Excess entropy and thermal behavior of Cu- and Ti-doped bioactive glasses

Bioactive glasses belong to the ceramic family. They are good materials for implantation due to their excellent capacities to create an intimate bond with bones. Copper is known for its anti-inflammatory, antibacterial, and antifungal properties. Titanium is biocompatible and resistant to corrosion. These chemical elements can be introduced in bioactive glasses to provide a wide variety of uses and to enhance the physiological properties of implanted biomaterials. In this work, bioactive glasses doped with different contents of copper and titanium were synthesized by the melting method. The purpose is to study the effect of doping metal element on the thermal characteristics (T _g, T _c, and T _f). The results revealed that the increase of the content of copper and titanium in the glass matrix decreases the melting temperature and induces an increase of the thermal stability. The excess entropies of pure and doped glasses were calculated. Obtained results highlighted the decrease of the excess entropy with the increase of metal elements contents.     

Study of crystallization process of soda lead silicate glasses by thermal and spectroscopic methods

The crystallization process of some glasses in the ternary Na₂O–SiO₂–PbO system with good chemical stability that can be used for waste inertization was studied using X-ray diffraction (XRD), infrared spectroscopy (FT-IR), differential thermal analysis (DTA) and scanning electron microscopy. The parent glasses were characterized by XRD and FT-IR, and their vitreous state was determined. DTA measurements evidenced glass transition (T _g) and crystallization temperatures (T _c). The thermal treatments were conducted at vitreous transition temperature (400 °C) and at highest effect of crystallization (650 °C). XRD evidenced the lead and sodium silicate crystalline phases in samples treated at 650 °C for 12 h. Micrometer crystallites dispersed in the glass matrices have affected the transparence of glasses and made them opaque after treatment at 650 °C. The influence of oxide quantities in compositions on the crystallization tendency was revealed. A PbO higher content than that of SiO₂ as well as lower Na₂O content decreased the tendency of crystallization.     

Elastic and dynamical properties of alkali-silicate glasses from computer simulations techniques

This paper shows recent progresses in the field of computer simulations of inorganic glasses. Molecular dynamics simulations and energy minimization methods have been applied to calculate the elastic and transport properties of alkali silicate glasses of compositions xM₂O · (100 ? x)SiO₂ (with x = 0, 10, 15, 20, 25, 30 % mol for M = Li, Na and K) and of a soda-lime glass with composition 15Na₂O · 10CaO · 75SiO₂, which has been employed to ascertain the effect of the replacement of CaO for Na₂O. The excellent agreement of the computed results with the experimental data highlights the important predictive and interpretative role reached by computer simulations techniques.     

Influence of MgO (CaO) on the structure of silicate-phosphate glasses

Thermal and structural properties of model silicate-phosphate glasses containing the different amounts of the glass network modifiers, i.e. Mg²⁺ and Ca²⁺ were studied. To explain the changes of the parameters characterizing the glass transition effect (T_g, Δc_p) and the crystallization process (T_c, ΔH) depending on the cations modifiers additions, analysis of the bonds and chemical interactions of atoms in the structure of glasses was used. ³¹P MAS-NMR spectra of SiO₂–P₂O₅–MgO(CaO)–K₂O glasses show that the phosphate complexes are mono- and diphosphate. It has been found that increasing amounts of Mg²⁺ or Ca²⁺ cations in the structure of glasses causes the reduction of the degree of polymerization of the phosphate framework (Q¹→Q⁰). The influence of increasing of modifiers in the structure of silicate- phosphate glasses on the number of non-bridging oxygens per SiO₄ tetrahedron and density of glasses was presented.     

Nucleation and crystal growth in Na2O · 2 CaO · 3 SiO2 glass: a DTA study

The non-isothermal devitrification of Na₂O · 2 CaO · 3 SiO₂ glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, T_m, and the activation energy values, E_c, for crystal growth.The temperature, T_m=580°C, is very close to the glass transition temperature, T_g=570°C, and the value of E_c=78 Kcal mole^?1 for the surface crystal growth is nearly the same as the value E_c=89 kcal mole^?1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped.     

