Sharif Digital Repository

MIL-101(Cr) metal–organic framework samples were successfully synthesized through the conventional electrical heating (CE), ultrasound (US), and microwave (MW) synthetic methods at three different temperatures and various synthesis times. These were done with the aim of understudying the crystallization kinetics of these complex MIL's structures. The nucleation and crystal growth steps were thus, quantified through measuring the relative crystallinity of the prepared MIL-101(Cr) utilizing the PXRD and FESEM analysis under various synthesis conditions. In addition, the textural properties of the fully crystallized samples measured through the N2 adsorption–desorption isotherms at 77 K. The... 

The fractal study of thin layer films has been concerned by numerous studies, but it is a novel idea to use this method for interpretation of layer formation during electrocrystallization, simultaneously. In present study, Scharifker's equations were derived for instantaneous and progressive nucleation and 3D growth of hemispherical centers under diffusion-controlled condition to calculate in situ change of fractal dimension of surface. It was assumed that the layer could be formed completely when fractal dimension of surface inclined to 2. Moreover, the fractal analysis of AFM images has confirmed the presumed model. © 2006 Elsevier Ltd. All rights reserved  

CdS nanoparticles were grown using CdSO4 and Na 2S2O3 as the precursors and thioglycerol (TG) as the capping agent. TG was shown to exhibit a catalytic role in the reaction and also acted as a capping agent. It was demonstrated that size growth is linearly related to the temperature of the reaction, i.e.the sizes can be controllably adjusted by temperature. The crystalline phase of the nanocrystals was also dependent on the temperature of growth: higher temperature favours the cubic phase. The pH also plays an important role in nanoparticle growth, as lower pH leads to a higher release rate of sulfur species. At pH as high as 10, the growth rate remains slow even at boiling temperature. This... 

Anodic aluminium oxide films were fabricated by well known two-step anodizing process in oxalic acid electrolyte. The ordering characteristics (ordered pore domains, average pore diameter size and through-pore arrangement) of anodic aluminium oxide films, obtained in different growth sequences, were identified by microscopic analysis such as ex situ contact-mode atomic force microcopy and scanning electron microscopy. Flattened areas in which some pits are seen mostly cover the electropolished surface of aluminium. Single anodizing of aluminium produces a broad distribution of nanopore size, whereas induces a highly ordered hemispherical pattern, which plays the ordered nucleation sites for... 

CoTiO3 nanocrystallites with an average diameter of 50 nm were synthesized successfully by the sonochemical method without a calcination step and using C10H16N2O8 (EDTA) as the chelating agent. To reach an in-depth understanding of the scientific basis of the proposed process, an in-detail analysis was carried out for characterization of nanoscale CoTiO3 particles via XRD, FTIR, FE-SEM and UV–vis diffuse reflectance spectroscopy (DRS). The crystallite size, average particle size and band gap are found to be 10.7 nm, in the range of 50 nm and 4.64 eV, respectively. The mechanism and the formation process of CoTiO3 in the sonochemical process were proposed. It was found that nanocrystals were... 

Crystal-size distribution (CSD) is one of the most important parameters in sugar production. The objective is to grow crystals of uniform sizes or narrow CSD. CSD appears to be determined by the growth-rate history of the crystals and the relative supersaturation (SS) of the solution from which crystals growth takes place. Three methods for preparation of nucleation seeds were described and used for industrial crystallization of raw and white sugars; these are wet milling filtered sugar (ML), agitating saturated solution (AS) and powdered sugars (PD). Rosin-Rammler (RR) and mathematical models were adopted to investigate CSD and the uniformity of the produced crystals. Higher uniformity... 

In the present article, a new model for inverse Hall-Petch relation in nanocrystalline materials has been proposed. It is assumed that lattice distortion along grain boundaries can cause internal stresses and high internal stresses along grain boundaries can promote the grain boundary yielding. The designed model was then verified using the nanocrystalline-copper data. The minimum grain size for inverse Hall-Petch relation is determined to be about 11 nm for Cu. © 2008 ASM International  

Design of nanoparticle synthesis by inert-gas condensation process was studied according to the mechanisms and kinetics of nucleation and growth in the vapor phase. The effect of process parameters, e.g., source temperature, evaporation rate, and the inert-gas pressure, on the particle size and particle shape was examined at the example for silver and copper-tin alloy. The synthesized nanopowders had near spherical shape with particle size range from 10 to 60 nm dependent on the processing condition. Scanning and transmission electron microscopy (SEM and TEM) analyses showed that the crystallites are subunits of larger agglomerate particles, and relatively large particles display crystal... 

In this letter a simple procedure to synthesize sodium tungsten oxide nano-thick plates from WO 3 films has been reported. WO 3 films were grown by pulsed-laser deposition method and then heat treated at temperatures up to 560 °C and times up to 120 min. Slide glass was used as both substrate and sodium source simultaneously. XRD analysis revealed presence of an amorphous structure for as-deposited WO 3 films. On the other hand, XRD showed formation of a monoclinic WO 3 structure with annealing in lower temperatures and a triclinic Na 0.5WO 3.25 structure with annealing at higher temperatures. Intensity of the triclinic phase peaks enhanced drastically by rising annealing temperature and... 

