Papers by Keyword: Fluorapatite

Abstract: The kinetic study for the synthesis of Fluorapatite has been done using the thermogravimetric technique under non-isothermal conditions and at four heating rates of 5, 10, 15 and 20 °C. Both model free and model-fitting methods were used to investigate kinetic parameters. Calcium oxide, phosphorus pentoxide and calcium fluoride were used as the precursor materials. The activation energy values were calculated through model-fitting and isoconversional methods and were used to predict the reaction model and pre-exponential factor. In this case several techniques were considered such as master plots and compensation effects. The results indicated that the reaction mechanism was chemically controlled with second and third order reaction models in the whole range of conversion which the activation energy varied from 25 to 43 kJ/mol.

Abstract: The effect of Bioactive Glass on remineralization of dentin is the focus of the present study due to its excellent regenerative properties in mineralized tissues. It is known that the effect of Bioactive Glass can be enhanced at the nanoscale. In addition, the incorporation of Fluorine in the glass structure makes possible the formation of Fluorapatite (FAP). The aim of this study was to synthesize and characterize a new system of Fluorine containing Bioactive Glass Nanoparticles (FBGNP), and evaluate the potential for in vitro dentin remineralization by occlusion of dentinal tubules. The FBGNPs produced were uniform, with spherical shape and nanoscale size. Agglomeration or partial sinterization of the particulate system probably occurred after heat treatment. The results suggest the formation of FAP crystals embedded within the matrix of the Bioactive Glass. The gel containing FBGNP produced was effective in obliterating the dentinal tubules in vitro, showing that FBGNP is a potential material to be used for treatment of dentin hypersensitivity.

Abstract: The use of biohydrometallurgical processes may be restricted by microbial inhibition due to inhibiting fluoride originating from the feed material. In this work, phosphorus bioleaching experiments on fluorapatite ore were conducted in a reactor using Fe-and S-oxidizing bacteria, resulting in 56 % leaching yield for P, despite abundant (800 mg l^-1) F in the pregnant leach solution. In further F toxicity experiments it was observed that aluminum had a significant role in decreasing the inhibition caused by F, by producing stable complexes with Al. The bioleached ore contained plenty of Al, explaining why bioleaching was not strongly inhibited.

Abstract: SiO₂, Al₂O₃, MgO, MgF₂, SrCO₃, CaCO₃, CaF₂ and P₂O₅ were used to prepare machinable glass-ceramic with 4 mol% of fluorapatite for restorative dental applications. XRD showed that the glass heat treated at 792°C (the first crystallization temperature+20°C) for 6 hours consisted of calcium-mica, fluorapatite, strontium apatite, anorthite, forsterite, fluorite and stishovite crystalline phases. The microstructures of the resultant glass-ceramic, observed by SEM, were found to exhibit plate-like mica crystals and many tabular particles embedded in the mica phases. The particles, determined by EDS, were rich in calcium. The three-point bending strength (158 MPa) closely matched that of nature tooth. Average Vickers hardness of the received glass-ceramic (2.6 GPa) was lower than that of natural tooth.

Abstract: The glass system of SiO₂-Al₂O₃-MgO-MgF₂-SrCO₃-CaCO₃-CaF₂-P₂O₅ was used to prepare machinable glass-ceramics for restorative dental applications. The aim of this study was to apply various heat treatments to produce mica-based glass-ceramics. Differential Thermal Analysis (DTA) was used to determine the optimal heat treatment conditions for nucleation and growth of the crystalline phases in the quenched glass. It was found that the optimum nucleation temperatures for the first and the second crystallization temperatures (T_p1 and T_p2) were 642°C and 635°C, respectively, and the optimum nucleation times were between 2 and 4 hours. X-Ray Diffraction (XRD) showed the phases developed were anorthite, calcium-mica, fluorapatite, strontium apatite, forsterite, fluorite and stishovite phases. The microstructures of glass-ceramics were observed by Scanning electron microscope (SEM), found to exhibit plate-like mica crystals with high interlocking and randomly oriented with a higher soaking temperature and prolongation of the soaking time for crystallization.