Thermal characterisation of raw aluminosilicate glazes in SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaO–K<Subscript>2</Subscript>O–Na<Subscript>2</Subscript>O–ZnO system with variable content of ZnO

Thermal properties of raw aluminosilicate ceramic glazes in the multicomponent system of SiO₂–Al₂O₃–CaO–K₂O–Na₂O–ZnO modified by ZnO addition were studied by differential thermal analysis (DTA), dilatometry (DIL), hot-stage microscopy (HSM), X-ray diffraction and fourier transform infrared spectroscopy (FTIR). Using the method of differential thermal analysis, the ways in which zinc oxides affect the temperature of transition (T _g), crystallisation (T _c) were determined. An analysis of the DTA data obtained during thermal tests showed that an increase in ZnO content results in decreasing the T _g value. Also, the influence of ZnO on characteristic temperatures and viscosity of glazes was checked. The introduction of zinc oxide (ZnO) into the glaze composition contributes to the decrease in viscosity of such glazes. An increasing ZnO content in the glazes also causes the reduction in softening (T _s), half-sphere (T _half-sphere) and fusion (T _fusion) temperatures. The mid-infrared spectroscopy showed that the thermal properties of glazes in SiO₂–Al₂O₃–CaO–K₂O–Na₂O–ZnO system modified by addition of ZnO can be associated with the depolymerising influence of zinc ions on the structure of the tested glazes.     

Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

The vitrification of alkali borate and alkali silicate melts

Glasses and crystals of compositions corresponding to the congruently melting compounds M₂O·2SiO₂ (M = Na. Rb, and Cs) and M₂O·4SiO₂ (M = K, Rb, and Cs) were studied by differential scanning calorimetry. The structure temperatures (T _f) and excess entropies at T _f of glasses were measured depending on the rate of cooling of the corresponding melts. The activation energies of glass formation (ΔE) and scale of cooperative motion in the transition region (ξ_a) were estimated. The totality of the data obtained were used to compare the thermodynamic (the ratio between the excess (with respect to the corresponding crystals) entropy of glass at T _f and the entropy of crystal melting), kinetic (fragility m = f(ΔE, T _f)), and microscopic (ξ_a) parameters of the vitrification of alkali silicate melts. The behaviors of alkali silicate and alkali borate melts were shown to be similar.     

Some physical properties concerning the thermal conductivity data of BaO-containing silicate glasses in relation to structure

The thermal conductivity, density, refractive index and viscosity of glasses with base composition (wt%): Na₂O, 20; CaO, 15; SiO₂ 65, in which CaO is partially replaced by BaO, have been investigated.Both the thermal conductivity and the viscosity—temperature values progressively decreased by introducing BaO to replace CaO in the glasses. Meanwhile, this replacement caused an increase in other properties, i.e., density and refractive index. The experimental measurements and calculated values of either thermal conductivity or viscosity agree fairly well. The observed effects were correlated to factors such as polarization, field strength and ionic radii of the incorporated divalent cations, and their effect on the geometrical arrangement of the building units of the glassy network.     

Effect of boron oxide on the thermal conductivity of some sodium silicate glasses

The thermal conductivity of some ternary silicate glasses was measured by the steady-state method at 25°C. Experimental results show that introducing B₂O₃ to replace Na₂O or increasing the SiO₂ content of the glass increased the thermal conductivity. The results are discussed in terms of the possible variation in network structure with the change in glass composition, which may virtually affect the phonon mean-free-path.     

Thermal,IR, Raman characteristics,Raman gain coefficient and bandwidths in quaternary glasses

Tellurite glasses with composition 75TeO₂–5WO₃–15Nb₂O₅–5M_xO_y in mol%, where M_xO_y = (Na₂O, Ag₂O, ZnO, MgO, CuO, NiO, TiO₂, MnO₂) have been prepared by using the conventional melt-quenching method. Thermal characteristic of prepared glasses were investigated by using DTA techniques. It was found that the glass with the composition 751TeO₂–5WO₃–15Nb₂O₅–5TiO₂ had high thermal stability (ΔT = 122 °C at heating rate 15 K/min). Raman gain coefficients and bandwidths of prepared glasses for Raman gain media were evaluated. The glass with composition 75TeO₂–5WO₃–15Nb₂O₅–5Na₂O had the maximum value of Raman gain coefficient (g = 4.43 × 10⁻¹² m/W) and it was 24 times as large as silica glass. The highest value of full width half maximum (FWHM ≈ 185 cm⁻¹) was observed in glass system 75TeO₂–5WO₃–15Nb₂O₅–5NiO. Finally, the structure of the glasses was investigated through deconvolution Raman and IR spectra.     

