Formation and Stabilization of Vaterite Calcium Carbonate by Using Natural Polysaccharide

This paper aimed to study the effects of natural polysaccharide (gum arabic, GA) on the formation of vaterite calcium carbonate and its stability in aqueous solution. Gum arabic is a macromolecule that has a high molecular weight and is amphoteric in character. A 0, 2.5, 5 or 10 ml of GA solution (30%) was added to the calcium chloride solution with various initial concentrations to prepare the vaterite calcium carbonate. The calcium carbonate particles were characterized using FTIR, XRD, SEM, TEM and DSC-TG as well as calculation of phase contents. The results of XRD and FTIR analysis were showing that the presence of GA during the precipitation changes the behavior of calcium carbonate to form vaterite until at lower dose used. In addition, the molar content of vaterite increased at the expense of content of calcite with increasing the GA dose. There are slightly improvements in the vaterite content by increasing the initial concentration. The formed vaterite calcium carbonates composed of aggregates as broccoli-like or spherical shape and with particle size 1.6 - 2.5 μm in diameter. TEM images showed that these aggregates composed of the sub spherical unit with diameter 15 - 30 nm. The thermal behavior of prepared vaterite was conformed the mineral composition of these phases. The prepared calcium carbonate, which is formed in the presence of different doses of gum, has a stability in the aqueous solutions at different temperatures, as the analyzes indicated that a very small percentage of the vaterite were converted to calcite. The gum arabic prevented or depressed the transformation of vaterite to calcite through capped the surface of particles, i.e. it is more effective in stabilizing the vaterite phase with increasing in initial concentration and time.

Comparing the regeneration potential between PLLA/Aragonite and PLLA/ Vaterite pearl composite scaffolds in rabbit radius segmental bone defects

Mussel-derived nacre and pearl,which are natural composites composed CaCO3 platelets and interplatelet organic matrix,have recently gained interest due to their osteogenic potential.The crystal form of CaCO3 could be either aragonite or vaterite depending on the characteristics of mineralization template within pearls.So far,little attention has been paid on the different osteogenic capacities between aragonite and vaterite pearl.In the current work,aragonite or vaterite pearl powders were incorporated into poly-L-lactic acid(PLLA)scaffold as bio-functional fillers for enhanced osteogenesis.In intro results revealed that PLLA/aragonite scaffold possessed stronger stimulatory effect on SaOS-2 cell proliferation and differentiation,evidenced by the enhanced cell viability,alkaline phosphatase activity,collagen synthesis and gene expressions of osteogenic markers including osteocalcin,osteopotin and bone sialoprotein.The bone regeneration potential of various scaffolds was evaluated in vivo employing a rabbit critical-sized radial bone defect model.The X-ray and micro-CT results showed that significant bone regeneration and bridging were achieved in defects implanted with composite scaffolds,while less bone formation and non-bridging were found for pure PLLA group.Histological evaluation using Masson's trichrome and hematoxylin/eosin(H&E)staining indicated a typical endochondral bone formation process conducted at defect sites treated with composite scaffolds.Through three-point bending test,the limbs implanted with PLLA/aragonite scaffold were found to bear significantly higher bending load compared to other two groups.Together,it is suggested that aragonite pearl has superior osteogenic capacity over vaterite pearl and PLLA/aragonite scaffold can be employed as a potential bone graft for bone regeneration.

Assembly Synthesis of Sheet-like Calcite Array and Stable-Vaterite by Supported Liquid Membrane

Sheet-like calcite array and stable vaterite were synthesized by bio-mimetic supported liquid membrane system under different reaction conditions. Both of the FTIR spectra of products showed narrower peak at 1418 cm?1 than that of bulk CaCO3, and that of vaterite has a split in this peak.

Regulation of Microstructure of Calcium Carbonate Crystals by Egg White Protein

Crystal growth of calcium carbonate in biological simulation was investigated via egg white protein with different volume fractions,during which calcium carbonate was synthesized by calcium chloride and sodium carbonate.The morphology,thermal properties and microstructure of the calcium carbonate micro-to-nanoscale crystals were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,Fourier transform infrared spectroscopy（FTIR）,thermogravimetric analysis（TG） and X-ray diffraction（XRD） analysis.The results show that the volume fraction of egg white protein has great influence on the shape,size and morphology of calcium carbonate crystals.The calcium carbonate crystals were the mixtures of calcite-vaterite-like crystals including spherical and rough surface,which are different from that formed in pure water.With the increase of egg white protein concentration,the diameter of calcium carbonate crystals changed,the amount of formed spherical calcium carbonate particles decreased and that of vaterite increased.These results indicate that the coordination and electrostatic interaction between egg white protein and Ca2＋ significantly affect the calcium carbonate crystalization.