The early stages of nucleation and growth of nanostructures can control the shape and final size of the fabricated nanostructure. Therefore, the study of the nucleation and growth mechanism of nanostructures is of great importance. The purpose of this study is to investigate the nucleation and growth mechanism of nickel nanocones from a chloride-based bath containing ethylene ammonium dichloride as a crystal modifier. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry tests were employed to investigate the nucleation and growth mechanism and also the mechanism of crystal modifier performance on the growth of nanocones. Electrochemical studies revealed... 

The antisolvent method has been used extensively to induce the growth of high-quality perovskite layers for efficient solar cells. However, uncontrollable nucleation and crystallization increases the risk of formation of undesirable defects. Here, we report a facile way to control the nucleation and crystallization stages in perovskite formation by changing the temperature of chlorobenzene (CB) in the antisolvent method. When CB is injected on the spinning substrate with a precursor solution, CB temperature affects the nucleation process as well as the crystallization process. As the CB temperature increases, nuclei increase in size, leading to the formation of larger perovskite crystals... 

In this study, accumulative roll bonding (ARB) process was carried out on an AA1100 aluminum sheet up to 10 cycles. Electron backscattering diffraction (EBSD) method was utilized to investigate the microstructural evolution during the ARB process. It was observed that the ARB is a promising process for fabricating ultra-fine grained structures in aluminum sheets. The results indicate that several mechanisms are responsible for the microstructural changes at different levels of strain during this process. Grain subdivision as well as the development of sub-grains are the major mechanisms at the early stages of ARB. Strain induced transition of low angle to high angle grain boundaries and the... 

Nanostructured and mesoporous TiO2-Ta2O5 films and powders with various TiO2:Ta2O5 molar ratios and high specific surface area (SSA) have been prepared by a straightforward particulate sol-gel route. Titanium isopropoxide and tantalum ethoxide were used as precursors and hydroxypropyl cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the SSA. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that powders contained both hexagonal δ-Ta2O5 and monoclinic β-Ta2O5 phases, as well as anatase and rutile. It was observed that Ta2O5 retarded anatase-to-rutile transformation. Furthermore, δ → β phase transformation temperature increased... 

Hydroxyapatite (HA) coatings were deposited on commercially pure titanium plates using a hydrothermal-electrochemical deposition method in an electrolyte containing calcium and phosphate ions. The deposition conditions used in this study were the followings: electrolyte temperature (33-80 °C), current density (1-8 mA/cm2), and deposition time (10-120 min). Needle-like and granular crystals of apatite coating were created with different concentrations of calcium (0.0021-0.042 M) and phosphate (0.00125-0.025 M) salts. The size of HA crystals of the coating was considerably changed with different concentration of calcium and phosphate salts, temperature of the electrolyte, and deposition time.... 

In this investigation, a neural network model was used to predict mechanical properties of dual phase (DP) steels and sensivity analysis was performed to investigate the importance of the effects of pre-strain, deformation temperature, volume fraction and morphology of martensite on room temperature mechanical behavior of these steels. In order to train the neural network, dual-phase (DP) steels with different morphology and volume fractions of martensite were deformed between 2 and 8%, at high temperature range of 150-450 °C. The results of this investigation show that there is a good agreement between experimental and predicted values and the well-trained neural network has a great... 

In this study, TiO 2-SiO 2 nanocomposite films with different amounts of SiO 2 were prepared by sol-gel process and were coated onto stainless steel 316L. The effect of addition of various amount of SiO 2 in the precursor solution on the photocatalysis, photo-generated hydrophilicity and self-cleaning property of TiO 2 thin films was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, water contact angle measurements and UV spectroscopy. In the tested ranges of SiO 2 content and sintering temperature, the highest photocatalytic activity and self-cleaning property were observed in the 15 mol% SiO 2 sample sintered at 750 °C. Addition of less than 30 mol% SiO 2 had a... 

Zero discharge desalination process is the most promising technology to prevent salinity and thermal shocks to ecosystem by effluent streams of desalination unit drained into the sea. Pretreatment, solar pond and forced circulation crystallizer are the major steps of one option to provide the purposes of zero discharge desalination process. Reduction of total hardness of wastewater occurs in pretreatment unit and the solar pond is proposed for effluent concentrated brine wastewater of pretreatment unit which seeks production of potable water and concentrated brine. The effluent stream from solar pond is conveyed to one forced circulation evaporator in order to produce salt and distilled... 

Highly active unsupported MoO3 and Co -MoO3 catalysts were prepared by a simple solution reaction method in the presence of different organic additives. Catalysts were characterized by the XRD, BET surface area measurement, SEM and TEM techniques. Results suggested that utilizing different additives produced different morphologies OfMoO3 microstructures. Optimizing reaction conditions was found to produce more active molybdenum oxide nanoparticles when urea and PEG200 additives were utilized. XRD and TEM results indicated crystal growth restriction after cobalt incorporation. Catalytic activities of prepared materials were evaluated in the hydrodesulfurization reaction of Naphtha. Products... 

Superstrate configuration CuInS2 (CIS) solar cells are fabricated using a spray pyrolysis method. We avoided selenization process, cyanide etching and CdS buffer layer, to keep the process 'green'. CIS layers are formed by spray pyrolysis of an aqueous precursor ink containing metal chloride salts and thiourea at 350 °C. We investigated the effect of intentional Zn doping on structural, morphological and photovoltaic response of the fabricated CIS films by dissolving ZnCl2 in aqueous precursor solution. At a zinc doping level ranging between 0.25 and 1.00 mol%, Zn doping is found to improve the CIS crystal growth and surface morphology of CIS films. Compared with the performance of the...