Preparation Of Nano-CaCO₃ And Size,Morphology Control

Nano-CaCO₃ is an important inorganic material.In the fields of rubber,plastic,paper,paint,textile,ink,toothpaste,cosmetic,food,pharmaceutical and etc.,it has begun to be widely used as inorganic filler with superior functional properties.Currently the amount of calcium carbonate accounts for more than 80%of inorganic filler used in polymer,and the proportion of the used nano calcium carbonate with excellent performance is rising year by year.It has three different crystal forms:calcite,aragonite and vaterite.Calcite is the most stable.The carbonation is the main method of industrial production for nano-CaCO₃.With the developlent of nano-CaCO₃ production technology and the improvement of its application requirements,CaCO₃ production is prompted to the direction of narrow particle size distributions,small particle sizes and function of new features.At the same time,due to the different application scope of the different nano-CaCO₃ particles,the carbonization methods appeared to be modified.Therefore,it has important significance to research the preparation,espically for the controllable morphology and size particles.In this project,we firstly prepared nano-CaCO₃.particles by the typical bobbling method（one-step carbonization method）,oil-water interface method,two-step carbonization method.Secondly,we prepared calcite nano-CaCO₃ with the seed-carbonization method.Then,according to the optimal experiment conditions,we used 5L reactor to produce nano-CaCO₃ particles and compared the reaction results with those produced in three-necked flask.The scale-up experiment would lay the foundation of controllable size and morphology for nano-CaCO₃ production.This study was carried out in the following five aspects:（1）Calcium carbonate nanoparticles were prepared by one-step carbonation method,and added different crystal shape-controlling agents,the products were characterized by XRD,TEM,FT-IR and the bulk density test.Furthermore,the effects of operation conditions on the carbonization process were initially discussed.The results showed the prepared nano-CaCO₃ were calcite,diameter distributions were wide and agglomeration phenomenons were quite serious.（2）The nano-CaCO₃ were prepared using oil-water interface method and the reaction conditions were as following:the concentration of calcium oleate solution as oil phase was 0.1M and the Na2Co3 solution as water phase was also 0.1M,the reaction time was 2 h,and the reaction temperature of the system were 40℃ and 15℃ respectively.When the reaction temperature was 40℃,the hydrophobic nano-CaCO₃ particles were successfully synthesized and the crystal forms were vaterite type.However,the crystal grain size was large and the morphology was not well-defined.When the reaction temperature was 15℃,spining cone products were obtained,whereas the product was not CaCO₃.（3）The different carbonization numbers had significant effects on the aspect ratio of nano-CaCO₃ particles and the carbonization process.The obtained nano-CaCO₃ particles using two-step carbonation method were more evenly-distributed and the crystal forms were much better.In addition,the effects of different crystal shape-controlling agents on CaCO₃ nanoparticles during the two-step carbonation process were discussed.The addition of NaHCO₃ during the aging stage made nano-CaCO₃ particles more uniform,less aspect ratio and their bulk densities were larger.（4）Nano-CaCO₃ particles were successfully prepared by seed-carbonization method.And the more seeds,the shorter carbonization time,which has a great reference value for the industrialization of CaCO₃.The results showed that:the addition order and adding amount of crystal shape-controlling agents,concentration of Ca（OH）2,the initial reaction temperature of carbonization,the content and flow rate of CO₂ and even the stirring speed affected not only the size of nano-CaCO₃,but also the morphology,size distribution,dispersion and the bulk density.（5）According to the optimum reaction conditions obtained in small scale experiments,we amplified the experiment in a 5L reaction kettle.The products were tested by TEM,XRD,bulk density,contact angle and FT-IR.The results showed that:amplification products were hydrophilic calcite nanoparticles,which were slightly different with the small scale experiments.It is believed that the research on preparations of nano-CaCO₃,especially for the low-cost,easy production mode,improve the productions of ultra-fine and functional CaCO₃ will contribute to the mature of nano-CaCO₃ manufacturing,so as to promote the development of CaCO₃ industry in our country.