IR study of Pb-Sr titanate borosilicate glasses

The infrared spectra (IR) of various glass compositions in the glass system, [(Pb _x Sr_1−x )O·TiO₂]-[2SiO₂·B₂O₃]-[BaO·K₂O]-[La₂O₃], were recorded over a continuous spectral range (400–4000 cm⁻¹) to study their structure systematically. IR spectrum of each glass composition shows a number of absorption bands. These bands are strongly influenced by the increasing substitution of SrO for PbO. Various bands shift with composition. Absorption peaks occur due to the vibrational mode of the borate network in these glasses. The vibrational modes of the borate network are seen to be mainly due to the asymmetric stretching relaxation of the B-O bond of trigonal BO₃ units. More splitting is observed in strontium-rich composition.     

Optical absorption and infrared studies of some silicate glasses containing titanium

The optical absorption and infrared (IR) spectra of mixed alkali silicate glasses in the system 3SiO₂–(1 − x)Na₂O–xK₂O + 2.5–20 g of TiO₂ were measured. Absorption bands due to Ti³⁺ ions, at 500 and 570 nm, were observed in the spectrum of Na₂O-free glasses. The intensities of such bands were followed with the variation in TiO₂ content from 2.5 to 20 g (per 100 g of glass). The incorporation of titanium oxide as Ti³⁺ in the Na₂O-free glass, conferring a violet hue to it, was explained on the basis of the acidity–basicity character of the glass. The IR measurements have been used to explore the structural changes throughout the compositional variations. This revised version was published online in November 2006 with corrections to the Cover Date.     

FT-IR,Raman and UV–VIS spectroscopic studies of copper doped 3Bi<Subscript>2</Subscript>O<Subscript>3 </Subscript>·B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass matix

FT-IR, Raman and UV–VIS experimental results were presented for xCuO·(100-x)[3Bi₂O₃·B₂O₃] glass system, where 0 ≤ x ≤ 50 mol%. The FT-IR measurements indicate the presence in xCuO·(100-x)[3Bi₂O₃·B₂O₃] glasses of BO₃, BO₄ units, BiO₃ pyramidal and distorted BiO₆ octahedral units and their dependence of CuO content. The Raman scattering data indicate that for 0 ≤ x ≤ 10 mol% the structure of studied glasses consist from BiO₃ pyramidal and distorted BiO₆ octahedral units, ring and chain type of metaborate groups, ortoborate and pyroborate groups. For higher concentration the Raman spectra suggest that the structure become more disordered. The FT-IR and Raman bands characteristic for CuO were not directly evidenced, but the absorption bands specific for the glass matrix are influenced by the presence of copper ions in the glass network structure. The optical absorption confirms the presence of Cu²⁺ in the CuO doped 3Bi₂O₃·B₂O₃ glass matrix.     

Effect of secondary heat treatment on the spectroscopic properties of Na<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

We have studied the optical absorption and luminescence spectra of 45Na₂O · xNb₂O₅ · (55 − x)P₂O₅ glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb₂O₅. The results indicate that the absorption band around 26000 cm⁻¹, responsible for the yellow color of the glasses, is due to the [Nb^(5+)--O⁻] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu³⁺ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu³⁺ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.     

Kinetics and mechanisms of converting bioactive borate glasses to hydroxyapatite in aqueous phosphate solution

Borate bioactive glasses are receiving increasing attention as scaffold materials for bone repair and regeneration. In this study, the kinetics and mechanisms of converting three groups of sodium–calcium–borate glasses with varying CaO:B₂O₃ ratio to hydroxyapatite (HA) in 0.25 M K₂HPO₄ solution were investigated at 10–70 °C. Glass disks with the composition 2Na₂O·(2 − x)CaO·(6 + x)B₂O₃ (x = 0, 0.5, and 1.0) were immersed for up to 8 days in the potassium phosphate solution. The conversion kinetics to HA were monitored by measuring the weight loss of the glass, while X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy were used to study structural and compositional changes. All three groups of glasses formed HA on their surfaces, showing that the glasses were bioactive. At 10–37 °C, the conversion kinetics was well fitted by the contracting sphere model. Also, the contracting sphere model has a good fit for the early stage of conversion at 70 °C, whereas a three-dimensional (3D) diffusion model provided a good fit to the data of the later stage. The results of this study provide kinetic and structural data for the design of borate bioactive glasses for potential applications in bone tissue engineering.     

