Sol-gel Preparation and Preliminary in vitro Evaluation of Fluorapatite/Hydroxyapatite Solid Solution Films

Fluorapatite/hydroxyapatite solid solution has better biological properties than other apatites, especially used as films or coatings. In this work, sol-gel preparation and in vitro behavior of fluorapatite/hydroxyapatite solid solution films on titanium alloy were investigated. Ca(NO3)2·4H2O and PO(OH)K(OEt)3-x. were selected as precursors, and hexafluorophosphoric acid (HPF6) was used as a fluorine containing reagent. The Ca and P precursors were mixed with HPF6 to keep the Ca/P molar ratio 1.67. The mixtures refluxed for 12 h were used as dipping sols for the preparation of the films. The phase of the films obtained at 600℃ was apatite. The F contents in the films increased with the concentrations of HPF6 in the dipping sols. The solid solution films were shown to have better stability than hydroxyapatite films, and a reasonably good bioactivity in the in vitro evaluation.

Utilization of DTAB as a collector for the reverse flotation separation of quartz from fluorapatite

Reverse flotation desilication is an indispensable step for obtaining high-grade fluorapatite. In this work, dodecyltrimethylammoni- um bromide (DTAB) is recommended as an efficient collector for the reverse flotation separation of quartz from fluorapatite. Its collectivity for quartz and selectivity for fluorapatite were also compared with figures corresponding to the conventional collector dodecylamine hydrochlor- ide (DAC) via microflotation experiments. The adsorption behaviors of DTAB and DAC on minerals were systematically investigated with surface chemical analyses, such as contact angle determination, zeta potential detection, and adsorption density measurement. The results re- vealed that compared to DAC, DTAB displayed a similar and strong collectivity for quartz, and it showed a better selectivity (or worse col- lectivity) for fluorapatite, resulting in a high-efficiency separation of the two minerals. The surface chemical analysis results showed that the adsorption ability of DTAB on the quartz surface was as strong as that of DAC, whereas the adsorption amount of DTAB on the fluorapatite surface was much lower than that of DAC, which is associated with the flotation performance. During the floatation separation of the actual ore, 8wt% fluorapatite with a higher grade can be obtained using DTAB in contrast to DAC. Therefore, DTAB is a promising collector for the high-efficiency purification and sustainable utilization of valuable fluorapatite recourses.

Elaboration and characterization of alumina - fluorapatite composites

Alumina and fluorapatite powder were mixed in a wet medium in order to elaborate biphasic ceramics composites. The effect of fluorapatite addition (26.5 wt%) in the densification and the mechanical properties of the alumina matrix were measured. The phase developments have been systematically analysed by scanning electronic microscopy, X-ray diffraction, Infrared spectroscopy and 31P and 27Al magic angle scanning nuclear magnetic resonance. The Brazilian test was used to measure the mechanical resistance of alumina - 26.5 wt% fluorapatite composites. The densification and strength rupture of composites increase versus sintering temperature and holding time. At 1600°C, the composites densities reached 85% and the rupture strength was about 22 MPa. Also, the composites sintering at 1500°C for 5 hours provides samples with similar density and having higher mechanical resistance, above 26 MPa. For longer holding times, the mechanical properties were hindered by the exaggerated grain growth and the formation of intragranular porosity. From 1400°C, the characterization of the alumina - 26.5 wt% fluorapatite composites indicates the formation of calcium aluminates.

Synthesis of Co-Cr-Mo Fluorapatite Nano-Composite Coatings by Pulsed Laser Deposition for Dental Applications

Aim: The study was to fabricate FA nanopowder/Co-Cr-Mo dental alloy nanocomposite using pulsed laser deposition (PLD), and to evaluate bioactivity properties on simulated body fluid. Methods: In this work, the FA nanopowder was prepared by mixing calcium hydroxide (Ca(OH)2), phosphorouspent oxide (P2O5) and calcium fluoride (CaF2) in a planetary high energy ball mill using zirconium vial. Fluorapatite (FA) nanopowder was processed in the form of pellet for pulsed laser deposition process. The Co-Cr-Mo alloy was coated with FA nanopowder which was approximately 35 - 65 nm at various laser energy, pressure and time. The X-ray diffraction (XRD) was used to analyze phase, crystallinity and size distribution of Co-Cr-Mo/FA nanocomposite. The surface analysis was by scanning electron microscopy (SEM), Atomic Force microscopy (AFM) and Energy dispersive spectroscopy (EDS). Results: From the results obtained, It was shown that FA nanopowder deposited on Co-Cr-Mo alloy was stable during 14 days of incubation on simulated body fluid. It was also observed that the FA nanopowder coated on the surface of the alloy was still intact after the deposition process, which indicated the bioactivity and biocompatibility of the material. Conclusions: The fabrication of FA nanocomposite based dental alloys (Co-Cr-Mo) using PLD was done successfully. This was confirmed by various characterization techniques, which included XRD, AFM, SEM and EDS.

