Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
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Article Citation - WoS: 39Citation - Scopus: 43Adsorption of Peo/Ppo Triblock Co-Polymers and Wetting of Coal(Elsevier Ltd., 1999) Polat, Hürriyet; Chander, SubhashThe adsorption characteristics of PEO/PPO/PEO triblock co-polymers on coal were investigated using surface tension and contact angle measurements. Although these surfactants have been widely used as wetting agents, it was observed that they increased the hydrophobicity of coal at concentrations below about 10-6 M. Surface tension studies were carried out to explain the reasons for this behavior. The surface tension versus concentration profiles displayed three distinct regions. In region I, surface tension decreased linearly and monomers were proposed to be the dominant species. This region extended to a surfactant concentration of about 10-6 M. In region II, a transition region between regions I and III, dimers, trimers, etc., were considered to form. In region III, micelles formed and surface tension was independent of concentration. The concentration at which monomers associate to form dimers, etc., is referred to as the critical association concentration (cac). The contact angle of coal increased when concentration was raised from low values to the cac. It decreased when the reagent concentration was above the cac. Finally, at concentrations above the cmc, the wetting of coal was complete and contact angle was zero.Article Citation - WoS: 21Citation - Scopus: 24Kinetics of Oil Dispersion in the Absence and Presence of Block Copolymers(John Wiley and Sons Inc., 1999) Polat, Hürriyet; Polat, Mehmet; Chander, SubhashA phenomenological model proposed describes droplet breakup in the turbitlently agitated lean oil-in-water dispersions and provides a correlation between the median droplet size in an agitated vessel of standard geometry and the time of dispersion. It was assumed that the droplet breakup takes place in the dispersion-only region and coalescence is negligible. Vie model described the data from this study and the literature quite satisfactorily under these conditions. The effect of adding triblock PEO/PPO/PEO copofymeric surfactants on the dispersion kinetics of oil was also investigated. Addition of surfactant reduced the median oil droplet size significanfty, and the extent of this reduction was a strong function of surfactant concentration. Application of the model on these data demonstrated that the change in the median droplet size could be divided into two distinct regions. The breakage rate was high initially, most probably due to continuous adsorption of surfactant molecules at the oil/water interface. A lower breakage rate was attained at longer tunes, as the surfactant molecules were depleted from the solution. The time of transition bet\veen the t\vo was affected strongly by the concentration of the surfactant added. Furthermore, the time of addition of the surfactant did not affect the final droplet-size distribution in the system.Article Citation - WoS: 47Determination of Technetium in Sea-Water Using Ion Exchange and Inductively Coupled Plasma Mass Spectrometry With Ultrasonic Nebulisation(Royal Society of Chemistry, 1998) Eroğlu, Ahmet Emin; McLeod, Cameron W.; Leonard, Kinson S.; McCubbin, DavidAn enrichment–separation scheme employing a strong-base type anion-exchange resin was developed for the determination of99Tc in sea-water by inductively coupled plasma mass spectrometry utilising ultrasonic nebulisation with membrane desolvation. Samples were processed through an anion-exchange column to enrich Tc and to eliminate sea-water matrix ions. The limit of detection for 99Tc in sea-water based on processing a 14 ml sample was 0.03 ng l–1. Accuracy was verified with spike recovery experiments. The potential for rapid on-line sample processing via a microcolumn–flow injection system was demonstrated.Article Citation - WoS: 57Determination of Plutonium in Seawater Using Co-Precipitation and Inductively Coupled Plasma Mass Spectrometry With Ultrasonic Nebulisation(Elsevier Ltd., 1998) Eroğlu, Ahmet Emin; McLeod, Cameron W.; Leonard, Kinson S.; McCubbin, DavidA flow injection–inductively coupled plasma–mass spectrometric (FI–ICP–MS) procedure, utilising ultrasonic nebulisation with membrane desolvation (USN/MD), has been developed for the determination of plutonium (Pu) in seawater at fg l−1 concentration levels. Seawater samples (1 l), after filtration, were subjected to co-precipitation with NdF3, followed by ion exchange to enrich Pu and to reject seawater matrix ions and co-existing uranium. The seawater concentrate (1.0 ml) was then analysed by FI–ICP–MS. The limit of detection for in seawater based on an enrichment factor of 1000 was 5 fg l−1, and precision at the 0.80 pg l−1 level was 12% RSD. Accuracy was verified via recovery experiments, and by comparing survey data for the Irish Sea with that derived by standard methodology based on co-precipitation and α-spectrometry. Concentrations for dissolved in the Irish Sea were in the range of 0.267–0.941 pg l−1 (0.614–2.164 mBq l−1) and 0.051–0.196 pg l−1 (0.428–1.646 mBq l−1), respectively.