Crystallization Of Glass Powders Research Articles

X-ray absorption spectroscopy and neutron-diffraction study of persistent luminescent Sr2MgSi2O7 glass-ceramics

Glass-ceramics based on the Eu2O3/Dy2O3-doped Sr2MgSi2O7 phosphor have been obtained from sintering and crystallization of glass powders. The doped parent glasses show red emission under excitation of UV light. After thermal treatment, the corresponding glass-ceramics show persistent blue emission which emanates from Eu2+ incorporated in the crystals; red emission also occurs from Eu3+ in the residual vitreous phase.The aim of this work is to investigate the structure of defects such as oxygen and strontium vacancies in the Sr2MgSi2O7 crystals and the environment, oxidation state and coordination of the Eu and Dy ions in the glass-ceramics, their partitioning between crystalline and glassy phase and their influence on luminescence properties, employing X-ray absorption spectroscopy (XAS) and neutron diffraction (ND) as investigative structural tools. We suggest that the luminescence mechanism involves the presence of shallow electron traps that are abruptly emptied for temperatures above 100 K. The most persistent luminescence is likely due to an effective concentration of Eu2+ in the dendritic-shaped crystals in one of the particular compositions, and with a suitable level of Sr vacancies, even though Sr vacancies are most likely formed in all the investigated samples.

Processing and luminescence of Eu/Dy-doped Sr2MgSi2O7 glass-ceramics

Glass-ceramics based on the Eu/Dy-doped Sr2MgSi2O7 phosphor have been obtained from sintering and crystallization of glass powders. Electric and gas furnaces were employed for glass melting. The doped parent glasses show red emission under excitation of UV light whereas the corresponding glass-ceramics show blue emission.The microstructure of the glass-ceramics and the crystals responsible for the blue emission were observed by scanning electron microscopy-cathodoluminescence. The composition of the crystallised phases and the distribution and incorporation of rare-earth (RE) ions into the crystals and remaining glassy phase were determined by X-ray diffraction and energy dispersive X-ray analysis, respectively.Photoluminescence emission spectra showed a main peak at 484 nm assigned to the typical Eu2+ transitions under excitation at 390 nm in the glass-ceramics. The presence of Dy3+ improved persistence in the samples melted in the gas furnace. The glass-ceramics are sensitive to temperature, which modifies both the persistence time and red-blue luminescence.

Simulation and experimental study of the particle size distribution and pore effect on the crystallization of glass powders

Surface nucleation is a frequent phenomenon and plays an essential role in the crystallization of most glasses, especially glass powders used in sintered glass-ceramics, for example. A technique often employed to study the crystallization kinetics of glassy powders is Differential Scanning Calorimetry (DSC). However, the shape of the crystallization peak profile is usually very complex. For instance, in certain cases of surface nucleation, the crystal growth dimensionality may change during crystallization after crystal impingement, and a large density difference between the parent glass and the resulting crystalline phases may produce cavitation pores in the particle volume. Finally, crushed glass particles are not regularly shaped, as assumed in most models. Hence, to evaluate the crystallization kinetics of glass powders by DSC experiments, in this work, we modified and tested a particle crystallization model using the DSC crystallization peaks of jagged powders of a non-stoichiometric (0.95CaO·0.73MgO·2SiO2) diopside glass having different granulometries and a large crystal/glass density difference. The Reis-Zanotto model was adapted to include two complex variables: particle size distribution and crystallization-induced porosity. As predicted by the modified model, we confirmed the radical change of the DSC peak shape for some particle sizes as a result of crystal impingement and pore formation. This combined experimental-simulation study demonstrates that the adapted model can describe this type of complex and yet frequent crystallization case.

Effect of Ti+ 4 on in vitro bioactivity and antibacterial activity of silicate glass-ceramics

A novel glass-ceramic series in (48-x) SiO2-36 CaO-4 P2O5-12 Na2O-xTiO2 (where x=0, 3.5, 7, 10.5 and 14mol %) system was synthesized by crystallization of glass powders, obtained by melt quenching technique. The differential scanning calorimetric analysis (DSC) was used to study the non-isothermal crystallization kinetics of the as prepared glasses. The crystallization behaviour of glasses was analyzed under non-isothermal conditions, and qualitative phase analysis of glass-ceramics was made by X-ray diffraction. The in vitro bioactivity of synthesized glass-ceramics was studied in stimulated body fluid at 37°C under static condition for 24days. The formation of hydroxyl-carbonated apatite layer; evident of bioactivity of the material, was elucidated by XRD, FTIR, AAS, SEM and EDX analysis. The result showed that partial substitution of TiO2 with SiO2 negatively influenced bioactivity; it decreased with increase in concentration of TiO2. As Ti+4 having stronger field strength as compared to Si+4 so its replacement became the cause for reduction in degradation that in turn improved the chemical stability. The compressive strength was also enhanced with progress addition of TiO2 in the system. The antibacterial properties were examined against Staphylococcus Epidermidis. Strong antibacterial efficacy was observed with the addition of TiO2 in the system.

