Shahida B. Niazi

Spectrophotometric determination of traces of iodide by liquid—liquid extraction of Brilliant Green—iodide ion pair

Abstract Iodide in natural waters at the 10 −6 M level is determined spectrophotometrically as the Brilliant Green—iodide ion pair. Iodide is first oxidized to iodine with hydrogen peroxide—sulphuric acid to separate it from other chemical species and extracted into carbon tetrachloride. It is then extracted back into aqueous medium by its reduction with sodium thiosulphate and stabilized as the ion pair with Brilliant Green. At pH 7 the ion pair is extracted into chloroform and the absorbance is measured at 625 nm against chloroform. A linear calibration graph is obtained over the range 5 × 10 −7 − 3.5 × 10 −6 M iodide with a relative standard deviation of 0.38% at the 2 × 10 −6 M iodide level. The apparent molar absorptivity for iodide is 3.0 × 10 5 1 mol −1 cm −1 .

EFFECT OF Mg2+ SUBSTITUTIONS ON THE STRUCTURAL AND MAGNETIC PROPERTIES OF Co–Mg W-TYPE HEXAGONAL FERRITE

W-type hexagonal ferrites having the formula BaCo2-xMgxFe16O27 with x = 0, 0.4, 0.8, 1.2, 1.6, 2.0 were synthesized by the chemical coprecipitation method. XRD analysis shows that the structure of all the compositions is W-type hexagonal ferrite. The c/a ratio varies from 5.48 to 5.52, consistent with the standard values. It was observed that the bulk density and X-ray density decrease whereas porosity increases with increasing concentration of Mg2+. Room temperature resistivity increases, from 103 to 107 (Ω cm) by increasing the concentration of Mg2+, due to an increased number of grain boundaries. The remanence and saturation magnetization decrease with increasing Mg2+ content while coercivity increases as the Mg2+ increases according to the relation Hc ∝ 1/r. The measured coercivity values are suitable for use in high frequency applications such as microwave absorber materials.

Hazardous Emissions from Combustion of Fossil Fuel from Thermal Power Plants Based on Turbine Technologies

ABSTRACT Thermal power generation is associated with the emission of hazardous gaseous and particulate pollutants, which is one of the major contributors to deteriorated local ambient air quality. A comprehensive emissions assessment was carried on three thermal power plants and one oil refinery operating on fossil fuel, mainly heavy residual oil. The background ambient air quality was also monitored for criteria pollutants around three thermal power plants and one oil refinery to assess the impact of plant emissions on ambient air quality. Emissions of the critical air pollutants carbon monoxide, carbon dioxide, oxides of nitrogen, sulphur dioxide, particulate matter, lead, and mercury were monitored from the stacks of each plant. The emissions from all the stacks of these plants were monitored for a period of 6 months. The emission concentrations were compared with the National Environmental Quality Standards (NEQS) of Pakistan and with World Bank (WB) guidelines for thermal power plants. The study found that the emissions of sulphur dioxide, oxides of nitrogen, and particulate matter were exceeding the permissible levels in power plants fueled by heavy residual fuel, whereas the power plants that were fueled by mixed fuel (natural gas and heavy residual oil) showed comparatively low emissions of pollutants.

MAGNETIC PROPERTIES OF CO-PRECIPITATED MnZn FERRITE-SiO2 COMPOSITES

A series of composite ferrites with chemical formula (1–x)[Mn0.5Zn0.5Fe2O4]·x[SiO2](x = 0.0, 0.20, 0.30, 0.40, 0.50) were prepared by the co-precipitation technique. The samples were finally sintered at 1150°C followed by air quenching. The x-ray diffraction analysis confirms the phases precipitated out in the samples. AC magnetic susceptibility of these samples has been measured using the low field mutual inductance technique over the temperature range 298 K to 550 K at a frequency of 250 Hz. The magnetic parameters like Curie constant, C, Curie temperature, Tc, Lande splitting factor, g, effective magnetic moment, Peff, exchange integral, J/kB, and characteristic temperature, θ(K) were calculated. The reciprocal of susceptibility versus temperature curves of each sample follows the Curie Weiss behaviour above the Curie temperature. Below the Curie temperature, all the samples show the ferrimagnetic behaviour. It was concluded that the magnetic properties were enhanced by the addition of silicon as is evident by the variation of magnetic interactions J, with Si-concentration and followed subsequently by the Peff, θ(K) and Tc etc.