Thermal behaviour and excess entropy of bioactive glasses and Zn-doped glasses

Bioactive glasses prepared in SiO₂–CaO–Na₂O and P₂O₅ system are used as biomaterials in orthopaedic and maxillofacial surgery. Zn presents high physiological interest. It enhances physiological effects of implanted biomaterials. In this work, the thermal characteristics (T _g, T _c and T _f) of pure bioactive glass elaborated with different amounts of CaO, Na₂O in pure glass and with different amounts of introduced Zn in glass (ranging from 0.1 to 10 in mass%), were studied. The excess entropy was calculated for different compounds. Glasses were prepared by the melting process. The thermal behaviour of obtained bioactive glasses was determined using differential thermal analysis. Therefore, the glass transition (T _g), the crystallization (T _c) and the melting temperatures (T _f) were revealed. Moreover, according to Dietzel formula, the thermal stability (TS) of the studied bioactive glasses has been calculated. The first results concerning the impact of different oxides, revealed a decrease of the TS, T _g, T _c and T _f when the SiO₂/CaO increases and revealed an increase of these thermal characteristics when the SiO₂/Na₂O and CaO/Na₂O ratios increase. Introducing Zn into the bioactive glasses induces a decrease of T _f and an increase of TS. Contrary to crystals, prepared glasses have entropy different to zero at T = 0 K and vary versus T _f. The excess entropy of pure glasses and Zn-doped glasses were calculated. The significant variations were registered.     

Influence of fluorine on thermal properties of lead oxyfluoride glass

Oxyfluoride glasses are the basic materials for obtaining transparent glass–ceramic (TGC) which can be used in a wide range of optoelectronics devices such as: amplifiers, up-conversion, telescopes, laser sources. Oxyfluoride TGC is obtained by the control heat treatment of the parent glass due to low phonon nanocrystalline phases. The oxyfluoride glasses from the sodium–lead–silica system were the object of investigation. The influence of fluoride content on the thermal properties of glasses was analyzed. Thermal characteristics of glasses like the transition temperature T _g, the temperature for the crystallization onset T _x, and the maximum crystallization temperature T _c, thermal stability parameter were determined by DTA/DSC method. The linear expansion coefficients of oxyfluoride glasses as a function of temperature were measured using a thermo-mechanical analyzer (TMA 7 Perkin-Elmer). The effect of crystallization on the thermal expansion coefficient and softening temperature T _s was found.     

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.     

Effect of Y2O3 addition on viscosity and crystallization of the lithium aluminosilicate glasses

The melting and crystallization behaviors of lithium aluminosilicate (LAS) glasses containing Y₂O₃ were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and viscosity test. Effects of Y₂O₃ on the viscosity of LAS glasses were investigated from the softening point temperature to melting temperature. It was indicated that the introduction of yttria effectively decreased the melting temperature and viscosity of LAS glasses. The DTA and XRD results showed that yttria controlled the crystallization of LAS glasses by increasing the crystallization peak temperature (T_p) and activation energies (E), and the main crystalline phase of glass-ceramics was β-spodumene.     

Thermoanalysis of quasi-ternary As2(S,Se, Te)3 semiconductor glasses

In comparison with other chalcogenide glassy systems, less attention has been paid to the quasi-ternary (quaternary) system As₂(S, Se, Te)₃. In this paper, thermal methods were used to characterize ten different quaternary homogenous semiconductor glasses that were prepared by mixing the stoichiometric binary systems As₂S₃, As₂Se₃ and As₂Te₃. The ratios of the constituent binaries in the quasi-ternary glasses exerted a great influence on their thermal spectrum. The samples poor in As₂Te₃ showed neither the exothermic nor the endothermic peak due to crystallízation (T _c) and melting (T _m), respectively, but only the glass transition (T _g). Three transition temperatures,T _g, T_c andT _m, were detected for other compositions. On the other hand, a phase separation was observed in the samples rich in As₂Te₃. A cyclic scanning technique was used to investigate the thermally-induced phases during two consecutive heat ing-cooling cycles covering the temperature rangeT _g?T_m. The energy of decompositionE _d decreased on increase of the ratio As₂S₃/As₂Se₃ (at constant As₂Te₃), whereas it increased on increase of the ratio As₂Te₃/As₂Se₃ (at constant As₂Se₃ or As₂S₃).     

