Immiscibility in the TeO2-B2O3 system

Experimental investigations have been carried out to study the phase separation process in the TeO₂-B₂O₃ system. It was found that the phase diagram is of a eutectic-like type (monotectic invariant reaction), with a wide region of stable and metastable phase separation. During the cooling of the melts two phases are obtained. One has a high TeO₂ content and is a transparent glass. The other, richer in B₂O₃, is opaque and in structure constitutes a complicated microheterogeneous system.     

Phase equilibrium in the TeO2-B2O3-V2O5 system

Journal of Materials Science Letters -     

Phase equilibria and immiscibility in the TeO2-P2O5 system

The phase equilibria and immiscibility of mutual glass formers up to 50 mol% P₂O₅ have been studied. Phase analysis indicates the formation of three new phases — incongruent melting Te₄P₂O₁₃, Te₂P₂O₉, and a supposed metacompound. Electron microscope investigations established stable and metastable phase separation. The immiscibility confines the tendency to glass formation up to 25.8 mol % P₂O₅. A reliable interpretation in relation to the morphology of liquid-liquid immiscibility and crystallization is considered.     

Optical,infrared and electrical conductivity of glasses in the TeO2-B2O3 system

Infrared (IR) and optical absorption spectra were measured in order to study the structure of some tellurite glasses containing boric oxide. The compositions (mol%) were (100-X) TeO₂,XB₂O₃ whereX=5, 10, 20, 25, 30. The optical spectra were measured at room temperature in the wavelength range 350–450 nm, and the results show that the fundamental absorption edge is a function of composition, with the optical absorption due to indirect transitions. The optical band gap increases with increasing B₂O₃ content. The validity of the Urbach rule was investigated. The IR results prove the distribution of the TeO₄ polyhedra which determines the network and the basic oscillations of the building units in the tellurite glasses. The IR results also prove the distribution of the boroxal group. The electrical conductivity was measured as a function of temperature in the temperature range (300–573 K). Both the conductivity and activation energy were found to be a function of added oxide type.     

Electrical properties and infrared spectra of TeO2-Fe2O3 glasses

The d.c. and a.c. electrical properties on TeO₂-Fe₂O₃ glasses with various compositions of PbO, B₂O₃ and SiO₂ were studied over a frequency range of 10²–10⁵ Hz and in the temperature range 300–500 K. The a.c. conductivity is proportional tow ⁿ, and the conduction mechanism is due to an electronic hopping process. The effects of composition and temperature on the dielectric constant and loss factor (tan ) were studied. The infrared absorption spectra of these glasses reveal that the addition of PbO, B₂O₃ and SiO₂ of these glasses does not introduce any new absorption band in the infrared spectrum of TeO₂-Fe₂O₃ glasses. These results prove the distribution of TeO₄ polyhedra which determines the network and basic oscillation of the building units in the tellurite glasses.     

Phase equilibrium,glass-forming,properties and structure of glasses in the TeO2-B2O3 system

Phase equilibrium, glass-forming, properties and structure of the glasses in the TeO₂-B₂O₃ system have been investigated. The phase diagram is a simple eutectic-like type without any compound formation. A wide region of stable phase separation has been established. A monotectic temperature at 934 K and nonvariant point at 73.6% TeO₂ has been determined. The temperature dependence of the stable phase separation in the system has been studied. Some properties (density, transformation temperature, softening point, coefficient of thermal expansion, hardness, absorption in the UV and VIS region) of the tellurite borate glasses have been investigated. A structural interpretation of the glasses, on the basis of B¹¹ NMR spectra was undertaken and two coordination states of boron atoms have been established. A simple model of two tellurium-boron-oxygen building units is presented.     

Glass formation in the system CaO-Al2O3-CaF2

The formation of glass in the system CaO-Al₂O₃-CaF₂ has been investigated in sealed platinum capsules having about one atmosphere pressure of AlF₃ vapour. Transparent colourless glass could be obtained in the low-fluoride moderate-alumina region of the system (Al₂O₃ 35 to 60%, CaF₂ 0 to 20%). With the concentration of CaF₂ exceeding 20% considerable amount of quench crystals of CaF₂ appeared in the glass. Moderate-alumina low-lime melts containing more than 35% CaF₂ occur in an immiscibility zone. At the low-fluoride periphery of the liquid immiscibility zone a small zone of metastable liquid immiscibility has been found. The results of electron microscopic and infra-red spectroscopic studies of a few selected glasses have been analysed in combination with the molar refractivity data to reflect upon the co-ordination characteristics of aluminium in these glasses.     

