Preparation and characterization of Li<Subscript>2</Subscript>O–CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> glasses as bioactive material

The aim of the present investigation was to study the role of Al₂O₃ in the Li₂O–CaO–P₂O₅–SiO₂ bioactive glass for improving the bioactivity and other physico-mechanical properties of glass. A comparative study on structural and physico-mechanical properties and bioactivity of glasses were reported. The structural properties of glasses were investigated by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and the bioactivity of the glasses was evaluated by in vitro test in simulated body fluid (SBF). Density, compressive strength, Vickers hardness and ultrasonic wave velocity of glass samples were measured to investigate physical and mechanical properties. Results indicated that partial molar replacement of Li₂O by Al₂O₃ resulted in a significant increase in mechanical properties of glasses. In vitro studies of samples in SBF had shown that the pH of the solution increased after immersion of samples during the initial stage and then after reaching maxima it decreased with the increase in the immersion time. In vitro test in SBF indicated that the addition of Al₂O₃ up to 1.5 mol% resulted in an increase in bioactivity where as further addition of Al₂O₃ caused a decrease in bioactivity of the samples. The biocompatibility of these bioactive glass samples was studied using human osteoblast (MG-63) cell lines. The results obtained suggested that Li₂O–CaO–Al₂O₃–P₂O₅–SiO₂-based bioactive glasses containing alumina would be potential materials for biomedical applications.     

Evaluation of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Na<Subscript>2</Subscript>O–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> bioglass-ceramics for hyperthermia application

Magnetic bioglass ceramics (MBC) are being considered for use as thermoseeds in hyperthermia treatment of cancer. While the bioactivity in MBCs is attributed to the formation of the bone minerals such as crystalline apatite, wollastonite, etc. in a physiological environment, the magnetic property arises from the magnetite [Fe₃O₄] present in these implant materials. A new set of bioglasses with compositions 41CaO · (52 ? x)SiO₂ · 4P₂O₅  · xFe₂O₃ · 3Na₂O (2 ≤ x ≤ 10 mol% Fe₂O₃) have been prepared by melt quenching method. The as-quenched glasses were then heat treated at 1050°C for 3 h to obtain the glass-ceramics. The structure and microstructure of the samples were characterized using X-ray diffraction and microscopy techniques. X-ray diffraction data revealed the presence of magnetite in the heat treated samples with x ≥ 2 mol% Fe₂O₃. Room temperature magnetic property of the heat treated samples was investigated using a Vibrating Sample Magnetometer. Field scans up to 20 kOe revealed that the glass ceramic samples had a high saturation magnetization and low coercivity. Room temperature hysteresis cycles were also recorded at 500 Oe to ascertain the magnetic properties at clinically amenable field strengths. The area under the magnetic hysteresis loop is a measure of the heat generated by the MBC. The coercivity of the samples is another important factor for hyperthermia applications. The area under the loop increases with an increase in Fe₂O₃ molar concentration and the. coercivity decreases with an increase in Fe₂O₃ molar concentration The evolution of magnetic properties in these MBCs as a function of Fe₂O₃ molar concentration is discussed and correlated with the amount of magnetite present in them.     

Effect of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on the dynamics of Li<Superscript>+</Superscript> ions in Li<Subscript>2</Subscript>O·P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Lithium ion transport has been studied in bismuth lithium phosphate glasses in the frequency range 20 Hz–1 MHz and in the temperature range 423–573 K using impedance spectroscopy. The addition of Bi₂O₃ in Li₂O·P₂O₅ glass is related to the modification of the glass structure and facilitates the Li⁺ ions migration. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency are extracted from the impedance spectra. Conductivity of the present glass system is found to be ionic in nature. The electrical response of the glasses has been studied using both conductivity and electric modulus formalisms. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of the dynamic processes for ions in these glasses. Nearly identical values of activation energy for dc conduction and for conductivity relaxation time indicate that the ions overcome same energy barrier while conducting and relaxing.     