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.     

Multiple melting behavior of poly(butylene succinate)

The multiple melting behavior of poly(butylenes succinate) (PBS) isothermally crystallized from the melt was investigated using differential scanning calorimetry (DSC), temperature modulated DSC (MDSC) and polarized optical microscopy. PBS exhibits at most four melting endotherms (denoted as T_m1, T_m2, T_m3, and T_m4 from high to low temperatures) and a crystallization exotherm (denoted as T_re) in the DSC heating trace. Multiple melting endotherms were observed even at high heating rates. The origins of each endothermal and exothermal peak were discussed in detail. It is suggested that: (i) the crystallization exothermic peak, T_re, relates to the recrystallization of the melt of the crystallites with lower thermal stability; (ii) the T_m1 is ascribed to the melting of crystallites formed through recrystallization; (iii) two crystal populations with different thermal stability are responsible for the T_m2 and T_m3; (iv) the T_m4, which is the annealing peak, represents the transition of the rigid amorphous fraction (RAF) from solid-like RAF into liquid-like amorphous fraction.     

Structure and properties of glasses in the system Li2O–SnO–B2O3

Glasses in the system Li₂O–SnO–B₂O₃ system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B₂O₃ glasses exhibited relatively low glass-transition temperatures (T_g) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of T_g indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B₂O₃ binary system.     

Viscosity and thermal expansion of soda-lime-silica glass doped with Gd2O3 and Y2O3

In order to reveal the effects of rare earth elements on the rheological behavior of silicate melt, the properties of viscosity and thermal expansion of soda-lime-silica glass doped with Gd₂O₃ and Y₂O₃ were investigated by the rotating crucible viscometer and dilatometry. The results show that, introduction of Gd₂O₃ and Y₂O₃ increases the coefficient of thermal expansion and decreases viscosity of soda-lime-silica glass. When the amount of Gd₂O₃ and Y₂O₃ increases from 0 to 1.00 mol%, the coefficient of thermal expansion of soda-lime-silica glass increases firstly from 7.67 to 7.79 and 8.05, and then decreases to 7.78 and 7.66 ( × 10⁻⁶ °C⁻¹) respectively. In the case of melting temperature, its value decreases from 1830K to 1714 K, and then elevates to 1727 K as the content of Gd₂O₃ up to 1.00 mol%, however, as Y₂O₃ content increases from 0 to 1.00 mol% the melting temperature decreases monotonously from 1830K to 1737 K. The viscosity, melting temperature and coefficient of thermal expansion of soda-lime-silica glasses co-doped with Gd₂O₃ and Y₂O₃ are larger, comparing with glasses doped solely with Gd₂O₃ or Y₂O₃. The effect of co-doping with Gd₂O₃ and Y₂O₃ on thermal expansion and viscosity properties of soda-lime-silica glass, which is similar with the mixed-alkali effect in silicate glasses, is also observed.     

Thermal properties and applications of low molecular weight polyhydroxybutyrate

The properties of the low molecular weight polyhydroxybutyrate (LMWPHB) and LMWPHB plasticized polyhydroxybutyrate (PHB) are studied using differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM), mechanical, and biodegradation tests. The results of DSC, WAXD, and POM indicate that LMWPHB has a lower glass transition temperature (T _g), crystallinity, crystallization rate, melting temperature (T _m), and crystal size than PHB due to its much smaller molecular weight. The tensile strength, T _g, T _m, crystallinity, crystallization rate, and thermal stability of LMWPHB plasticized PHB decrease, while the flexibility and biodegradation rate increase with the increasing content of the added LMWPHB. It is confirmed that LMWPHB can be used to improve the brittleness and control the biodegradation rate of PHB.     

