performance of proposed thermostat is verified by comparing the distribution of velocities to the Maxwell-Boltzmann distribution. The single-atom sub-system thermostat is then incorporated into the concurrent multi-scale model to relate the temperature field between the continuum and atomistic domains with complex lattice thermal fields. In order to illustrate the... 

Samples of regular gamma and nano-structured alumina were prepared and their porosimetric properties evaluated by N 2 porosimetry method. Moreover, cobalt based catalysts for Fischer-Tropsch (FT) Synthesis were prepared by loading cobalt under two calcinations using these alumina supports. Then the porosimetric properties of these materials as well as; their reactor behaviors assessed. Although the nano-structured favored the gamma alumina from pore volume and surface points of view, comparison of porosimetric properties of fresh alumina samples with corresponding catalysts prepared revealed that calcination effect in decreasing those factors was more pronounced for the nano-structured... 

Nano-structured CuO granules catalyze the C-N cross-coupling of amines with iodobenzene in excellent yields. The reaction is simple, efficient, and operates in air under ligand-free conditions  

The effects of relaxation and nanocrystallization on magnetic properties of (Fe0.5Co0.5)73.5Si13.5B 9Nb3Cu1 ribbons have been investigated. Ribbons were melt-spun at wheel speed of 38 m/s and then annealed at different temperatures. The results indicated that the relaxation processes shift the Curie temperature of amorphous phase to the higher temperatures. It was also found that through crystallization phenomena the saturation magnetization increases due to the super-exchange between Fe and Co atoms in the crystalline phase. A slight variation in magnetization was observed at ~700 °lC during heating due to the ordering transition in FeCo system. At early stage of crystalline phase... 

Cobalt supported on carbon nanotubes (CNTs)-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis (FTS). Problems associated with shaping of Co/CNTs into extrudates or pellets as well as catalyst attrition rendered these materials unfavorable for industrial applications. In this investigation regular γ- and nano-structured (N-S) alumina as well as CNTs-covered regular γ- and N-S-alumina supports were impregnated by cobalt nitrate solution to make new cobalt-based catalysts which were also promoted by Ru. The catalysts were characterized and tested in a micro reactor to evaluate their applicability in FTS. γ-Al2O3 was prepared by... 

In this study, copper oxide nano particles were synthesized by batchwise supercritical hydrothermal method. After preparation of CuO nano particles, they were immobilized into the porous matrix of sodium alginate. The drying process formed a very porous structure that is useful for enhancing of adsorption activity. Produced CuO particles were characterized by X-ray diffractometery (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and BET for measuring the surface area. The prepared materials were then used as adsorbent in the removal of toxic metal ions in aqueous solution. To optimize the adsorption system, the effect of various parameters such as adsorbent... 

In this paper, the effects of van der Waals and Casimir forces on the static deflection and pull-in instability of a micro/nano cantilever gyroscope with proof mass at its end are investigated. The micro/nano gyroscope is subjected to coupled bending motions which are related by base rotation and nonlinearities due to the geometry and the inertial terms. It is actuated and detected by capacitance plates which are placed on the proof mass. The extended Hamilton principle is used to find the equations governing the static behavior of the clamp-free micro/nano gyroscopes under electrostatic, Casimir and van der Waals forces. The equations of static motion are discritized by Galerkin's... 

The aim of this study was to assess the effects of two different types of SiO2 nanoparticles (N and M series) with different ratios on the workability and compressive strength of developed binary blended concretes cured in water and lime solution as two different curing media. N and M series SiO2 nanoparticles with an average size of 15 nm were used as obtained from the suppliers. Fresh and hardened concretes incorporating 0.5%, 1.0%, 1.5% and 2.0% of N and 2% of M series nanoparticles with constant water to binder ratio and aggregate content were made and tested. Fresh mixtures were tested for workability and hardened concretes were tested for compressive strength at 7, 28 and 90 days of... 

Mechanical alloying and sintering were used to fabricate nanostructured Ti6Al4V scaffolds of highly controllable pore geometry and fully interconnected porous network. Elemental powders were milled for different periods of time (10, 20, 30, 40 and 60 h), mixed with 40-60 vol.-% of 200-400 μm cuboidal NaCl, compacted at 500-600 MPa and sintered according to single or double stage heat treatment regimes at 790 and 950°C under vacuum. After sintering, the samples were soaked in distilled water to washout the NaCl. Foamy microstructures were obtained showing well shaped biopores and fragmentary embedded micropores. The shape of initial NaCl was copied into the biopores which had highly... 

In this study, titanium substrates which previously oxidized through Micro arc oxidation method, was coated by Hydroxyapatite (HAp) coating once more by means of the same method. Morphology, topography and chemical properties as well as phase composition and thickness of layers were studied to reveal the effect of the electrolyte concentration on coating features. According to results, the obtained coatings are consisted of HAp and titania as the major phases along with minor amounts of calcium titanate and α-tri calcium phosphate. Ca and P are present on surface of obtained layers as well as predictable Ti and O based on the XPS results. Thickness profile of coatings figured out that by... 

One of the most popular constitutive rules that correlate the continuum and atomic properties in multi-scale models is the Cauchy-Born (CB) hypothesis. Based on this constitutive law of continuum media, it assumes that all atoms follow the deformation subjected to the boundary of crystal. In this paper, the validity and failure of CB hypothesis are investigated for the silicon nano-structure by comparison of the continuum and atomic properties. In the atomistic level, the stresses and position of atoms are calculated using the molecular dynamics (MD) simulation based on the Tersoff inter-atomic potential. The stresses and strains are compared between the atomistic and continuous media to... 

Undoped and copper doped nanostructured zinc oxides were synthesized by using a series of synthetic layered material, undoped and copper doped zinc hydroxide nitrates at various molar percentages of copper (2-10) within the layers as precursors. The layered materials were heat-treated at 500 °C to produce zinc oxide nanostructures with crystallite sizes in the range of 23-35 nm. Optical studies of the nanostructured copper doped zinc oxides showed the decrease in band gap with increasing content of the doping agent, copper  

Researchers in Germany and Iran have looked at methods of manufacturing wear parts using nanostructured hardmetal combined with a cheaper stainless steel component in pursuit of cost effectiveness. Nanostructured WC-10%Co-0.9%VC and 316L SS powders were used as starting materials. A polymer-wax binder composed of polyethylene copolymer-ethylene vinyl acetate, carnauba wax, paraffin and stearic acid was used to prepare the hardmetal feedstock in a laboratory kneader with z-mixing blades at a temperature of 120°C. The assembled PIM parts were sintered in a laboratory sintering furnace under nitrogen according to different sintering cycles in the temperature range of 1320-1360°C with a heating... 

Simple synthesis of silver doped TiO2 nanostructured layers by micro arc oxidation process is reported for the first time. The layers consisted of anatase and rutile phases whose characteristic XRD-peaks shifted toward lower diffraction angles when compared to the pure micro arc oxidized TiO 2 layers. Silver-doping was confirmed by XPS technique. The anatase phase crystalline size was determined as 27.6 and 21.8 nm for the layers grown under the voltages of 350 and 500 V. Employing a UV-Vis spectrophotometer, a red shift in the absorption edge of the layers was observed when silver was incorporated into the titania lattice  

The uniaxial viscosity and sintering stress of WC-10Co-0·9VC (wt-%) were obtained by a loading dilatometer as functions of fractional density (0·64<ρ<0·93) and temperature (1084