Synthesis of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> mesoporous bioactive glasses with high P<Subscript>2</Subscript>O<Subscript>5</Subscript> content by evaporation induced self assembly process

Mesoporous bioactive glasses (MBGs) of the CaO–SiO₂–P₂O₅ system containing relatively high P₂O₅ contents (10–30 mol%) were prepared from a sol–gel. An evaporation-induced self-assembly (EISA) technique was used with poly(ethylene oxide)-block–poly(propylene oxide)-block–poly(ethylene oxide) (EO₂₀–PO₇₀–EO₂₀, P123) acting as a template. The structural, morphological and textural properties of MBGs were investigated by small-angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and a N₂ sorption/desorption technique. SAXRD and TEM results display the reduced long-range ordering of mesopores with increasing P₂O₅ content. N₂ sorption/desorption analysis shows that all three samples exhibit a type IV isotherm with type H1 hysteresis loops, characteristic of independent cylindrical slim pore channels and this material has a Barret–Joyner–Halenda (BJH) model pore size of ~4 nm and BET specific surface area ~430 m²/g. NMR results indicate a more condensed framework for samples with 30 mol% P₂O₅ than samples with 10 mol% P₂O₅. For in vitro bioactivity tests where samples were soaked in simulated body fluid (SBF), samples with 30 mol% P₂O₅ showed higher crystallinity than those with lower P₂O₅ contents Silicon concentration increased in SBF solution during the soaking period, which indicates MBGs can be degradable in SBF solution.     

Characterization of microstructure and properties of Al–Al<Subscript>3</Subscript>Zr–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

Aluminium-based metal matrix composite strengthened by in situ Al₂O₃ and Al₃Zr particles were synthesized by powder metallurgy route. Phase analysis by X-ray diffraction and scanning electron microscopy revealed that the reaction between Al and ZrO₂ produced Al₂O₃ and Al₃Zr phases in the sintered composites. The hardness of the composite is a strong function of sintering temperature as well as the volume fraction of reinforcements. The dry sliding wear test results clearly indicated that increasing the volume fraction of zirconia particles in the composite improved the wear resistance. Microcutting, ploughing, delamination and oxidation were the main mechanisms of wear.     

Structural investigation of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–K<Subscript>2</Subscript>O glass system with antibacterial potential

The xV₂O(1?x)[0.8 P₂O₅ ? 0.2 K₂O] glass system with 0 ≤ x ≤ 50 mol% was prepared and the structural changes induced in these glasses by increasing the vanadium oxide content were investigated by IR and ESR spectroscopies. The dual behaviour role of V₂O₅ oxide, as network modifier (for x ≤ 10 mol%) and the network former (x ≥ 20 mol%), as a consequence of phosphate network depolymerization and P–O–V and V–O–V linkages appearance was also highlighted. The antibacterial effect of the glasses with x ≤ 20 mol% V₂O₅ content was tested by optical density (OD) measurements. A linear correlation between the amount of vanadium and the antibacterial effect was evidenced.     

Phytic acid derived bioactive CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> gel-glasses

The possibility of using phytic acid as a precursor to synthesize CaO–P₂O₅–SiO₂ glasses by sol–gel method has been explored and the pseudo ternary phase diagram has been established. It was shown that gel-glasses over a broader range of compositions could be prepared compared to other phosphorus precursors or melt-quenching method. Furthermore, phytic acid was found to assist calcium being incorporated into glass networks. In vitro tests in simulated body fluid (SBF) were performed on the above gel–glasses and it was found that they were bioactive over a much broader compositional range especially at high phosphate content, thus enabling one to design bioactive materials with various degradation rates by adjusting the phosphate content.     

Compositional dependence of some physical properties of ZnO–PbO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Six glasses of the chemical composition 10ZnO–xPbO–(90−x) P₂O₅ were prepared. With an increase in PbO content a non-monotonous step like increase in the density, in the glass transition temperature, and in the refractive index was observed. From the Raman and IR spectra studied the evidence is given for the phosphate network depolymerization as PbO content increases. Increase in PbO content leads also to an increase in refractive index (n) up to n = 1.74, for x = 55, and to an increase in the glass transition temperature (T _g) from T _g = 270 °C (x = 30) to T _g = 360 °C (x = 55).

---

Microwave dielectric properties of temperature-stable (Mg<Subscript>0.95</Subscript>Co<Subscript>0.05</Subscript>)<Subscript>2</Subscript>TiO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite ceramics for LTCC applications

In this paper, the effects of Li₂O–B₂O₃–Bi₂O₃–SiO₂ (LBBS) glass on the phase formation, sintering characteristic, the microstructure and microwave dielectric properties of temperature-stable (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ ceramics were investigated. (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ powders were obtained by using the traditional solid-state process. A small amount of LBBS doping can effectively reduce sintering temperature and promote the densification of the ceramics. X-ray diffraction analysis revealed not only the primary phase (Mg·Co)₂TiO₄ associated with Li₂TiO₃ minor phase but also a third phase (Mg·Co)TiO₃. The dielectric constant and Qf values vary with the doping amount of LBBS and sintering temperatures. With the compensation of the positive temperature coefficient (τ _f ) of Li₂TiO₃ and the negative τ _f of (Mg_0.95Co_0.05)₂TiO₄, the τ _f of the specimens fluctuates around zero. The (Mg_0.95Co_0.05)₂TiO₄ ceramic with 2.5 wt% LBBS addition and sintering at 900?°C for 4 h exhibited excellent microwave dielectric properties: ? _r ?=?19.076, Qf?=?126100 GHz, and τ _f ?=?0.98 ppm/°C.     

