Controllable Synthesis Of CaCO₃ Polymorphs And Investigation On Growth Mechanism

As one of the most important minerals,calcium carbonate plays an important role in the process of biomineralization and oilfield mineralization.The polymorph and morphology of CaCO₃ determine its performance and application,providing a new insight on controllable synthesis of inorganic functional materials.In the meanwhile,CaCO₃ is a kind of byproduct of ASP flooding technology,and the formation of oil field scale is the direct reason which makes it's difficult to handle with produced fluid and degrade the quality of crude oil,threatening the production of oil field seriously.Hence,it may have great scientific significant and application value to study the crystallization behavior and growth mechanism of CaCO₃ in oil field,providing theoretical basis for thoroughly solving the problem of oil field scaling.We firstly introduce the basic concept of calcium carbonate,its structure,physical properties,crystal growth theory and the regulatory effect of different organic additives on the crystallization of calcium carbonate,thus leading to the research plan of this paper.In this paper,0.5 generation polyamide-amine?G0.5 PAMAM?,polyacrylamide?HPAM?,heavy alkylbenzene sulfonate?HABS? were selected by one-step precipitation method to study the crystallization behavior of calcium carbonate in pure water system and crude oil-water binary system with different proportions.And the interaction of additives with ions/crystals was discussed subsequently,leading to the formation mechanism of various CaCO₃ polymorphs.The main research contents and results are as follows:?1?Controllable synthesis of amorphous calcium carbonate?ACC?by G0.5 PAMAM by one-step precipitation menthod was achieved.PAMAM,as a crystalline inducer,could chelate with calcium ions with its eater group in solution and further delay the crystallization of ACC.In addition,a kinetic transformation mechanism of ACC was proposed,according to the change of surface tension,including:primary nucleation,secondary nucleation,fast growth and slow growth.?2?Controllable synthesis of monodisperse spheroidal vaterite CaCO₃ by HPAM-HABS in crude oil emulsion system by one-step precipitation method was achieved.HABS can promote the formation of stable emulsion,and its terminal sulfonate could attract calcium ions,so that CaCO₃ could nucleate and grow on the oil-water interface,which was conducive to the formation of metastable calcium carbonate.On the other hand,the molecular structure of HPAM chain increased steric hindrance,hindering the assemble of CaCO₃ particles.The interfacial self-nucleation and growth mechanism of vaterite were proposed,including:oriented aggregation of Ca²⁺,oriented absorption of CO₃^2-,formation of prenucleation clusters and ACC,nucleation and growth of vaterite.?3?Controllable synthesis of labyrinth-like calcite CaCO₃ by HPAM-HABS in water system by one-step precipitation method was achieved.HABS can form micelles in water system,and become a nucleation site of CaCO₃ by the attraction of Ca²⁺,which could decrease CaCO₃ surface activity and inhibit its further transformation.According to the non-classical nucleation theory,the“terrace-ledge-kink growth”formation mechanism of calcite was proposed.HPAM adsorbed on the steps or kinks of CaCO₃,and HABS-stabilized ACC adsorbed on the growth site of calcite selectively,further dissolved and grew into calcite crystal,resulting in the formation of crystal with growth defects.At last,the auther summarized the research content,aim and significance of research results in the aboved three chapters,not only expand people's understand of controllable synthesis of different CaCO₃ polymorphs,but also provide new insights for the controllable preparation of other inorganic functional materials.