Luminescence of the Sb3+ ion in calcium fluorapatite and other phosphates

Luminescence spectra and decay times of Sb³⁺ in AlPO₄, LaPO₄, LiLaP₄O₁₂ and calcium fluorapatite (Ca₁₀(PO₄)₆F₂) are reported. The luminescence properties of Sb³⁺ in AlPO₄, LaPO₄ and LiLaP₄O₁₂ are explained by using existing models. The luminescence properties of Sb³⁺ in calcium halophosphate have been reported before, but were not completely understood. We find that a strong Jahn-Teller interaction is working on the relaxed excited state of the Sb³⁺ ion from which the luminescence properties can be explained. Evidence is given that Sb³⁺ in calcium fluorapatite occupies a Ca²⁺ site.     

四价钒离子VO2+在几种阳离子交换膜中的自扩散行为

研究了VO2 在3种阳离子交换膜PE01,NF120以及Nafion1135中的自扩散行为,采用UV-3802可见-紫外分光光度仪测定VO2 浓度,建立浓度与时间的关系,用Ct=Ct∞(1-exp(-αt))经验方程拟合实验数据,得到VO2 在3种膜PE01,NF120以及Nafion1135中的自扩散方程.结合Fick扩散理论,推导出了VO2 在膜中的扩散系数D与方程中经验常数α的关系,计算出了VO2 在3种阳离子交换器Nafion1135,PE01以及NF120中的扩散系数分别为2.66×10-13,2.09×10-13和3.26×10-13m2/s.在所研究的阳离子交换膜中,PE01膜对VO2 具有最好的阻隔作用.     

Monte Carlo simulation on the cation diffusion via vacancies in simple spinels

The correlation factors of cations and vacancies for diffusion in simple spinels were calculated by using the Monte Carlo simulation technique. Since the predominant point defects are cationic vacancies at high temperature and especially at high oxygen partial pressures in many spinels, the cations are considered to move primarily via cationic vacancies in this study. Several input parameters including the lattice size, the number of jumps per cation, etc., were optimized to calculate the correlation factors. Then the correlation factors of cations moving via vacancies in simple spinels were calculated in different types of exchange jumps, i.e., diffusion that occurs on tetrahedral or octahedral or both cationic sites. Results were obtained with satisfactory accuracy. The influence of the vacancy concentration on the correlation factors was also analyzed.     

Double-layer oxide film formation on elemental metals by cation vacancy diffusion

A theoretical development for the simultaneous formation of two-layered oxide phases on a planar elemental metal by means of cation vacancy diffusion is presented.     

氟磷酸钙真空碳热还原反应机理

在真空条件下,本文采用热力学分析、XRD及化学分析等方法与手段,对SiO2在氟磷酸钙碳热还原制磷的过程进行了研究,考察了SiO2的添加量对磷矿还原率的影响.通过热力学研究,在压力100Pa温度低于1075℃ 时,Ca5(PO4)3F与C、SiO2的反应满足反应发生的热力学条件.实验研究表明:在真空度10Pa～80Pa,温度达到实验最高温度1550℃时,二氧化硅不能使氟磷酸钙发生脱氟反应,与热力学计算结果一致.还原率随着温度升高而增大,在低于1450℃时,添加SiO2有利于提高还原率;随m增加,还原率也增加,在1350℃时,还原率增大速度较快.由此作者提出了SiO2对氟磷酸钙真空碳热还原的反应机理.     

Neutron diffraction of chlorine substituted fluorapatite

Fluorapatite, chlorapatite and a mixed apatite synthesised by a high temperature solid state reaction route were analysed using time-of-flight neutron diffraction of the series Ca₅(PO₄)₃F_1 − xCl_x, where x = 0.0, 0.5 and 1.0. Fluorapatite and the mixed apatite were found to be hexagonal in crystal structure. The chlorapatite was monoclinic in structure. The lattice parameters a and b increased with chlorine addition while c decreased. The unit cell volume increased linearly with chlorine content and the density decreased. The Ca(1)O₆ metaprism twist angle (φ) decreased with chlorine addition indicating a tendency towards ideal hcp packing.     

