Study On Preparation Conditions Of Nano-CaCO₃ And The Carbonization-Crystallization Process

Nano-CaCO3 is extensively used as filler and reinforcing materials in the industries of plastics,rubber,inks,paper,paint and so on.The nano-CaCO3 product with suited morphology,uniform particle size,narrow size distribution and better dispersion is of more economic value.The carbonization process can obviously influence the quality of nano-CaCO3.Therefore,it's of great importance to study and optimize the carbonization process and crystallization process.In this paper,nano-CaC03 was prepared by intermittent bubbing carbonization method with quick lime and CO2 as materials,meanwhile,the ultrasonic was adopted in the carbonization process.Then the crystal guiding agents were screened to prepared cubic nano-CaCO3.The prepared CaCO3 was characterized by SEM,XRD,FT-IR and laser particle sizer.The main research contents and results were as follows:1.The carbonation temperature and concentration of Ca(OH)2 had significant influence on the morphology and particle size of the CaCO3.The ultrasonic could improve the dispersibility and decrease the particle size of nano-CaCO3.The optimal preparation conditions of nano-CaCO3 were determined as following:the carbonation temperature,20?;the concentration of Ca(OH)2,0.3 mol/L;the flow of carbonization gas,300 L/h;the percentage of CO2,55%;the aging time,0.5 h;the ultrasonic frequency,60 kHz.Under the conditions,round nano-CaC03 was prepared with the average particle size of 50 nm and the particle size distribution of 30?80 nm.2.After the investigation and analysis of crystal guiding agents by classifications,the research results showed that,The adding of crystal guiding agents,especially maltose and NaHC03,could promote the crystallization and improve the dispersibility of cubic nano-CaCO3 with the average particle size of 50 nm and the particle size distribution of 36?72 nm,3.The SEM and XRD characterization results showed that,Amorphous CaC03 particles with high activity were attached on the surface of Ca(OH)2 to form wire-like substances in the initial stage.Then Ca(OH)2 in the wire-like substances took part in the carbonation reaction and dissolved.In the end,these wire-like crystals were disaggregated into cubic CaCO3.4.A preliminary study of the CaC03 crystal was conducted with density functional theory.The results showed that,calcite had a higher energy over aragonite.The(104)and(110)surfaces of calcite were the most stable faces.Calcite was generated with the addition of NaCl as the crystal guiding agent,and the NaCl molecules were mainly adsorbed on the(104)suface.The stable adsorption geometry of NaCl molecules adsorbed on the(104)surface of calcite was that Cl atom of NaCl molecule adsorbed on two Ca atoms of the suface.