Influence of SiO2 on the structure and optical properties of lithium bismuth silicate glasses

Bismuth silicate glasses containing lithium oxide with composition 20Li₂O·(80 − x)Bi₂O₃·xSiO₂ (5 ? x ? 70 mol%) have been prepared by melt-quench technique. Density (D), molar volume (V_M) and glass transition temperature (T_g) for all the glass samples have been measured. FTIR spectroscopy has been employed to investigate the structure of these glasses in order to obtain information about the competitive role of Bi₂O₃ and SiO₂ in the formation of glass network. The increase of SiO₂ content in the glass matrix results in increasing the Si-O-Si bond angle and hence the ionicity of Si-O bond increases with decrease in Bi₂O₃/SiO₂ ratio. The optical transmittance spectra of all the glasses have been recorded in the wavelength range 200-3300 nm. The values of optical band gap (E_g) have been determined from the cutoff wavelength of these glasses. The average electronic polarizability of oxide ion () and the optical basicity (Λ_th) have been estimated from the calculated values of the E_g and were found to be dependent directly on Bi₂O₃/SiO₂ ratio. The variation in different physical parameters such as D, V_M and T_g and optical parameters; viz., E_g, , Λ_th with Bi₂O₃/SiO₂ ratio have been analyzed and discussed in terms of change in the glass structure.     

Thermal properties of oxide glasses

A criterion based on the length of induction period of crystallization was used to evaluate the thermal stability of M₂O·SiO₂ (M?=?Li, Na) glasses against crystallization. It was founded out that the stability of studied glasses against crystallization is Li₂O·SiO₂?<?Na₂O·SiO₂. The results coincide with the order determined by stability criteria based on temperatures and the values of activation energy. A criterion based on the length of induction period enables to discriminate among the thermal stabilities of the silicate glass systems.     

Approach to thermal properties and electronic polarizability from average single bond strength in ZnOBi2O3B2O3 glasses

The glass transition temperature (T_g), density, refractive index, Raman scattering spectra, and X-ray photoelectron spectra (XPS) for xZnO-yBi₂O₃-zB₂O₃ glasses (x=10-65, y=10-50, z=25-60 mol%) are measured to clarify the bonding and structure features of the glasses with large amounts of ZnO. The average electronic polarizability of oxide ions (α_O2−) and optical basicity (Λ) of the glasses estimated using Lorentz-Lorenz equation increase with increasing ZnO or Bi₂O₃ content, giving the values of α_O2−=1.963 Å³ and Λ=0.819 for 60ZnO-10Bi₂O₃-30B₂O₃ glass. The formation of BOBi and BOZn bridging bonds in the glass structure is suggested from Raman and XPS spectra. The average single bond strength (B_MO) proposed by Dimitrov and Komatsu is applied to the glasses and is calculated using single bond strengths of 150.6 kJ/mol for ZnO bonds in ZnO₄ groups, 102.5 kJ/mol for BiO bonds in BiO₆ groups, 498 kJ/mol for BO bonds in BO₃ groups, and 373 kJ/mol for BO bonds in BO₄ groups. Good correlations are observed between T_g and B_MO, Λ and B_MO, and T_g and Λ, proposing that the average single bond strength is a good parameter for understanding thermal and optical properties of ZnOBi₂O₃B₂O₃ glasses.     

Crystallization and second harmonic generation in potassium-sodium niobiosilicate glasses

Transparent glasses having molar composition (23−x)K₂O·xNa₂O·27Nb₂O₅·50SiO₂ (x=0, 5, 10, 15 and 23) have been synthesized by the melt-quenching technique and their devitrification behaviour has been investigated by DTA and XRD. Depending on the composition, the glasses showed a glass transition temperature in the range 660-680 °C and devitrified in several steps. XRD measurements showed that the replacement of K₂O by Na₂O strongly affects the crystallization behaviour. Particularly, in the glasses with only potassium or low sodium content the first devitrification step is related to the crystallization of an unidentified phase, while in the glass containing only sodium, NaNbO₃ crystallizes. For an intermediate sodium content (x=10 and 15) a potassium sodium niobate crystalline phase, belonging to the tungsten-bronze family, is formed by bulk nucleation. This system looks promising to produce active nanostructured glasses as the tungsten-bronze type crystals have ferroelectric, electro-optical and non-linear optical properties. Preliminary measurements evidenced SHG activity in the crystallized glasses containing this phase.     