Limited role of cation bulk diffusion in the oxidation of pure iron to magnetite

Recent experimental results for the oxidation of pure iron to magnetite below the eutectoid temperature for the formation of wüstite (570 °C) are re-analysed with respect to the mechanisms which control the overall reaction kinetics. The experimental parabolic rate constants are compared with those expected for cation bulk diffusion controlled reaction kinetics. The comparison shows that the experimental rate constants are as much as two orders of magnitude larger than the calculated values suggesting that processes other than cation bulk diffusion contribute to the overall reaction kinetics in the set of experiments investigated.     

One-pot synthesis of hierarchical fluorapatite hollow microparticles

Hierarchical fluorapatite (FHAp) microparticles with hollow interiors were prepared by a one-pot hydrothermal method using Na₂EDTA/citric acid (CA) as additive. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results showed that the resultant hollow FHAp microparticles with uniform shape and size are hierarchically constructed by many small FHAp crystallites building units. Time-dependent experimental results indicated that Ostwald ripening process could be used to explain the formation mechanism for the hollow FHAp microparticles.     

Role of cation diffusion in the formation mechanism and properties of cobalt-doped n-type pyrite thin films

Binary and ternary chalcogenides are relevant compounds for photovoltaic and thermoelectric energy conversion processes. The prototype material in this wide family is FeS₂ (pyrite). In this work, we have investigated the simultaneous formation and doping (n-type) of FeS₂ thin films. Sulphuration of Fe over Co metallic bilayers at constant pressure and temperature has allowed to get the necessary experimental information. Through the analysis of the chemical composition (Rutherford backscattering/elastic recoil detection analysis, energy dispersive X-ray) and structural (XRD) experimental data we have been able to propose a detailed mechanism to explain the formation of pyrite doped with Co thin films. In this mechanism the most relevant role is played by the diffusion of cationic (Fe and Co) species. Measured transport properties of the films reflect the different steps of the formation and doping processes.     

Effect of cation stoichiometry on the transport properties of calcium ruthenium oxide ceramics

Seebeck coefficient and electrical resistivity have been determined on a series of compounds having the general composition Ca _n Ru_1−n O _y . From property and structural considerations, these compounds have been divided into two categories: one group resembling Ca₂RuO₄ and the second category exhibiting properties similar to CaRuO₃. While the former is an antiferromagnetic insulator, the latter is a paramagnetic metal. The Seebeck coefficient remains relatively unchanged within the members of the two groups, irrespective of the molar ratios of the cations. Even between the two groups of compounds, the Seebeck coefficient exhibits minimal difference even as the cation ratio (Ru/Ca) of the compounds is varied from 0.35 (n = 0.74) to 1.94 (n = 0.34). The resistivity, however, varies by nine orders of magnitude as the cation ratio is varied in the same range. Consequently, the resulting power factor (s ²σ, where s is the Seebeck coefficient and σ is the electrical conductivity), which is a measure of the usefulness or thermopower conversion efficiency of a thermoelectric material, is found to vary by nine orders of magnitude.     

Synthesis,characterization and cation adsorption of p-aminobenzoic acid intercalated on calcium phosphate

Crystalline lamellar calcium phosphate retained 4-aminobenzoic acid inside its cavity without leaching. The intense infrared bands in the 1033 and 1010 cm^?1 interval confirmed the presence of the phosphonate groups attached to the inorganic layer, with sharp and intense peaks in X-ray diffraction patterns, which gave basal distances of 712 and 1578 pm for the original and the intercalated compounds, respectively. Solid-state ³¹P nuclear magnetic resonance spectra presented only one peak for the phosphate groups attached to the main inorganic polymeric structure near ?2.4 ppm. The adsorption isotherms from ethanol gave the maximum adsorption capacities of 6.44 and 3.34 mmol g^?1 for nickel and cobalt, respectively, which stability constant and distribution coefficient followed Co > Ni.     

