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kinetics of silver Dissolution in Nitric Acid from Ag-Au_(0.04)-Cu_(0.10) and Ag-Cu_(0.23) scraps

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Journal of Materials science & Technology 2006年第5期22卷 696-700页

作者： s.k.sadrnezhaad E.Ahmadi M.Mozammel Center of Excellence for Advanced Processes of Production of Materials Department of Materials science and Engineering Sharif University of TechnologyTehranIran

kinetics of dissolution of silver present in precious metal 26～85℃. Dissolution rate of silver was much faster than scraps in HNO3 was studied in temperature range of that of copper at all temperatures. Effects of particle size, stirring speed, acid concentration and temperature on the rate of dissolving of silver were evaluated. Dissolution rate decreases with particle size and increases with temperature. Dissolving was accelerated with acid concentrations less than 10 mol/L. Concentrations greater than 10 mol/L resulted in slowing down of the dissolution rate. shrinking core model with internal diffusion equation t/τ=1-3（1-x）^2/3＋2（1-x） could be used to explain the mechanism of the reaction. silver extraction resulted in activation energies of 33.95 kJ/mol for Ag-Au0.04-Cu0.10 and 68.87 kJ/mol for Ag-Cu0.23 particles. Inter-diffusion of silver and nitrate ions through the porous region of the insoluble alloying layer was the main resistance to the dissolving process. Results were tangible for applications in recycling of the material from electronic silver-bearing scraps, dental alloys, jewelry, silverware and anodic slime precious metal recovery.

关键词： silver Copper kinetics, Dissolution shrinking core model Internal diffusion

kinetic Parameters Estimation of MgO-C Refractory by shrinking Core Model

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Journal of Materials science & Technology 2006年第6期22卷 826-832页

作者： B.Hashemi Z.A.Nemati s.k.sadrnezhaad Z.A.Moghimi Department of Materials science School of EngineeringShiraz UniversityShirazIran Department of Materials science and Engineering Sharif University of TechnologyTehran 11365-9466Iran

kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. samples containing 4.5-17 wt pct graphite were isothermally oxidized at 1000-1350℃. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range of 0.08 to 0.55 cm^2/s. These values can be utilized to determine the corresponding tortuosity factors of 6.85 to 2.22. Activation energies related to the pore diffusion mechanism appeared to be around （46.44±2） kJ/mol. The estimated intermolecular diffusion coefficients were shown to be independent of the graphite content, when the percentage of the graphite exceeded a marginal value of 10.

关键词： Modeling kinetics MgO-C Oxidation Diffusion coefficient

Chloroform Aided Extraction spectrophotometric Determination of Rhenium Using Thiocyanate Complexing Agent

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Journal of Materials science & Technology 2005年第2期21卷 239-242页

作者： E.keshavarz Alamdari s.k.sadrnezhaad Z.Mos-hefi shabestari Department of Mining and Metallurgical Engineering Amirkabir University of Technology Hafez Ave. TehranIranDepartment of Materials Science and EngineeringSharif University of Technology P.O.Box 11365-9466 Tehran IranDepartment of Mining and Metallurgical Engineering Amirkabir University of Technology Hafez Ave. TehranIran

A new technique is developed for quantitative determination of rhenium in aqueous media containing molybdenum, iron and copper ions. The method seems easier and more accurate than the traditional ones. It consists of the formation of rhenium thiocyanate complex, which is extracted with chloroform at the presence of hydrochloric acid. This complex is a highly visible light absorbent that can easily be detected with the aid of a spectrophotometer. The maximum absorbance (λmax) observed for this complex was in the visible range of 430-435 nm. The experimental results showed that in a concentration range from 0.5-8 mg/L, the absorbance behavior of the rhenium thiocyanate complex is followed to the Beer-Lambert law.

关键词： Rhenium solvent extraction spectrophotometry Thiocyanate Chloroform

Oxidation Mechanisms in MgO-C Refractories

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China's Refractories 2004年第2期13卷 13-20页

作者： B.Hashemi Z.Ali Nemati s.k.sadrnezhaad Department of Materials science and Engineering Department of Materials Science and Engineering Department of Materials Science and Engineering Sharif University of Technology TehranIran11365-9466Sharif University of Technology TehranIran11365-9466Sharif University of Technology TehranIran11365-9466

An investigation on the oxidation mechanism of the graphite in the MgO-C refractory materials is helpful to improving both the quality of these materials and to preventing and/or lowering of the adverse effects of the high-temperature oxidation. In this research, the oxidation behavior of the MgO-C refractories containing 5～20 wt% graphite was studied via weight-loss method. Atmospheric air was used for oxidation at temperatures ranging from 900℃ to 1300°C and the experimental data were compared with those obtained from the dimensionless kinetic equations of the shrinking core model, in order to determine the oxidation mechanisms of the refractories. The best fit was achieved with the porous layer diffusion control regime. Oxidation mechanism tends, however, to slightly deviate from pure pore diffusion control to pore diffusion-external gas transfer regime in the samples having more graphite contents (e.g. 20%).

关键词： MgO Carbon Diffusion Refractories Oxidation

Pulsed-Laser Annealing of NiTi shape Memory Alloy Thin Film

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Journal of Materials science & Technology 2009年第1期25卷 135-140页

作者： s.k. sadrnezhaad E. Rezvani s. sanjabi A.A. Ziaei Moayed Materials and Energy Research Center P.O. Box 14155-4777 Tehran Iran Department of Materials science and Engineering Sharif University of Technology P.O. Box 1156-9466 Tehran Iran Department of Materials science and Engineering Tarbiat Modarres University P.O. Box 14115-143 Tehran Iran

Local annealing of amorphous NiTi thin films was performed by using an Nd：YAG 1064 nm wavelength pulsed laser beam. Raw samples produced by simultaneous sputter deposition from elemental Ni and Ti targets onto unheated si （100） and silica （111） substrates were used for annealing. Delicate treatment with 15.92 W/mm^2 power density resulted in crystallization of small spots; while 16.52 and 17.51 W/mm^2 power densities caused ablation of the amorphous layer. Optical microscopy, scanning electron microscopy, X-ray diffraction and atomic force microscopy were performed to characterize the microstructure and surface morphology of the amorphous/crystallized spot patterns.

关键词： Local heat treatment NiTi thin film Pulsed laser annealing Amorphous/crystallized spot composite