Morphological control and in vitro bioactivity of nanoscale bioactive glasses

In this study, nanoscale bioactive glasses with different morphologies were prepared through sol-gel process using lactic acid as hydrolysis promoter. The effect of lactic acid concentration on the morphology of bioactive glass was characterized. The influence of the morphology on the in vitro bioactivity of samples was investigated in simulated body fluid and examined by various methods. The results showed that nanoscale surface morphologies with high roughness, created by addition of lactic acid, greatly enhanced the in vitro bioactivity of as-prepared samples. It was found that the morphology with nanoscale surface feature and pore size distribution, in addition to specific surface area and pore volume, plays an important role in accelerating the formation of carbonated hydroxyapatite. According to our results, bioactive glasses possessing surface morphology with significant numbers of nanoscale bioactive glass particles and a narrow unimodal or bimodal mesopore structure, exhibit the best in vitro bioactivity.     

Synthesis and characterization of calcium phosphate based bioactive quaternary P2O5-CaO-Na2O-K2O glasses

Calcium phosphate based bioactive quaternary glass systems P₂O₅-CaO-Na₂O-K₂O were prepared by melt growth technique. Glasses were prepared in five different compositions by fixing P₂O₅ at 47 mol% and CaO at 30.5 mol% and by varying the K₂O and Na₂O concentrations. The structural properties of the glasses are analyzed using X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) studies; and the composition of the glasses are studied using energy dispersive X-ray spectrum (EDS). The microhardness of the glass systems are studied by Vickers hardness measurements and the bioactivity of the glasses are studied using in vitro study. The thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The ultrasonic velocity measurements show that the addition of K₂O contents produces non-bridging oxygen ion and hence weaken of the glass structure. The weakening of the glass structure reduces the ultrasonic velocity and hence an increase in attenuation.     

Acetic acid derived mesoporous bioactive glasses with an enhanced in vitro bioactivity

In this paper, a novel mesoporous bioactive glass (MBG) with a nanoscale surface feature in the SiO₂–CaO–P₂O₅ system has been synthesized by means of the acetic acid-assisted sol–gel process. As a comparison, the normal sol–gel derived bioactive glass (NBG) with the same composition was also synthesized. The structure and in vitro bioactivity of as-prepared samples were characterized using various methods. The results indicated that using acetic acid as a structure-assisted agent and hydrolysis catalyst is in favor of preparing the bioactive glass with nanoscale surface morphology, larger specific surface area, relatively homogeneous sized mesopore distribution. Depending on this novel structure, MBG presented an enhanced formation of hydroxyl-carbonate apatite layer and high in vitro bioactivity.     

Sintering process of glasses in the system Na2O-B2O3-SiO2

In this work, the sintering process of different glasses in the system Na₂O-B₂O₃-SiO₂ has been studied. The studied compositions are suitable for sealing the gas manifolds of molten carbonate fuel cells. Sealing glasses are usually applied on the surfaces to be sealed using powder glass mixed with an organic medium. The agglomerant elimination and the sintering of the glass powder take place during the thermal treatment. Three different particle sizes of glass powder and different sintering temperatures and times have been used to reveal the influence of the specific surface area and viscosity on sintering. The control of these parameters allows optimization of the sealing conditions of the glasses. Dense materials have been characterized as well as the sintering mechanism. Two processes take place during the thermal treatment: the sintering process and the quartz crystallisation. Both processes act in opposite directions on the glass densification. Crystallisation is the dominant process at long times and high temperatures. The viscous flow Scherer model has been adequately applied to the experimental data.     

Thermally modulated differential scanning calorimetry of a glass of composition 45Na2O-40B2O3-10Al2O3-5In2O3

The kinetics of structural relaxation and of glass transition of the 45Na₂O-40B₂O₃-10Al₂O₃-5In₂O₃ glassforming melt is studied by means of standard DSC and of temperature modulated DSC. In this way the dependence of the fictive temperature on cooling rate is determined simultaneously with the determination of the dependence of the dynamic glass transition temperature on modulation frequency. Both sets of data are fitted together in terms of the equation of Ritland-Bartenev. It was found that the activation energy of the structural relaxation exhibits a moderate dependence on temperature with the dimensionless fragility parameter α=3.3 (for strong systems, α is about 1 and increases to about 8 for some very fragile polymeric systems).     

