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Regulation Of The Growth Of Calcium Carbonate Crystals By Cationic Surfactants

Posted on:2011-11-19Degree:MasterType:Thesis
Country:ChinaCandidate:S X LiFull Text:PDF
GTID:2121360305951903Subject:Physical chemistry
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In recent years, many scholars have been preparing functional inorganic materials with special morphologies and different sizes, and using them in medicine, catalysis, electronics, ceramics, paints, cosmetics, and many other fields. The effects of the organic matter in aqueous solution in vitro in inducing inorganic minerals and controlling crystal morphology have become the research hotspot in recent years. As one kind of them, surfactant molecular assembly can effectively control the size and morphology of nanomaterials, and it is a good reactor to prepare nano-materials. This thesis has studied the effects of different cationic surfactant additives on the growth process of calcium carbonate crystals. And four parts tasks have been done and reached the following conclusions.Chapter one firstly outlines the research background of this work. The basic methods for preparing calcium carbonate crystals and the research for the regulation of the growth of calcium carbonate crystals by various ordered molecular assemblies of surfactants in recent years are summarized, which provides a theoretical basis and technical support for this thesis. Based on it, the scientific significances and basis of topic of this thesis are described.Chapter two is primarily concerned with the effects of three surfactants, dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide(TTAB), and cetyltrimethylammonium bromide(CTAB) on the growth of calcium carbonate crystals. And we emphasize to systematically study the effects of cationic surfactant-DTAB on the growth of calcium carbonate and barium sulfate crystals. Flowers-shaped, ladder-like, coral-like, branch-like and multi-antennae-like calcium carbonate crystals were prepared by changing DTAB concentration, experimental temperature and pH value. Firstly, the effects of DTAB concentration of 12.5,15.0,20.0,25.0 mmol/L on the growth of calcium carbonate were studied. The morphologies of calcium carbonate crystals change from multi-petal-flower-shaped to multi-step-cube-shaped. The crystalline forms are all calcite and unchanged with the increasing of DTAB concentration. Then the effects of temperature (25,60 and 80℃) on the growth of calcium carbonate crystals were investigated. The morphologies of calcium carbonate change from flower-shaped to coral-shaped and then to dendrite-shaped. And it has been found that the contents of aragonite increased with the increase of temperature. When the temperatures are 60 and 80℃, the contents of aragonite are 47.82% and 93.23%, respectively. Finally, the effects of pH value range from 11 to 13 on the growth of calcium carbonate crystals have been studied. The morphologies of calcium carbonate crystals change from flower-shaped to multi-antenna-shaped structures. While the crystal forms are all calcite. The formed flower-shaped barium sulfate crystals by the regulation of DTAB can further confirm the good regulation of DTAB micelles in preparing inorganic nanomaterials.Chapter three studies the effects of cationic surfactant with different hydrophobic group and hydrophilic group on the growth of calcium carbonate crystals, compared with DTAB. Didodecyldimethyammonium bromide (DDAB) and 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) are chosen to prepare calcium carbonate crystals. The effects of their concentration on the crystalline form and morphology of calcium carbonate crystals were investigated. The result shows that the morphologies of calcium carbonate crystals change from cube-shaped to ball-shaped and the crystalline forms change from calcite to vaterite with the increase of DDAB concentration from 2.5 to 10.0 mmol/L; The morphologies change from cube-shaped to string-shaped when the [C12mim]Br concentration increases from 15.0 to 60.0 mmol/L. While the crystalline forms of crystals are all calcite. Based on the obove, possible mechanisms for the regulations of calcium carbonate crystals by cationic surfactants with different hydrophobic group and hydrophilic group (DTAB,DDAB and [C12mim]Br) are proposed.Chapter four investigates the effects of mixed cationic surfactants DDAB and [C12mim]Br on the growth of calcium carbonate crystals. Firstly, the critical micelle concentrations (cmc) of the DDAB/[C12mim]Br mixed solution at different concentrations ratio were measured. And the concentrations for DDAB/[C12mim]Br mixed solution were selected above cmc to regulate calcium carbonate crystals. The crystals were formed by changing the concentration of one surfactant and fixing the concentration of the other surfactant at 5.0 mmol/L. When DDAB concentration increases from 5.0 to 20 mmol/L. The morphologies of crystals are all flower-shaped, but the number of petals increases. The crystals are all cacite without convertion. The morphologies of crystals change from floccus-shaped to flower-shaped with the increase of [C12mim]Br concentration from 5.0 to 60.0 mmol/L. The crystals are still calcite without convertion. Finally, the possible mechanisms are given for the formation of calcium carbonate crystals with various morphologies by mixed cationic surfactants.
Keywords/Search Tags:Cationic surfactant, Calcium carbonate, Regulation, Morphology, Crystalline form
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