Studies on the thermal properties of caprolactam/long chain lactam copolymer

The thermal properties of caprolactam/long chain lactam copolymer were studied with a Perkin-Elmer DSC 7. The melting point (T _m), heat of fusion (δH _m), crystalline degree (X _c), crystallization temperature (T _c) and glass transition temperature (T _g) of the copolymers increase with decrease of the content of the log chain lactam. From the changes in the mechanical properties with corresponding changes in the thermal properties, it is clear that the copolymers are thermal plastic and elastic. In addition, it is found that the results at a heating rate of 10 deg·min^?1 are almost the same as that at 20 deg·min^?1 after thermal history is erased.     

Monoelemental polymers: Structure and properties

Monoelemental polymers with various chemical constitutions and different spatial structures (linear Te _n , Se _n , and S _n ; planar graphite C _n , black phosphorus P _n , As _n , Sb _n , and Bi _n ; and chemically bonded three-dimensional diamond C _n , B _n , Si _n , and Ge _n ) were considered and categorized as a class of covalent macromolecular compounds. Quantitative expressions relating the thermal (melting point, thermal expansion coefficient, heat conductivity) and elastic (microhardness, bulk compression modulus of elasticity) properties of polymers to the energy of intra-and intermolecular interactions and the equilibrium length of chemical bonds in the crystalline and glassy states are given. A numerical correlation between the spatial structure of polymers and their thermal and elastic properties was obtained. The hypothetical melting point of diamond at normal pressure was calculated as T _f = 3155 K.     

Kinetics of phase transition and thermal stability in Se80?x Te20Zn x (x?=?2, 4, 6, 8, and 10) glasses

Se_80?x Te₂₀Zn _x (x?=?2, 4, 6, 8, and 10) glasses have been prepared using conventional melt quenching technique. The kinetics of phase transformations (glass transition and crystallization) have been studied using differential scanning calorimetry (DSC) under non-isothermal condition at five different heating rates in these glasses. The activation energy of glass transition (E _t), activation energy of crystallization (E _c), Avrami exponent (n), dimensionality of growth (m), and frequency factor (K _o) have been investigated for the better understanding of growth mechanism using different theoretical models. The activation energy is found to be highly dependent on Zn concentration. The rate of crystallization is found to be lowest for Se₇₀Te₂₀Zn₁₀ glassy alloy. The thermal stability of these glasses has been investigated using various stability parameters. The values of these parameters were obtained using characteristic temperatures, such as glass transition temperature T _g, onset crystallization temperature T _c, and peak crystallization temperature T _p. In addition to this, enthalpy-released during crystallization has also been determined. The values of stability parameters show that the thermal stability increases with the increase in Zn concentration in the investigated glassy samples.     

A new method of calculation of the melting temperatures of crystals of Group 1A metal halides and francium metal

A new method of calculation of melting temperatures of binary ionic crystals has been suggested. The method is based on finding a matrix relation between the ionic radii (the lattice energy U) and melting temperature of ionic crystals of the MX type, where M is a Group 1A metal, and X is a halogen. From the equation for the lattice energy U, a new equation has been derived for calculation of the melting temperature of ionic crystals with the use of only the ionic radii and the degree of bond ionicity ?: T _m = f(U, ?). The average error of determination of T _m for alkali-metal halides is 2.80%. The melting temperatures of francium halides and alkali-metal astatides (including FrAt) have been calculated. It has been shown that the accuracy of calculation of the melting temperature of ionic crystals depends on the degree of bond ionicity: the error increases with an increase in the covalent contribution. On the basis of the melting temperatures of metal halide crystals, a method has been developed for the calculation of the melting temperatures of corresponding metals. The melting temperature of francium has been calculated to be 24.861 ± 0.517°C.     

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.     

