Morphology Control And Surface Modification Of Calcium Carbonate

Calcium carbonate is the extensive chemical industrial products as a novel functional material used in the fields such as plastics,rubber,paint,printing ink, weaving,toothpaste,makeup,commodity,foodstuff,and so on.Nanoparticles as an important harvest of nanotechnology have attached many attentions in the field of materials science.In recent years,the controlled synthesis of inorganic particle materials with specific size and morphology has attracted more and more attracted due to their wide potential applications in many fields.However,calcium carbonate nanoparticles are easily aggregate because of the very small particle size,high surface activity and high surface energy.Therefore,controlling the particle size during the preparation process,avoiding the aggregation of particles and inducing the powders to redisperse in the medium are current 'hot topics' in the field of nanomaterials.Surface modification of CaCO₃ would lead to a great expansion in its applications since mineral particles are hardly dispersed in a polymer matrix.The key to the successful synthesis of an inorganic-organic composite is an understanding of the parameters that control the nucleation and growth of inorganic crystals under the organic substrate in aqueous solution.In this thesis,a research on join the techniques of chemical synthesis and surface modification are performed.As a result,a series of functional calcium carbonate nanoparticles are prepared under kinds of effective controls.The results indicate it is an available and ideal strategy.If the calcium carbonate produces exert farthest action in the goods,the technologies are eligible necessarily such as purity,granularity,whiteness of calcium carbonate products.At present,the mainstream aspect of this industry is the synthesis of products with high purity,good dispersion and small granularity.It is realized by improving technologies,equipments and optimizing the reaction conditions.In the paper,the novel calcium carbonate materials are synthesized using a series of organic substrates via the chemical controlling and surface modification.The organic substrates can not only change the surface properties of calcium carbonate but also control the nucleation and growth of products.The technology has certain innovation and the extensive application foreground.Firstly,the CaCO₃ hollow spheres were successfully synthesized by facile precipitation reaction of aqueous solutions CaCl₂ and Na₂CO₃ in the presence of polyvinylpyrrolidone(PVP) and sodium dodecyl sulfonate(SDS).Introducing the surfactant/polymer composite into reaction system is in order to not only understand the effects of the surfactant/polymer composite on the crystallization and aggregation of calcium carbonate,but also explore a possible realized and simple preparation method. The products were characterized by FESEM,TEM and XRD.At the same time,the experimental conditions were investigated to explore the crystallization and aggregation of calcium carbonate.The reaction mechanism was discussed in this work.Secondly,the butterfly-like aragonite calcium carbonate particles were successfully prepared through a facile precipitation reaction of Na₂CO₃ with CaCl₂ in the presence of polyacrylic acid sodium(PAAS).The as-prepared products were characterized with scanning electron microscope and X-ray diffraction.The effects of the reaction temperature and the concentration of PAAS on the nucleation and growth of aragonite crystals were investigated.The possible growth mechanism of the dendrite-shaped aragonite particles was discussed.This research not only can make us further understood the general principles of the reaction,but also can open up a new avenue of industrial production of CaCO₃ particles with exquisite and unique morphologies due to the preparation method employed by us is simple,low-cost,mild condition.Thirdly,needle-shaped calcite CaCO₃ nanoparticles were prepared in aqueous solution via carbonation method in the presence of polyacrylic acid sodium(PAAS). In this paper,the organic substrate could not only control the morphology of calcium carbonate but also induce the nucleation and growth of CaCO₃.The needle-like CaCO₃ with a length about 1μm,a diameter about 70 nm and the ratio of length to diameter about 15:1 was prepared.The products were characterized by XRD,FESEM, TEM,FT-IR,DT-TGA,Whiteness and the contact angle.The results reveal that the surfactant plays important roles in determining the structure and morphology of the sample.Fourthly,the rod-like CaCO₃ with a diameter about 100 nm and the ratio of diameter to length about 1:4 was successfully synthesized via bubbling CO₂ gas in the presence of polyethlence glycol(PEG).The bubbling effect of PEG increased the retention time and contact area of CO₂ in the solution thus the higher carbonation efficiency was observed.The presence of PEG accelerates the period of absorption and shortens the time of carbonation.We have succeeded in surface modification of CaCO₃ with PEG.Finally,Modified calcium carbonate(CaCO₃) nanoparticles with cubic and spindle-like configuration were synthesized by the typical bobbling(gas-liquid-solid) method.Such modifiers as sodium stearate(NaSt),octadecyl dihydrogen phosphate (ODP) and oleic acid(OA) were used to obtain hydrophobic nanoparticles.The different modification effects of the modifiers were investigated by measuring the active ratio,whiteness and the contact angle.Moreover,transmission electron microscope(TEM),X-ray diffraction(XRD) and thermogravimetry analysis(TGA) were employed to characterize the obtained products.A preliminary reaction mechanism is discussed in this paper.According to the results,the active ratio of CaCO₃ modified by ODP was ca.99.9%and the value of whiteness was 97.3%when the dosage of modifiers reached to 2 wt.%.Moreover,the contact angle was 122.25°for the CaCO₃ modified in the presence of NaSt,ODP and OA.A conclusion could be drawn from the above results that the compatibility and affinity between the modified CaCO₃ nanoparticles and the organic matrixes were greatly improved.In this thesis,we attempted a biomimetic method to obtained calcium carbonate nanoparticles with special properties,introduced a novel ideal to synthesis calcium carbonate nanoparticles.Surface modification technique employed during preparation process,which introduced functional groups upon the surface of calcium carbonate nanoparticles overcoming the agglomeration of nanoparticles.For the benefits of simple,uninterrupted and inexpensive,this innovatory technique has potential use in application and guide meaning in large-scale production of calcium carbonate in the future.