Formulation and characterization of glass–ceramics based on Na2Ca2Si3O9–Ca5(PO4)3F–Mg2SiO4-system in relation to their biological activity

Glasses having a chemical composition based on combeite [Na₂Ca₂Si₃O₉]–fluoroapatite [Ca₅(PO₄)₃F] and forsterite [Mg₂SiO₄] system were crystallized through controlled heat-treatment. Two forms of sodium calcium silicate e.g. combeite Na₂Ca₂Si₃O₉ and pectolite Na₂CaSi₃O₈, were formed together with diopside (CaMgSi₂O₆) and monticellite (CaMgSiO₄) in addition to fluoroapatite (Ca₅(PO₄)₃F) phases by thermal treatment of the glasses. Selected glass–ceramics were exposed to a simulated body fluid solution (SBF) which is close to human plasma for 3 weeks. Energy dispersive X-ray analysis (EDX) and inductive coupled plasma (ICP) analysis confirmed the formation of an apatite layer which indicate bioactivity in the all crystallized sample. A decreasing of surface bioactivity with increasing Mg₂SiO₄/Na₂Ca₂Si₃O₉ replacement was observed as indicated by the decrease in the amount of apatite layer on the surface of the crystallized specimens. The Vicker’s microhardness of the studied glass–ceramic materials are between 5,047 and 6,781 MPa.     

Mechanical and thermal properties of hot pressed neodymium-substituted britholite Ca9Nd(PO4)5(SiO4)F2

Neodymium-substituted britholite, a phosphate–silicate apatite Ca₉Nd(PO₄)₅(SiO₄)F₂, is considered as a potential host matrix for specific immobilization of radionuclides. Complementary investigations have been carried out to complete the database concerning this compound. The aim was to establish mechanical and thermal properties of dense britholite. Hot pressing was used to nearly fully densify the material. Low values of mechanical properties were found: 0.75 MPa m^1/2 for the fracture toughness and 95 MPa for the flexural strength. The Young's modulus and the Poisson's ratio were 108 GPa and 0.30, respectively. The specific and the thermal conductivity at 298 K were Cp=0.75 J g⁻¹ K⁻¹ and λ=1.15 W m⁻¹ K⁻¹. The average coefficient of thermal expansion in the 20–1000 °C temperature range was α=21×10⁻⁶ K⁻¹.     

Preparation of Zn-doped β-tricalcium phosphate (β-Ca3(PO4)2) bioceramics

Pure β-tricalcium phosphate (β-TCP) and Zn-doped (600, 2900, 4100, 7000, 9300 and 10,100 ppm) β-TCP samples were prepared by using a wet chemical/coprecipitation synthesis technique, followed by calcination at 1000 °C in air. Precursor powders of the coprecipitation process were Ca-deficient nanoapatites (i.e., Ca/P molar ratio varying from 1.49 to 1.51) with needlelike but agglomerated particles of 30 nm thickness. In vitro culture tests performed by mouse osteoblast-like cells showed that the samples doped with 2900 to 4100 ppm Zn showed the highest cell viability (via Live/Dead counts), and with a further increase in the Zn-content towards 1 wt.% the number of dead cells in the well plates started to increase. Alkaline phosphatase (ALP) activity peaked for the β-TCP sample doped with 4100 pm Zn. The sample surface roughness, measured by non-contact profilometry, was also found to have an effect on the Live/Dead cell counts, and the highest cell viability encountered in this study corresponded to the surface with the least roughness.     

Effects of carbonate on hydroxyapatite formed from CaHPO4 and Ca4(PO4)2O

Carbonated hydroxyapatites were formed via reactions in NaHCO₃/NaH₂PO₄ solutions from a mixture of particulate tetracalcium phosphate (TetCP) and anhydrous dicalcium phosphate (DCPA). Reactions were followed by determinations of pH and ion concentrations. The solids formed were analyzed by XRD and FTIR. Rates of heat evolution were established by isothermal calorimetry. Reactions in the absence of NaH₂PO₄ did not reach completion within 24 h. Constitution of reactants to achieve a DCPA-to-NaHCO₃ ratio of 1, in conjunction with the presence of NaH₂PO₄ as a buffer, was found to be optimal for formation of apatite with no remaining reactant. The amount of carbonate incorporated in this apatite was 4–5 wt%. Calorimetry indicated the reaction mechanism to depend on the bicarbonate concentration in solution. The presence of NaH₂PO₄ was found to increase the reaction rate but decrease the extent of carbonate uptake.     

