Mechanism and kinetics of glass-ceramics formation in the LiO2-SiO2-CaO-P2O5-CaF2 system

Two glasses based on lithium disilicate (LS₂), with and without fluorapatite (FA), were synthesised in the Li₂O-SiO₂-CaO-P₂O₅-CaF₂ system with P₂O₅: CaO: CaF₂ ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle sizes. Inclusion of FA in the LS₂ favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS₂ glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (₂99 ± 1 kJ mol-1 for pure LS₂ glass and ₂88 ± 7 kJ mol⁻¹ for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS₂ glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like phases after soaking in SBF.      

Crystallization, mechanical properties and in vitro bioactivity of sol–gel derived Na2O–CaO–SiO2–P2O5 glass–ceramics by partial substitution of CaF2 for CaO

The partial substitution of CaF₂ for CaO in the Na₂O–CaO–SiO₂–P₂O₅ system was conducted by the sol–gel method and a comparison of the glass–ceramic properties was reported. Based on thermogravimetric and differential thermal analysis, the gels were sintered with a suitable heat treatment procedure. The glass–ceramic properties were characterized by X-ray diffraction, fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectrometer and so on, and the bioactivity of the glass–ceramic was evaluated by in vitro assays in simulated body fluid. Results indicate that with the partial substitution of CaF₂ for CaO in glass composition, the volume density, apparent porosity, bending strength and microhardness of the glass–ceramics have been significantly improved. Furthermore, CaF₂ promotes glass crystallization which does not inhibit the glass–ceramic bioactivity.     

Thermodynamic study of some solid solutions in the CaOZrO2 system by emf method

The thermodynamic properties of some solid solutions in the CaOZrO₂ system have been investigated by using solid electrolyte galvanic cells of the type: O₂, Pt|CaO, CaF₂|CaF₂ (t_F = 1)| δCaO(1 ? δ)ZrO₂, CaF₂|Pt, O₂. The influence of CaF₂ added in electrodes on the thermodynamic equilibrium was investigated. It was shown that the heterogeneous field with cubic solid solution reaches the composition x = 0.17 mole of CaO. The results indicate that addition of ZrO₂ to the saturated solid solution produces a significant decrease in the activity of CaO. Measured data were used to calculate thermodynamic parameters of reactions with saturated solid solutions Ca_0.17 Zr_0.83 O_1.83, ZrO₂, and CaZrO₃. At temperatures below 820°C, saturated solid solutions have a tendency to decompose into CaZrO₃ and ZrO₂. A comparison of the thermodynamic results with available data on phase relationships in the CaOZrO₂ system is presented. High thermodynamic stability of SrZrO₃ and BaZrO₃ is one of the reasons for the absence of cubic solid solutions in the system MeOZrO₂ (MeSr, Ba).     

Thermodynamic model and structure of CaO–P2O5 glasses

The distribution of Q-units of CaO–P₂O₅ glasses was described by the thermodynamic model of Shakhmatkin and Vedishcheva. The glass was considered as the ideal solution of CaO, P₂O₅, CaP₂O₆, Ca₂P₂O₇, and Ca₃P₂O₈. In the first step, molar Gibbs energies of considered species were taken from the FACT thermodynamic database. The obtained result was compared with ³¹P solid-state NMR study of Roiland. It was shown that the calculated values were in fairly good agreement with the experimental values. After that, the nonlinear regression treatment was used for optimization of molar Gibbs energies by minimizing the sum of squares of deviations between experimental and calculated Q-distribution. In such a manner, the non-ideality of the system was reflected. In the studied case, no significant improvement of obtained results was achieved by this procedure—thus, the ideal solution assumption included in the thermodynamic model of Shakhmatkin and Vedishcheva holds very well for the studied binary glasses.     

