Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
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Article Citation - WoS: 14Citation - Scopus: 22Characterization of Airborne Particles and Droplets: Relation To Amount of Airborne Dust and Dust Collection Efficiency(John Wiley and Sons Inc., 2002) Polat, Mehmet; Polat, Hürriyet; Chander, Subhash; Hogg, RichardWater sprays have been commonly used to suppress airborne dust. Water is doped with surface-active agents to enhance the dust capture efficiency through a reduction of surface tension. Nevertheless, dust collection efficiencies have been less than satisfactory historically. A detailed characterization of freshly generated airborne dust particles and spray droplets was carried out in order to explain this observation. Such properties as the agglomeration state of the freshly generated airborne dust particles and the airborne dust production capacity of various materials were defined and quantified. Electrostatic charges on individual airborne particles and spray droplets were measured. It was demonstrated that freshly generated airborne dust particles were extensively agglomerated. The magnitude of agglomeration was a function of material type and decided the amount of dust becoming airborne from a given material. This explains why certain materials such as quartz and anthracite produce more dust than some others. It was demonstrated that surfactants could be employed to charge the spray droplets selectively. The sign and magnitude of the droplet charge was a function of surfactant type and concentration. A strong correlation between the droplet charge and dust collection efficiencies by spray droplets was observed for cationic surfactants, suggesting that surfactants affected collection efficiency in addition to enhancing wetting.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.