Papers by Keyword: Vaterite

Abstract: Abstract. In this study, the CaCO₃ powder has been successfully synthesized by mixing CaCl₂ from natural limestone and Na₂CO₃ in the same molar ratio. The mixing process of solutions was carried out by employing the molar contents of 0.125, 0.25, 0.375 and 0.5M at varying temperatures of 30, 40, 60 and 80ᴼC. The produced CaCO3 microparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The highest content of aragonite phase with morphology rod-like of the samples is around 29 wt%, resulting from the process using solution of 0.125 M at 80 ᴼC. While at 30 ᴼC and 40 ᴼC produced 100 wt% calcite phase.

Abstract: Spherical calcium carbonate (CaCO₃) is a potential component in many industrial fields such as high-grade papermaking, high-grade painting, environment, and pesticide. This paper describes a novel approach to synthesize spherical calcium carbonate (CaCO₃) particles via passing CO₂ bubbles into phosphogypsum salt leaching solution (CaSO₄) in the presence of ammonia (NH₃) at different temperatures. The influence of the initial solution pH and concentration of calcium ions on the polymorph and morphology of CaCO₃ was studied. The physical characteristics of the precipitate were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that compared with different calcium sources the phase and morphology of CaCO₃ synthesized by phosphogysum leaching solution had some regularity. The grain size of spherical CaCO₃ became bigger, surface became smoother, and particle dispersion became better with the increase of calcium ion concentration. The content of vaterite increased and particle grain size changed a little with the increase of pH. The research results had important environmental significance for phosphogysum resource utilization and CO₂ fixation.

Abstract: Calcium carbonate (CaCO₃) has been known as one of the components of carbonate apatite (CO₃Ap) cement. Calcite is one of the polymorph of CaCO₃ with big particle size and excellent stability. In contrast, vaterite has small particle size and a metastable phase. To discover the effect of particle size on the properties of CO₃Ap cement, this study investigated the different particle size of vaterite; calcite from vaterite, which has almost similar particle size and shape with vaterite; grounded calcite and ungrounded calcite. The powder phase of calcite or vaterite combined with dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of Na₂HPO₄ solution in 0.45 liquid to powder ratio. The paste was packed into a split stainless steel mold, covered with glass slide and kept at 37°C and 100% relative humidity for a period of time. XRD and FT-IR analysis revealed that CO₃Ap cement consisted of vaterite and DCPA transformed to pure B-type CO₃Ap in 72 hours while CO₃Ap cement that consisted of calcite with different particle size was not completely transformed to CO₃Ap even until 240 hours. We concluded that CO₃Ap cement consisted of vaterite with small particle size and metastable phase properties is more effective as starting material due to its fast transformation to CO₃Ap.

Abstract: The aim of the present study is to fabricate bone cement that could transform to carbonate apatite (CO₃Ap) completely at body temperature. The powder phase of vaterite and dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of NaH₂PO₄, Na₂HPO₄, and Na₃PO₄ aqueous solution, respectively, with liquid to powder ratio (L/P ratio) of 0.45, 0.55, and 0.65. The paste was packed into split stainless steel mold, covered with the glass slide and kept at 37°C and 100% relative humidity for up to 96 hours (h). XRD analysis revealed that the cement became pure CO₃Ap within 24 h for Na₃PO₄, 72 h for Na₂HPO₄, and 96 h for NaH₂PO₄, respectively. FT-IR results showed that all of the obtained specimens could be assigned to B-type CO₃Ap. CHN analysis showed the carbonate content of the specimen were 10.4 ± 0.3% for NaH₂PO₄, 11.3 ± 0.7% for Na₂HPO₄, and 11.8 ± 0.4% for Na₃PO₄, respectively. Diametral tensile strength of the set CO₃Ap cement was 1.95 ± 0.42 MPa for NaH₂PO₄, 2.53 ± 0.53 MPa for Na₂HPO₄, and 3.45 ± 1.53 MPa for Na₃PO₄, respectively. The set CO₃Ap cement had low crystallinity similar to bone apatite since it was synthesized at body temperature. We concluded, therefore, that CO₃Ap cement prepared from the present method has higher possibility to be used as an ideal bone replacement.