Calcium hydroxyapatite,Ca10(PO4)6(OH)2 ceramics prepared by aqueous sol–gel processing

Aqueous sol–gel chemistry routes based on ammonium–hydrogen phosphate as the phosphorus precursor and calcium acetate monohydrate as source of calcium ions have been developed to prepare calcium hydroxyapatite samples with different morphological properties. In the sol–gel processes, an aqueous solutions of ethylene diamine tetra-acetic acid (EDTA) or tartaric acid (TA) as complexing agents were added to the reaction mixture. The monophasic Ca₁₀(PO₄)₆(OH)₂ samples were obtained by calcination of precursor gels for 5 h at 1000 °C. The phase transformations, composition and micro-structural features in the polycrystalline samples were studied by thermoanalytical methods (TGA/DTA), infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD) and scanning electron microscopy (SEM). It was shown that adjusting the nature of complexing agent in the aqueous sol–gel processing can be used to control the morphology of the ceramic samples.     

Na3V2(PO4)2F3@V2O5-x复合材料的制备及储钠性能研究

当前制约钠离子电池发展的主要因素包括较低的能量/功率密度和较差的循环性能, 而在正极材料表面包覆含氧缺陷金属氧化物层, 可以有效提高材料的电子导电率, 保证高振实密度、能量密度和功率密度。本文通过温和的溶剂热反应制备Na₃V₂(PO₄)₂F₃纳米片前驱体并结合高温煅烧合成Na₃V₂(PO₄)₂F₃@V₂O_5-x复合材料。其结构通过XRD、TEM、SEM、XPS和TGA测试进行表征。作为钠离子电池的正极材料, 展现了优异的循环性能和倍率性能。在0.2C倍率下, 首圈放电比容量为123 mAh?g ^-1, 循环140圈后容量保持在109 mAh?g ^-1。当电流密度提高至1C, 首圈放电比容量达到72 mAh?g ^-1, 充放电循环500圈后, 容量保持率高达84%。优异的电化学性能归因于材料表面包覆的具有丰富结构缺陷的无定型层, 有效提高了离子的扩散和电子导电率。此方法将有助于钠离子电池的实际应用。     

Ca_(0.5)Zr_2(PO_4)_3掺杂CaO的缺陷模型

研究了在Ｃａ０．５Ｚｒ２（ＰＯ４）３组成中引入ＣａＯ后的缺陷反应。少量的Ｃａ２＋离子进入空隙ＭⅠ位增大了ｃ轴尺寸，ａ轴略有减小。Ｃａ２＋离子超过１．５个后，进入ＭⅠ位，造成ａ增大而ｃ值略有降低。     

Phase-pure Na3V2(PO4)2F3 embedded in carbon matrix through a facile polyol synthesis as a potential cathode for high performance sodium-ion batteries

In this study, a pseudo-layered Na super-ionic conductor of Na₃V₂(PO₄)₂F₃ (NVPF)/C cathode for sodium-ion batteries is prepared successfully using a facile polyol refluxing process without any impurity phases. The X-ray diffraction and Rietveld refinement results confirm that NVPF possesses tetragonal NASICON-type lattice with a space group of P₄₂/mnm. In this preparative method, polyol is utilized as a solvent as well as a carbon source. The presence of nanosized NVPF particles in the carbon network is confirmed by field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). The existence of carbon is analyzed by Raman scattering and elemental analysis. When applied as a Na-storage material in a potential window of 2.0–4.3 V, the electrode exhibits two flat voltage plateaus at 3.7 and 4.2 V with an electrochemically active V³⁺/V⁴⁺ redox couple. In addition, Na₃V₂(PO₄)₂F₃/C composite achieved a retention capacity of ~ 88% even after 1,500 cycles at 15 C. Moreover, at high current densities of 30 and 50 C, Na₃V₂(PO₄)₂F₃/C cathode retains the specific discharge capacities of 108.4 and 105.9 mAh·g^–1, respectively, revealing the structural stability of the material prepared through a facile polyol refluxing method.

