Precipitation Of Crystalline Phase Research Articles

Efficient energy transfer mediated by intrinsic SiO2 nanocrystals in Eu+3-doped lead borosilicate glasses

Lead borosilicate glass (SiO2–B2O3–PbO2) doped with different Eu3+ ion concentrations have been synthesized by fusion method and characterized through optical absorption, photoluminescence (PL) and time-resolved PL spectra in the temperature range from 15 to 300 K. The PL spectra show characteristic ions Eu3+ transitions followed by a red emission at 695 nm and a green emission at 550 nm. The red and green emissions were associated with a non-bridging oxygen hole center (NBOHC) and OH groups stabilized on the SiO2 nanocrystal surface, respectively. Atomic Force Microscopy images confirm a precipitated crystalline phase with size of 21 nm in the glass matrix. Inhibition of the intrinsic nano-crystallization process of the SBP glass template has been observed as Eu3+ ions concentration increases. As sample temperature increases, an efficient energy transfer process from SiO2 nanocrystal surface states toward Eu3+ states takes place. This leads to a strong increase in the PL emission intensity of Eu3+ states followed by a decreasing PL peak intensity of the surface states. The energy transfer process leads also to an abnormal average lifetime of SBP:Eu3+ luminescent states with increasing temperature.

Zr-Cu-Al バルク金属ガラスマトリックス複合材料の形状記憶効果と機械的性質

Zr-Cu-Al bulk metallic glass matrix composite with precipitated crystalline phase was fabricated. The major precipitated phase of the composite is B2 type ZrCu. Compressive tests were carried out using the composite specimens with high volume fraction of B2 type ZrCu in order to investigate the mechanical properties and shape memory effect of the composite. As the results, it was found that the composite has not only high strength but also low elastic modulus. In addition, it was confirmed that a stress-induced martensitic transformation in B2 type ZrCu occurs during compressive test. Furthermore, it was confirmed that the composite exhibits shape memory effect.

廃棄物溶融－徐冷スラグの結晶化挙動に及ぼす主成分組成の影響

Effect of the composition of major components on the crystallization behavior of the melt-solidified slag by slow cooling process (2 K·min−1) was studied. In case of the synthetic melt-solidified slag with minor components, crystallization of the slag is progressed by slow cooling process when the basicity (= (%CaO)/(%SiO2)) is higher than 0.8. The precipitated crystalline phase is only Gehlenite (2CaO·Al2O3·SiO2). Crystallization of the slag initiates from the interface of the slag and the crucible, and from the surface of the slag. The basicity higher than 0.9 is required in order to precipitate the crystal phases over the entire slag. The influence of Al2O3 content on the crystallization is very little compared with that of the basicity. On the other hand, in case of SiO2-CaO-Al2O3 slag without minor components, the crystallization is promoted at higher Al2O3 content and lower basicity. Only few amounts of minor components in the slag can influence on the crystallization behavior, and even change the crystallized phase.

The role of TiO2, ZrO2, BaO and SiO2 on the mechanical properties and crystallization behavior of fluorapatite–mullite glass–ceramics

The effect of TiO2, ZrO2, BaO and extra addition of silica on the crystallization behavior, microstructure and mechanical properties of an apatite–mullite based glass–ceramic system were investigated by means of X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The precipitated crystalline phases were fluorapatite [Ca10(PO4)6F2] and mullite [Al6Si2O13], which apart from the extra bearing SiO2 specimen were rod-like in the other specimens. The rod-like crystalline phases' lengths were small, i.e. <20μm, in the TiO2 and BaO containing glass–ceramics, but small addition of ZrO2 enhanced the length of crystalline phases to approximately 50μm. The flexural strength and fracture toughness of the prepared glasses and glass–ceramics were also studied. The results showed that the additive oxides affected both parameters differently. The highest fracture strength and fracture toughness values belonged to the TiO2 and BaO containing glass–ceramics which contained smaller crystal size. The mechanical properties of the prepared glass–ceramic samples did not differ strongly and/or were even decreased by addition of ZrO2 and extra amount of SiO2.

Up- and down-conversion luminescence in the oxyfluoride glass ceramics containing Ba2+1.5xYb1−xF7:Tb3+ nanocrystals

Transparent oxyfluoride borosilicate glass ceramics containing Ba2+1.5xYb1−xF7:Tb3+ nanocrystals were successfully prepared by a melt-quenching method with subsequent heat treatment. The precipitated crystalline phase in the glass matrix changed gradually from BaF2 to Ba2+1.5xYb1−xF7 with the increase of YbF3 content, which was confirmed by the results of XRD, HRTEM and EDX measurements. The ultraviolet and visible up-conversion and near-infrared quantum cutting down-conversion emissions were observed and interpreted. These materials could be used to modify the solar spectrum and enhance the silicon solar cell efficiency by the up-conversion and down-conversion luminescence of Tb3+–Yb3+ couples in the oxyfluoride borosilicate glass ceramics.

