Solubility and phase behaviour of ferric dodecyl benzene sulphonate in aqueous solutions
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Precipitation processes, solubility and phase behaviour in aqueous solutions of ferric nitrate—dodecyl benzene sulphonic acid (HDBS)—nitric acid, were investigated in various pH regions. Precipitation diagrams were made using light scattering. The solubility product and the enthalpies of precipitation were calculated taking into account the hydrolytic constants of Fe+3, Fe(OH)+2, Fe(OH) 2 + species and the dissociation constant of HDBS. The solubility product of ferric dodecyl benzene sulphonate (Fe(DBS)3) was calculated to be K s 0 =(1.23±0.80)x10−24 for pH 2.2 at 293 K. The slope of the straight line from which the solubility product was calculated, (0.317) is close to the theoretical value for 3∶1 electrolyte.
Using a polarization microscope and X-ray diffraction different phases were characterized: the solid crystal, the lamellar liquid crystal and the mixtures of solid and liquid crystalline phases. The enthalpies of crystallization and liquid crystal formation were determined as ΔH=−33 kJ mol−1 and ΔH=23 kJ mol−1, respectively.
Key wordsPhase behaviour liquid crystals solubility product
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