     

Dielectric characteristics of biocompatible Ca10(PO4)6(OH)2 ceramics

The temperature dependence of the dielectric permittivity and losses of biocompatible Ca₁₀(PO₄)₆(OH)₂ ceramics were studied in a temperature range from 20 to 500°C. An approach to the interpretation of anomalies (bending points) observed in the dielectric characteristics of the ceramic samples is proposed, which takes into account features of the crystal structure of calcium hydroxyapatite and the defects formed in the course of thermal treatments.     

Luminescence properties of Eu2+-activated Sr5(PO4)2(SiO4) for green-emitting phosphor

A green-emitting phosphor of Eu²⁺-activated Sr₅(PO₄)₂(SiO₄) was synthesized by the conventional solid-state reaction. It was characterized by photoluminescence excitation and emission spectra, and lifetimes. In Sr₅(PO₄)₂(SiO₄):Eu²⁺, there are at least two distinguishable Eu²⁺ sites, which result in one broad emission situating at about 495 nm and 560 nm. The phosphor can be efficiently excited in the wavelength range of 250–440 nm where the near UV (～ 395 nm) Ga(In)N LED is well matched. The dependence of luminescence intensities on temperature was investigated. With the increasing of temperature, the luminescence of the phosphor shows good thermal stability and stable color chromaticity. The luminescence characteristics indicate that this phosphor has a potential application as a white light emitting diode phosphor.     

Crystallization from Na2O-P2O5-Fe2O3-MIIO (MII = Mg, Ni) melts and the structure of Na4MgFe(PO4)3

We have studied general trends of phosphate crystallization from Na₂O-P₂O₅-Fe₂O₃-M^IIO (M^II = Mg, Ni) high-temperature solutions at Na/P = 1.0?1.4, M^II/Fe = 1.0, and Fe/P = 0.15 or 0.3, and identified the stability regions of the phosphates Na₄M^IIFe(PO₄)₃ (M^II = Mg, Ni), NaFeP₂O₇, and Na₂NiP₂O₇. The synthesized compounds have been characterized by X-ray powder diffraction and infrared spectroscopy. The structure of Na₄MgFe(PO₄)₃ (sp. gr. $R\bar 3cWe have studied general trends of phosphate crystallization from Na₂O-P₂O₅-Fe₂O₃-M^IIO (M^II = Mg, Ni) high-temperature solutions at Na/P = 1.0−1.4, M^II/Fe = 1.0, and Fe/P = 0.15 or 0.3, and identified the stability regions of the phosphates Na₄M^IIFe(PO₄)₃ (M^II = Mg, Ni), NaFeP₂O₇, and Na₂NiP₂O₇. The synthesized compounds have been characterized by X-ray powder diffraction and infrared spectroscopy. The structure of Na₄MgFe(PO₄)₃ (sp. gr. R[`3]cR\bar 3c, a = 8.83954(13) ?, c = 21.4683(4) ?) has been determined by Rietveld powder diffraction analysis.     

Crystallization and characterization of Na2(La,Me)Zr(PO4)3

Na₂(La, Me)Zr[PO₄]₃ (where Me=Co, Al, Cr) crystals have been grown by three methods: by chemical reaction; from highly concentrated phosphoric acid solutions; and by a hydrothermal technique. The advantages and disadvantages of each method to obtain these crystals have been discussed. Morphological, X-ray, chemical analysis and IR-spectral studies were performed on these crystals.     

