Sharif Digital Repository

In precipitation hardenable materials, it is desirable to determine the precipitate dissolution temperature for homogenizing the microstructure by controlling the size and distribution of the precipitates. In this research, the influence of various heat treatment and hot deformation conditions on the kinetics of γ ′ dissolution and its morphological evolution in Nimonic 115 was studied. In addition, hot deformation behavior of the material was investigated using hot compression experiments at varying temperature (between 1,050°C and 1,175°C) and strain rates (between 0.01 and 1 s-1) up to a true strain of 0.8. The values obtained for the solvus temperature of γ ′ precipitates by two methods... 

This work concerns observing the pressure as well as CO2 mole percentage effects on asphaltene molecular weight distributions at reservoir conditions. A high-pressure, high-temperature asphaltene measurement setup was applied, and the amount of precipitated asphaltene at different pressures as well as CO2 mole percentage in an Iranian heavy crude oil was measured. Moreover, the asphaltene molecular weight distributions during titration of crude oil with different n-alkanes were investigated. The gel permeation chromatography (GPC) apparatus was used for characterization of asphaltene molecular weight under different conditions. It has been observed that some thermodynamic changes such as... 

The effect of temperature and impeller speed on the performance of induced gas flotation (IGF) systems for the removal of oil from produced water in different ranges (5-300 g/L) of total dissolved solids (TDS) was investigated in a pilot plant study. Furthermore, it was evaluated whether the IGF pilot plant effluent could reach the 15 mg/L outlet oil content as required by Article VI of the Kuwait Convention for Persian Gulf region, before being discharged to the sea. The results showed that oil removal efficiencies up to 90% could be reached at high temperature (80°C) in just one single flotation cell without adding any chemicals. Flotation unit, however, should be followed by at least one... 

A novel sulfoxide containing bis(ether amine) monomer, 2,2'-sulfoxide- bis[4-methyl(2-trifluoromethyl)4-aminophenoxy) phenyl ether] (M2), was synthesized from the halogen displacement of 2-chloro-5-nitrobenzotrifluoride with dibenzosulfoxide (DH) in the presence of potassium carbonate, followed by catalytic reduction of bis(ether nitro) intermediate with Zinc/Ammonium chloride. A series of organic-soluble poly(ether amide)s (PA1-7) bearing sulfoxide and electronwithdrawing trifiuoromethyl group were synthesized from bis(ether amine) with various aromatic diacids (1-7) via a direct polycondensation with triphenyl phosphite and pyridine. The resulting polymers had inherent viscosities ranging... 

Two-segmented gold-copper nanorods were electrodeposited inside the pores of polycarbonate track-etched membranes from two separate solutions. The PCT membranes were dissolved in dichloromethane (CH2Cl2) and the solvent was replaced by methanol solution. Optical absorption spectra of two-segmented Au-Cu nanorods dispersed in methanol showed two peaks which were related to the transverse mode of copper and the longitudinal mode of gold. By increasing the length of the gold segment, when the total length of both metals was fixed at 1 μm, the copper and gold peaks shifted to the blue and red wavelengths, respectively. We observed that the wavelengths of the extinction peaks are not in good... 

The recrystallization behavior of a commercial nickel-cobalt base superalloy, AEREX 350, is investigated by means of hardness test, X-ray diffraction, and microscopy. It is found that the alloy resists recrystallization up to a high temperature of 1025 °C. Recrystallized grains are readily formed at grain boundaries below this temperature; however, the growth of these new grains is inhibited by Widmanstätten η particles having coherent facets with the nickel matrix (γ). The passage of the recrystallization front results in coherency loss and consequently dissolution of the η platelets. Recrystallization proceeds with a discontinuous precipitation of the η phase behind the moving boundary  

Removal of dissolved oxygen (DO) from water has gained much attention in recent decades to prevent different problems such as corrosion, bio-fouling, and performance degradation in many industries. The traditional physical and chemical methods for DO removal have found wide application in industries. However, physical methods have low efficiency and chemical methods often produce undesirable products. Therefore, catalytic reduction by hydrogen has been regarded by a variety of industries recently. In this study, catalytic reduction of DO from water is examined using membrane reactors. The mathematical model of this system is developed while considering the axial dispersion, membrane... 

