Sharif Digital Repository

Objectives: The aim of this study was to assess and compare the crystalline structures of both powder and bulk human dental enamel by X-ray diffraction analysis (XRD). Methods: The buccal surfaces of 60 selected noncarious third molars were divided into two groups of powdered and bulk enamel specimens. To prepare enamel powders, the enamel tissues were ground and powdered manually using a mortar and pestle. For bulk samples, the enamel slabs were sectioned using a low-speed diamond saw. The crystalline structures of samples were analyzed by XRD, and the obtained data were analyzed. The values of the lattice parameters were obtained using the equation of hexagonal crystalline structures. The... 

The main aim of this paper was to study the effect of a new tripodal chelating agent on La1-x Sr x Co1-y Fe y O3-δ perovskite prepared by the complexation method. For this purpose, a phenolic derivative of glycine (L) was synthesized applying the Mannich reaction and characterized by NMR and IR spectroscopies as well as by elemental analysis. To evaluate the complexation capability of L, its formation constants with the perovskite cations were measured. Comparison of these results with those reported for the complexaion with glycine, introduced L as a good candidate for the complexation with Fe(III) and La(III) cations. Furthermore, the powder XRD observations confirmed an improvement in the... 

Synthesis and characterization of metal dithiocarbamate complexes of N 1 ,N 3 -dicinnamylpropane-1,3-diamine, N 1 ,N 4 -dicinnamylbutane-1,4-diamine and N 1 ,N 6 -dicinnamylhexane-1,6-diamine are reported. The ligands are prepared using cinnamaldehyde and primary diamines to provide the corresponding diimines, followed by reduction with NaBH 4 to afford the corresponding secondary diamines. Diamines react with carbon disulfide in basic medium to furnish the corresponding bis(dithiocarbamate) salts, which underwent complexation with metals. The prepared complexes were characterized by IR, 1 H and 13 C NMR, TGA and elemental analyses. Although the dinuclear metal dithiocarbamate macrocyclic... 

The compound, lead hydroxide Pb6O4(OH)4, was prepared by a method used for the first time in the authors laboratory. The compound was identified by XRD and it's purity was determined by analytical methods (100%). The thermal characteristics of this compound were investigated by using a thermogravimetry (TGA). This compound was found to be stable at room temperature and at 160°C will decompose completely to produce lead (II) oxide. © Sharif University of Technology, April 2007  

Because of corrosion resistance and antibacterial effects, shape memory Ni-Ti-Ag alloy can be considered for different biomedical applications. Mechanical alloying is used to produce nanostructured Ni-Ti-Ag alloy from elemental powders. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are used to characterize the product. Results show that after 1h milling, homogenous distribution of the elements occurs; while no intermetallic compounds is observed. After 3h milling, titanium dissolves in nickel to form amorphous and nanostructured solid phases. Peaks of B2 phase appear in the XRD pattern after the 3h milling of the powder mixture. Sintering of the 3h-milled... 

The title complex [Mn(tptz)(CH3COO)(OH2) 2]NO3 was synthesized through the reaction of tptz (2,4,6-tris(2-pyridyl)-1,3,5-triazine), nitric acid and manganese(II) acetate. The molecular structure was characterized by X-ray diffraction, elemental analysis, electrochemistry, EPR, IR, fluorescence and UV-Vis spectroscopy and its oxygen evolving activity has been studied. X-ray structure analysis shows that each Mn(II) ion is seven coordinated by a bidentate acetate, three nitrogen atoms of tptz and two oxygen atoms from two water ligands, which are coordinated in axial positions. The complex acts as an oxygen evolving complex with oxone (2KHSO5·KHSO4·K 2SO4) as primary oxidant in aqueous... 

The synthesis, characterization, structural and computational studies of mononuclear Re(I) tricarbonyl complexes of 2,2′-bipyridine (2,2′-bpy) and 2,9-dimethylphenantroline (2,9-Me2Phen), [Re(CO)3(NN)(X)], where NN = 2,2′-bpy, X = Br (1) and X = [sbnd]ONO (3); NN = 2,9-Me2Phen, X = Br (2) and X = [sbnd]ONO (4), are reported. The complexes characterized by crystallographic and spectroscopic methods and elemental analyses. In each complex the Re(I) centre shows the distorted octahedral geometry. Single crystal X-ray diffraction data revealed the endo-nitrito (κ1–ONO) coordination in complexes 3 and 4. It has been shown that the replacement of the bromo ligand in complexes 1 and 2, either by... 

For the first time, the simultaneous effects of sulfate reducing bacteria (SRB), soil type and moisture content on corrosion behavior of a pipeline steel were investigated. Corrosion weight loss measurements were performed in abiotic control and SRB-active conditions, at three different moisture contents, and in two types of soils. Results showed that the presence of SRB in the soils, although increased the corrosion rate and aggravated pitting corrosion at low moisture contents, had a protective effect at high moisture contents. The corrosion rates showed a maximum at the saturation moisture content (SMC) of the soils. Soil physicochemical analyses showed that the corrosion rate and soil... 

The production of high-purity aluminum nanoparticles (Al-NPs) is challenging due to the highly reactive nature of Al metals. Electromagnetic levitation gas condensation (ELGC) is a promising method to produce high-purity metallic particles as it avoids the interaction between molten metal and refractory-lined, which guarantees the removal of impurities such as oxygen (O). In this research, high-purity Al-NPs were successfully fabricated via ELGC process and fully characterized. The effects of power input and gas flow rate on particle size and distribution were analyzed using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and dynamic light... 

