Calorimetric investigation of reaction Ca(NO3)2 + Na3PO4 in water and microemulsions saturated with CO2

✍ Scribed by Zhongyu Du; Xueqin An; Dashuang Fan; Weiguo Shen

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 369 KB
• Volume: 43
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20557

✦ Synopsis

Abstract

The reactions of Ca(NO~3~)~2~ + Na~3~PO~4~ in water and water/sodium bis(2‐ethylhexyl) sulfosuccinate (AOT)/hydrocarbon microemulsions saturated CO~2~ with various molar ratios of water to surfactant R, oil phases, and surfactant concentrations were investigated by isothermal titration calorimetry. The product of the reaction was confirmed to be sodium‐and‐carbonate‐substituted hydroxyapatite (NaCO~3~HAP) by Fourier transform infrared spectra (FTIR), energy dispersive spectrometry (EDS), and X‐ray diffraction (XRD). From calorimetric measurements, the molar enthalpies of solution of water in the AOT/n‐dodecane system, and the molar enthalpies, the rate constants, and the activation energies of the reactions were determined. It was found that the enthalpy of solution of water in AOT/n‐dodecane micells and the molar enthalpy of the reaction in the microemulsions increased with the decreases of R until R = 7; below that they kept almost constant. It may be attributed to the increase of the ratio of the bound water to the free water with the decrease of R until there was no free water when R < 7. However, the reaction rate constant k~1~ was affected by the ionic strength of the medium and log k~1~ showed a linear dependence on 1/R in the whole range of R we investigated. It was also observed that the rate constant and the enthalpy of the reaction remained almost unchanged when the surfactant concentration and the nature of oil phase varied. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 322–330, 2011