The catalytic reduction of dissolved oxygen (DO) from water was examined using membrane reactors and a mathematical model that considers axial dispersion, membrane permeation, and chemical reaction. The model is solved in steady state mode and the effect of various parameters on the DO removal was assessed. The results of steady state mode were employed as initial conditions for solving the model in dynamic mode. The impact of operating conditions, e.g., water flow rate, DO concentration of influent water, hydrogen flow rate, and hydrogen pressure on the performance of the DO process was studied. Results of the dynamic simulation suggested that hydrogen pressure is the best option to be used... 

Effects of cooling slope angle and the temperature of molten metal on the globular structure of M2 high speed steel after holding at the semisolid state have been investigated. The globular structure was achieved by pouring the molten metal at 1595 °C on the ceramic cooling slope with the length of 200 mm and the angle of 25°. The globular structure of M2 high speed steel in the form of rolled-annealed and as cast condition after holding at semisolid state has been achieved. The size of globular grains of cooling slope sample was smaller than that of the rolled-annealed and as cast samples. Solid particles of rolled-annealed sample after holding at semisolid state had better roundness... 

Hydroxyapatite (HAp) nanostrips were rapidly obtained during a mild microwave heating method. Applying microwave irradiation to Ca(NO3)2·4H2O/CTAB/Na2HPO4 precursor solution, the HAp precipitation process was occurred directly and without common crystallographic transformations including dissolution and slow recrystallization. The cationic surfactant CTAB was used as a soft template to modify nucleation and growth process. TEM investigations showed that the fabricated nanostrips had a width and length of about 10 and 55 nm, respectively. The X-ray diffraction pattern revealed that the fabricated well-crystallized and high purity hydroxyapatite nanostrips had a pattern similar to the bone... 

One of the key factors in drug's efficacy is the value of their bioavailability that increases by the reduction of particle size through improvement of dissolution rate. In this study, raloxifene particle size was reduced by Rapid Expansion of Supercritical Solution (RESS). The effect of extraction temperature (40-80 °C), extraction pressure (10-18 MPa) and spray distance (5-10 cm) were investigated on size and particle size distribution of the nanoparticles. Particles were characterized using X-ray diffraction (XRD), Fourier Transform Infrared Analysis (FTIR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS). The average size of... 

Since compactness is a disadvantageous characteristic of chitosan-based membranes, two different methods were used to increase the porosity of the chitosan/poly(vinyl alcohol)/polyethyleneimine (CS/PVA/PEI) membrane, and its effect on copper ion adsorption was studied. In the first method, selective dissolution of poly(vinyl pyrrolidone) (PVP) induced porosity and for the second method, a mixed solvent system, which consists of a volatile solvent (acetone), was used to improve the porosity of the membrane. Different percentages of PVP showed inadequate performance, but acetone improved the operation efficiency of adsorption. The membranes were characterized by the analysis of FT-IR, SEM,... 

In this study, cellulose acetate (CA) fibers were prepared using different solvent systems in electrospinning. The recorded scanning electron microscopy micrographs indicated that the morphology of the prepared fibers is closely associated with the type of electrospinning solvents. The prepared CA fibers were used as an extractive phase for on–line micro–solid phase extraction (μ-SPE) of nonsteroidal–inflammatory drugs (NSAIDs) in biological samples pursued by HPLC–UV determination. Work conducted on this research ascertained that the use of dichloromethane:acetone (3:1, v/v) solvent system in the CA dissolution for electrospinning, leads to the formation of porous ribbon–like fibers and... 

A continuum hydrodynamic model with immersed solid/fluid interface is developed for simulating calcite dissolution by hydrochloric acid (HCl) at the pore scale, and is most accurate for a mass-transfer-controlled dissolution regime under laminar flow conditions. The model uses averaged Navier-Stokes equations to model momentum transfer in porous media and adopts a theoretically developed mass-transfer formulation with assumptions. The model includes no fitting parameter and is validated using experimental results. The findings of previous research and existing models are briefly discussed and their shortcomings and advantages are elucidated. The present model is used in some pore-scale... 

