Abstract:The corrosion monitoring of galvanized steel in 1 h wet and 7 h dry cyclic condition in 0.05 M NaCl has been carried out using AC impedance technique. During the wet-dry cycles, the polarization resistance, R p , and solution resistance, R s , were continuously monitored. The instantaneous corrosion rate of the coating was estimated from the obtained R p -1 and time of wetness (TOW) was determined from the R s values. The corrosion potential, E corr , was measured twice a day during the immersion period of wet-dry cycle. The corrosion was accelerated by the wet-dry cycles in the early stage followed by a decrease in the final stage of wet-dry cycle. The corrosion potential shifted to more negative direction for the first 8 cycles due to dissolution of air formed oxide. A gradual shift in the corrosion potential with the progress of corrosion in the later stage of the wet-dry cycle was observed due to deposition of corrosion products. The corrosion mechanism of galvanized steel is discussed based on the results of corrosion monitoring and corrosion potential variation.

The polycrystalline materials obtained by co-precipitation of silver sulphide and appropriate silver halide are used to prepare silver sulphide based membrane electrodes selective to the silver, chloride, bromide, iodide, and sulphide ions. The powder materials are characterized by x-ray diffraction, SEM equipped with EDAX. These membrane electrodes are found to give Nernstian response with the appropriate ions in the concentration range from 1x10-1 to 1x10-5 M. The performance of these home made electrodes is at par with the commercial electrodes. The electrodes have been successfully used for the quantitative determination of chloride, bromide iodide, silver, and sulphide ions and also for the determination of thiamine in pharmaceutical preparations. For developing countries like Nepal, who can not afford to procure high cost commercial ion selective electrodes, these home made ion selective electrodes are especially appealing since the electrode can be fabricated with ease in low cost and the electrode is well behaved and sufficiently accurate for the analysis with ion selective electrodes. Key words: Ion selective electrode; Home made ion selective electrode; Silver sulphide; Thiamine; Vitamin B1. DOI: 10.3126/sw.v7i7.3818 Scientific World Vol.7(7) 2009 pp.19-23

In the present research work, combination of artificial aging (pre and post) and natural aging was performed on 7075 Al alloy. Aging parameters were optimized using response surface methodology model to get the maximum value of Vickers micro-hardness, hardness value, and tensile strength. Three factors with five levels each were used to develop the center composite rotatable design (CCRD-approach). The three factors were pre-artificial aging temperature, natural aging time, and post-artificial aging temperature. The contour plots, surface plots, and mean effects plots were drawn to study the effect of individual factors and interactions of the factors on micro hardness. The coefficient of the regression R2 was 0.9962 which shows the excellent accuracy of the developed model. One hundred and fifty-one percent increment in the micro hardness and 115% increment in the value of the ultimate tensile strength were observed in optimized sample compared to annealed sample. The Vickers micro-hardness, optical microstructural, tensile test, X-ray diffraction analysis, energy dispersive X-ray spectroscopy analysis, and fractography using scanning electron microscopy of fractured tensile specimen were conducted in this research work.

Home made silver sulphide ion selective electrode was prepared and applied for argentometric titration in alkaline media for the determination of thiamine hydrochloride.The amount of thiamine hydrochloride estimated from titration of ionisable chloride with silver nitrate was found to be 637 mg/g of the vitamin B1 tablet. This result is in agreement with the value obtained from ion chromatographic (IC) and cyclic voltammetric (CV) techniques. In presence of chloride from other sources, these techniques fail, but thiamine in pharmaceutical preparation, however, can be determined by potentiometric titration in highly alkaline medium using silver- sulphide membrane electrode with silver nitrate solution at which there is no interference due to the presence of chloride from other sources. The results showed that home made silver- sulphide electrode can be used as an indicator electrode for the potentiometric determination of thiamine in pharmaceutical preparation. Keywords: Silver sulphide electrode; Potentiometric titration; Thiamine; Vitamin B1. DOI: 10.3126/sw.v8i8.3853 Scientific World Vol.8(8) 2010 pp.69-72