Glass transition temperature of glasses in the SiO2-Na2O-CaO-P2O5-Al2O3-B2O3 system

A total of 24 glasses in or near the bioactive region in the system SiO₂-Na₂O-CaO-P₂O₅-Al₂O₃-B₂O₃ were studied. By differential thermal analysis their glass transition temperatures,T _g, were determined. On basis of an experimental plan for 16 glasses, two phenomenological equations describing the relationship betweenT _g and glass composition were developed. The equations describeT _g within the compositional ranges: SiO₂, 38.0–65.5 Na₂O, 15.0–30.0; CaO, 10.0–25.0; P₂O₅, 0–8.0; B₂O₃, 0–3.0; Al₂O₃, 0–3.0 wt%. The glass transition temperature shows a linear dependence of the Na₂O content. The higher the Na₂O content, the lower theT _g. Compositional alterations not including Na₂O influencesT _g little in comparison with changes in the Na₂O content.     

Crystallization kinetics and structure of (TeO2-TiO2-Fe2O3) Glasses

Crystallization kinetics and structure of (85TeO₂ + 15TiO₂) and (85TeO₂ + 10TiO₃ + 5Fe₂O₃) glasses are studied using differential scanning calorimetry DSC, IR spectroscopy and XRD. DSC curves in the temperature range from 50 to 525°C with different heating rates from 10 to 40°C/min are used to study the crystallization behavior of the glasses and effects of different heating rates on the glass transition and crystallization temperatures (T_g and T_p). The activation energies of the glass transition and crystallization processes were determined from the shift of T_g and T_p with the heating rates using Kissinger's formula. Effects of the polymorphic nature of TeO₂ on the crystallization mechanisms are discussed and the phases crystallized during the DSC process were identified by XRD. IR spectra in the frequency range (500–4000 cm^-1 ) are measured and possible coordination states of the constituent oxides are discussed for heat-treated and untreated glasses.     

Magnetic bioactive glass ceramic in the system CaO-P2O5-SiO2-MgO-CaF2-MnO2-Fe2O3 for hyperthermia treatment of bone tumor

Magnetic bioactive glass ceramic (MG) in the system CaO–SiO₂–P₂O₅–MgO–CaF₂–MnO₂–Fe₂O₃ for hyperthermia treatment of bone tumor was synthesized. The phase composition was investigated by XRD. The magnetic property was measured by VSM. The in vitro bioactivity was investigated by simulated body fluid (SBF) soaking experiment. Cell growth on the surface of the material was evaluated by co-culturing osteoblast-like ROS17/2.8 cells with materials for 7 days. The results showed that MG contained CaSiO₃ and Ca₅(PO₄)₃F as the main phases, and MnFe₂O₄ and Fe₃O₄ as the magnetic phases. Under a magnetic field of 10,000 Oe, the saturation magnetization and coercive force of MG were 6.4 emu/g and 198 Oe, respectively. After soaking in SBF for 14 days, hydroxyapatite containing CO₃ ²⁻ was observed on the surface of MG. The experiment of co-culturing cells with material showed that cells could successfully attach and well proliferate on MG.     

Structural studies of some V2O5-P2O5-B2O3-Fe2O3 glass systems

X-ray diffraction and infrared measurements were performed on vanadium borophosphate glass containing different amounts of iron ranging from 0–7.5 mol % and heat treated at 300 °C for various times. The structure and phase separation could be determined for each glass composition. V₂O₅ was the main precipitated phase in all heat-treated samples, and its amount was dependent on the heat-treatment time and Fe₂O₃ content. Also FeP was detected in samples heat treated for 24 h. The infrared measurements showed the presence of both V⁴⁺ and V⁵⁺. The symmetry of V₂O ₇ ⁴⁻ and VO ₄ ³⁻ groups was found to increase with increasing Fe₂O₃ content. It was also found that some PO₄ changed to BO₃, forming a non-bridging oxygen.