Influence of phosphorus sources on lithium ion conducting performance in the system of Li2O–Al2O3–GeO2–P2O5 glass–ceramics

NASICON-type structure lithium ion conductors have been considered as promising solid electrolytes due to its very high Li+-ion conductivity and chemical stability. In this paper, NASICON-type structured Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass–ceramics are prepared from crystallization of glass powders, which are obtained by a simple melt-quench method. NH4H2PO4, H3PO4, P2O5 and H3PO4&Al(PO3)3 are used as phosphorus sources, respectively. The obtained LAGP glass–ceramics are systematically characterized with X-ray diffraction, field emission scanning electron microscopy, differential scanning calorimetry and AC impedance spectroscopy. The different impurities are formed depending on the phosphorus sources, which further influence the microstructure. As a result, the lithium ion conductivity is significantly affected by the phosphorus sources. The highest conductivity of 5.21×10−4S·cm−1 is obtained when H3PO4 is used as the phosphorus source under optimum conditions.

Thermal Expansion of BaO · 2B2O3 in the Vitreous and Crystalline States: II. Thermal Expansion of Polycrystalline Barium Diborate Prepared by Crystallization of Glass Powder of the Same Composition

The thermal expansion of polycrystalline barium diborate prepared by crystallization of the glass powder of the same composition is investigated. It is revealed that the dilatometric parameters are characterized by a hysteresis, which manifests itself in a substantial difference between the dilatometric curves upon heating and cooling. The hysteresis characteristics depend on the temperature of preliminary heat treatment during crystallization, the temperature range of measurements, and the direction of the temperature change in the course of dilatometric experiments. It is assumed that transformations of structural modifications occur in the low- and high-temperature ranges and that the quantitative ratio between the modifications in these ranges depends on the temperature.

Gel synthesis and crystallization of glass powders in the Li2Ge4O9-Na2Ge4O9 composition range

The gel synthesis and the crystallization behaviour of glass powders in the lithium tetragermanate-sodium tetragermanate composition range were studied. The objective was to evaluate the effect of replacing Li 2 O by Na 2 O on the glass transition temperature and devitrification behaviour in tetragermanate glasses

Sintering and Crystallization of Glass at Constant Heating Rates

The densification and shear behavior of glass powder compacts were determined by measuring their axial strain and radial strain during uniaxial compression. The experiments were conducted nonisothermally at constant rates of heating. The densification and the shear strain were plotted as a function of temperature. Both showed sigmoidal behavior, reaching a plateau at high temperature. The density saturated because the powder compact had sintered to completion, but the shear strain saturated because of the onset of crystallization. The technique offers a method for studying the interaction between densification and crystallization of glass powders.

Sintering and crystallization of titanium‐containing lead borate glasses

AbstractThe sintering and crystallization of glass powders with chemical composition 47 PbO—38 B2O3—15 TiO2 (mole %) was investigated under non‐isothermal conditions by shrinkage measurements, differential thermo‐analysis (DTA), X‐ray diffraction (XRD), dielectric measurement and positron annihilation (Doppler broadening). The correlation between changes of macroscopic properties and positron annihilation results recommends this method for the detection of structural changes in glasses.

Kinetic Processes Involved in the Sintering and Crystallization of Glass Powders

Viscometry, crystal growth kinetics, and glass powder sintering were used to determine the activation energies of viscous flow, crystal growth, and sintering behavior of a standard NBS 710 glass and two crystallizable glass powders in the calciaaluminosilicate system. In a system which sintered successfully to zero porosity, the activation energy for sintering was comparable to the activation energy of viscous flow. When the apparent activation energy for the sintering process was lower than that of viscous flow, sintering was found to proceed at a slower rate because the precipitated crystalline phase retarded viscous flow and the shrinkage of the pores. Initial crystallization appeared to occur on the surfaces of coalesced particles. A chemical treatment was partially successful in suppressing the onset of surface nucleation of the precursor powder.

Preparation of Apatite-Containing Glass-Ceramics by Sintering and Crystallization of Glass Powders

Preparation of Apatite-Containing Glass-Ceramics by Sintering and Crystallization of Glass Powders