Densification and Microstructure of Fluorapatite Sintered with Alkaline and Alkaline-Earth Additives

A study was performed to investigate the effect of some selected sintering additives on the densification and microstructure of fluorapatite (FAp, Ca10(PO4)6F2). The sintering aids, used for improving the material densification at lower than 1080℃ temperature, were classified according to their cations as alkaline such as Li2CO3, NaF, Na2CO3, Na3PO4, KCl, K2CO3, and alkaline-earth such as CaF2, CaCl2 and MgCl2. Amounts of 0.1;1 and 3 wt% were vigorously homogenized with FAp powders then the solid mixture was pressurelessly sintered under argon flow with 10℃ .?min-1 heating and cooling speed. The density of each sintered material was determined by calculation of the pellet dimension and weight, the crystalline phases were identified using X-ray diffraction (XRD) and the phase morphology was examined by scanning electron microscopy (SEM). The dependence of densification and microstructure on sintering temperature range 900℃ - 1000℃ and amount of sintering aids was studied. It was found that all sintering additives were able to ameliorate the sintrability of the material at temperatures 900℃ and 1000℃. Maximums of about 96% were reached with adequate amounts and sintering temperatures. An exception was found with KCl which had no effect on the density. The microstructures of sintered specimens strictly follow the densification ratios and the sintering mechanism depended on the melting point of the additive.

Facile Synthesis of Nitriles and Amides from Aldehyde over Heterogeneous Reusable Copper Fluorapatite (CuFAP) Catalyst under Neat Reaction Condition

A new robust heterogeneous, versatile, an environmentally benign, eco-friendly, recyclable CuFAP catalyst has been developed for the direct synthesis of nitriles and amides from aldehydes at 100°C for 6 h and 4 h, respectively, under neat reaction condition using hydroxylamine hydrochloride in the presence and the absence of tosyl chloride, respectively. Also the recyclability of catalyst as well as influence of solvents, additives on catalysts performance was investigated. The protocol can be considered as an alternative to conventional method for the synthesis of nitriles and amides in good to excellent yields. A highlight of our protocol is the easy separation of catalyst from reaction mixture, hence the catalyst is reused several times without significant loss of its catalytic activity.

Sodium-Modified Fluorapatite: A Mild and Efficient Reusable Catalyst for the Synthesis of <i>α,α</i>’-Bis(Substituted Benzylidene) Cycloalkanones under Conventional Heating and Microwave Irradiation

A versatile and environmentally friendly method for α,α’-bis(substituted ben-zylidene) cycloalkanones has been developed using a heterogeneous catalysis technology. We have synthesized a series of the α,α’-bis(substituted benzylidene) cycloalkanones, a biologically important class of compounds, via the cross aldol condensation between arylaldehydes and cycloketones using sodium-modified fluorapatite (Na/FAP) as a highly efficient solid catalyst under conventional heating in aqueous media and solventless conditions under microwave. Catalyst reuse, ease of separation of the pure product, and high yields are some of the unique features of this process. Shorter reaction times (4 - 7 min) and higher yields (80% - 94%) were achieved under microwave irradiation conditions.