Structural investigations of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–CaO glass system by FT-IR and EPR spectroscopies

xV₂O₅·(100 − x)[0.7P₂O₅·0.3CaO] glass system was obtained for 0 ≤ x ≤ 35 mol% V₂O₅. In order to obtain information regarding their structure, several techniques such as X-Ray diffraction, FT-IR, and EPR spectroscopies were used. X-Ray diffraction patterns of investigated samples are characteristic of vitreous solids. FT-IR spectra of 0.7P₂O₅·0.3CaO glass matrix and its deconvolution show the presence in the glass structure of all structural units characteristic to P₂O₅. Their number are increasing for x ≤ 3 mol% V₂O₅ then, for higher content of vanadium ions, the number of phosphate structural units are decreasing leading to a depolymerization of the structure. The structural units characteristic to V₂O₅ were not evidenced but their contribution to the glass structure can be clearly observed. EPR revealed a well resolved hyperfine structure (hfs) typical for vanadyl ions in a C_4v symmetry for x ≤ 3 mol% V₂O₅. For 5 < x < 20 mol% V₂O₅ the spectra show a superposition of two EPR signals one due to a hfs structure and another consisting of a broad line typical for associated V⁴⁺–V⁴⁺ ions. For x ≥ 20 mol% V₂O₅ only the broad line can be observed. The composition dependence of the line-width suggests the presence of dipole–dipole interaction between vanadium ions up to x ≤ 5 mol% V₂O₅ and superexchange interactions between vanadium ions for x > 5 mol% V₂O₅.     

Frequency dependence of dielectric properties of CaO–SrO–Li<Subscript>2</Subscript>O–Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

CaO–SrO–Li₂O–Ln₂O₃–TiO₂ ceramics were prepared by solid state reaction method, where Ln₂O₃ consists of equal proportions of Nd₂O₃ and Sm₂O₃. Dielectric properties and crystal structure were investigated with respect to the content of TiO₂. Single phase with an orthorhombic perovskites structure was formed within the composition range of investigation. The frequency dependence of dielectric properties of the present ceramics was extensively investigated. Dielectric constant was less sensitive to frequency. However, dielectric loss and temperature coefficients were both very sensitive to frequency and gradually decreased with increasing frequency, such as the variation was more than ten times between 1 MHz and several GHz. The relationship between the temperature coefficient and dielectric loss was also discussed at different frequencies. And the mechanism of the frequency dependence was discussed in term of the role of Li ions.     

Thermophysical Properties of Ceramic Filler-Added BaO–ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glass Composites for Barrier Ribs of Plasma Display Panels

The capability of BaO–ZnO–B₂O₃–P₂O₅ glass in hosting various ceramic fillers (up to 20 mass% of Al₂O₃, TiO₂, and ZnO) has been investigated. All the investigated filler-added glasses have demonstrated a reasonable densification at 550 °C to form stable ceramic filler-glass composites. Modifications of the thermophysical properties, such as coefficient of thermal expansion (CTE), glass transition temperature, and dilatometric softening temperature, by the addition of the fillers have been investigated and correlated to phase and microstructural evolution. The CTE of the fabricated composites with varying filler addition is well correlated with theoretical predictions based on the Turner equation considering the modification by phase evolution, which indicates the thermal property tuning potential of the BZBP-based glass composites for application to barrier ribs of plasma display panels.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Thermodynamics and kinetics of MgH<Subscript>2</Subscript>–nfTa<Subscript>2</Subscript>O<Subscript>5</Subscript> composite for reversible hydrogen storage application

The thermodynamics and kinetics of hydrogen absorption–desorption of nfTa₂O₅–Mg–MgH₂—composite (nf stands for nano-flakes) have been studied. The nfTa₂O₅–Mg composite could absorb hydrogen at room temperature (17 °C). The hydrogen desorption of nfTa₂O₅–MgH₂ composite starts at 200 °C. The remarkably improved hydrogen absorption–desorption of catalyzed Mg–MgH₂ could be attributed to the nano-engineered surface by nfTa₂O₅. The enthalpies of hydrogen absorption–desorption were found to be 80 ± 2, and 76 ± 3 kJ/mol respectively. The activation energy of hydrogen absorption was evaluated as 49 ± 5 kJ/mol which is same as the energy barrier for diffusion of hydrogen in Mg matrix. The apparent activation of hydrogen desorption of nfTa₂O₅–MgH₂ was found to be 74 ± 7 kJ/mol. The nfTa₂O₅–MgH₂ composite has shown cyclic stability up to fifty hydrogen absorption–desorption without significant changes in the kinetics and hydrogen storage capacity.     

