Study On The Synthesis Of CaCO₃ By Mechanochemical Method And Its Reaction Mechanism

Mechanochemical method is a way to prepare new materials,it has always been the hotspot of research.Dry mechanochemical method and wet mechanochemical method were employed to prepare calcium carbonate（CaCO₃）powder and the factors affecting the polymorphs and morphologies of CaCO₃ were researched.Meanwhile,the synthesis of CaCO₃ via ethanol-calcium method was also explored,and the formation mechanism of Ca CO₃ particles was investigated.Firstly,the effect of milling times,milling speeds,ball/material ratios,grinding ball mass and three kinds of additives（sodium hexametaphosphate（SHMP）,sodium dodecyl sulfonate（SDSN）,nickelous nitrate hexahydrate（Ni（NO₃）₂·6H₂O））on the polymorphs and morphologies of CaCO₃ was studied by dry mechanochemical method,calcium chloride（CaCl₂）and sodium carbonate（Na₂CO₃）solid powder as raw material.X-ray diffractometer（XRD）,scanning electron microscope（SEM）and transmission electron microscope（TEM）were used to analyze and observe the polymorph and morphology of CaCO₃,respectively.Results show that increasing milling speed,ball/material ratio or decreasing grinding ball mass and prolonging milling time can all be beneficial to the formation of rhombohedral calcite.The addition of SHMP and SDSN can promote the formation of spherical vaterite,while aragonite phase,except for vaterite and calcite,can also be obtained when Ni（NO3）2·6H2O is added.Then CaCO₃ powder prepared by ethanol-calcium method,CaCl₂ ethanol solution and Na₂CO₃ aqueous solutions as raw material,was explored,in which three systems（ethanol,ethylene glycol and glycerol）were employed.The effect of aging times and reaction temperatures in three systems on the polymorphs and morphologies of CaCO₃was researched.The polymorphs and morphologies of CaCO₃ powder were characterized by XRD,SEM and Fourier infrared spectrometer（FT-IR）,and the results indicate that a two-phase mixture of vaterite and calcite can be obtained in three alcohol systems at room temperature,and the amount of vaterite decreases as the increase in aging time and temperature.As increasing temperature,the amount of spherical vaterite decreases and no aragonite is formed in ethanol system.The amount of spindle-like and spherical vaterite also decreases as increasing temperature in ethylene glycol system and glycerol system,however,aragonite is formed at 80℃and 60℃in two systems,respectively.Finally,based on ethanol-calcium method,CaCO₃ was fabricated through wet mechanochemical method,CaCl₂ ethylene glycol solution and Na₂CO₃ solid powder as raw material.The effect of ethylene glycol-calcium solution concentrations,milling times and milling speeds on the polymorphs and morphologies of Ca CO₃ was researched.The polymorphs and morphologies of CaCO₃ powder were also characterized by XRD,SEM and TEM.The results indicate that CaCO₃ is composed of vaterite（spindle-like,flower-shaped and spherical）and rhombohedral calcite,and the amount of vaterite firstly increases and then decreases as increasing the ethylene glycol-calcium solution concentration,while decreases as increasing milling time and milling speed.CaCO₃ powder was prepared successfully through dry and wet mechanochemical method and the polymorphs,morphologies of CaCO₃ and reaction mechanism were investigated,which provides theoretical foundation for the preparation of CaCO₃ via mechanochemical method.Meanwhile,the research on the preparation of CaCO₃ by ethanol-calcium method presents a new approach to prepare vaterite and enrich the preparation of this metastable phase.