Bioactive glasses in the system CaO-B2O3-P2O5: Preparation, structural study and in vitro evaluation

Glasses in the system x B₂O₃(1 − x) [y CaO P₂O₅], (x = 0, 0.1, 0.2, 0.3, y = 2, 2.6, 3, 4, 5) have been prepared by fast quenching of high temperature melts. The presence of B₂O₃ affected the glass forming ability, allowing the preparation of calcium phosphate glasses with y ? 2.6. The structure of glasses was analyzed by μ-Raman and infrared spectroscopy. The analysis indicated that the glass network is dominated by highly charged species from phosphate tetrahedra with 3 (pyro) or 4 (ortho) NBOs, while the boron atoms are incorporated mainly in 3 coordinated sites in the form of B∅₃ or B∅₂O⁻ units. A small fraction of units was also evident from the spectra analysis of glasses with high CaO content. All calcium borophosphate glasses exhibited bioactivity after soaking in SBF solution within a few days. This was observed by μ-Raman and SEM microscopy, while XRD patterns clearly revealed growth of hydroxyapatite phase. The presence of boron in the glass network has a catalytic effect at favoring bioactivity of the otherwise bioinert calcium phosphate glasses.     

Viscosity of (GeSe2)x(Sb2Se3)1−x undercooled melts

Viscosity of (GeSe₂)_x(Sb₂Se₃)_1−x undercooled melts (x = 0.4-0.8) was measured using parallel-plate method and penetration method. By using these two techniques viscosity of the whole measurable region of undercooled melt and of the part of glass region can be measured. In this relatively broad viscosity interval (seven orders of magnitude) all measured samples show Newtonian behavior and the dependence of their viscosity on temperature can be described by a simple Arrhenius equation. The kinetic fragilities calculated from these dependencies show similar compositional dependence as heat capacity changes at glass transition measured by DSC.     

Preparation of bioactive glass ceramic nanoparticles by combination of sol-gel and coprecipitation method

SiO₂-CaO-P₂O₅ ternary bioactive glass ceramic nanoparticles were prepared via the combination of sol-gel and coprecipitation processes. Precursors of silicon and calcium were hydrolyzed in acidic solution and gelated in alkaline condition together with ammonium dibasic phosphate. Gel particles were separated by centrifugation, followed by freeze drying, and calcination procedure to obtain the bioactive glass ceramic nanoparticles. The investigation of the influence of synthesis temperature on the nanopartilce’s properties showed that the reaction temperature played an important role in the crystallinity of nanoparticle. The glass ceramic particles synthesized at 55 °C included about 15% crystalline phase, while at 25 °C and 40 °C the entire amorphous nanopowder could be obtained. In vitro testing showed that the bioactive glass ceramic nanoparticles can induce the formation of hydroxylaptite from simulated body fluid rapidly. As a result, this bioactive glass ceramic nanoparticle with excellent bioactivity would be a promising filler material for bone tissues engineering.     

Raman scattering study of crystalline and melting states of BaO·2B2O3

Melting and crystallization scenarios of barium tetraborate BaB₄O₇ (BaO·2B₂O₃) are studied in situ by Raman spectroscopy. It is shown that the scenario depends on the temperature–time history of melt. Crystallization conditions of the beta modification of barium tetraborate (β-BaB₄O₇) from a stoichiometric glass structure BaO·2B₂O₃ were investigated.     

Investigation of the structure evolution process in sol-gel derived CaO-B2O3-SiO2 glass ceramics

A sol-gel method was used to prepare CaO-B₂O₃-SiO₂ (CBS) glass powder for making low-temperature cofired ceramics. This paper was focused on the mechanism of hydrolysis and polymerization and also on the structural evolution of xerogel at various temperatures. The xerogel was transformed into glass ceramics containing CaSiO₃ and CaB₂O₄ crystalline phases through nucleation and crystallization processes. The results indicated that the xerogel exhibits [BO₄] or [SiO₄] based three-dimensional network structure whose interstices Ca ions fill in, which becomes more orderly and stable after heat treatments. The CBS glass ceramics through controlled crystallization have a potential as electronic packaging materials.     

