Papers by Keyword: Dissolution-Precipitation

Abstract: The aim of this study is to investigate the effect of soaking time on the compositional and morphological changes of dicalcium phosphate dihydrate (DCPD)-coated β-tricalcium phosphate (β-TCP) bioceramic. In this study, an established method from our research group was used to prepare the β-TCP bioceramic pellets and expose them to acidic calcium phosphate solution for 2, 4, 6, and 8 hours to obtain DCPD coated layer on β-TCP pellets through dissolution-precipitation reaction. Characterization methods such as x-ray diffraction analysis (XRD) and scanning electron microscope (SEM) were carried out on the specimen. XRD and SEM analyses indicated that the peak intensity and density of DCPD crystal precipitated on the pellets were increased when increasing the soaking time. Therefore, it was confirmed that the DCPD coated layer formation on the β-TCP pellet surfaces depended on the exposure time to acidic calcium phosphate solution.

Abstract: Introduction: Carbonate apatite type B (C-Ap) has been used as a bone replacement material because of its osteoconductive properties. Clinically, the pores formed in bone replacement material aid in cell mobility and nutrient supply, thereby increasing the bone regeneration ability. CO₃^2- ions found in this material are useful for maintaining a stable physiological environment in the bone in order for it to be easily absorbed by osteoclasts. Porous C-Ap type B is formed using the dissolution–precipitation method by immersing porous anhydrous CaSO₄ in a mixture of carbonate and phosphate solutions. Purpose: The present study aimed to evaluate the effect of immersion ofCaSO₄using the dissolution–precipitation method on the formation of porous C-Ap type B with calcium sulfate precursor hemihydrate. Method: Porous C-Ap type B was produced usinga mixture of calcium sulfate hemihydrate precursors with 50 wt% polymethylmethacrylate (PMMA) porogen and distilled water. After hardening, the calcium sulfate dihydrate containing PMMA was burned in an oven at 700°C for 4 h to remove the PMMA. The specimen was immersed in a mixture of sodium phosphate (Na₃PO₄) and sodium carbonate (Na₂CO₃) for 6, 12, and 24 h. Phase testing through X-ray diffraction (XRD) using CuKα radiation at 40 kV and 40 mA was performed. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR, Thermo Fisher Scientific, Waltham, Massachusetts, USA) was used for detecting the functional groups of CO₃^2- and PO₄^2-. Results: XRD results showed the formation of C-Ap at 6 and 12 h, but the anhydrous CaSO₄ phase remained; alternatively, this phase was absent after 24 h of immersion phase andFTIR showed the presence of the functional groups of CO₃^2- compounds. Conclusion: Porous C-Ap type B can be formed from CaSO₄ precursors after 24 h of immersion using the dissolution–precipitation method.

Abstract: Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) can be obtained from calcium carbonates through dissolution-precipitation reaction in a phosphate solution under a hydrothermal condition, with keeping its external shape. In this study, we assumed preparation of hydroxyapatite honeycombs from a calcite (CaCO₃) honeycomb. Calcite honeycomb was hydrothermally treated in a phosphate solution. After hydrothermal processing for 24 h, calcite transformed partially to hydroxyapatite phase and its external shape was kept. Moreover, specific surface areas of the specimens were increased after the hydrothermal processing. Consequently, this processing is useful to prepare honeycomb structure of hydroxyapatite from calcium carbonates.

Abstract: Hydride precipitation due to the spontaneous and fast hydrogen diffusion is often pointed as causing embrittlement and rupture in zirconium alloys used in the nuclear industry. Transmission Electron Microscopy (TEM) and X-Rays Diffraction (XRD) have been used to study the precipitation of hydride phases in zirconium alloys as a function of the hydrogen content. The orientation relationships observed between the hydride phase and the substrate were similar to those previously observed in Titanium hydrides grown on Titanium. Dislocation emission from the hydride precipitates has been directly related to the relaxation of the misfit stresses appearing during the transformation. The stability of the hydride phases after several dissolution-reprecipitation cycles have been studied by DSC, TEM and XRD for different total hydrogen content in several alloys. The energy of precipitation observed is lower than that of the dissolution in each case studied. The temperature associated with these two processes slightly increase as a function of the cycle number, as a result of the homogenizing hydrogen distribution in the alloy bulk. The same hydrides phases present before cycling were also observed after 20 cycles. However, transition phases poorer in hydrogen than the dominant one may precipitate at the interface with the substrate. The evolution of these transitions phases with the temperature increase will be investigated by TEM in-situ heating in the next future.