Divalent chromium in alkaline earth silicate systems

Journal of Materials Science -     

Development of fluorapatite cement for dental enamel defects repair

In order to restore the badly carious lesion of human dental enamel, a crystalline paste of fluoride substituted apatite cement was synthesized by using the mixture of tetracalcium phosphate (TTCP), dicalcium phosphate anhydrous (DCPA) and ammonium fluoride. The apatite cement paste could be directly filled into the enamel defects (cavities) to repair damaged dental enamel. The results indicated that the hardened cement was fluorapatite [Ca₁₀(PO₄)₆F₂, FA] with calcium to phosphorus atom molar ratio (Ca/P) of 1.67 and Ca/F ratio of 5. The solubility of FA cement in Tris–HCl solution (pH = 5) was slightly lower than the natural enamel, indicating the FA cement was much insensitive to the weakly acidic solutions. The FA cement was tightly combined with the enamel surface, and there was no obvious difference of the hardness between the FA cement and natural enamel. The extracts of FA cement caused no cytotoxicity on L929 cells, which satisfied the relevant criterion on dental biomaterials, revealing good cytocompatibility. In addition, the results showed that the FA cement had good mechanical strength, hydrophilicity, and anti-bacterial adhesion properties. The study suggested that using FA cement was simple and promising approach to effectively and conveniently restore enamel defects.     

Thermoluminescence in fluorapatite doped with Eu2O3 and PbO

Thermoluminescence (TL) of fluorapatite Ca5(PO4)3F doped with Eu2O3 has been investigated for UV and X ray irradiation. Two TL glow peaks for the Eu2O3 doped sample appeared in the temperature regions about (1) 353 to 380 K and (2) 508 to 510 K, when heated at rate of 20 K.min(-1) after UV or X ray irradiation at room temperature. It has been found that the peak 2 (508 to 510 K) intensity of the samples doubly doped with Eu2O3 and PbO became strong compared with that doped with only Eu or Pb ions. From the TL spectra for the Ca5(PO4)3F doped activators, it is concluded that the TL of Eu2+ ions is sensitised by the existence of Pb2+ ions. On the other hand, the TL of Eu3+ ions is not intensified by addition of PbO. The TL emission may be due to the recombination reaction: Eu3+ + e-->Eu2+*-->Eu2+ + hv. EU2+ + hole --> Eu3+* --> Eu3+ + hv. The 510 K TL peak may be also being suitable for use as a dosemeter.     

Processing of concentrated aqueous fluorapatite suspensions by slip casting

In order to produce stable aqueous fluorapatite (FA) suspensions, its surface reactivity in an aqueous solution having two initial pH values with a concentration of ammonium polyacrylate (NH₄PA) was investigated as a function of time. The rheological behaviour of concentrated aqueous FA slips stabilized with NH₄PA was studied; besides, the effect of poly(vinyl)alcohol (PVA) addition on the relative viscosity of the suspensions was investigated. The influence of the slip rheology on the microstructure of the resultant green slip cast compacts and their sintering behaviour were determined. Upon the FA introduction in the aqueous solutions, an initial release of F anions located at the surface was found, which was not dependent on the pH and the presence of dispersant. The increase in the initial pH of the solution above 7 and/or the addition of NH₄PA markedly reduced the Ca⁺⁺/H⁺ exchange reaction rate. As a result, well-stabilized concentrated aqueous suspensions could be obtained at pH close to 9. The minimum viscosity of 40 vol.% slips at pH 8.9 occurred at 0.6 wt% of NH₄PA added. The addition of 0.5 wt% PVA to a well-stabilized FA slip caused aggregation of particles by a depletion flocculation mechanism, thereby increasing the slip viscosity. The greater permeability of cakes produced from slips with high viscosity values (0.5 wt% PVA) increased the casting rate. The highest sintered densities were obtained for the compacts prepared from the slips without PVA, due to the denser particle packing achieved in the green bodies.     