Viscosity properties of sodium borophosphate glasses

The viscosity behavior of (1 − x)NaPO₃−xNa₂B₄O₇ glasses (x = 0.05-0.20) have been measured as a function of temperature using beam-bending and parallel-plate viscometry. The viscosity was found to shift to higher temperatures with increasing sodium borate content. The kinetic fragility parameter, m, estimated from the viscosity curve, decreases from 52 to 33 when x increases from 0.05 to 0.20 indicating that the glass network transforms from fragile to strong with the addition of Na₂B₄O₇. The decrease in fragility with increasing x is due to the progressive depolymerization of the phosphate network by the preferred four-coordinated boron atoms present in the low alkali borate glasses. As confirmed by Raman spectroscopy increasing alkali borate leads to enhanced B-O-P linkages realized with the accompanying transition from solely four-coordinated boron (in BO₄ units) to mixed BO₄/BO₃ structures. The glass viscosity characteristics of the investigated glasses were compared to those of P-SF67 and N-FK5 commercial glasses from SCHOTT. We showed that the dependence of the viscosity of P-SF67 was similar to the investigated glasses due to similar phosphate network organization confirmed by Raman spectroscopy, whereas N-FK5 exhibited a very different viscosity curve and fragility parameter due to its highly coordinated silicate network.     

Spectroscopic investigations of Cu2+ in Li2O-Na2O-B2O3-Bi2O3 glasses

Pure and copper doped glasses with composition,x Li ₂ O-(40-x)Na ₂ O-50B ₂ O ₃-10Bi ₂ O ₃,have been prepared over the range 0 ≤ x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu²⁺ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, α² and β², have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO₃ and BO₄ units in the disordered manner.     

Ultrasonic velocity in sodium borate glasses

Ultrasonic velocities in sodium borate glasses are measured as a function of composition at a frequency of 10 MHz and at a temperature of 298 K by making use of the ultrasonic pulse echo overlap method. Elastic properties of these glasses are analysed in terms of the elastic internal energy due to deformation; elastic resistances of the network-former, B₂O₃, and the modifier, Na₂O, are obtained as a function of composition from the plot ofMV ² againstx ₂, whereM is the molar mass of sodium borate glasses,V the velocity of sound andx ₂ the mole fraction of Na₂O. The elastic resistances of B₂O₃ and Na₂O are as follows: (i) forx ₂<0.33, the elastic resistance of B₂O₃ is smaller than that of Na₂O; (ii) atx ₂=0.33, the elastic resistances of B₂O₃ and Na₂O are equal; (iii) forx ₂>0.33, the elastic resistance of B₂O₃ is greater than that of Na₂O; (iv) atx ₂≈0.15, the elastic resistances of B₂O₃ and Na₂O become respectively maximal and minimal; (v) atx ₂≈0.23, the elastic resistances of B₂O₃ and Na₂O become respectively minimal and maximal; (vi) abovex ₂=0.36, the elastic resistance of Na₂O becomes negative.     

Kinetics and mechanisms of the conversion of silicate (45S5), borate, and borosilicate glasses to hydroxyapatite in dilute phosphate solutions