Evaluation the Properties of Polycaprolactone/Fluorapatite Nano-biocomposite

In this study,nano-biocomposites of polycaprolactone(PCL)as the matrix and different amounts of nanofluorapatite(nFA)(0,10,20 and 30 wt.%)as the reinforcement were prepared for possible scaffold fabrication using the fused filament fabrication(FFF)3D printer.Field Emission Scanning Electron Microscopy(FE-SEM)and Energy Dispersive Spectroscopy(EDS)showed that nFA particles were well distributed in the PCL matrix.X-ray diffraction analysis(XRD)and Fourier Transform Infrared Spectroscopy(FTIR)depicted no chemical interaction between the elements of the composite.Differential Scanning Calorimetric(DSC)analysis was then used to assess the thermal properties of the composites,suggesting that this could be due to the amorphous phase formation of the intermolecular hydrogen bonds between PCL and nFA,resulting in the suppression of PCL crystallization.The results of mechanical characterization also showed that the addition of nFA up to 20 wt.%to the PCL increased the tensile and yield strength,as well as reducing the elongation at both yield and failure points and increasing the Young modulus.The best mechanical properties were obtained for the PCL/20nFA composite.Tensile strength and Young modulus were increased by 30%and 179%,respectively;meanwhile,elongation of PCL/20nFA was decreased by 70%,as compared to the naked PCL.These changes could be attributed to the better distribution of the nFA filler in the PCL matrix.According to the obtained results,PCL/20nFA could be regarded as a good composite in terms of the mechanical properties for the regeneration of the bone tissue.

Characterization of single-crystal fluorapatite nanoparticles synthesized via mechanochemical method

The synthesis of nanostructured fiuorapatite （FA; Calo（PO4）6F2） was explored from the starting materials of CaHPO4, Ca（OH）2, CaO, P205 and CaF2 via a mechanochemical process. In this research, the suitability of using the mechanochemical process to prepare a high crystalline phase of FA was studied. The characterization and structural features of the synthesized powders were evaluated using powder X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FT-IR）, energy dispersive X-ray spectroscopy （EDX）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM） techniques. The results from the structural studies indicate that the maximum lattice disturbance in the apatite structure after the mechanochemical process was at the （0 0 2） plane. Furthermore, the maximum particle size was below the crystallite size after 60 h of milling and subsequent thermal treatment at 600 ℃ for 1 h （heated up to 600 ℃ and kept for 1 h at this temperature）. We determined that this method gives rise to the single-crystal FA with an average size in the range of 25 ± 5 to 29 ± 9 rim. The present findings suggest that the solid-state reaction and appropriate thermal process simultaneously lead to the formation of nanostructured FA with spheroidal shape.

Effect of Titania Additive on Structural and Mechanical Properties of Alumina–Fluorapatite Composites

Mechanical properties of alumina-fluorapatite composites with different titania additive amounts （0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%） have been investigated between 1200 and 1600℃. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500℃ for 1 h. Thus, the rupture strength of alumina-26.52 wt% Fap-1.4 wt% TiO2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO2 ,the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction （XRD） analysis of alumina-Fap-TiO2 composites shows the formation of aluminium titanate （Al2O3-TiO2：Al2TiO5 ）. The 27Al magic angle scanning nuclear magnetic resonance analysis of Al2O3-Fap-TiO2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.

Fabrication of Titanium/Fluorapatite Composites and In Vitro Behavior in Simulated Body Fluid

Titanium/fluorapatite （Ti/FA） composites with various FA additions were fabricated by powder metallurgy. The decomposition of FA during sintering was accelerated by the presence of Ti. The main reaction products of FA and Ti were identified as CaO, Ti phosphides, and CaTiO3. The addition of FA significantly inhibited the densification of Ti. The in vitro bioactivity of the composites was evaluated in a simulated body fluid （SBF）. After immersion into the SBF, all the Ti/FA composites induced nucleation and growth of bone-like carbonated apatite on the surface. Co-precipitation of CaCO3 and Mg（OH）2 was also detected on the surface of the composite with high FA addition at an early stage of immersion. Furthermore, the release of fluorine ions from the composite was confirmed, which could promote bone regeneration and retard the formation of caries in the biological environment. The in vitro behavior was attributed to multiple factors, including the surface conditions and the constituents of the composite. The results demonstrated that the Ti/FA composites were bioactive in nature even with a low FA addition and they could introduce the benefit of fluorine ions in the service.

