Study On The Growth Regulation Of Bionic Mineral Calcium Carbonate Under Thermal Field

The understanding of the formation mechanism and artificial control with precision towards crystal structure and morphology has been a core subject of research for scientists.As a common biological inorganic material in nature,calcium carbonate not only has important value and wide applications in the field of industry,geological science and life science,but also is an ideal model for law studies of crystal growth because of its rich crystal structure and versatile crystal morphology.Especially in probing influence of temperature on crystal growth and the structure regulation,it has attracted close attention from researchers recently.In this thesis,we primarily studied the effect of ambient temperature on the growth of calcium carbonate crystals under a temperature-homogeneous system.Then we designed different thermal fields in the aqueous system by using a method of photothermal conversion,including constant temperature gradient field,cold-hot alternant temperature gradient field,hot-cold alternant temperature gradient field and cold-hot-cold alternant temperature gradient field.The regulation effect of different thermal fields on crystal growth of calcium carbonate was deeply studied and a series of complex calcium carbonate crystals with multi-stage structures were synthesized.Moreover,we have carried on a preliminary analysis and discussion about the related mechanisms from the perspective of thermodynamics and kinetics.Our study found that the temperature has a specific selectivity towards the type of calcium carbonate crystals: from low temperature to high temperature(5-70 ?),the crystallization product has a distribution of calcite?calcite and vaterite?calcite,vaterite and aragonite?aragonite and calcite(in a small percentage).In the cold-hot alternant thermal field,aragonite@calcite and aragonite@vaterite were synthesized.We assume that the surface steps of calcite formed in the low temperature,the immature surface of vaterite and the rapid deposition of aragonite in the high temperature together make key contributions to their formation.In the hot-cold alternant thermal field,calcite@aragonite was synthesized.We analyze that the rough surface of aragonite with defects which is rapid precipitated in the high temperature deseases the energy barrier for calcite's nucleation.And in the cold-hot-cold alternant thermal field,the three-stage composite structure of calcite@aragonite@calcite and calcite@aragonite@vaterite were obtained successfully.