Sharif Digital Repository

In this work we report a new thermochemical method for the synthesis of ZnS:Mn nanocrystals. Zn(NO3)2 and Na2S 2O3 were used as the precursors and Mn(NO 3)2 was the source of impurity. Thioglycerol (TG,C 3H8O2S) was also used as the capping agent and the catalyst of the reaction. Na2S2O3 is a heat sensitive material which releases S species upon heating. Consequently, the reaction proceeds in temperatures higher than room temperature. The reaction was done in two steps. In the first step, the precursors were heated at 96 °C for an hour without TG. In the second step, TG was injected to the solution and the heating process was continued for longer heating durations. A fast growth occurred in... 

Abstract The effects of both Lithium modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15% Mg2Si composite were investigated. Adding 0.3%Li reduced the average size of Mg2Si primary particles from ~30 μm to ~ 6 μm. The effect of cooling rate was investigated by the use of a mold with different section thickness from 3 to 9 mm. The results show a refinement of primary particle size as a result of both Li additions and increased cooling rate, and their effects were additive. Similarly, both effects increased UTS and elongation values. The refinement by Li and enhanced cooling rate is discussed in terms of an analogy with the effect of Sr and... 

The effects of both Lithium modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15% Mg 2Si composite were investigated. Adding 0.3%Li reduced the average size of Mg2Si primary particles from ∼30 μm to ∼6 μm. The effect of cooling rate was investigated by the use of a mold with different section thickness from 3 to 9 mm. The results show a refinement of primary particle size as a result of both Li additions and increased cooling rate, and their effects were additive. Similarly, both effects increased UTS and elongation values. The refinement by Li and enhanced cooling rate is discussed in terms of an analogy with the effect of Sr and cooling... 

TCVD growth of multiwalled carbon nanotubes (MWCNTs) was reported by catalytic decomposition of liquefied petroleum gas (LPG) at a temperature range of 580800 °C. Laser ablation was employed as a simple and rapid technique to produce Pd nanoparticles which possess effective catalytic activities for CNT synthesis. UVvisible spectroscopy and TEM images confirmed that the Pd nanoparticles are stable for a long time and have rather spherical shape with average size of 7 nm. SEM and TEM observations and Raman spectroscopy demonstrated that the CNTs have a wavy structure, dense morphology and acceptable crystallinity. Since Pd nanoparticles are inactivated or agglomerated at extremes of the... 

TiO2 nanorods have been successfully grown into a track-etched polycarbonate (PC) membrane by a particulate sol-electrophoretic deposition from an aqueous medium. The prepared sols had a narrow particle size distribution around 17 nm and excellent stability against aging, with zeta potentials in the range of 47-50 mV at pH 2. It was found that TiO2 nanorods were grown from dilute aqueous sol with a low, 0.1-M concentration. Fourier transform infrared spectroscopy (FT-IR) analysis confirmed that a full conversion of titanium isopropoxide was obtained by hydrolysis, resulting in the formation of TiO2 particles. X-ray diffraction (XRD) results revealed that TiO2 nanorods dried at 100 °C were a... 

Thorium dioxide (thoria) nano-particle was synthesized by employing supercritical water (SCW) as an excellent reaction environment for hydrothermal crystallization of metal oxide particles. This method is ideal for production of ultrafine powder having controlled stoichiometry, high quality, purity and crystallinity. The nano-crystalline thoria was prepared in a stainless steel (316 L) autoclave, fed with an aqueous solution of Th(NO 3) 4.5H 2O as a reactant and took place under SCW condition up to 450 °C for 45 min. The product was recovered and characterized by X-Ray Diffraction (XRD), Thermal Gravimetry Analysis (TG/DTA) and Brunauer, Emmett and Teller (BET) surface area analysis. The... 

Single-crystal hydroxyapatite (HAp) nanorods and nanogranules have been synthesized successfully by a mechanochemical process using two distinct experimental procedures. The experimental outcomes are characterized by transmission electron microscopy (TEM), and powder X-ray diffraction (XRD) techniques. In this work, the feasibility of using polymeric milling media to prepare hydroxyapatite nanoparticles is described. The resulting hydroxyapatite powder exhibits an average size of about 20 to 23 nm. Final results indicate that the proposed synthesis strategy provides a facile pathway to obtain single-crystal HAp with high quality and suitable morphology. © 2008 Elsevier B.V. All rights... 

