Study On The Phase Behavior Of CTAB Reverse Microemulsion System And Preparation For Nano-sized CaCO₃Composites

A series of quasi ternary phase diagram of hexadecyl trimethyl ammonium bromide(CTAB)+n-butanol+n-hexane+water (brine) system have been drawn based on experiments.We investigated the influence of cosurfactant n-butanol with different addition and CaCl2solution with different molar concentration on the microemulsion region respectively. Wefound that the area of microemulsion region in the ternary system gradually decreased withthe relative proportions of cosurfactant n-butanol increase, these results shown that they arenot conducive to the formation of microemulsion phase when the amount of n-butanol inrelatively high levels; We found that the area of microemulsion region in the ternary systemdecreased with the increase of the molar concentration of calcium chloride, these resultsshown that strong electrolytes has an important effect on the microemulsion phase, higherconcentration of CaCl2will make part of CTAB lose surface activity and will make thesystem difficult to form microemulsion, these leads to the decreasing of microemulsion phasearea. The rules of conductivity changing with the added amount of water (or CaCl2aqueoussolution) were measured experimentally, the microscopic structure of microemulsion hadbeen discussed according to the electrolytic theory. It provides an experimental andtheoretical basis to further study the preparation of nanoparticles by microemulsion method.In the nature, we can see the coexistence of magnesium ions and calcium ions,magnesium ions will affect calcium ions in the formation of carbonate. So the effect ofmagnesium ion on the morphology and composition of nanometer calcium carbonate inmicroemulsion were further studied. We systematically drew a series of inverse-microemulsion quasi-ternary system phase diagrams of CTAB+n-butanol+n-hexane+brine(MgCl2/CaCl2) by adjusting the ratio of MgCl2and CaCl2. On this basis, we preparedmicroemulsion with five different molar ratios of magnesium ion to calcium ion, and obtainedcalcium carbonate and magnesium carbonate coprecipitation product by reaction with anequimolar amount of sodium carbonate. The samples were characterized by scanning electronmicroscopy (SEM), Fourier transform infrared spectrometer (FTIR) and X-ray diffraction(XRD). The SEM photographs indicated that when the content of Ca2+was higher, some largefusiform aggregates of coprecipitation particles were formed in solution, but with the contentof Mg2+increased gradually, they eventually formed small and uniform sphere particles. Themeasurement results of XRD and FTIR indicated that the crystal structures of calciumcarbonate in coprecipitation changed gradually from vaterite into aragonite and finally turnedinto amorphous with the increasing of the proportion of magnesium ions. Studies have shownthat Mg2+ions can significantly change the morphology of calcium carbonate crystals, whichplays an extremely important role in the formation of calcium carbonate crystals.