Crystallization behavior of glasses in the system of Na2O-CaO-MgO-Fe2O3-Al2O3-SiO2 with high contents of nickel oxide

The structural behavior of nickel oxide in glassy and glass-ceramic materials, obtained in the system of Na₂O-CaO-MgO-Fe₂O₃-Al₂O₃-SiO₂, was investigated. The influence of the NiO content on the vitrification, crystallization, structure and exploitation properties of two model compositions, with different ratios [CaO]/[MgO] was analyzed. On the basis of DSC and XRD data, it is shown that NiO promoted the formation of bunsenite crystals, as nuclei for crystallization. On the other hand, NiO promoted formation of pyroxenes even for compositions with low MgO contents, which formed gehlenite without NiO admixtures. It is shown that in the composition with relatively high MgO contents, NiO could participate in the formation of two types of pyroxenes with the structure and chemical composition similar to (MgO_0.4NiO_0.6)(CaO_0.9NiO_0.1)Si₂O₆ and diopside-hedenbergite solid solutions. The optimal contents of NiO in both model compositions was about of 7 wt%, since higher contents reduced the exploitation properties. The glass-ceramics with optimal contents of NiO were also produced using Ni bearing galvanic slurry and coal ash; the resulting materials showed similar exploitation properties to those mentioned above.     

Vitrification and crystallization in the system of K2O-B2O3-TiO2

The vitrification and crystallization behavior of melts produced at 1400 °C in the ternary system of K₂O-B₂O₃-TiO₂ is investigated. It is shown that there are two fields of compositions (indicated in mol%) which allow obtaining the glass-ceramic materials with continuous glassy matrix after the cooling of molten compositions. In the first field [TiO₂] = 25-57, [K₂O] = 30-50 and [B₂O₃] = 0-25, the glass-ceramics consisted of the potassium-titanium-borate glassy phase and different crystalline potassium titanates (K₄Ti₃O₈, K₂Ti₂O₅, K₂Ti₄O₉, K₂Ti₆O₁₃). The ratio of TiO₂:K₂O in the obtained titanates increases with [TiO₂] and [B₂O₃]. In the second field, [TiO₂] = 7-37, [K₂O] = 0-25 and [B₂O₃] = 52-93, the obtained glass-ceramics consisted of a similar vitreous phase, as mentioned above, and TiO₂ crystals. During the cooling of the melts, short whiskers-like crystals of anatase formed in the compositions with relatively low [TiO₂] and relatively high [K₂O], whereas long fiber-shaped crystals of rutile appeared with the compositions characterized with relatively high [TiO₂] and relatively low [K₂O]. The possible application of the obtained glass-ceramic materials as a source of fibrous TiO₂, for composite reinforcement, and as solid lubricants is discussed.     

Crystallization processes of Li2O-Ga2O3-SiO2-NiO system glasses

Crystallization processes of Li₂O-Ga₂O₃-SiO₂-NiO system glasses have been studied by X-ray diffraction, differential calorimetry and optical absorption. Transparent glass-ceramic containing LiGa₅O₈:Ni²⁺ as the sole crystalline phase has been obtained from glass with the composition of 13Li₂O-23Ga₂O₃-64SiO₂-0.1NiO (in mol%) by the heat treatment in the temperature range from 923 to 953 K. It was revealed that the specific surface area of samples enhances crystallization of LiGaSi₂O₆ but obstructed that of LiGa₅O₈. LiGa₅O₈ grew to nano-sized crystallites dispersed in the glass matrices and did not affect the transparency seriously. In contrast, LiGaSi₂O₆ grew to crystallites with diameters more than 100 nm on the surface and made the glasses opaque. Optical absorption measurements revealed that doped Ni²⁺ occupied five-folded trigonal bipyramidal sites in the as-quenched glass matrices but six-folded octahedral sites of precipitated LiGa₅O₈ in the glass-ceramics. It was confirmed that transparent glass-ceramic containing Ni²⁺:LiGa₅O₈ was effectively obtained by the heat treatment at a temperature of 953 K for 10 h.     

Glasses and glass-ceramics in the oxyfluoride ternary system Pb(PO3)2-WO3-PbF2

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO₃)₂-WO₃-PbF₂ and doped with Er³⁺ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF₂ content. For low PbF₂ concentrations, only one crystallization peak due to Pb₃(PO₄)₂ is observed whereas samples containing more than 15% of PbF₂ present another exothermic event at lower temperatures related with precipitation of PbF₂, Pb₂P₂O₇ and Pb₂OF₂. Structural investigations by Raman spectroscopy suggest that PbF₂ modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb₃(PO₄)₂ is nucleated on the surface whereas PbF₂, Pb₂P₂O₇ and Pb₂OF₂ crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF₂ crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF₂ and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC.     