Linear-dendritic ABA triblock copolymers containing poly(ethylene glycol) (PEG) as B block and hyperbranched poly(citric acid) (PCA) as A blocks were synthesized through polycondensation. The molecular self-assembly of synthesized PCA-PEG-PCA copolymers in water led to formation of nanoparticles and fibers in different sizes and shapes depending on the time and size of PCA blocks. Ten days after dissolving PCA-PEG-PCA copolymers in water, the size of fibers had reached several millimeters. Mixing a water solution of fluorescein as a small guest molecule and PCA-PEG-PCA copolymers led to the encapsulation of fluorescein by products of molecular self-assembly. To investigate their potential... 

Understanding controls of P movement through watersheds are essential for improved landscape management in intensively managed regions. Here, we analyze observational data from 104 gaged river sites and 176 nongaged river sites within agriculturally dominated watersheds of Minnesota, USA, to understand the role of landscape features, land use practices, climate variability, and biogeochemical processes in total, dissolved and particulate P dynamics at daily to annual scales. Our analyses demonstrate that factors mediating P concentration-discharge relationships varied greatly across watersheds and included near-channel sediment sources, lake and wetland interception, assimilation by algal P,... 

The sol gel method was employed to prepare peroxopolytungstic acid (P-PTA). Palladium chloride salt was dissolved in the sol with different Pd:W molar ratios and coated on Al2O3 substrates by spin coating method. XRD and XPS techniques were used to analyze the crystal structure and chemical composition of the films before and after heat treatment at 500 °C. We observed that Pd can modify the growth kinetic of tungsten trioxide nanoparticles by reducing the crystallite size and as a result can improve hydrogen sensitivity. Resistance-sensing measurements indicated sensitivity of about 2.5 × 104 at room temperature in hydrogen concentration of 0.1% in air. Considering all sensing parameters,... 

By using the planar laser induced florescence experiment (PLIF), a resorufin (RSRF) dye solution was tested as an oxygen probe. The photoreaction of RSRF dye was investigated and the oxidation process of this fluorescent probe molecule was demonstrated. The effect of the oxygen bubbles on tracing dissolved oxygen was also investigated in this study. Results obtained for this sensitive molecular probe dye are very interesting and verify that such an agent can be used effectively for investigating different interesting phenomena affecting the fluorescence. The temporal and spatial behaviors of the oxidation and fluorescence processes were described in this report. For a delay time of 4500 ms... 

In this study the bioleaching of a low-grade uranium ore containing 480 ppm uranium has been reported. The studies involved extraction of uranium using Acidithiobacillus ferrooxidans derived from the uranium mine samples. The maximum specific growth rate (μ max) and doubling time (t d) were obtained 0.08 h-1 and 8.66 h, respectively. Parameters such as Fe2+ concentration, particle size, temperature and pH were optimized. The effect of pulp density (PD) was also studied. Maximum uranium bio-dissolution of 100 ± 5 % was achieved under the conditions of pH 2.0, 5 % PD and 35 °C in 48 h with the particles of d 80 = 100 μm. The optimum concentration of supplementary Fe2+ was dependent to the PD.... 

The Ni-P/Zn-Ni compositionally modulated multilayer coatings CMMCs were electrodeposited from a single bath by switching the deposition current density. The corrosion resistance of the deposits was studied and compared with that of monolayers of Ni-P and Zn-Ni alloys via Tafel polarization, EIS and salt spray tests. Characterization of corrosion products by means of EDS and XRD revealed more details from the corrosion mechanism of the monolayers and multilayers. The corrosion current density of Ni-P/Zn-Ni CMMCs were around one tenth of Zn-Ni monolayer. The CMMC with incomplete layers performed lower polarization resistance and higher corrosion current density compared to the CMMC with...