Bioactive glasses with controllable conversion rates to hydroxyapatite (HA) may provide a novel class of scaffold materials for bone tissue engineering. The objective of the present work was to comprehensively characterize the conversion of a silicate bioactive glass (45S5), a borate glass, and two intermediate borosilicate glass compositions to HA in a dilute phosphate solution at 37°C. The borate glass and the borosilicate glasses were derived from the 45S5 glass by fully or partially replacing the SiO₂ with B₂O₃. Higher B₂O₃ content produced a more rapid conversion of the glass to HA and a lower pH value of the phosphate solution. Whereas the borate glass was fully converted to HA in less than 4 days, the silicate (45S5) and borosilicate compositions were only partially converted even after 70 days, and contained residual SiO₂ in a Na-depleted core. The concentration of Na⁺ in the phosphate solution increased with reaction time whereas the PO₄^3– concentration decreased, both reaching final limiting values at a rate that increased with the B₂O₃ content of the glass. However, the Ca²⁺ concentration in the solution remained low, below the detection limit of atomic absorption, throughout the reaction. Immersion of the glasses in a mixed solution of K₂HPO₄ and K₂CO₃ produced a carbonate-substituted HA but the presence of the K₂CO₃ had little effect on the kinetics of conversion to HA. The kinetics and mechanisms of the conversion process of the four glasses to HA are compared and used to develop a model for the process.     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.     

Spectroscopic characterization of alkali borosilicate glasses containing iron ions

Structural properties of alkali borosilicate glasses containing iron ions were investigated using infrared, laser Raman and Mössbauer spectroscopy. Two types of glasses were prepared: SRL-type with the composition 18.5 wt% Na₂O, 10.0 wt% B₂O₃, 52.5 wt% SiO₂, 4.0 wt% Li₂O, 10 wt% TiO₂ and 5.0 wt% CaO, and sodium borosilicate glass with the composition 16.7 wt% Na₂O, 18.7 wt% B₂O₃ and 64.6 wt% SiO₂. Raman spectroscopy showed that orthosilicates are the dominant amorphous phase in the SRL-type of glass. Incorporation of iron in the SRL-type of glass induced polymerization of silicate units and -Si-O-Fe- copolymerization. It was concluded that different amorphous phases are simultaneously present in the SRL-type of glass containing iron ions. Interpretation of the Raman spectra is given. Incorporation of iron ions into the sodium borosilicate glass also affected the corresponding IR spectra. The valence state of iron and its coordination were determined by⁵⁷Fe Mössbauer spectroscopy.     

FTIR and Raman spectroscopic investigation of some strontium–borate glasses doped with iron ions

Structural investigation of xFe₂O₃·(100 − x)[3B₂O₃·SrO] glass system, with 0 ≤ x ≤ 40 mol%, was performed by means of X-Ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies. The purpose of this work was to investigate the structural changes that appear in the 3B₂O₃·SrO glass matrix with the addition and increasing of iron ions content. The XRD pattern for the prepared samples shows that vitreous phase is present only for x ≤ 40 mol%. For sample containing 50 mol% Fe₂O₃ was evidenced the presence of a unique crystalline phase, Fe₂O₃, embedded in an amorphous matrix. FTIR data show that BO₃ and BO₄ are the main structural units of the glass system and the iron ions are located in the network. The Raman spectrum of glass matrix indicates a structure with several borate groups (di-, meta-, pyro-borate, etc.). In higher concentrations the iron ions break the regulate glass network and determines the appearance of BO₄ isolated units.     

Crystallization characteristic and properties of some zinc containing soda lime silicate glasses

The crystallization behaviour of some soda lime silicate glasses modified by ZnO/CaO replacement to give the composition (Na₂O)₂·CaO_1−x ·(ZnO) _x ·3SiO₂ (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been investigated using differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD). The thermal expansion coefficients and AC electrical properties in the frequency range 40 Hz–5 MHz of the obtained crystalline products were determined. Two forms of sodium calcium silicate (Na₄CaSi₃O₉ & Na₂Ca₂Si₃O₉), sodium metasilicate-Na₂SiO₃, two types of sodium zinc silicate (Na_1.31Zn_0.655Si_1.345O₄ & Na₂ZnSiO₄) and α-quartz phases were mostly developed in the crystallized glasses using various heat-treatment processes. The coefficient of thermal expansion of the obtained glass–ceramic materials are between 120 × 10⁻⁷°K⁻¹ and 168 × 10⁻⁷°K⁻¹ in the 25°–600 °C temperature range. The increase of frequency generally resulted in the increase of the conductivity and decrease the dielectric constant together with the loss tangent of the glass–ceramic materials.     