New insights into the bioactivity of SiO2–CaO and SiO2–CaO–P2O5 sol–gel glasses by molecular dynamics simulations

The structures of binary xCaO · (100 ? x)SiO₂ glasses with x = 10, 20 and 30 mol-% and ternary (20 ? x)CaO · xP₂O₅ · 80SiO₂ glasses with x = 3, 10, 15, 17 and 20 mol-% have been studied by means of classical molecular dynamics simulations using both the melt-quenched and the sol–gel protocols. The structural picture derived correlates the bioactive behaviour to the combined effects of the connectivity of the extended silicate network and to the tendency to form (or not to form) non-homogeneous domains. In this context, a mathematical relationship that relates the Ca/P ratio in the Ca phosphate micro-segregation zones to the P₂O₅ content in ternary glasses has been developed and this has been used to fine-tuning the optimum amount of P in a glass for its highest in vitro bioactivity. The composition with optimal Ca/P ratio, 80Si–14.8Ca–5.2P, has been synthesized and the results of bioactivity tests have confirmed the prediction.     

Phase relations in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system in the subsolidus region

Phase relations in the CaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction and differential thermal analyses, and the isothermal section at 600°C has been constructed. The formation of ternary compounds at the component ratios 1CaO: 1Bi₂O₃: 1B₂O₃ (CaBi₂B₂O₇) and 1CaO: 1Bi₂O₃: 2B₂O₃ (CaBi₂B₄O₁₀) has been established X-ray diffraction characteristics of these phases are presented.     

Investigations of molybdenum redox phenomenon in Li2O-MoO3-P2O5 phosphate glasses

Two series of glasses have been prepared and characterized. One with varying Li₂O/P₂O₅ ratio and the other with varying Mo/P ratio. The relationship between the formation of the reduced state of molybdenum in phosphate glasses and the type of gases released in heating batch materials has been investigated. Effect of temperature on the valence state of molybdenum is also studied. Oxidation-reduction (redox) equilibrium of Mo⁵⁺/Mo⁶⁺ and environment of molybdenum (V) in these series of lithium-molybdenum-phosphate glasses are related to the glass composition and the possible structural units formation in the glasses.     

The system Y2O3−CaO−P2O5

The ternary system Y₂O₃?CaO?P₂O₅ has been examined by DTA, X-ray diffraction, IR and microscopic methods. Its phase diagram has been provided within the composition range YPO₄?Ca₃(PO₄)₂?P₂O₅. The occurrence of four mixed phosphates: Ca₃Y(PO₄)₃, CaYP₃O₁₀, CaY(PO₃)₅, Ca₂Y(PO₃)₇ has been discovered in the system. Basic X-ray data have been determined for these newly discovered compounds and several methods of their synthesis developed.     

Thermal Study of A2O–(MoO3)2–P2O5 (A=Li, Na) Glasses

Alkali phosphomolybdate glasses have been prepared by quenching melted mixtures of P₂O₅, MoO₃ and A₂O(A=Li, Na). The composition dependence of the transition temperature of glasses belonging to ternary A₂O–(MoO₃)₂–P₂O₅ (A=Li, Na) systems is studied for several series of glasses corresponding to either a fixed A₂O rate or a constant Mo/P ratio. The interpretation of the results is based on the presence of different types of molybdenum and phosphorous structural groups and P–O–M (M=P, Mo) linkages in glasses. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal behaviour of Fe-doped silicate–phosphate glasses

Thermal behaviour and structure of glasses from the SiO₂–P₂O₅–K₂O–MgO–CaO system modified by Fe₂O₃ addition were studied by DSC, XRD and FTIR methods. It has been found that the replacement of MgO and CaO modifiers by Fe₂O₃ in the structural network of silicate–phosphate glass results in decrease of the glass transition temperature (T _g) and heat capacity change (ΔC _p) accompanying the glass transformation. Simultaneously, the ability for crystallization, its course and the type of the forming phases depend on the relative proportions between iron and phosphorus as components forming the silicate–phosphate structure. The type of the crystal phases forming in the course of heating the considered glass has been found to be in agreement with the character of the domains occurring in this glass, confirmed by FTIR examinations.     

Sol-Gel Synthesis of Humidity-Sensitive P2O5-SiO2 Amorphous Films

The sol-gel synthesis of silicophosphate gels using phosphoryl chloride and tetraethoxysilane as molecular precursors is reported and discussed. Gel-derived glasses and films having the molar compositions 10P₂O₅ · 90SiO₂ and 30P₂O₅ · 70SiO₂ have been obtained. The structure of the dried gels as well as the structural modifications that occurs during the transformations in gel-derived glasses are analyzed by Fourier transform infrared spectroscopy (FTIR). It has been found that the evidence of the P—O—Si linkages begins to appear only on the FTIR spectra of the bulk gels heat treated up to 400°C while they are well resolved on the FTIR spectra of the bulk gel samples heated up to 1000°C indicating that at this temperature the transformation in the corresponding gel-derived glasses occurs. The humidity sensitive properties of the gel-films have been evaluated by electrochemical impedance spectroscopy (EIS). The phosphorous content as well as the temperature of the heat treatments strongly affect the sensitivity to RH of the gel-derived films.     

