Sharif Digital Repository

Herein, the CO methanation reaction is studied over Ni/Fe–Al mixed oxides with various Fe and Al contents. The mesoporous nanocrystalline supports are prepared by a novel sol–gel process using propylene oxide as a gelation agent. The deposition–precipitation method is used for the deposition of nickel on the catalyst support. The samples are characterized by Brunauer–Emmett–Teller (BET), X-ray diffractometry (XRD), temperature programmed reduction (TPR), temperature programmed oxidation (TPO), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that increasing the iron content and reducing the Al percentage in the catalyst support reduces the... 

A systematic comparison of single and binary metal oxide T1O2, TiO2-Ga2O3, TiO2-Er 2O3 and TiO2-Ta2O5 gas sensors with nanocrystalline and mesoporous microstructure, prepared by sol-gel route, was conducted. The gas sensitivity was increased by secondary phase introduction into TiO2 film via two mechanisms, firstly through the inhibition of anatase-to-rutile transformation, since the anatase phase accommodates larger amounts of adsorbed oxygen, and secondly through the retardation of grain growth, since the higher surface area provides more active sites for gas molecule adsorption. The binary metal oxides exhibited a remarkable response towards low concentrations of CO and NO2 gases at low... 

In micron-scale, powder consolidation process is driven by diffusion phenomenon, while in nano-scale the higher surface energy of particles leads to some anomalous behaviors within the process. In order to investigate the nano-sintering occurrence, an atomistic approach is employed via molecular dynamics simulations. Within this approach, the effect of particle size and temperature is examined. The study of particle structure emphasizes on a transition on the governing mechanism of process depending on the material energy levels. The results show that in a specific particle size at low temperatures, the main sintering mechanism is the plastic deformation, while at elevated temperatures it... 

CuCo2O4 spinel nanopowders were synthesized by sol–gel method. The optimal values of pH and molar ratio of citric acid to metal ions (RC), and the influence of the calcination temperature and time were investigated. As-prepared materials were characterized by XRD, TGA, DSC, FE-SEM and electrical and coefficient of thermal expansion (CTE) measurements. It was found that pH = 4.5 and RC = 1 are the optimum conditions to produce pure CuCo2O4 nanopowders. The electrical conductivity was increased remarkably from 15.2 to 27.5 S cm−1 with an increase in temperature from 500 to 800 °C. Over the temperature range of 25–800 °C, the CTE of... 

Nickel-titanium (NiTi) shape memory alloys have been widely used as implant materials, due to their superior shape memory properties and similar mechanical behavior to bone tissue. The presence of nickel on the surface of nickel-titanium alloy and release of this ion in the body environment will result in some allergic reactions. In current study, we used shot pinning process to produce nanocrystalline nickel-titanium alloy with increased corrosion resistance. Field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) analysis, and atomic force microscopy were employed to investigate the surface features of samples. The quantitative chemical analysis of NiTi and modified... 

Ferrite nanocrystals are an interesting material due to their rich physical properties. Here we add nonmagnetic dopants Zn and Cu to nickel ferrite nanocrystals, Ni1-xMxFe2O4 (0 ≤ x ≤ 1, M = Cu, Zn), and study how relevant properties of the samples are modified accordingly. Basically, these dopings cause a rearrangement of Fe +3 ions into the two preexisting octahedral and tetrahedral sites. In fact, this, we show, induces pertinent magnetic properties of the doped samples. In the case of the Cu-doping, the Jahn-Teller effect also emerges, which we identify through the Fourier Transform Infra-Red Spectroscopy of the samples. Moreover, we show an increase in the lattice parameters of the... 

TiO2, transition metal (Cr, Mn, Fe, Co, Ni, Cu, and Zn)- and aluminum-doped TiO2 nanoparticles were prepared by the sol-gel technique. The sulfated catalysts were prepared by the impregnation method with H2SO4 solution. The catalysts were characterised by X-ray diffraction (XRD), BET surface area measurement, diffuse reflectance spectroscopy (DRS), and Fourier transform infrared (FTIR) techniques. The sulfate content of the metal-incorporated samples was considerably higher than for SO4 2-/TiO2. The metal doping brought about a considerable reduction in the extent of sulfate loss from the catalyst surface due to the wide dispersion on the surface. The SO4 2-/TiO2 and SO4 2-/M/TiO2... 

