Reversed Polarity Mode Research Articles

Comparison of reversed-polarity capillary electrophoresis and adsorptive stripping voltammetry for the detection and determination of reactive textile dyes

Reversed-polarity capillary electrophoresis (CE) and adsorptive stripping voltammetry (AdSV) using a hanging mercury drop electrode are compared for the separation and determination of six reactive textile dyes. Only four of the six starting dyes could be separated in the reversed-polarity mode of CE. No change in pH, temperature, run buffer, acetonitrile concentration of surfactant brought about separation of all six dyes. Optimum separation of the hydrolysed dyes was achieved using an electrolyte of 0.05 mol dm–3 citric acid (pH 3.25) with 10% acetonitrile. Stacking of the dyes was performed using a 0.05 mol dm–3 citric acid buffer (pH 2.23), containing 0.006 mol dm–3 diethylenetriamine. Electrokinetic injections were investigated using 0.05 mol dm–3 citric acid (pH 2.23) buffer with an injection time of 30 s at a voltage of 10 kV. AdSV studies were carried out using a 0.2 mol dm–3 acetate–acetic acid buffer (pH 4.5) and a 5 min accumulation time at the mercury electrode. The correlation coefficients of the calibration graphs and limits of detection for both techniques are also compared.

Metallurgical characteristics of electroslag-refined MDN 250 maraging steel

MDN-250 maraging steel was electroslag-refined in a 350 kVA DC ESR unit using a slag of composition, CaF2-65, CaO-9, Al2O3-2O, TiO2-5, and MoO3-1 (wt % basis) in straight as well as reverse polarity modes of melting. The chemical homogeneity of the ingots was established by X-ray fluorescence, plasma scan and spectrovac methods. The dissolved gas content (O and N) in the ingots was determined by a LECO gas analyser. Volume fraction, density and size distribution of inclusions in the ingots and the electrode were determined in a Quantimet image analyser. These results were supplemented by EPMA and SEM studies on selected inclusions. Mechanical properties of the ingots in the heat-treated and aged conditions were assessed and compared with those of the electrode material.The present results confirm that the reverse polarity mode of melting is best suited for producing quality maraging steels for the ingots produced by this mode of melting were found to possess superior metallurgical characteristics in terms of cleanliness and mechanical properties compared to those produced by the straight polarity ESR route and other conventional methods.