A Modified Integrated Model of the Internal Structure of Chinese Cultured Pearls

Optical and micro-infrared microscope were used to observe the internal structure and mineral composition of high and low quality Chinese seawater and freshwater cultured pearls.Results clearly reveal that aragonite and calcite are found in seawater cultured pearls,but vaterite is not found.In contrast,vaterite and aragonite are found in freshwater cultured pearls,but calcite is not found.Based on our analysis and observations of the internal structure of high and low quality cultured pearls,a modified integrated model of the internal structure of Chinese cultured pearls was established.Our revisions to the previous model focus on significant differences within the prismatic layer of Chinese cultured pearls.

Carbonation of low heat portland cement paste precured in water for different time

The carbonation technique was applied to accelerate the hydration of low heat portland cement （LHC）. Before carbonation, the demoulded pastes were precured in water for 0, 2, 7, and 21 d, respectively. The results show that precuring time in water strongly influences the carbonation process. The phenolphthalein test indicates that the paste precured in water for a shorter time is more quickly carbonated than that for a longer time. The content of calcium hydroxide increases with increasing the precuring time in water, whereas, the amount of absorbed carbon dioxide changes contrarily. Scanning electron microscope （SEM） observation shows that portlandite always fills up big air bubbles in the paste during precuring in water, and the mercury intrusion porosimetry （MIP） results show that there are less large capillary pores in the paste precured in water for a longer time. It is found that the paste without precuring in water has more carbon dioxide absorption during curing in carbon dioxide atmosphere, and its total pore volume decreases remarkably with an increase in the carbonation time than that precured in water. X-ray diffraction （XRD） and Brunauer-Emmett-Teller （BET） surface area analyses indicate that the carbonate products are vaterite and calcite; CxSHy formed from carbonation has low BET surface area in comparison with that of C-S-H formed from curing in water.

Investigation of scale inhibition mechanisms based on the effect of scale inhibitor on calcium carbonate crystal forms

To probe the scale inhibition mechanisms,calcium carbonate scale occurring before and after the ad- dition of scale inhibitors was collected.The results from scale SEM confirm that,without scale inhibitor, calcium carbonate scale shows rhombohedron and hexagon,which are the characteristic feathers of calcite.After addition of inhibitors,morphology of scale is changed,and the more efficient the scale inhibitor is,the more greatly the morphology is modified.To elucidate the scale constitute,they were further analyzed by FT-IR,XRD.Besides calcite,vaterite and aragonite occur in calcium carbonate scale after addition of inhibitors,and the higher scale inhibition efficiency is,the more vaterite presents in scale.It can be concluded that the alteration of morphology is ascribed to the change of crystal form. There are three stages in the crystallizing process including occurrence and disappearing of unstable phase,occurrence and disappearing of metastable phase,development of stable phase.Without scale inhibitors,metastable phases usually transform into stable phase,thus the main constitute of formed scale is calcite.When scale inhibitors are added,both formation and transformation of metastable phases are inhibited,which results in the occurrence of aragonite and vaterite.From the fact that more vaterite presents in scale with a more efficient scale inhibitor added,we can see that the function of scale inhibitor is realized mainly by controlling the crystallizing process at the second stage.

Effect of silk sericin on morphology and structure of calcium carbonate crystal

In this paper, silk sericin was employed to regulate the mineralization of calcium carbonate （CaC03）. CaCO3 composite particles were prepared by the precipita- tion reaction of sodium carbonate with calcium chloride solution in the presence of silk sericin. The as-prepared samples were collected at different reaction time to study the crystallization process of CaCO3 by scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FTIR）, thermogravimetric analysis （TGA） and X-ray diffraction （XRD）. The results showed that silk sericin significantly affected the morphology and crystallographic polymorph of CaCO3. With increasing the reaction time, the crystal phase of CaCO3 transferred from calcite dominated to vaterite dominated mixtures, while the morphology of CaCO3 changed from disk-like calcite crystal to spherical vaterite crystal. These studies showed the potential of silk sericin used as a template molecule to control the growth of inorganic crystal.

Formation Process and Thermodynamic Poperties of Calcite

The fast mixing of aqueous solutions of calcium chloride and sodium carbonate resulted in crystalline forms of vaterite and calcite under vigorous stirring. Then, the vaterite was transformed to pure calcite within about 180 rain. The crystalline forms all grew with experimental time increase. Scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FT-IR）, and X-ray diffraction spectroscopy （XRD） techniques were employed to characterize the as-prepared samples. The heat capacity of the stable as-synthesized calcite was determined by means of an adiabatic calorimeter from 80 to 390 K. The thermodynamic functions of the calcite were derived based on the relationships among the thermodynamic functions and the function of the measured heat capacity with respect to temperature.