Calculation of viscosity–temperature curves for glass obtained from four wastewater treatment plants in Egypt

This article establishes the relationship between the chemical composition, temperature and viscosity of glasses obtained from the four sludge treatment plants of urban and industrial wastewater from the Nile Delta in Egypt. In order to determine the working conditions of these glasses and their growth temperature, different techniques have been used: differential thermal analysis, hot stage microscopy and dilatometry. We used a prototype of hot stage microscopy, with the help of an image analysis programme developed in the present study. The chemical composition of major oxides sludge ranging from: SiO₂ (36–48 wt%), Al₂O₃ (9–16 wt%), CaO (5–25 wt%), P₂O₅ (1.5–11 wt%), and Fe₂O₃ (~9 wt%), this composition is close to a basalt rock, being necessary to incorporate some raw materials to adjust it to the basalt rock that has a good viscosity-temperature curve. The glass transition temperatures of the four glasses obtained vary between 650 and 725 °C and the growth occurs between 938 and 1,033 °C. We also obtained the viscosity–temperature curves with the aid of the hot stage microscopy that has allowed us to determine the working temperatures of the four glasses, ranging from 926 to 1,419 °C, depending on the type of forming process used.     

Crystallization of nano calcium fluoride in CaF2–Al2O3–SiO2 system

The effects of alumina and CaF₂ content on the crystallization behavior, fluorine loss, phase separation mechanism and optical properties of oxyfluoride glass ceramics were investigated. Three series of glasses in which their SiO₂/Al₂O₃ ratio was different such as 1.8, 2.18 and 2.5 were examined. Results showed that the adopted ratios played key role significantly in the mechanism of phase separation of the glass. It modified from spinodal decomposition to nucleation and growth by decreasing the mentioned ratio.UV spectroscopy showed that owing to the small size of precipitated CaF₂ crystals, i.e. 20 nm, in the glass with a silicon oxide to alumina ratio of 2.18 and initial CaF₂ amount of 35 mol%, it remained transparent after heat treatment at 740 °C.     

Effect of CaCl2 on the desulphurization by CaO of a carbon-saturated Fe-Si-S alloy

The desulphurization of a carbon-saturated Fe-Si-S alloy by CaO and CaO-7.5% CaCl₂ slags at 1300 °C, and by CaO-10% CaF₂ and CaO-7.5% CaCl₂ slags at 1450 °C were investigated. The results indicated that the addition of 7.5% CaCl₂ to CaO improved the desulphurization of the carbon-saturated Fe-Si-S alloy at 1300 °C by forming a liquid reaction surface. X-ray diffraction studies on the reaction surface of CaO showed that solid CaS formed on the lime surface. This solid reaction product reduces the transfer of sulfur to the CaO surface. At 1450 °C, CaO-10% CaF₂ and CaO-7.5% CaCl₂ slags contain both liquid and solid phases. X-ray diffraction studies showed that a smaller amount of solid CaS formed on the reaction surface of the CaO-7.5% CaCl₂ slag than on the CaO-10% CaF₂ slag. The formation of a smaller amount of solid CaS and the presence of a liquid phase at the metal-slag interface enhanced the desulphurization with CaO-7.5% CaCl₂ at 1450 °C.     