The effect of Fe contents on the local structure and crystallization behavior of SiO<Subscript>2</Subscript>–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The glass and glass ceramics containing SiO₂–CaO–Fe₂O₃–P₂O₅ were prepared by sol–gel method. The influence of the Fe contents on the crystallization and local structure of the glass and glass ceramics was systematically investigated. The crystal structure of the glass ceramics was identified by XRD characterization. Hematite phase can be precipitated from the glass matrix in all glass ceramics with various Fe contents, and the crystallographic parameters of hematite were determined by XRD Rietveld refinement. The crystallization kinetics of the glasses was investigated in detail. Relative low activation energies were obtained at low Fe contents. The local structure evolution of the glass and glass ceramics has been studied in-depth by means of FTIR and Mössbauer spectroscopy. Fe element is present both as network former and network modifier which significantly influenced the crystallization activation energies of the glasses. The results of this work may be of great significance for the material design and practical applications of bioactive magnetic glass ceramics for hyperthermia.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.     

Synthesis,bioactivity and preliminary biocompatibility studies of glasses in the system CaO–MgO–SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–CaF<Subscript>2</Subscript>

New compositions of bioactive glasses are proposed in the CaO–MgO–SiO₂–Na₂O–P₂O₅–CaF₂ system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO₄) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts’ cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C).     

Fabrication of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.     

Synthesis of Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Co<Subscript>0.13</Subscript>Ni<Subscript>0.13</Subscript>O<Subscript>2</Subscript> by sol–gel method and its electrochemical properties as cathode materials for lithium-ion batteries

Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ was synthesized by sol–gel method at 700, 800, 900 and 1000 °C, respectively, characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and measured as the cathode materials for lithium-ion batteries (LIBs). After their performances have been compared, 800 °C was considered as the optimum synthesis temperature for Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ as the cathode materials for LIBs. When charge–discharged at 20 mA g^?1 in a voltage window of 2.0–4.8 V, the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ synthesized at 800 °C (LMNCO-800) showed charge and discharge capacities of 376.2 and 276.3 mAh g^?1, respectively, with irreversible capacity of 99.9 mAh g^?1 and Coulombic efficiency of 73.4%, in the first charge–discharge cycle. The discharge capacity was 239.0 mAh g^?1 in the 50th charge–discharge cycle, with capacity retention of 86.6%. The LMNCO-800 also showed superior high-rate performances. When cycled at the rates of 0.5, 1, 2 and 5 C rate (1 C?=?200 mA g^?1), the discharge capacities of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ can reach 241, 171, 150 and 110 mAh g^?1, respectively. When characterized with high-resolution transmission electron microscopy (TEM), nanodomains with two different structures can be found in LMNCO-800, with some nanodomains showing monoclinic Li₂MnO₃ structure and the other nanodomains showing hexagonal LiMO₂ structure.     

3D printing of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Cu–O interpenetrating phase composite

Porous alumina preforms were fabricated by indirect 3D printing using a blend of alumina and dextrin as a precursor material. The bimodal granulate powder distribution with a bed density of 0.8 g/cm³ was increased to 1.4 g/cm³ by overprinting. The porosity of the sintered bodies was controlled by adjusting the printing liquid to precursor powder ratio in the range of 33–44 vol%. The green bodies exhibited bending strengths between 4 and 55 MPa. An isotropic linear shrinkage of ~17% was obtained due to dextrin decomposition and Al₂O₃ sintering at 1600 °C. Post-pressureless infiltration of the sintered preforms with a Cu–O alloy at 1300 °C for 1.5 h led to the formation of a dense Al₂O₃/Cu–O interpenetrating phase composite (IPC). X-ray analysis of the fabricated composites showed the presence of α-Al₂O₃, Cu and Cu₂O. CuAl₂O₄ spinel was not observed at the grain boundaries during HRTEM examination. The Al₂O₃/Cu–O interpenetrating phase composite revealed a fracture toughness of 5.5 ± 0.3 MPam^1/2 and a bending strength of 236 ± 32 MPa. In order to demonstrate technological capability of this approach, complex-shaped bodies were fabricated.