Infrared,Raman and XPS spectroscopic studies of Bi2O3–B2O3–Ga2O3 glasses

Glasses with compositions 60Bi₂O₃–(40?x)B₂O₃–xGa₂O₃ (x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga₂O₃. The glass transition temperature (T_g), the onset crystallization temperature (T_x), ΔT (T_x?T_g) decrease with the content of Ga₂O₃. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga₂O₃. On the other hand, the addition of Ga₂O₃ causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi⁵⁺ and Bi³⁺ exist in 5 mol% Ga₂O₃ content, while Bi⁵⁺ amounts decrease with the increase of Ga₂O₃ contents. The glass is mainly composed of [BiO₆], [BO₃], [BO₄] and [GaO₄] polyhedra. Glasses are supposed to have layer structure. [BO₃] triangle and [BO₄] tetrahedra may be located between the [GaO₄] tetrahedral and [BiO₆] octahedra to prevent crystallization and to compensate electric charge.     

Synthesis and electro-optical features of a high T g polymer system with excellent electro-optic activity and thermal stability

Three chromophores with tricyanofuran and tricyanopyrroline electron acceptors were synthesized and doped in high glass transition temperature (T _g) polymer poly(N-(4-acetoxylphenyl)maleimide-co-styrene, NAPMI-co-ST). The electro-optic (EO), optical, and thermal properties of the doped poly(NAPMI-co-ST) were characterized and discussed. After being corona poled under 12?kV, this high T _g polymer material showed excellent EO activity and thermal stability. The highest EO coefficient (r ₃₃) reached 48.2?pm?V^?1 (1,310?nm) and could remain 90?% of the original value for 100?h at 85?°C. The EO coefficient was relatively higher compared with other high T _g EO polymers. The thermal stability was also very good and the manufacture process was convenient and applicable for device fabrication.     

Study of the thermal behaviour of some transition metal acrylate-styrene copolymers

The processes of thermal destruction of copolymers of styrene with zinc, cobalt, nickel and copper acrylates have been studied by TG and the temperature characteristics have been determined. While the thermal stability of zinc-containing copolymers increases at higher metal contents, that of other metal-containing copolymers decreases and, depending on the metal, changes in the sequence Co > Ni > Cu. The kinetic parametersn, E _a ,Z and ΔS have been determined by the Horowitz-Metzger method and discussed. The resultingE _a sequence is in agreement with the observed sequence of thermal stability of the copolymers. The entropy factor suggests thermodynamic hindrance in the decomposition of copolymers of low thermal stability and a preference for the decomposition of copolymers of high thermal stability.     

Kinetics of non-isothermal crystallization in Cu50Zr43Al7 and (Cu50Zr43Al7)95Be5 metallic glasses

The crystallization kinetics of Cu₅₀Zr₄₃Al₇ and (Cu₅₀Zr₄₃Al₇)₉₅Be₅ metallic glasses was studied using differential scanning calorimetry (DSC) at four different heating rates under non-isothermal condition. The glass transition temperature T _g, the onset temperature of crystallization T _x, and the peak temperature of crystallization T _p of the two metallic glasses were determined from DSC curves. The values of various kinetic parameters such as the activation energy of glass transition E _g, activation energy of crystallization E _p, Avrami exponent n and dimensionality of growth m were evaluated from the dependence of T _g and T _p on the heating rate. The values of E _g and E _p, calculated from many different models, are found to be in good agreement with each other. The average values of the Avrami exponent n are (2.8 ± 0.4) for Cu₅₀Zr₄₃Al₇ metallic glass and (4.2 ± 0.3) for (Cu₅₀Zr₄₃Al₇)₉₅Be₅ metallic glass, which are consistent with the mechanism of two-dimensional growth and three-dimensional growth, respectively. Finally, the parameter H _r, S, and crystallization enthalpy ΔH _c are introduced to estimate the glass-forming ability and thermal stability of metallic glasses. The result shows that the addition of Be improves the glass-forming ability and thermal stability of Cu₅₀Zr₄₃Al₇ metallic glass.     

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.