Thermal treatment effect on structural features of mechano-synthesized fluorapatite-titania nanocomposite: A comparative study

The influence of thermal treatment on the structural features of mechano-synthesized fluorapatite-titania composite nanopowders was studied.A mixture of calcium and phosphate reagents was mixed with a certain amount of titania(20 wt%)and then was mechanically activated for 5 h,10 h and 15 h respectively.After that,the mechano-synthesized powders were annealed at 700℃for 2 h.The crystallite size of the composite nanopowders estimated from Williamson-Hall method was in good agreement with transmission electron microscopy(TEM)analysis.Scanning electron microscopy(SEM)/TEM images confirmed the formation of a cluster-like composite which was composed of ellipse-like nanoparticles with an average size of about 16±7 nm after 15 h of milling.During the milling process,large variations in mechanochemical behavior of the CaHPO_(4)-Ca(OH)_(2)-CaF2-TiO_(2) system were detected.After the beginning of milling,no trace of the composite was found due to the lack of sufficient time for the mechanical activation.When the mechanical activation time increased to 15 h,composite nanopowders with the crystallite size of around 21.66 nm were formed.During heating at 700℃,the recovery of crystallinity occurred and the fraction of crystalline phase reached a maximum around 88.79%for the 10-h milled sample.Results indicated that the structural features of the composite were strongly influenced by the subsequent annealing.

Mineral Chemistry of REE-Rich Apatite and Sulfur-Rich Monazite from the Mushgai Khudag, Alkaline Volcanic-Plutonic Complex, South Mongolia

The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magmatic rocks which consist of porphyritic syenite, microsyenite and quartz syenites. Three types of LREE-rich apatite can be found in the carbonatite, apatite, and monazite zones. Crystal-1 type of apatite exists as hexagonal prismatic shape and is mostly found in the apatite zone, and in syenite. Crystal-2 type of apatite can be exposed also at the apatite zone, and carbonatite zone as brecciated massive crystalline aggregate. Crystal-3 type of apatite demonstrates the compositional zoning texture with monazite as inter-zoning, and is only found in monazite zone. The LREE-bearing apatites from the Mushgai khudag complex are mostly fluorapatite to hydroxyl-bearing fluorapatite with variable REE content. Apatites from the monazite zone present individual sulfur-rich monazite grain, and are formed by comprehensive substitutions.

Mineral Chemistry of REE-Rich Apatite and Sulfur-Rich Monazite from the Mushgai Khudag, Alkaline Volcanic-Plutonic Complex, South Mongolia

The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magmatic rocks which consist of porphyritic syenite, microsyenite and quartz syenites. Three types of LREE-rich apatite can be found in the carbonatite, apatite, and monazite zones. Crystal-1 type of apatite exists as hexagonal prismatic shape and is mostly found in the apatite zone, and in syenite. Crystal-2 type of apatite can be exposed also at the apatite zone, and carbonatite zone as brecciated massive crystalline aggregate. Crystal-3 type of apatite demonstrates the compositional zoning texture with monazite as inter-zoning, and is only found in monazite zone. The LREE-bearing apatites from the Mushgai khudag complex are mostly fluorapatite to hydroxyl-bearing fluorapatite with variable REE content. Apatites from the monazite zone present individual sulfur-rich monazite grain, and are formed by comprehensive substitutions.

Acknowledgments to reviewers of World Journal of Methodology

Many reviewers have contributed their expertise and time to the peer review,a critical process to ensure the quality of World Journal of Methodology.The editors and authors of the articles submitted to the journal are grateful to the following reviewers for evaluating the articles(including those published in this issue and those rejected for this issue)during the last editing time period.

Phosphorus migration mechanism between iron and high phosphorus gangue phase at high temperatures

The phosphorus migration mechanism during melting separation of non-carbon-reduced high phosphorus iron ore was investigated.Firstly,the equilibrium compositions of hydrogen-reduced high phosphorus iron ore at different temperatures were simulated by the use of equilibrium composition module of HSC Chemistry software.Then,thermodynamic calculation was verified by the real heat treatment of simulated hydrogen-reduced high phosphorus iron ore with several pure reagents including self-made pure fluorapatite.The iron particles in the simulated samples gathered and grew up during heat treatment.Meanwhile,the hypoeutectic structure of Fe-P with grid shape of high phosphorus phase and circular shape of low phosphorus phase emerged within those iron particles.With the penetration of phosphorus from the periphery into the iron particles,the grid structure became denser and denser.It proves that the elemenlal phosphorus can be reduced from the gangue phase by metallic iron without solid carbon at high temperatures.