Industrial dehydrogenation of ethylbenzene to styrene is performed using potassium-promoted iron oxide catalyst. Many attempts have been made to understand the deactivation mechanism of the catalyst based on the chemical differences between the fresh and used catalysts. In the present work, in addition to the effect of chemical changes, the effect of structural changes of the internal areas on the catalyst activity was investigated. A fresh and used commercial catalyst from an industrial reactor which had been continuously used for two years under severe conditions (LHSV = 1 h-1, T = 610 °C, mass ratio of steam to ethylbenzene = 1.2, P = 1.2 atm) was studied. Nitrogen adsorption, Hg... 

Optimization of high strength and high formability of multiphase cold rolled sheet TRIP-aided steels is based on the composition and the austempering conditions. The effect of intercritical annealing temperature on the volume fraction and carbon concentration of the retained austenite was investigated in two different TRIP-aided steels. Experimental results show that the optimum annealing temperatures are 860 °C for Al-containing and 810 °C for Si-containing TRIP steels. It was demonstrated that the measurement of retained austenite can be successfully performed for textured TRIP steels by XRD. © 2006 Elsevier Inc. All rights reserved  

Polycrystalline (Pr1-x Bax)Ba2Cu 3O7-δ samples (0.0 ≤ x ≤ 0.6) is prepared by the standard solid state reaction technique. X-ray measurements confirm the formation of the 123 phase for x ≤ 0.3, but for 0.4 ≤ x ≤ 0.6, due to the solubility limit, the 123 phase is not a dominant phase. Resistivity measurements show the increasing of resistivity with the increase of Ba-doping up to about x=0.08, and then decreases in the 123 phase up to x = 0.3. There is no observation of superconducting state in our samples, but we observe the sharp decrease of resistivity for x>0.1, which is related to possible superconductivity in Pr123 system by Ba-doping. It is concluded that the Pr/Ba disorder has... 

We have studied the electrical and magnetic properties of single phase polycrystalline Gd(Ba2-x Lax)Cu3O 7+δ and Gd(Ba2-xNdx)Cu3O 7+δ (0≤ x ≤ 0.5) samples. The samples were prepared by the standard solid-state reaction technique. The electrical measurements show the decrease of Tc and increase of ΔTc with the increase of Nd and La-doping. The magnetoresistance of samples has been studied within the thermally activated flux creep (TAFC) model. The pinning energy decreases with the increase of magnetic field and doping for both systems in a similar way. The decrease of pinning energy with applied magnetic field can be scaled with two power law relations for the magnetic field: smaller and... 

An unusual hump on the resistivity vs. temperature curve of Gd(Ba 2-xPrx)Cu3O7+δ samples have been observed for particular values of Pr doping. Investigation of the origin of this effect has led to an important result. Based on the Rietveld refinement of the XRD patterns, we have found that the Ba atom substitution at the rare earth site could lead to superconductivity in some parts of the grains at T p ∼ 80-90 K, which appears as a hump on the p(T) curve. Our result is in line with the previously proposed possibility of existence of superconductivity in Pr-123 due to the Ba atom substituted at Pr site. © 2004 WILEY-VCH Verlag GmbH & Co. KOaA, Weinheim  

Tetragonal Gd1-xPrxBaSrCu3O 7-δ polycrystalline samples (0 ≤ x ≤ 0.9) have been prepared by the standard solid-state reaction and characterized by XRD. A hump on the ρ(T) curve have been observed at about 80 K for large values of x. The normal state resistivity have been investigated with two and three dimensional variable range hopping (2&3D-VRH) and Coulomb gap (CG). For low concentration of Pr, 2D-VRH is the dominant mechanism, but with the increase of x, 3D-VRH is dominant. The magnetoresistance measurements of the samples have been analysed by the Ambegakor and Halperin (AH) phase slip model. The field dependences of the pinning energy and critical current density have been studied for... 

Investigation of BSCCO 2223 phase formation in superconducting thin films of Bi-based cuprates deposited on MgO substrate is reported. A series of films were made by in situ dc-magnetron sputtering method and another series were made by ex situ rf-magnetron sputtering technique. Same target have been used in both technique. In the case of the ex situ method, the films were annealed for different period of time at 800°C, and in the case of in situ method, the films were deposited at different temperature substrate. The influence of annealing time and the temperature of the substrate on the quality and the phase formation for ex situ and in situ method have studied, respectively. The results... 

Knowledge of the complete multiaxial residual stress distribution in engineering components is essential for assessing their integrity. Often, however, only limited measurements are made. Here, an analysis is presented for determining the multiaxial distribution from a limited set of measurements. These measurements are used with an assumed plastic strain distribution. Residual stress measurements were made on hot forged and shot blasted steel bars using X-ray and neutron diffraction techniques. The residual stresses were measured on the surface and at selected interior points of the specimens. The predicted multiaxial distributions were compared with experimental measurements obtained using... 

This paper deals with an experimental investigation into the mechanical performance and microstructure characteristics of the cementitious mortars containing recycled waste materials subjected to acidic, neutral and alkaline environments. The recycled waste materials include glass, eggshell, iron and rubber powder in various amounts, namely 7, 14 and 21% by volume, as the replacement for ordinary Portland cement (OPC). In this respect, to examine the mechanical performance of the specimens, the compressive, tensile and bending strength tests as well as water absorption test were carried out at the ages of 7, 28 and 90 days. Moreover, to study the microstructure of the specimens, the scanning... 

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