Abstract: We report on the synthesis and characterization of porous monodisperse vaterite containers with controllable average sizes from 400 nm to 10 μm. Possible release strategies of enclosed substances via recrystallization or by pH-change are presented. As a model experiment, a fluorescent marker was encapsulated and imaged by two-photon microscopy to monitor the dye release. The release process was found to be controllable via the immersion medium’s properties. Release times can be further tuned by covering the containers with additional polymer layers, creating a flexible system with promising perspectives for pharmaceutical applications.

Abstract: Worm-like vaterite crystals were directly formed via an oriented attachment progress from nanocrystals in the presence of 50% volume ration of dimethyl sulfoxide (DMSO) at ambient temperature. The complex and unusual morphogenesis of the precipitated vaterite under ambient experimental conditions may imply that a simply synthesis routine which can be provided for certain materials with special morphologies.

Abstract: Carbon dioxide curing was adopted to accelerate the hydration of foam concrete samples with a lower bulk density level of around 450 kg/m³ and a higher level of around 1150 kg/m³. The bending strength, compressive strength and ultrasonic transmission velocity of carbonated harden foam concrete were tested, the hydration products were analyzed by means of XRD and TG/DSC. The results show as: (1) By comparing with standard curing samples, there are more than 47% increments of specific strengths of carbonated foam concrete with the higher density level at a certain curing time before 14d. However, for the lower density level one, there is just a significant improvement of specific bending strength obtained before 7d. (2) The carbonated foam concretes with the lower density level show lower ultrasonic transmission velocity than standard curing ones. The velocities have hardly difference for both carbonated and standard curing samples with the higher density level. (3) Vaterite can’t be found in carbonated foam concrete with the lower density level at curing time before 28d, while it becomes a common phase in 3d’s carbonated sample with the higher density level. Vaterite was considered to be an important factor that influences the ultrasonic transmission velocity.

Abstract: Carbonation curing was adopted to accelerate the hydration of foam concrete with lower density of around 450 kg/m³. After standard curing in mold for 2d, the foam concrete samples were marked into two groups. The first one is directly cured in ‘Carbonation Test Chamber for Concrete’ with CO₂ concentration 20%, RH 70% and temperature 20°C (it was called ‘carbonation curing’) for 3d to 56d. The second one is cured in ‘Standard Curing Room for Concrete’ with RH ≥95% and temperature 20°C (it was called ‘standard curing’) for 7d, and then at carbonation curing for 3d, 7d and 21d. The strengths of harden foam concrete were tested, the hydration products were analyzed by means of XRD and TG/DSC. The results were compared with those of standard curing samples. It indicates that foam concrete with lower density is easier to be carbonated; the hydration of both C₃S and C₂S accelerates by carbonation curing, which results in higher early strength improvement. Vaterite is popular in the second group of samples, while it only appears in the first group of sample with longer carbonation time of 56d. Vaterite was considered to be formed from the further carbonation of C_xSH_y.

Abstract: Various crystal forms of calcium carbonate were successfully synthesized with CaCl2 and Na2CO3 in 10%(V/V) egg white protein solution system at 20 °C, 40 °C and 60 °C, respectively. The obtained calcium carbonate were characterized by SEM, XRD, FTIR and TG. In addition, the possible mechanism of crystal formation were analyzed. The results indicated that egg white protein could regulate the crystal forms of calcium carbonate and the calcium carbonate, which contained a small amount of egg white protein and consisted of mixed calcite and aragonite, was mainly spherical. With the temperature rosing, the vaterite content gradually increased while the calcite decreased.

Abstract: Microfiber meshes releasing a trace amount of silicon species were prepared by electrospinning silicon-doped vaterite (SiV) and poly(lactic acid) (PLA) hybrids for application to membranes for guided bone regeneration (GBR). A trace amount of silicon-species has been reported to enhance the mineralization and bone-forming abilities of osteogenic cells. The microfiber meshes prepared by electrospinning are regarded to be a useful candidate for the GBR membrane, because they have adequate flexibility and porosity for it. In this study, hydroxyapatite (HA)-forming abilities in simulated body fluid, silicon-releasabilities, compatibility with osteoblast-like cells of the prepared microfiber meshes were examined. The meshes were completely coated with HA after soaking in simulated body fluid for 1 day. The meshes coated with HA released 0.2 -0.7 mg/L of silicon species in a cell culture medium for 7 days. The cells elongated on the microfibers of the meshes and some of them entered the mesh after 1 day-culturing. The meshes are expected to provide an excellent substrate for bone regeneration and enhance bone-forming ability of the cells.