We have synthesized CdS nanocrystals (NCs) by a microwave activated method. CdSO4 and Na2S2O3 were used as the precursors and thioglycolic acid (TGA) was used as capping agent molecule. The aqueous synthesis was based on the heat sensitivity of Na2S 2O3. In this method, microwave irradiation creates the activation energy for dissociation of Na2S2O3 and leads to the CdS NCs formation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses demonstrated hexagonal phase CdS NCs with an average size around 3 nm for sample prepared at 5 min irradiation time. A band gap range of 3.38-2.89 eV was possible only by increasing the microwave irradiation time, corresponding to a... 

To improve the hydrogen kinetics of magnesium hydride, TiCr 1.2Fe0.6 alloy was prepared by vacuum arc remelting (VAR) and the alloy was co-milled with MgH2 to process nanostructured MgH2-5 at.% TiCr1.2Fe0.6 powder. The hydrogen desorption properties of the composite powder were studied and compared with pure magnesium hydride. X-ray diffraction (XRD) analysis showed that the composite powder prepared by VAR/mechanical alloying (MA) procedure consisted of β-MgH2, γ-MgH2, bcc Ti-Cr-Fe alloy, and small amount of MgO. The average size of particles and their grain structure after 4 h MA were determined by a laser particle size analyzer and XRD method and found to be 194 nm and 11 nm,... 

In this study, electrochromic properties of cuprous oxide nanoparticles, self-accumulated on the surface of a sol-gel silica thin film, have been investigated by using UV-visible spectrophotometry in a lithium-based electrolyte cell. The cuprous oxide nanoparticles showed a reversible electrochromic process with a thin film transmission reduction of about 50% in a narrow wavelength range of 400-500 nm, as compared to the bleached state of the film. Using optical transmission measurement, we have found that the band gap energy of the films reduced from 2.7 eV for Cu2O to 1.3 eV for CuO by increasing the annealing temperature from 220 to 300 °C in an N2 environment for 1 h. Study of the band... 

This paper deals with simulation of transport phenomena in micro and nano pores. The number of cavities and the cavity radius were estimated by using Henry's law for adsorption of Argon onto ZSM-5 and NaX zeolites. This work showed both of zeolites have pores with average size less than 1 nm. Then with using micro- nano channel assumption instead of micro-nano pores, gas flow and heat transfer were investigated. Subsonic nonideal gas flow and heat transfer for different Knudsen number are investigated numerically using the Direct Simulation Monte Carlo method modified with a consistent Boltzamnn algorithm. The collision rate is also modified based on the Enskog theory for dense gas. It is... 

Linear-dendritic triblock copolymers of linear poly(ethylene glycol) and hyperbranched poly(citric acid) (PCA-PEG-PCA) were used as the reducing and capping agents to encapsulate gold and silver nanoparticles (AuNPs and AgNPs). PCA-PEG-PCA copolymers in four different molecular weights were synthesized using 2, 5, 10 and 20 citric acid/PEG molar ratios and were called A 1, A 2, A 3 and A 4, respectively. Nanoparticles were encapsulated simultaneously during the preparation process. AuNPs were simply synthesized and encapsulated by addition a boiling aqueous solution of HAuCl 4 to aqueous solutions of A 1, A 2, A 3 and A 4. In the case of silver, an aqueous solution of AgNO 3 was reduced... 

Using a combined hydrothermal and sol-gel route, TiO 2 -capped ZnO nanoparticles with an average size of 60 nm were prepared. The titania shell was amorphous with a thickness of ∼10 nm. Formation of Zn 2TiO 4 phase at higher calcination temperature was noticed. Effects of Ti/Zn molar ratio and coating time on the thickness of TiO 2 shell and the photoactivity of the particles for decolorization of Methylene Blue (MB) under UV lamp irradiation (3 mW/cm 2) were investigated. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, fourier-transform infrared spectrometry (FTIR), diffuse reflectance spectroscopy (DLS), and atomic absorption spectroscopy.... 