Abstract: Microcracks and trabecular fractures can be observed in physiological bone. Biomimetic hydroxyapatite (HAp) scaffolds have been strongly needed in bone regenerative medicine. We have been developing the combination method of the partial dissolution-precipitation techniques involving the stirring-supersonic treatment in 1.7×10^-2 N HNO₃ solution containing Ca^2＋and PO₄^3- ions to improve the surface and the bulk of commercially available synthetic HAp block (82.5% in porosity, 50-300µm in macropore). The modified HAp was named as a partially dissolved and precipitated HAp (PDP-HAp). The aims of this study are to characterize the PDP-HAp and to observe cell response for the ceramics in rat scalp tissue. The PDP-HAp exhibited the macropore sizes of 50-200µm, the porosities of 85-90%, and the specific surface areas of 1.0-2.0 m²･g^-1, with many micro-cracks. Twenty rats were divided into 2 groups. At 9 months, bone induction occurred inside the many pores in the PDP-HAp group, while bone and cartilage were not found in the HAp group. We believe that osteoinduction by the PDP-HAp is different from the process of BMP-loaded HAp-induced bone formation. The PDP-HAp might be applied as potential ceramics with osteoinductive properity and excellent biocompatibility in difficult bone regenerative cases.

Abstract: Inorganic component of bone is not hydroxyapatite but carbonate apatite. Although pure carbonate apatite (CO₃Ap) has not been prepared due to the limited thermal stability of CO₃Ap, dissolution - precipitation method using precursor block allows fabrication of pure CO₃Ap. Fabrication of CO₃Ap, cell response, tissue response and improvement of CO₃Ap will be discussed.

Abstract: On the basis of hydrogeology investigation, the groundwater, river water, seawater and the medium in the lower reaches of the Dagu River were collected respectively, their compositions and nature were determined, then the permeability and the regularity of the main ions were determined during simulating seawater intrusion with transfusion installment. Finally, hydro-geochemical action was studied with the numerical simulation method during seawater intrusion. The result indicts that the mineral dissolution and precipitation take place with ion exchanges, Calcite is in a supersaturated situation after the percent of seawater reaches 40％; the saturation index of Gypsum arises gradually at first, and then decreases after the peak, finally it increases again but it is always in unsaturated condition from beginning to the end.

Abstract: Carbonate apatite (CO₃Ap) is expected to be an ideal bone substitute since it can harmonize with the bone remodeling cycle. The aim of this study is to fabricate a CO₃Ap bone substitute from gypsum (calcium sulfate, CaSO₄·2H₂O) hardening bodies based on dissolution-precipitation reaction. Calcium sulfate hemihydrate mixed with water at a water-to-powder ratio of 0.5 was packed in a split stainless mold and kept at room temperature for 24 hours to obtain set CaSO₄·2H₂O. The set CaSO₄·2H₂O was hydrothermally treated in the presence of disodium hydrogen phosphate (Na₂HPO₄) and sodium hydrogen carbonate (NaHCO₃). The results of powder X-ray diffraction and Fourier transform infrared spectroscopy indicated that CO₃Ap block could be fabricated from the set CaSO₄·2H₂O block by hydrothermal treatment with Na₂HPO₄ and NaHCO₃. When the treatment temperature was increased, the conversion rate to CO₃Ap increased. However, the carbonate content decreased with increasing treatment temperature.

Abstract: Bio-absorbable and biomimetic composites (HA-C) of hydroxyapatite (HAp) and collagen were designed utilizing salmon bone and skin at 298K and pH 7.5-7.9 by a dissolution-precipitation method. The HA-C powders were consistuted by Ca²⁺-deficient HAp containing small amounts of Na⁺ and Mg²⁺ ions and I type-collagen. Microstructure and surface characteristics of the HA-C powders gradually changed depending on the composition ratio of HAp to collagen (H/C). The HA-C powder of H/C=3.5 had frock like-agglomerated particles consisted of nano-crystals, micro-pore, and meso-pore so that it exhibited high specific surface area (75m²¥g^-1) and large total pore volume (0.543 cm³¥g^-1). From adsorption isotherms of water vapor at 298K for the HA-C powders, hysteresis - curves of the amounts of water vapor adsorbed were obtained in the adsorption-desorption processes. The amounts of water vapor adsorbed for the H/C=3.5 powder were the highest values under the relative partial pressures of 0.73-0.93. At 2 weeks after implantation of the HA-C powders into the subcutaneous tissue of the back region in rats, collagen was completely bio-absorbed and body fluid permeated into large agglomerated particles, although bio-absorption by multi-giant cell- infiltration was recognized around the surface layers of HAp particles.

Abstract: TiSi2 (Titanium disilicide) has attracted great research interest due to its large silicon content, remarkably low electrical resistivity (about13–16μΩcm), good photocatalytic property, high temperature stability, and good corrosion resistance. It is an excellent electronic material and potential photocatalyst and high temperature structure material. In this work, TiSi2 was prepared by using the “chemical oven” enhanced self-propagating combustion method from the elemental powder compact. The mixture of Si and Ti (atomic ratio 3:5) were ignited as chemical oven. The composition of product was detected by XRD. Result shows the product is a single phase titanium disilicide with trace impurities. The maximum combustion temperature of Ti+2Si compact was up to 1472°C, which exceeds the lowest eutectic point (1330°C) of the Ti-Si binary mixture. Thus it can be predicted the formation of TiSi2 is primarily dominated by the solid-liquid mechanism, which includes dissolving solid reactants and precipitating silicide product. It could also be convinced by SEM photos of the combustion product and reacting zone of the compact.