The effect of PbF2 content on the microstructure and upconversion luminescence of Er-doped SiO2-PbF2-PbO glass ceramics

The Er³⁺ doped transparent oxyfluoride glass ceramics were obtained by appropriate heat treatment of the precursor glasses with composition (mol%) 50SiO₂-xPbF₂-(50 − x)PbO-0.5ErF₃. The microstructure and optical properties of the glasses and glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), absorption spectra and luminescence spectra. The intensity of upconversion luminescence significantly increased in glass ceramics compared to that in precursor glass. The emission bands centered around 660 nm (⁴F_9/2 → ⁴I_15/2) and 410 nm (²H_9/2 → ⁴I_15/2) were simultaneously observed in glass ceramics but cannot be seen in the corresponding precursor glass. The influence of different PbF₂ content on the microstructure and upconversion luminescence of the samples was analyzed in detail. The results indicated that with the increase of PbF₂ content, the Ω₂ was almost the same and the ratios of red to green upconversion luminescence decreased in glass ceramics.     

Density-structure correlations in Na2O-CaO-P2O5-SiO2 bioactive glasses

Relations for Na₂O-CaO-SiO₂ glasses have been developed to calculate the density of Na₂O-CaO-P₂O₅-SiO₂ bioactive glasses. The calculation makes use of NMR results of O’Donnell et al. indicating that P₂O₅ forms a separate phase, containing Na₃PO₄ and Ca₃(PO₄)₂, in the investigated glasses. The volume of the silicate units is the same as that found in Na₂O-CaO-SiO₂, Na₂O-SiO₂, and CaO-SiO₂ glasses. Similarly, the volume of PO₄ units is equivalent to that in Na₃PO₄ and Ca₃(PO₄)₂. Calculated densities are consistent with the experimental data.     

Thermo-optic properties of B2O3 doped Li2O-Al2O3-SiO2 glass-ceramics

Reduction in the temperature coefficient of the optical path length, dS/dT of Li₂O-Al₂O₃-SiO₂ glass-ceramics with near-zero thermal expansion coefficient was attempted using control of the temperature coefficient of electronic polarizability, ?, and the thermal expansion coefficient, α. The dS/dT value of 2.6 mol% B₂O₃-doped glass-ceramic was 12.5  × 10⁻⁶/°C, which was 0.9 ×  10⁻⁶/°C smaller than that of B₂O₃-free glass-ceramic. On the other hand, reduction in dS/dT through B₂O₃ doping was not confirmed in precursor glasses. Results showed that reduction in dS/dT of the glass-ceramic through B₂O₃ doping is caused by the reduction in ?. The reduction in ? from B₂O₃ doping was probably attributable to numerical reduction in non-bridging oxide ions with larger ? value by the concentration of boron ions in the residual glass phase. In addition, application of hydrostatic pressure during crystallization was effective to inhibit precipitation of β-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B₂O₃-doped glass-ceramic crystallized under 196 MPa was 11.7 ×  10⁻⁶/°C. That value was slightly larger than that of silica glass. The α value of this glass-ceramic was smaller than that of silica glass.     

Electric conductivity of glasses in the system Na2O/CaO/SiO2/Fe2O3

The addition of polyvalent transition metal ions to the usually insulating traditional soda-lime-silica glasses can lead to semiconducting properties. We report on synthesis of glasses and glass-ceramics in a soda-lime-silicate based system containing Fe₂O₃ in the concentration range from 5 to 30 mol%. Two sub-systems were considered, in one of them the ratio [Na₂O]/[Fe₂O₃] was varied while in the other one, the ratio [SiO₂]/[Fe₂O₃] was changed. The phase composition of the synthesized products was characterized by X-ray diffraction and energy dispersive X-ray analysis, while the electrical properties were studied by impedance spectroscopy. Partially crystallized non-reduced samples are semiconducting even at room temperature while the glassy samples (both reduced and non-reduced) exhibit semiconducting properties at temperatures equal or larger than 100 °C. An attempt is done to predict the physical approximation explaining the conduction process in the glasses.     

