ماهنامه نمایش
پیاپی 115-116 (فروردین و اردیبهشت 1388)

A new chromate-selective electrode, based on the N, N'' butylen bis (saliciliden iminato) copper (II) complex as the membrane carrier, was developed. The electrode exhibited a good Nernstian slope of 􀀀28:8  0:5 mV/decade and a linear range of 3:0  10􀀀6 􀀀 1:0  10􀀀1 mol.L􀀀1 for chromate. The limit of detection was 3:0  10􀀀6 mol.L􀀀1. It had a fast response time of 5-10 sec and could be used for more than three months. The selective coecients were determined by the Fixed Interference Method (FIM). A chromate-selective electrode could be used in the pH range of 6.5-10.5. It was employed as an indicator electrode for the direct determination of chromate in real samples.

drop electrode in aqueous media and in the presence of Britton-Robinson bu er as the electrolyte. In this study, the electroinactive 2,4-D was rst converted to electroactive nitrated 2,4-D. Subsequent determination was carried out by di erential pulse polarography. Under optimum conditions (pH = 11;  = 90 mV s􀀀1; modulation amplitude = 120 mV), the relative standard deviation was 4.5% and limit of detection in terms of nitrated 2,4-D was 5 g L􀀀1 (1:8810􀀀8 M) with linear concentration range from 8 to 300 g L􀀀1(310􀀀8 􀀀1:1210􀀀6M). The proposed method o ered high sensitivity as well as good selectivity. A mechanistic study, showed fourelectron reduction of nitrated 2,4-D to its hydroxylamine derivative. The proposed method was, also, applied to the determination of 2,4-D in environmental samples such as soil samples.

The e ect of Alkali-Aggregate Reactions (AAR) in concrete dams was investigated using the nite element method. Two models have been presented to assess the e ects of the AAR in concrete dams. The stress dependency of AAR strains has been taken into account in the models and the degradation of concrete properties during the reaction has been implemented in the nite element program. The results of the isothermal and nonisothermal analyses of a gravity section of a Beauharnois power plant have been presented and compared with the measured data and the results are in close agreement. The results of the analysis demonstrate the importance of the AAR in concrete dams. High stresses and large de ections occur in the dam during the reaction. Because of the stress dependency of the reaction, vertical displacements are smaller than horizontal displacements.