Influence of fluorapatite minor additions on behavior of hydroxyapatite ceramics

Fluorinated hydroxyapatite is known to be less soluble by body fluids, resulting in enhanced resistance to biodegradation in vivo conditions, as compared to the pure hydroxyapatite ceramics. The present work was aimed at the investigation of the effect of minor additions of ultrafine fluorapatite (up to 10 wt%) on the sintering behavior and mechanical properties of hydroxyapatite ceramics. In vitro testing for the osteoblast-like cells viability and proliferation was performed with the samples of varying fluorapatite content. It was found that the fluorapatite addition hinders the sintering shrinkage and lowers the strength, but does not generally affect negatively the viability of the cells.     

Evaluating hydrothermal synthesis of fluorapatite nanorods: pH and temperature

ABSTRACT

In this study, the fluorapatite was synthesised by a hydrothermal technique in different pH and temperature using apricot tree gum surfactant. The fluorapatite was synthesised in different shapes such as spherical, Chrysanthemum flower and rod. The effect of two factors (pH and temperature) on the shape and dimension of synthesised fluorapatite was investigated through the full factorial design. An experimental strategy was developed based on the analysis of variance to create mathematical models for the shape and dimension of synthesised fluorapatite. Findings revealed that the pH of hydrothermal solution is more significant factor than temperature in terms of shape and dimension of the synthesised fluorapatite. It was illustrated that similar nanorods structure to the human tooth enamel can be achieved in pH of 10 and temperature of 70 °C The transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) spectroscopy were carried out for characterisation of synthesised fluorapatite.     

Double Cyclohexaphosphates of Cesium and Divalent Metals

The double cyclohexaphosphates Cs₂Mg₂P₆O₁₈ (forms I and II) and Cs₂Zn₂P₆O₁₈ (II) are prepared by reacting Cs₂CO₃ and MgO or ZnO in molten polyphosphoric acids in the presence of Ln₂O₃ (Ln = Lu, Yb) or V₂O₅ at 250–350°C. Their structures and lattice parameters are determined. Cs₂Mg₂P₆O₁₈-I: a = 18.243 Å, b = 12.023 Å, c= 12.021 Å, = 96.86°, sp. gr. Pc; Cs₂Mg₂P₆O₁₈-II:a= 12.042 Å, sp. gr. P2₁3; Cs₂Zn₂P₆O₁₈: a= 12.023 Å, sp. gr. P2₁3. Yb and Lu do not form mixed-cation phosphates with Cs, Mg, or Zn but are favorable for cyclization and the formation of the double cyclohexaphosphates Cs₂Mg₂P₆O₁₈ and Cs₂Zn₂P₆O₁₈.     

Synthesis and characterization of hydroxyapatite, fluoride-substituted hydroxyapatite and fluorapatite

Powders of hydroxyapatite (HA), partially fluoride-substituted hydroxyapatite (fHA), and fluorapatite (FA) were synthesized in house using optimum methods to achieve relatively pure powders. These powders were assessed by the commonly used bulk techniques of X-ray diffraction (XRD), Fourier transform infra-red (FTIR) and FT-Raman spectroscopies, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and F-selective electrode. In addition, the current study has employed transmission electron microscopy (TEM), involving morphological observation, electron diffraction and energy-dispersive X-ray spectrometry (EDX), as an effective analytical technique to evaluate the powders at a microscopic level. The HA and fHA particles were elongated platelets about 20×60 nm in size, while FA particles were over twice this size. Calcination of the HA and fHA powders at 1000 °C for 1 h resulted in increased grain size and crystallinity. The calcined fHA material appeared to possess a crystal structure intermediate between HA and FA, as evidenced by the (3 0 0) peak shift in XRD, as well as by the position of the hydroxyl bands in the FTIR spectra. This result was consistent with electron diffraction of individual particles. Small levels of impurities in some of the powders were identified by EDX and electron diffraction, and the carbonate content was detected by FTIR. The use of TEM in conjunction with the bulk techniques has allowed a more thorough assessment of the apatites, and has enabled the constituents in these closely related apatite powders to be identified.