Growth,thermal and optical properties of a new nonlinear optical crystal: ZnBi2B2O7

Single crystals of ZnBi₂B₂O₇ (ZBBO) have been successfully grown by the top-seeded growth method from a high-temperature melt. The crystal was colorless and transparent with size of 15×10×5 mm³. The orientation of ZBBO crystal has been discussed. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystal were determined to be 964.02 K, 110680.36 J mol⁻¹, and 113.92 J K⁻¹ mol⁻¹, respectively. The transparency range of the crystal extends from 370 to 2100 nm.     

Crystallization behavior of (GeS2)0.1(Sb2S3)0.9 glass

The crystal growth kinetics of antimony trisulfide in (GeS₂)_0.1(Sb₂S₃)_0.9 glass has been studied by microscopy and DSC. The linear crystal growth kinetics has been confirmed in the temperature range 492 ? T ? 515 K (E_G = 405 ± 7 kJ mol⁻¹). The applicability of standard growth models has been assessed. From the crystal growth rate corrected for viscosity plotted as a function of undercooling it has been found that the most probable mechanism is interface controlled 2D nucleated growth. The non-isothermal DSC data, corresponding to the bulk sample, can be described by the Johnson-Mehl-Avrami equation.     

Non-isothermal crystallization kinetics of ZnO-BaO-B2O3-SiO2 glass

Glass of composition 40SiO₂-30BaO-20ZnO-10B₂O₃ (mol%) was made by conventional melting and casting process. Crystallization kinetics of above glass has been investigated under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The procedure is applied to the experimental data obtained by differential thermal analysis (DTA), using continuous-heating techniques. The crystallization results are analyzed, and both the activation energy of crystallization process as well as the crystallization mechanism is characterized. Dilatometric measurement of this glass was also done and data obtained was used to calculate the viscosity of the formed glass. Development of crystalline phases on thermal treatments of the glass at various temperatures has been analyzed by X-ray diffraction. Microstructure of the crystalline phases was investigated by scanning electron microscopy (SEM) and the development of various structural features with variation in heat treatment cycle was observed. The nucleation and growth of these phases in the matrix of glass has been described and discussed.     

Synthesis and characterization of single-crystalline PrCO3OH dodecahedral microrods and its thermal conversion to Pr6O11

Single-crystalline PrCO₃OH dodecahedral microrods with an orthorhombic structure have been successfully synthesized by the hydrothermal method used urea as the precipitator. Pr₆O₁₁ dodecahedral microrods have been obtained by thermal conversion of PrCO₃OH dodecahedral microrods at 600 °C in air for 6 h. The as-synthesized products were characterized by X-ray powder diffraction, field-emission scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectra, fourier transform infrared spectroscopy and thermogravimetry–differential thermal analysis. The effect of the reaction parameters on the morphology of the product has been investigated. The dodecahedral microrods with larger size and better crystallinity can be obtained under the higher reaction temperature. The possible formation mechanism of PrCO₃OH microrods was discussed.     

Numerical description for the recalescence of bulk-undercooled Cu70Ni30 alloy

Assuming thermal balance and solute conservation, a numerical model has been proposed to describe the recalescence behavior of bulk-undercooled Cu–Ni melts. Applying a finite-difference scheme, the transformed solid fraction upon recalescence is given as a function of the liquid temperature, while the average liquid concentration can be tracked by calculation of the liquid/solid (L/S) Gibbs energy difference, in combination with a dendrite growth model. Accordingly, a transition from non-equilibrium to equilibrium process has been described from the evolution of L/S Gibbs energy difference. Applying the present model, the experimentally observed maximum recalescence temperature can be well predicted.     

Floating-zone growth of large high-quality CoAl2O4 single crystals

We report the first successful floating-zone growth of high-quality CoAl₂O₄ single crystals with volume up to 1 cm³ free from inclusions and sub-grains. The neutron rocking curves of the CoAl₂O₄ crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a₀=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μ_eff=4.63 μ_B per Co⁺² ion in a good agreement with previous measurements on ceramic samples.     

Effect of BaO content on the sintering and physical properties of BaO-B2O3-SiO2 glasses

A BaO-B₂O₃-SiO₂ glass system was chosen as a candidate composition for the application to Pb-free low temperature sinterable glass. The effect of BaO content on the crystallization, sintering behavior, and properties of the glasses was examined. Both the glass transition temperature and crystallization temperature decreased as the BaO content increased. Crystallization easily occurred during sintering with a BaO content of more than 50 mol%, which effectively inhibited the over-firing phenomenon. The dielectric characteristics and thermal expansion coefficient of the glasses were examined and the results were explained on the basis of the crystallization and densification of the specimens.     