Investigations on the Thermal and Elastic Properties of ZnO-Incorporated Phosphate Glasses and Glass Ceramics

Abstract

Glasses of the 45P₂O₅-(40-x)CaO-15Na₂O-xZnO system with increasing zinc oxide (ZnO) concentrations within the ranges of 3 ≤ x ≤ 12 mol% were obtained by employing the melt-quench technique. ZnO inclusions in the phosphate glass network lead to increases in its density and, conversely, a decrease in its molar volume. On the basis of the obtained thermal analysis data, the glasses underwent thermal treatment, which helped to derive their glass ceramic equivalents. The evaluations of structural and elastic properties of glasses before and after thermal treatments were made using X-ray diffraction (XRD) studies and ultrasonic nondestructive testing. The differential thermal analysis data show the reduction in the crystallization tendency and increase in thermal properties, such as crystallization temperature (T _P), thermal stability

(T _c – T _g) (where T_c is crystallization onset temperature and T _g is glass transition temperature), thermal stability parameter (S), and degree of glassification (D _g) of phosphate glasses against the progressive additions of ZnO. The XRD of glass ceramics confirmed the dominance of metaphosphate, pyrophosphate, and ZnO-related crystalline features. The measured elastic moduli, such as longitudinal (L), shear (G), Young's (Y), and bulk (K), and Vicker's microhardness values increased in both glass and glass ceramics with an increase in ZnO incorporation.     

Effect of copper addition on glass transition of silicate–phosphate glasses

Glass transformation effect of mixed SiO₂?CP₂O₅?CK₂O?CMgO?CCaO?CCuO glasses was studied by DSC, XRD, SEM, and Raman spectroscopy methods. The relationship between the parameters characterizing glass transformation effect and an amount of phosphorous and copper forming the glassy structure was discussed. It was shown that an increasing content of phosphorous increased solubility of copper in the structure of the studied glasses which was the result of P?CO?CCu bonds formation. Degree of changes of T _g, ?c _p, and time of relaxation values were higher in glasses with higher content of P₂O₅ and CuO. The observed relations were explained on the basis of the local atomic interactions in the structure of glass.     

Influence of thermal stability on dielectric properties of SiO<Subscript>2</Subscript>–K<Subscript>2</Subscript>O–CaO–MgO glasses

Compositions of 55SiO₂–10K₂O–(35–x)CaO–xMgO are prepared by melt and quench technique. Thermal parameters of the as-prepared glasses are studied using the differential thermal analyzer under non-isothermal conditions. Kissinger, Augis–Bennett and Lasocka models are employed to investigate the kinetics of crystallization and thermal stability of these glasses. Based on this, it is concluded that CM-15 glass exhibits highest thermal stability. Raman spectroscopy is used to reveal the structural units of the glasses. Dielectric properties are observed through impedance spectroscopy. All the glasses are phase separated. The ratio of CaO/MgO influences the thermal stability, which leads to affect the dielectric properties. The highest dielectric permittivity is observed ~22 at room temperature and 100 Hz for CM-15 glass, where CaO/MgO ratio is ~1.33.     

Correlation between glass transition effect and structural changes in multicomponent iron phosphate-silicate glasses

Iron phosphate-silicate glasses from P₂O₅–SiO₂–K₂O–MgO–CaO–Fe₂O₃ system were subjected to the thermal and spectroscopic studies in order to gain information about their structure and thermal behavior in the range of glass transition effect. Research includes results obtained via DSC, MIR and DRIFT spectroscopy. Designated values of glass transition temperature and specific heat change slightly increases with Fe₂O₃ incorporation. Spectra collected during thermal treatment of glasses containing 2 and 30 mol% Fe₂O₃ exhibited various changes. Fe₂O₃ addition affected the glass structure by its reinforcement and led to its preservation during thermal treatment. The connection between density, molar volume, oxygen packing density and the chemical composition’s alteration were also established because of the direct dependence of physical properties and the structure. Obtained results supported thermal and spectroscopic studies. Conducted research is considered as a contribution to the knowledge about the family of iron phosphate glasses, which are known from their interesting properties and widely used applications.

     

Influence of cerium oxide on properties of glass–ceramic sealants for solid oxide fuel cells

The influence of the cerium oxide concentration on the properties of glasses and glass ceramics of the SiO₂–Al₂O₃–CaO–Na₂O–MgO–K₂O–B₂O₃–CeO₂ system as potential adhesive and sealing materials for solid oxide fuel cells was studied. According to the data of differential scanning calorimetry, variation of the CeO₂ concentration does not appreciably influence the glass transition and crystallization temperatures of glasses. As the cerium oxide concentration is increased, the linear thermal expansion coefficient increases for the glasses but decreases for the partially crystalline samples. The gluing temperature of the glass sealants prepared allows their use for joining YSZ solid electrolytes with interconnectors of Crofer22APU type in solid oxide fuel cells..