Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 15Citation - Scopus: 15The Isoelectric Point of Lead Magnesium Niobate(John Wiley and Sons Inc., 2007) Deliormanlı, Aylin M.; Çelik, Erdal; Polat, MehmetLead magnesium niobate (PMN) is an important relaxor ferroelectric material commonly used in multilayer capacitor and actuator manufacturing owing to its high dielectric constant and superior electrostrictive properties. However, the isoelectric point of this material in water is not known and there is justification for a detailed investigation. In this work, the isoelectric point (IEP) of aqueous PMN suspensions were determined as a function of solids concentration. Results showed that IEP of the PMN suspensions strongly depended on the solids loading. The IEP was between pH 9 and 10 at particle concentrations between 10 to 20 vol%. The IEP shifted gradually to a lower pH value as the particle concentration decreased. Solubility experiments showed that Pb2+ and Mg2+ ions dissolved from the PMN surface, especially in the acidic pH range. The study provides a new insight on the aqueous stability of perovskite materials which possess more than one soluble cation in their structure.Article Citation - WoS: 19Citation - Scopus: 23Influence of Microstructure on the Rheological Behavior of Dense Particle Gels(John Wiley and Sons Inc., 2005) Wyss, Hans M.; Deliormanlı, Aylin M.; Tervoort, Elena V.; Gauckler, Ludwig JuliusRheological measurements are performed on highly concentrated alumina gels. By using an in situ mechanism based on enzyme-catalyzed internal reactions, we are able to form gels of highly concentrated particles without disturbing the microstructures that develop during the gelation process. These gels are produced by two different destabilization mechanisms: Either the pH of the suspension is shifted toward the isoelectric point (ΔpH method) or the ionic strength of the suspension is increased at a constant pH (ΔI method). The two destabilization mechanisms lead to gels of significantly different microstructures. We find notable differences in the rheological behavior of the two systems, suggesting a bond-bending mechanism for stress transmission in the case of ΔpH gels and a bond-stretching mechanism in the case of ΔI gels. In addition, for both kinds of gels we compare the in situ properties to those obtained after altering the microstructure by shearing. Results suggest an increase in elastic and yield properties of concentrated particle gels with decreasing homogeneity of their microstructures.