Crystallization processes of Li2O-Ga2O3-SiO2-NiO system glasses

Crystallization processes of Li₂O-Ga₂O₃-SiO₂-NiO system glasses have been studied by X-ray diffraction, differential calorimetry and optical absorption. Transparent glass-ceramic containing LiGa₅O₈:Ni²⁺ as the sole crystalline phase has been obtained from glass with the composition of 13Li₂O-23Ga₂O₃-64SiO₂-0.1NiO (in mol%) by the heat treatment in the temperature range from 923 to 953 K. It was revealed that the specific surface area of samples enhances crystallization of LiGaSi₂O₆ but obstructed that of LiGa₅O₈. LiGa₅O₈ grew to nano-sized crystallites dispersed in the glass matrices and did not affect the transparency seriously. In contrast, LiGaSi₂O₆ grew to crystallites with diameters more than 100 nm on the surface and made the glasses opaque. Optical absorption measurements revealed that doped Ni²⁺ occupied five-folded trigonal bipyramidal sites in the as-quenched glass matrices but six-folded octahedral sites of precipitated LiGa₅O₈ in the glass-ceramics. It was confirmed that transparent glass-ceramic containing Ni²⁺:LiGa₅O₈ was effectively obtained by the heat treatment at a temperature of 953 K for 10 h.     

Phase separation, crystallization and leaching of microporous glass ceramics in the CaO-TiO2-P2O5 system

Microporous glass ceramics belonging to the CaO-TiO₂-P₂O₅ system were prepared with the assumption of a 2:1 mole ratio for β-Ca₃(PO₄)₂:CaTi₄(PO₄)₆, the anticipated crystalline phases in the end product. The glasses formulated according to the above composition were melted and cast onto a steel mold and were crystallized to glass ceramics containing the above phases. Dilatometric/differential thermal analysis (DTA) techniques were utilized to determine the appropriate phase separation-nucleation and crystallization temperatures. The crystalline products and resulting microstructures in various stages of process were determined and observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). By leaching the resulting glass ceramics in HCl, β-Ca₃(PO₄)₂ was dissolved out leaving a porous skeleton of CaTi₄(PO₄)₆. It was found that the volume porosity, specific surface area and mean pore diameter of microporous glass ceramics can be managed through the proper selection of heat treatment conditions. In the optimized conditions for fabricating glass ceramics of minimum mean pore size the values of 41 ± 4%, 26 ± 3 m²/g and 14.3 ± 2 nm were obtained for porosity, surface area and pore diameter respectively.     

The effect of PbF2 content on the microstructure and upconversion luminescence of Er-doped SiO2-PbF2-PbO glass ceramics

The Er³⁺ doped transparent oxyfluoride glass ceramics were obtained by appropriate heat treatment of the precursor glasses with composition (mol%) 50SiO₂-xPbF₂-(50 − x)PbO-0.5ErF₃. The microstructure and optical properties of the glasses and glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), absorption spectra and luminescence spectra. The intensity of upconversion luminescence significantly increased in glass ceramics compared to that in precursor glass. The emission bands centered around 660 nm (⁴F_9/2 → ⁴I_15/2) and 410 nm (²H_9/2 → ⁴I_15/2) were simultaneously observed in glass ceramics but cannot be seen in the corresponding precursor glass. The influence of different PbF₂ content on the microstructure and upconversion luminescence of the samples was analyzed in detail. The results indicated that with the increase of PbF₂ content, the Ω₂ was almost the same and the ratios of red to green upconversion luminescence decreased in glass ceramics.     

Preparation and characterization of transparent Eu doped Y2O3 aerogel monoliths, for application in luminescence

This paper focuses on a new sol-gel preparation method of Eu doped Y₂O₃ aerogels, for application in luminescence and their characterization. The preparation method is based on a sol-gel technique using metal salts, by controlling the hydrolysis of these precursors with an epoxide. The monoliths prepared in this manner are transparent in the visible radiation domain. They have a mesoporous texture, a specific surface area of ≈350 to 400 m² g⁻¹ and they are X-ray amorphous. The gel network could be clearly observed by Transmission Electron Microscopy and showed the presence of localized poorly crystalline nanodomains, with some Eu segregation. A first evaluation of the luminescence which they develop during crystallization, has been carried out as a function of the heat treatment schedule.     

The glass transition temperature and infrared absorption spectra of: (70−x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Glasses of the system: (70−x) TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (T_g) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO₂ by Li₂O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm⁻¹. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure.     