Pechini process was used for preparation of three kinds of nanocrystalline powders of yttria-stabilized zirconia (YSZ): doped with 1.5 mol% nickel oxide, doped with 15 mol% ceria, and doped with 1.5 mol% nickel oxide plus 15 mol% ceria. Zirconium chloride, yttrium nitrate, cerium nitrate, nickel nitrate, citric acid and ethylene glycol were polymerized at 80 °C to produce a gel. XRD, SEM and TEM analyses were used to investigate the crystalline phases and microstructures of obtained compounds. The results of XRD revealed the formation of nanocrystalline powder at 900 °C. Morphology of the powder calcined at 900 °C, examined with a scanning electron microscope, showed that the presence of... 

Young’s modulus (E) is one of the most important parameters in the mechanical properties of solid materials. Young’s modulus is proportional to the stress and strain values. There are several experimental and theoretical methods for gaining Young’s modulus values, such as stress–strain curves in compression and tensile tests, electromagnetic-acoustic resonance, ultrasonic pulse echo and density functional theory (DFT) in different basis sets. Apparently, preparing specimens for measuring Young’s modulus through the experimental methods is not convenient and it is time-consuming. In addition, for calculating Young’s modulus values by software, presumptions of data and structures are needed.... 

As an important precursor of crystalline phases, amorphous calcium carbonate (ACC), especially ultrasmall ACC clusters, have been attracting great interest in fundamental research, materials chemistry, as well as industrial applications. However, it is still challenging to synthesize stable ACC clusters in water that can be isolated and concentrated without severe aggregation. Herein, we report a facile dialysis method for producing colloidally stable ACC clusters that are well dispersed in water with the protection of specific polycarboxylic acids, which could be also easily deprotected by small-molecule acids like sodium citrate. Inherent proto-calcite short-range order is found to be... 

As an important precursor of crystalline phases, amorphous calcium carbonate (ACC), especially ultrasmall ACC clusters, have been attracting great interest in fundamental research, materials chemistry, as well as industrial applications. However, it is still challenging to synthesize stable ACC clusters in water that can be isolated and concentrated without severe aggregation. Herein, we report a facile dialysis method for producing colloidally stable ACC clusters that are well dispersed in water with the protection of specific polycarboxylic acids, which could be also easily deprotected by small-molecule acids like sodium citrate. Inherent proto-calcite short-range order is found to be... 

In this research, solar cells sensitized with CdS and PbS Nanocrystalline metal sulfides, chemically grown by SILAR, were fabricated and characterized. PV experiments including I-V test in the presence of light and dark,Vocdecay, and Electrochemical impedance spectroscopy were performed on the Cells made through this method in the presence of light and dark and in the time period of 2, 3, 6 and 10 days. From these experiments, the changes in indicators including fill factor, efficiency, open-circuit voltage, short-circuit current, lifetime of electrons in nanostructured anode electrode, recombination resistance and capacitance of the anode electrode-electrolyte interface were observed. Also,... 

Co-Ce doped Ni nanocrystalline ferrites having composition Ni0.8Ce0.2CoxFe2-xO4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were fabricated by sol gel auto combustion method. Synthesized samples were investigated by thermal gravimetric and differential thermal analysis (TGA-DTA), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis (EDX) and vibrating sample magnetometer (VSM) to study the phase, vibrational modes, structure, surface analysis and magnetic properties respectively. Structural parameters (lattice parameters, cell volume, crystallite size and micro strains) were also calculated from XRD recorded data.... 

The hydrogen desorption properties of nanocrystalline magnesium hydride processed by high-energy mechanical milling was investigated. MgH2 powder was milled for various times (up to 16 h) under a high purity argon atmosphere and the effect of milling on the particle size and morphology, grain refinement, lattice strain, and desorption temperature was studied. It was shown that accumulated lattice strain combined with nanometric grain structure significantly decrease the desorption temperature. The effect of powder particle size was found to be of less importance. The lowest desorption temperature was obtained after 4 h high-energy milling. Nanostructured magnesium hydride with grain size of... 

To fabricate ceramic/metal complex-shaped part by co-powder injection moulding process (2KPIM), it is essential to tailor the sintering parameters in order to gain a low mismatch shrinkage, i.e. high sintering compatibility. In the present work, nanocrystalline 3Y-TZP and commercial 430L MIM grade stainless steel powders were co-sintered at various sintering cycles. Isothermal and non-isothermal sintering behavior of the individual and composite layers in argon and vacuum atmospheres were examined. High resolution scanning electron microscopy (HRSEM) coupled with energy dispersive X-ray (EDX) analysis was used to study the bonding interface between the ceramic and metal joints. It is shown...