Abstract: This paper studied the Na₂O-B₂O₃-SiO₂-CaO-P₂O₅-F glass-ceramics and obtained the complex biological glass-ceramics with low sintering temperature, high mechanical properties and good biological activity. In this paper, the better basic point was selected in phase region of Na₂O-B₂O₃-SiO₂ glass system. It was studied that the effect of different percent of CaO, P₂O₅ and F addition on the mechanical properties and biological activity of the glass-ceramics. The glass powder was prepared by melting and quenching in water, and then by molding and sintering, composite glass-ceramics materials was obtained. With the help of DSC, XRD and SEM analysis methods and testing means, the phases and heat treatment systems of the material were determined, and the microstructure of materials in the different heat treatment conditions was observed. The biological activity was tested in SBF simulated body fluid . Research shows that: the introduction of F can effectively reduce the melting temperature of the material and is helpful to crystallization. The introduction amount of CaO, P₂O₅ and F can affect the biological activity of glass-ceramics. In the range of introducing CaO, P₂O₅ and F in this paper, the mechanical properties and biological activity of glass-ceramics increase with the amount of the introduction of CaO, P₂O₅ and F.

Abstract: Solubility studies of apatite in water and acidic media have been focused on the solubility products. Aim at highlighting on current developments, the solubility products of calcium arsenate-phosphate hydroxyapatite/fluorapatite [Ca₅(P_xAs_1-xO₄)₃(OH)/Ca₅(P_xAs_1-xO₄)₃ F, 1≥x≥0] in literature is sorted out. Literature values of the solubility products vary greatly. These discrepant solubility products can be due to differences between the minerals, the way the experiments in the studies have been conducted, the failure to achieve equilibrium.

Abstract: The purpose of this work was to investigated the carbothermic reaction of fluorapatite process by the means of thermodynamics analyses, XRD and element analysis, respectively. Thermodynamic calculations indicated that phosphorus can be prepared by heating the mixture of Ca₅(PO₄)₃F₂ and C at 1173K under the system pressure of 100Pa. CO cannot react with Ca₅(PO₄)₃F₂ in the carbothermic reduction process at 973-1873K and 100Pa. Experimental results demonstrated that phosphorus can be produced by the reaction between Ca₅(PO₄)₃F₂ and C, the main reaction phase is P₂(g), CO(g), CaO and CaF₂, and with increasing temperature, the greater degree of response. The best technology conditions, the molar ratio of Ca₅(PO₄)₃F₂ to C is 1:7.5 at 1723K for 1h when the system pressure was about 100Pa. This study to provide experimental evidence for preparation of phosphorus by carbothermal reaction of fluorapatite in vacuum.

Abstract: In the present study, a simple method of regenerating microstructure of human tooth under near-physiological conditions (pH 7.0, 37 °C, 1 atm) was developed. Commercial gelatin was used as matrix materials in this method, which nucleated the formation of fluorapatite (FA) nanocrystals and regulated the growth of nanocrystals. As a result, the resulting thin FA coatings had been prepared on human tooth slices and sintered hydroxyapatite disks, which were in tight contact with the substrates. Besides, the morphologies of FA nanocrystals changed from acicular to hexagonal with the exchange cycle of gel increased. Electron dispersive spectrometer analysis indicated that some sodium and carbonate ions were incorporated into the FA crystal lattices and the calcium to phosphorus ratio was approximate 1.58. The mechanical properties of the resulting FA coating were investigated through nanoindentation system, which showed the similar hardness with dentin. In conclusion, this method demonstrated a potential application to repair tooth damage in dental clinics.

Abstract: Hydroxyapatite (HA) is a frequently used bioactive coating material. However, when HA coating is soaked in the simulated body fluid (SBF), it is usually detached from substrate material due to its high dissolution rate in the solution. Recently, it is found that Fluorapatite (FA) has a better anti-dissolution ability than HA. In this study, Fluorapatite was mixed with TiO₂ powder (either Anatase phase (A) or Rutile phase (R)) as a coating material precursor, and then be deposited on Ti-6Al-4V substrate to form the coating layer by using Nd-YAG laser cladding process. After soaking in SBF for various days, it is observed that dense ball-like apatite grew faster on the surface of the FA+R coating layer than that on the surface of the FA+A specimens. The corresponding Ca/P ratios of FA+R specimens also dropped faster than FA+A ones.