Spectroscopic investigations and physical properties of Mn doped mixed alkali zinc borate glasses

Spectroscopic investigations on Mn²⁺ doped 20ZnO + xLi₂O + (30−x)Na₂O + 50B₂O₃ (5 ≤ x ≤ 25) (ZLNB) glasses reveal the non-linear behavior in their physical and structural properties. FT-IR spectra of ZLNB glasses reveal diborate units in the borate network. EPR spectra exhibit characteristic resonance signals of Mn²⁺ ions. A well resolved six line hyperfine structure around g = 2.02 corresponds to the sites of Type II, and a weak broad shoulder around g = 2.7 followed by an unresolved intense signal at g = 4.25 corresponding to sites of Type I are observed for their respective transitions. A large value of zero-field splitting parameter (D) is observed and it behaves non-linearly, reaches a maximum at x = 15 mol% with increase in Li₂O content. Δg values reveal the ionic nature of glass systems. Optical absorption spectra suggest the distorted octahedral site symmetry of Mn²⁺ ions in the host. Mixed alkali effect is evident in bandgap and Urbach energies.     

The local structure of bismuth borate glasses doped with europium ions evidenced by FT-IR spectroscopy

Glasses of the xEu₂O₃ · (100 − x)[4Bi₂O₃ · B₂O₃] system, with 0 ≤ x ≤ 40 mol% were studied by FT-IR spectroscopy and density measurements. FT-IR spectroscopy and density data suggest that the europium ions play the network modifier role in the studied glasses. These data show that the glass structure consists on the BiO₃, BiO₆, BO₃ and BO₄ units, and the conversion among these units mainly depends on the Eu₂O₃ content.     

Fatigue limit and crack arrest in alkali-containing silicate glasses

Crack growth, including fatigue limit and crack arrest, have been investigated for glasses of the systemsxNa₂O-11Al₂O₃-(89-x)SiO₂,xNa₂O-(100-x)SiO₂ andxNa₂O-7CaO-(93−x)SiO₂ in water as well as in acid and alkaline solutions. From studies of the dependence of the crack arrest on the alkali content of the glass, the kind of alkali (K⁺, Na⁺, Li⁺), the pH of the corrosive medium, the ageing time and ageing loading in conjunction with measuring the alkali leaching behaviour, the basic mechanism of crack arrest and fatigue limit can be concluded. Owing to load- and medium-dependent diffusion processes, a crack-growth retarding leached layer at the crack is generated with modified strength and crack growth properties compared to the bulk properties. In high alkali-containing glasses the process is additionally stimulated by stresses produced in the leached layer at the crack tip and at the crack surfaces.     

Structure–property correlations in the SiO<Subscript>2</Subscript>–PbO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

SiO₂–PbO–Bi₂O₃ glasses having the composition of 35SiO₂–xPbO–(65−x)Bi₂O₃ (where x = 5, 10, 15, 20, 25, 35, 45; in mol%) have been prepared using the conventional melting and annealing method. Density, molar volume and Vickers microhardness of the prepared glasses were measured. Infrared (IR) and UV–visible spectroscopic techniques were used for structural studies of these glasses. Density as well as the microhardness increase systematically and, conversely, the molar volume decreases with increasing the lead oxide content. This behavior can be explained by the correlation with the glass structure. Increasing the lead oxide content (≥20 mol%) increases the network former PbO₄ groups which can play an important role in increasing the connectivity and compactness of the glass matrix via increasing the cross-linking with the other constituent silicate and bismuthate structural units. The increased compactness may explain, in turn, the increase of the density and microhardness. IR spectra reinforce the idea that bismuth participates in the glassy network predominantly as BiO₆ octahedral structural units. UV–VIS optical absorption spectra revealed UV-charge transfer absorption bands related to the contribution of Pb²⁺ ions in the region 350–385 nm; in addition to the extrinsic absorption of trace iron impurities in the range 220–290 nm. In the visible region, three optical bands in the ranges 415–435, 605–650 and 880–890 nm were correlated with the contribution of electronic transitions in Bi³⁺ ions. Calculation of the optical mobility gap and the width of the energy tail of glass from the UV–VIS absorption indicated a slight increase followed by a decrease in their values. The behavior change occurred at the glass in which PbO content is 20 mol% where lead oxide starts to participate into the glassy matrix as a network former. The combination of analytical FTIR and UV–visible spectroscopy provided a consistent picture of structure–property relations in this glass system.     

