Sharif Digital Repository

Electrochemical cells with two ion-selective electrodes, a cation ion-selective electrode against an anion ion-selective electrode, were used to measure the activity coefficient of amino acids in aqueous electrolyte solutions. Activity coefficient data were measured for (H2O + NaBr + glycine) and (H2O + NaBr + L-valine) at T = 298.15 K. The maximum concentrations of sodium bromide, glycine, and L-valine were (1.0, 2.4, and 0.4) mol · kg-1, respectively. The results show that the presence of an electrolyte and the nature of both the cation and the anion of the electrolyte have significant effects on the activity coefficients of amino acid in aqueous electrolyte solutions  

The activity coefficient data were reported for (water + potassium chloride + DL-valine) at T = 298.15 K and (water + sodium chloride + L-valine) at T = 308.15 K. The measurements were performed in an electrochemical cell using ion-selective electrodes. The maximum concentrations of the electrolytes and the amino acids studied were 1.0 molality and 0.4 molality, respectively. The results of the activity coefficients of DL-valine are compared with the activity coefficients of DL-valine in (water + sodium chloride + DL-valine) system obtained from the previous study. The results show that the presence of an electrolyte and the nature of its cation have a significant effect on the activity... 

In this work, the modified Wilson model was used to obtain the activity coefficients of amino acids and simple peptides in non-electrolyte aqueous solutions. The Wilson model was modified using the new local mole fraction proposed by Zhao et al. and non-random case for the reference state. The binary interaction parameters (BIP) of the modified Wilson model for amino acid-water pairs were obtained using the experimental data of the activity coefficients for amino acids available in the literature. The modified Wilson model was also used to correlate the solubility of amino acids in water and the values of Δh/R, Δs/R, and Δg/R of the solutions studied were reported. The results obtained... 

The effects of the current density on the microstructure and the corrosion property of the coating on AZ31 Mg alloy processed by the plasma electrolytic oxidation (PEO) were investigated. The present coatings were produced in an acid electrolyte containing K2ZrF6 with three different current densities, i.e., 100, 150, and 200 mA/cm2. From the microstructural observations, as the applied current density was increased, the diameter of micro-pores formed by the plasma discharges with high temperature increased. The coatings on AZ31 Mg alloy were mainly composed of MgO, ZrO 2, MgF2, and Mg2Zr5O12 phases. The results of potentiodynamic polarization clearly showed that the PEO-treated AZ31 Mg... 

Agglomerates of tungsten trioxide in the range of 90 nm to 1 μm are prepared by the acid precipitation method and characterized by XRD as well as scanning electron microscopy. The product when coated with platinum showed pseudocapacitance when in contact with acidic electrolyte in the potential range of 0. 1 to -0. 25 V/SCE. Capacitance in the range of 0. 014 to 0. 039 F cm-2 exhibiting moderate potential dependencies measured through both chronopotentiometry and impedance spectroscopy is presumed to be due to the insertion/de-insertion of protons into the lattice of tungsten trioxide. Equivalent circuit consisting of parallel simulators of mass transfer and capacitor charging... 

A pyrophosphate based solution, as an acidic electrolyte, was developed for bronze electroplating. By using a statistical experimental design, response surface method, the effects of five factors [copper concentration (Cu), tin concentration (Sn), pyrophosphate concentration (P), current density j and pH] on the composition of the electroplated alloy as well as the process efficiency were evaluated. Statistical analysis indicated that all the parameters were significant and a second order polynomial model was successfully fitted to the data for both the alloy composition and the process efficiency. Based on the results obtained, a solution of Cu(II)8.04 g L -1, Sn(II)=26.36 g L -1, P=113.22... 

A study has been carried out of the effect of an anodizing pre-treatment in a sulphuric acid electrolyte on the strength of AA 5052 alloy/polypropylene joints prepared using friction stir spot welding. Lap-shear tests were used to determine the joint strength. Comparisons were made with joints pre-treated using sand blasting. The failed specimens were examined by scanning and transmission electron microscopy. Anodizing improved the strength of the joints by a factor of about 6 compared with sandblasting. For the anodizing pre-treated joints, melted polymer infiltrated deeply within the nanoporous anodic film, forming a strong polymer-film bond. Joint failure occurred by ductile tearing of...