The application of differential thermal analysis to the study of isothermal and non-isothermal crystallization kinetics of coal fly ash based glasses

The crystallization kinetics of glasses obtained from coal fly ash was investigated by both isothermal and non-isothermal methods using differential thermal analysis (DTA) data. In DTA experiments, glass samples having coarse (800-1000 μm) and fine (<180 μm) particle sizes were used and the results were compared. The Avrami exponent (n) was calculated by means of Johnson-Mehl-Avrami (JMA) and Ozawa equations. Calculated kinetic parameters indicated that the appropriate crystallization mechanisms were bulk and surface crystallization for coarse and fine particles, respectively. Isothermal and non-isothermal DTA experiments showed that the crystallization activation energies of coarse glasses are changed in the range of 444-578 kJ/mol, while the crystallization activation energies of fine glasses are changed in the range of 610-662 kJ/mol. It was found that crystallization activation energies of fine glasses are higher than those of the coarse glasses. Results showed that isothermal and non-isothermal crystallization kinetics of glasses produced from coal fly ash is in agreement within the experimental error.     

Thermal and some physical properties of glasses in the La2O3−CaO−B2O3 ternary system

Glasses in the La₂O₃−CaO−B₂O₃ ternary system were studied. The glass forming range as determined by the appearance of the annealed cast was found to match previously published findings. Clear glasses were formed in the composition range of 5.7−19.1 mol% La₂O₃ with constant B₂O₃ content of 71.4 mol%, and in glasses of constant La₂O₃:CaO ratio of 1:4 with B₂O₃ content in the range of 71.4-55.0 mol%. The non-linear optical crystalline phase La₂Ca₂B₁₀O₁₉ was crystallized from the clear glasses after heat treatments, as determined by powder XRD. Two types of the LaBO₃ crystalline phases were detected in the partially and the fully crystallized glass compositions outside the glass forming range. Data are reported for the glass transition temperature (T_g), dilatometric softening point (T_d), linear coefficient of expansion (α), onset crystallization temperature (T_x), exothermal peak temperature (T_P), density (ρ) and index of refraction (n_D) in the clear glasses.     

Effect of ZnO and Bi2O3 addition on linear and non-linear optical properties of tellurite glasses

Glasses in the system TeO₂-Bi₂O₃-ZnO were studied with respect to their linear refractive indices and optical absorption in the UV-vis range. The third order non-linear refractive indices were measured using degenerated four wave mixing (DFWM). The optical Kerr susceptibilities calculated hereof were in the range from 5.49 to 6.58 × 10⁻¹³ esu and hence 34-41 times larger than that of fused SiO₂. They are roughly proportional to values theoretically calculated by the theory of Lines.     

Solubility of glasses in the system P2O5-CaO-MgO-Na2O-TiO2: Experimental and modeling using artificial neural networks

Phosphate glasses in the system P₂O₅-CaO-MgO-Na₂O-TiO₂ for use as degradable implant materials were produced. In order to classify their solubility behavior, dissolution experiments were performed in deionized water for 60 min at 98 °C. Resulting solutions were analyzed using ICP-OES. In addition, pH measurements were carried out in physiological NaCl solution. With increasing phosphorus oxide content, the glasses showed a higher solubility and gave lower pH values in aqueous solution. This was caused by changes in the glass structure, as long phosphate chains are more susceptible to hydration than smaller phosphate groups. These changes in glass structure were followed by ³¹P MAS-NMR experiments. Increasing sodium oxide concentrations in exchange for calcium or magnesium oxide also increased the glass solubility by disrupting ionic cross links between chains. By contrast, addition of titania made the glasses more stable towards dissolution by cross linking smaller phosphate groups. The aim of this study was to find a relationship between glass composition and solubility behavior. As classical linear methods of data analysis were unsuitable due to the complexity of the relationship, preliminary artificial neural networks analyses were performed and were found to be an interesting tool for modeling the solubility behavior of phosphate glasses.     

Remark on the optical gap in ZnO-Bi2O3-TeO2 glasses

Four ZnO-Bi₂O₃-TeO₂ glasses were prepared from high purity (4N5) oxides. From measurements of the optical transmission on very thin bulk samples the optical gap was determined at around 3.55 eV for the glasses studied. The temperature dependence of the optical gap was also determined from the room temperature close up to 500 K. Preliminary Raman scattering measurements indicate that with a decrease in TeO₂ content, TeO₄ trigonal bipyramid transformation proceeds into TeO₃ trigonal pyramids.