Structural investigations of some bismuth–borate–vanadate glasses doped with gadolinium ions

X-ray diffraction (XRD), Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) spectroscopies have been employed to investigate the xGd₂O₃ · (95 − x)[2Bi₂O₃ · B₂O₃] · 5V₂O₅ glass system, with 0 ≤ x ≤ 25 mol%. The glass samples have been prepared by melting at 1,100 °C for 10 min followed by rapid cooling at room temperature. The structure of samples was analyzed by means of XRD. The pattern obtained did not reveal any crystalline phase in the samples up to 25 mol%. FTIR spectroscopy data suggest that the gadolinium ions play the network modifier role in the studied glasses. These data show that the glass network consists of BiO₃, BiO₆, BO₃, BO₄, and VO₄ structural units. The FTIR data show that a conversion among these units takes place and this process mainly depends on the Gd₂O₃ content. The EPR spectra of the studied glasses exhibit three important features with effective g-values of ≈5.9, 2.85, 2.0 and a weaker feature at g _eff ≈ 4.8. For low Gd₂O₃ contents (x ≤ 10 mol%), the EPR spectra have the typical ‘‘U’’-type shape. For higher contents of Gd₂O₃ (x > 10 mol%), the spectral features are broadened and finally are dominated by a single broad absorption line located at g _eff ≈ 2.0. This broad EPR line is associated to the Gd³⁺ ions present predominantly as clustered species.     

Structural investigation of xAg2O · (100 − x)[2B2O3 · As2O3] glass system

Structural analysis of xAg₂O · (100 − x)[2B₂O₃ · As₂O₃] glass system, with 0 ≤ x ≤ 10 mol%, was performed by means of FT-IR and Raman spectroscopies. The purpose of this work is to investigate the structural changes that appear in the 2B₂O₃ · As₂O₃ glass matrix with the addition and increase of silver ions content. Boroxol rings, pyro-, ortho-, di-, tri-, tetra-, and penta-borate groups, structural units characteristic to As₂O₃ were found in the structure of the studied glasses. FT-IR spectroscopy measurements show that BO₃ units are the main structural units of the glass system. The presence of structural units characteristic to Ag₂O were not directly evidenced by FT-IR spectroscopy. Raman analysis leads to similar conclusions as that obtained from FT-IR measurements.     

Conductivity studies of lithium zinc silicate glasses with varying lithium contents

The electrical conductivity of lithium zinc silicate (LZS) glasses with composition, (SiO₂)_0.527 (Na₂O)_0.054(B₂O₃)_0.05(P₂O₅)_0.029(ZnO)_0.34−x (Li₂O) _x (x = 0.05, 0.08, 0.11, 0.18, 0.21, 0.24 and 0.27), was studied as a function of frequency in the range 100 Hz–15 MHz, over a temperature range from 546–637 K. The a.c. conductivity is found to obey Jonscher’s relation. The d.c. conductivity (σ _d.c.) and the hopping frequency (ω _h), inferred from the a.c. conductivity data, exhibit Arrhenius-type behaviour with temperature. The electrical modulus spectra show a single peak, indicating a single electrical relaxation time, τ, which also exhibits Arrhenius-type behaviour. Values of activation energy derived from σ _d.c., ω _h and τ are almost equal within the experimental error. It is seen that σ _d.c. and ω _h increase systematically with Li₂O content up to 21 mol% and then decrease for higher Li₂O content, indicating a mixed alkali effect caused by mobile Li⁺ and Na⁺ ions. The scaling behaviour of the modulus suggests that the relaxation process is independent of temperature but depends upon Li⁺ concentration.