Reaction of chlorapatite,Ca5(PO4)3(Cl,F) with sodium carbonate and silica

The conversion of insoluble phosphorous minerals such as apatite, Ca₅(PO₄)₃(F, OH, Cl), to phases containing phosphorous in soluble form is an essential step in the production of fertilizer grade phosphates. Developing countries lack the capital-intensive industrial base necessary to create a phosphate industry. We examine a process suitable for use in Sri Lanka which uses mainly indigenous raw materials. In this process, a chlorine-rich apatite is fused with Na₂CO₃ and SiO₂ at 900° C and 1300° C for 1 to 2 h to yield a product having >90% available phosphorous. Data necessary for the technological evaluation of the process are presented. Phase equilibria in the lime-rich portions of the system CaO-Na₂O-P₂O₅-SiO₂ have been studied. The section Ca₃(PO₄)₂-Ca₂SiO₄-CaNaPO₄ is shown to be a ternary system, and phase relations on the 1100° and 1300° C isothermal sections are presented. A reconnaisance of the system CaO-Ca₃(PO₄)₂-Ca₂SiO₄-CaNaPO₄ has been made. These data, combined with studies of the kinetics of the reaction, point to regions of composition and reaction conditions favouring high yields of available phosphorous.     

The kinetics of calcium deficient and stoichiometric hydroxyapatite formation from CaHPO4·2H2O and Ca4(PO4)2O

Isothermal calorimetry was performed on intimate mixtures of CaHPO₄·2H₂O and Ca₄(PO₄)₂O constituted at Ca/P molar ratios of 1.50 and 1.67 to form the hydroxyapatite compositions Ca₉HPO₄(PO₄)₅OH and Ca₁₀(PO₄)₆(OH)₂, respectively, at complete reaction. The temperature range investigated was 15–70°C. The effects of the reaction temperature on the rates of heat evolution during hydroxyapatite formation were determined. Reactions were carried out utilizing a liquid-to-solids weight ratio of 1.0. A two-stage reaction mechanism was observed regardless of the Ca/P ratio as indicated by the presence of two reaction peaks in the plots of the rates of heat evolution against time. An Arrhenius relationship was found between the rate and temperature for each reaction stage for both compositions. Apparent activation energies of 120 and 90 kJ/mol (Ca/P=1.67) and 118 and 83 kJ/mol (Ca/P=1.50), respectively, were calculated for the first and second reaction peaks. An Arrhenius relationship was also found between the time of maximum rate and temperature. The following qualitative reaction mechanism is proposed for each of the two reaction stages for both compositions studied. The first stage involves the complete consumption of CaHPO₄·2H₂O and the partial consumption of Ca₄(PO₄)₂O to form a noncrystalline calcium phosphate and nanocrystalline hydroxyapatite. During the second stage the remaining Ca₄(PO₄)₂O reacts with the noncrystalline calcium phosphate to form the final product, stoichiometric or calcium deficient hydroxyapatite.     

添加La2O3的AlN陶瓷的高压低温烧结

利用国产六面顶压机在5.0GPa,1300～1800℃条件下实现了以La2O3为助剂的AlN陶瓷体的高压低温烧结.用XRD、SEM、微区拉曼光谱对AlN高压烧结体进行了表征.研究表明,高压制备陶瓷体材料能够有效降低烧结温度和缩短烧结时间,烧结温度最低温度达到1300℃,可比传统烧结方法降低300℃以上,AlN高压烧结体的晶格常数比粉体的减小0.09%左右,其内部存在残余压应力,但AlN六方相的对称性没有发生改变.     

Manganese Local Environment Modulation via SiO4 Substitution to Boost Sodium Storage Performance of Na4MnCr(PO4)3

Manganese-based Na superionic conductors (NASICONs) Na₄MnCr(PO₄)₃ with three-electron reaction are attractive cathode materials for sodium-ion batteries. However, the irreversible distortion of Mn local structure leads to sluggish electrode kinetics, voltage hysteresis, and poor cycling stability. Here, SiO₄ is introduced to substitute PO₄ to modulate the local environment of Mn to activate the redox activity and stabilize the reversibility of Na₄MnCr(PO₄)_2.9(SiO₄)_0.1 (NMCP-Si). A combined experimental and theoretical investigation have been undertaken to reveal the evolution of electronic structures and Na storage properties associated with SiO₄ substitution. The NMCP-Si exhibits much-enhanced rate capability and cycling stability, being attributed to the unique Jahn-Teller distortion (Mn³⁺) that facilitates sodium de/insertion kinetics by optimizing the Na ion diffusion channels. This work addresses the challenge of stabilizing the structure of Mn-based NASICONs and represents a breakthrough in understanding how to improve the Na⁺ conductivity by regulating local structure.