CaF2对CaO-CaF2-B2O3-SiO2：Sm2O3玻璃的光致发光增强效应

用高温熔融法制备了掺杂Sm₂O₃的CaO-CaF₂-B₂O₃-SiO₂(CFBS:Sm)发光玻璃材料, 并借助X射线衍射(XRD)谱、傅里叶变换红外(FTIR)光谱以及光致发光(PL)光谱等分析手段研究了玻璃基体中CaF₂的摩尔分数及其结构、红外透过性能以及荧光性能的关系. XRD和FTIR测试表明, 玻璃基体中引入CaF₂并未引起非晶结构的变化但其红外透过峰发生移动. 光谱学测试表明, CFBS:Sm发光玻璃在404 nm波长激发下出现对应于Sm³⁺离子位于566、603和650 nm的特征荧光峰, 其发光颜色为橙红色(x=0.531, y=0.371). 此外, 随着玻璃基体中CaF₂摩尔分数的增加, CFBS:Sm发光玻璃的荧光发射强度、荧光寿命(Sm³⁺的⁴G_5/2能级)和荧光量子效率也表现出增大的趋势. 这种CFBS:Sm发光玻璃中荧光发射强度和荧光寿命的提高主要是由于玻璃基体中的CaF₂替代CaO引起基体相互作用和声子能量降低、无辐射跃迁减弱造成的.     

Phase equilibria in the Ce<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Ce₂O₃-K₂O-P₂O₅ ternary system has been investigated by thermoanalytical methods (DTA, DSC), powder X-ray diffraction, XPS and IR spectroscopy. The existence of three double potassium-cerium(III) phosphates has been confirmed and a new binary phosphate K₄Ce₂P₄O₁₅ has been found. Phase diagram and isothermal section at room temperature of the system Ce₂O₃-K₂O-P₂O₅ have been presented.     

Thermal behaviour and properties of Na<Subscript>2</Subscript>O-TiO<Subscript>2</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50-x)Na₂O-xTiO₂-50P₂O₅ and 45Na₂O-yTiO₂-(55-y)P₂O₅ glasses. The addition of TiO₂ to the starting glasses (x=0 and y=5 mol% TiO₂) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C. The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO₂ content. With increasing TiO₂ content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization were NaPO₃, TiP₂O₇ and NaTi₂(PO₄)₃. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na₂O or P₂O₅ by TiO₂, it increases sharply.     

Natural rubber–based composites filled with bioglasses from a CaO‐SiO2‐P2O5‐Ag2O system. Effect of Ag2O concentration in the filler on composite properties

Bioactive glass was first synthesized by L. Hench in 1971. There are many studies on the properties of several metals and metal ions dopants used in the SiO₂‐CaO‐P₂O₅ system of bioglasses, such as Ag, Cu, Zn, and Fe. A number of authors have carried out research related to the influence of silver oxide on the properties of bioglasses . However, publications on the properties of elastomer‐based composites containing bioactive glasses are relatively scarce. We have not found in the literature studies discussing how silver oxide concentration in bioglasses of the CaO‐SiO₂‐P₂O₅‐Ag₂O system affects the significant properties of a natural rubber biocomposite. In this regard, the purpose of the present work is to investigate the aforementioned influence on the properties of this type of composites, namely, vulcanization, physicomechanical, thermal, dynamic, dielectric, electric, and thermoconductive characteristics. We have established those parameters of the composites to be impacted considerably by both degree of filling with bioglass and the silver oxide content in the latter. The improvement in the composites thermostability and some of their physicomechanical performance is the most significant. The volume resistance decreases, and the thermal conductivity coefficients increase. Results from scanning electron microscopy and energy‐dispersive X‐ray (EDX) analyses have confirmed the influence of silver oxide initially on the phase composition of the bioglass, hence on the properties of the biocomposites through changes in the bioglass used as filler. The dielectric characteristics of some of the biocomposites suggest that they can be used as substrates and insulating layers in flexible antennas for short‐range wireless communications.     

Structural studies of copper-containing multicomponent glasses from the SiO2–P2O5–K2O–CaO–MgO system

Multicomponent glasses from the SiO₂–P₂O₅–K₂O–MgO–CaO–CuO system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of CuO and P₂O₅ addition on the structure of glasses was evaluated by FTIR, Raman, ³¹P, and ²⁹Si MAS NMR spectroscopies. The studies showed that the Cu²⁺ ions displacing Ca²⁺ ions and Mg²⁺ ions in the structure of glass prefer to associate with the phosphorus Q¹ species, forming the Q⁰ species with chemically stable POCu bonds. This is accompanied by the reduction of the degree of polymerization of the phospho-oxygen sub-network, with a simultaneous increased degree of polymerization of the silico-oxygen sub-network of the silicate–phosphate glasses.     

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.