Electrical conductivity of NbN-SiO2 films obtained by ammonolysis of Nb2O5-SiO2 sol-gel derived coatings

The studies of electrical conductivity of NbN-SiO₂ films are reported. To obtain these films, sol-gel derived xNb₂O₅-(100 − x)SiO₂ (where x = 100, 90, 80, 70, 60, 50 mol%) coatings were nitrided at 1200 °C. The nitridation process leads to the formation of some disordered structures, with NbN metallic grains dispersed in insulating SiO₂ matrix. The structure of the samples was studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The electrical conductivity was measured with the conventional four-terminal method in the temperature range from 5 to 280 K. The superconducting transition was not observed even for the sample that does not contain silica. All the samples exhibit negative temperature coefficient of resistivity. The results of conductivity versus temperature may be described on the grounds of a model proposed for a weakly disordered system.     

Structural investigations of copper doped B2O3-Bi2O3 glasses with high bismuth oxide content

Raman and infrared spectroscopy have been employed to investigate the 99.5%[xB₂O₃(1−x)Bi₂O₃]0.5%CuO glasses with different Bi/B nominal ratios (0.07?x?0.625) in order to obtain information about the competitive role of B₂O₃ and Bi₂O₃ in the formation of the glass network. The glass samples have been prepared by melting at 1100 °C and rapidly cooling at room temperature. In order to relax the structure, to improve the local order and to develop crystalline phases the glass samples were kept at 575 °C for 10 h. The influence of both Bi₂O₃ and CuO on the vitreous B₂O₃ network as well as the local order changes around bismuth and boron atoms in as prepared and heat treated samples was studied. Structural modifications occurring in heat treated samples compared to the untreated glasses have been observed.     

Electrical conductivity and dielectric properties of Bi2O3-GeO2-PbO-MoO3 glasses

Glasses having compositions 40Bi₂O₃-20GeO₂-(40−x)PbO-xMoO₃ (where x = 3, 6, 9, 12 and 15 mol%) were prepared by normal melt quenching technique. The density (d) decreases gradually with the increase of the MoO₃ content in such glasses. This may be due to the lower molecular weight MoO₃ is substituted by a higher molecular weight PbO. The dc conductivity decreases while the activation energy increases with the increase of the MoO₃ content. The dc conductivity in the present glasses is electronic depends strongly upon the average distance, R, between the Mo ions. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. Dielectric properties (constant ε, loss tan δ, ac conductivity σ_ac, over a range of frequency 0.12-100 kHz and temperature 325-650 K and frequency exponent s) of these glasses have been studied.     

Mössbauer spectra in the xNa2O·(1 − x − y)B2O3·yFe2O3 glass system

A Mössbauer spectroscopic study is made on xNa₂O·(1 ? x ? 7)B₂O₃·yFe₂O₃; 0.045 ? x ? 0.405 and y = 0.05, 0.10 and 0.15 samples quenched from the melt. The presence of two quadrupole doublets indicates that an amphoteric cation like Fe³⁺ occupies both the tetrahedral “network forming” and the octahedral “network modifying” sites in the glass structure. The observed variations of isomer shift and quadrupole splitting with the values of x are similar to the ones found earlier in lead borates but different from those observed earlier in soda borates and other alkali alumino borates. In samples with smaller values of x, an additional devitrified magnetic phase of Fe₂O₃ is seen. The distribution of Fe³⁺ ions in different sites and phases is also discussed.     

Influence of heat treatment on spectroscopic properties of Er in multicomponent ZrF4-ZnF2-AlF3-YF3-MF2 (M = Ca, Sr, Ba) based glass

Er³⁺ doped multicomponent fluoride based glass was prepared. These precursor fluoride glass samples were then heated using different schedules. Crystalline phase particles were successfully precipitated in the multicomponent fluoride glass samples after heat treatment. The influence of heat treatment on the spectroscopic properties of Er³⁺ in multicomponent fluoride based glass samples were discussed. Small changes of the Judd-Ofelt parameters Ω_i (i = 2, 4, 6) were found in multicomponent fluoride glass samples before and after heat treatment compared to oxyfluoride telluride glass. Preparation conditions used to produce transparent multicomponent fluoride glass ceramics doped with rare-earth ions are discussed.