A simple bio-conjugation procedure to surround a single horseradish peroxidase (HRP) enzyme molecule with dendritic polyester macromolecules (polyester-32-hydroxyl-1-carboxyl bis-MPA dendron, generation 5) was proposed. The characterization of resultant nanoparticles entitled HRP dendrozyme, was performed by transmission electron microscopy, dynamic light scattering, gel permeation chromatography and Fourier transform infrared spectroscopy. The results showed that HRP nanoparticles were spherical in shape and have an average size of 14 ± 2. nm in diameter. Furthermore, bio-conformational characterization of HRP dendrozyme was performed by means of circular dichroism and fluorescence... 

This paper presents a dry mechanochemical process to produce hydroxyapatite (HAp) nanoparticles. Two distinct chemical reactions are introduced to prepare HAp powders using milling process. Structural and morphological properties of the obtained materials are studied by X-ray diffraction and transmission electron microscopy. The results reveal that the single crystal HAp nanoparticles have been successfully produced in metallic and polymeric vials through two different experimental procedures. Tempered chrome steel and polyamide-6 materials are adopted as the metallic and polymeric vials respectively. Nanoellipse, nanorod and nanosphere powders are obtained in these experimental procedures.... 

Al-20Si-5Fe melt was rapidly solidified into particles and ribbons and then consolidated to near full density by hot pressing at 400°C/250 MPa/1 h. According to the eutectic-growth and dendritic-growth velocity models, the solidification front velocity and the amount of undercooling were estimated for the particles with different sizes. Values of 0.43-1.2 cm/s and 15-28 K were obtained. The secondary dendrite arm spacing revealed a cooling rate of 6 × 105 K/s for the particles with an average size of 20 μm. Solidification models for the ribbons yielded a cooling rate of 5 × 107 K/s. As a result of the higher cooling rate, the melt-spun ribbons exhibited considerable microstructural... 

Magnesium nanopowder (MgNP) of 17 nm average size was produced by planetary ball milling of Mg (φ=229 μm) with 10 wt% NaCl (φ=406 μm) for 50 h. NaCl was omissible by dissolution in saturated KOH. Partial oxidation of MgNP occurred, however, in presence of KOH. MgNP-NaCl mixture was, therefore, used for transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD), differential scanning calorimetry (DSC) and Sieverts equilibrium investigation. DSC analysis of ammonium perchlorate showed one endothermic and three exothermic reactions. MgNP did not noticeably affect on the initial endothermic reaction. But it decreased transformation temperatures of the... 

A facile sol-gel synthesis for self-agglomeration of metallic silver nanoparticles, with fcc crystalline structure, on the silica surface in a low annealing temperature has been introduced. X-ray photoelectron spectroscopy (XPS) revealed initial agglomeration (∼30 times greater than the nominal concentration of Ag) of the nanoparticles on the surface of the dried film (100 °C) and also their oxidation as well as easy diffusion (with 0.08 eV required activation energy) into the porous silica thin films, by increasing the annealing temperature (200-400 °C). By raising the Ag concentration from 0.2 to 1.6 mol% in the sol, the average size of the Ag nanoparticles increased from ∼5 to 37 nm... 

We have synthesized CdS NCs (NCs) by a thermochemical approach. CdSO 4 and Na2S2O3 were used as the precursors and thioglycolic acid (TGA) was used as capping agent molecule. The structure and optical property of the NCs were characterized by means of XRD, TEM, UV-visible optical spectroscopy and photoluminescence (PL). XRD and TEM analyses demonstrated hexagonal phase CdS NCs with an average size of around 2 nm. Synthesized NCs exhibited a band gap of about 3.21 eV and showed a broad band emission from 400 to 750 nm centered at 503 nm. This broad band emission is related to surface states of CdS and our results showed that the emission peak can be attributed to the interstitial sulfur. The... 

WO3 thin film photoanodes containing different concentrations of Ag nanoparticles were synthesized by solegel method. Based on UV-visible spectra, presence of a surface plasmon resonance peak at 470 nm of wavelength indicated formation of silver nanoparticles in the WO3 films. According to atomic force microscopy (AFM) analysis, the highest value for surface roughness and the effective surface ratio was observed for the sample containing 2 mol% of Ag. X-ray diffraction (XRD) patterns revealed that WO 3 nanocrystalline structure was formed in the monoclinic phase with the average size of about 18.2 nm while Ag nanocrystals were determined in cubic phase. X-ray photoelectron spectroscopy (XPS)...