Effects of Measurement Materials and Oxygen Partial Pressure on the Viscosity of Synthetic Eastern and Western United States Coal Slags

The viscosity of the molten ash (slag) resulting from the mineral constituents in carbon feedstock used in slagging gasifiers is critical for controlling the gasification process. The viscosity of two synthetic slags with compositions resembling the mineral impurities in average eastern and western coal feedstock was examined at temperatures from 1300–1500 °C using a rotating bob viscometer. A few combinations of atmospheres and experimental materials were investigated with respect to one another to determine slag viscosity. A CO/CO2 atmosphere (CO/CO2 = 1.8, corresponding to a PO2 = 10–8 atm) is required to sustain ferrous ions in FeO-containing slags, an environment that is oxidizing to most metals. Iron oxide in the slag prevents usage of Fe parts. In unpurified Ar, the Fe metal surface oxidizes. Using purified argon prevents iron measurement components from oxidation; however, the metallic surfaces act as nucleation sites for the reduction of the Fe oxide in the slag into metallic Fe. Dissolution of ceramic materials into the slag, including Al2O3 and ZrO2, occurs in both atmospheres. Therefore, evaluating slag properties in the laboratory is challenging. The measured viscosities of two synthetic slags in this study diverged depending upon material selection. This difference is likely attributable to container/spindle-slag interactions. Viscosity measurements of the eastern coal slag using all ceramic parts agreed best with FactSage prediction above 1350 °C, with an average activation energy of 271.2 kJ. For western coal slag, the dissolution of container/spindle materials was substantial during the measurement, with precipitation of crystalline phase noted. The experimental viscosity data of the western coal slag agreed best with Kalmanovitch prediction above 1350 °C. The activation energy changed dramatically for both data sets of western coal slag, likely indicating the Newtonian-to-non-Newtonian transition.

Phase composition and structure of boron-free and boron-containing sodium aluminum iron silicate glass materials for solid radioactive waste immobilization

Phase composition and structure of the glass materials obtained by fusing calcined emulator of radioactive solid waste (RW) with glassforming additives , namely, sodium disilicate or sodium tetraborate, have been studied. Materials obtained by quenching the melts are mostly amorphous; upon slow cooling (annealing), melts crystallize with the formation of materials containing phases of nepheline, britholite, and spinel. Their quantitative ratio depends on the mass ratio of calcinate and glassforming additives. Changes in the structure of the anionic motif of the quenched glass materials with increasing content of RW and pre� cipitation of crystalline phases in the annealed materials have been studied by IR and Raman spectroscopy.

Thermodynamic Analysis on the Precipitation of Crystalline Phase from LF Slag during Cooling Process

The precipitation of crystalline phase from LF slag during cooling process was discussed according to the thermodynamic analysis by using CaO-SiO2-Al2O3 system. The results showed that when the slag basicity was low, 2CaO•SiO2 (C2S) was precipitated firstly during the cooling process, and then it was followed by 2CaO•Al2O3•SiO2 (C2AS) and 12CaO•7Al2O3 (C12A7), and the precipitated crystalline phases existed uniformly in the slag. In the case of high basicity slag, 3CaO•SiO2 (C3S) and 3CaO•Al2O3 (C3A) with incongruent melting point temperature could be produced, and which would result in a non-uniform distribution in the slag.

Microstructure and magnetic properties of (Fe100−xCox)84.5Nb5B8.5P2 alloys

Partial substitution of Fe with Co in gradually devitrified Si-free Nanoperm-type alloys improves their soft magnetic properties, increases the Curie temperature of the amorphous matrix, and allows casting in air. In the present work we report the temperature dependence of structural and magnetic properties of (Fe100−xCox)84.5Nb5B8.5P2 (x=20, 40, 60) alloys using differential scanning calorimetry, magnetic, thermo-magnetic and X-ray diffraction measurements, to get complementary information on the microstructure, composition of the precipitated crystalline phase and their correlation with magnetic properties. Higher Co concentrations improve the magnetic softness of the alloy, whose properties can be further optimized by suitable thermal treatments. Magnetic data is discussed in terms of the precipitation of a Fe–Co crystalline phase consisting of different Co content.

Crystallization and optical properties of a transparent mullite glass ceramic

Transparent mullite – based glass ceramics in the system SiO 2–Al 2O 3–B 2O 3–ZnO–K 2O were prepared. The activation energy of crystallization, the Avrami constants and the mechanism of crystallization of mullite were determined by the Matusita method through differential thermal analysis. X-ray diffraction and scanning electron microscopy methods were also used to determine the type and morphology of the precipitated crystalline phase. In addition, the degree of crystallinity was determined by the internal standard method. The results showed that bulk crystallization was the main mechanism for crystallization of the glasses. Optical absorption and photoluminescence properties of the obtained transparent glass–ceramics and their initial glasses were also studied. The glass–ceramics exhibited two emissions at 680 and 700 nm.

Bioactivity of Hench Bioglass and Corresponding Glass-Ceramic and the Effect of Transition Metal Oxides

Glasses based on the Hench’s bioglass doped with (0.1%) of one of the 3d-transition metals were prepared. Infrared absorption spectra of the prepared samples were measured. The prepared glassy samples were crystallized through controlled thermal treatments and the precipitated crystalline phases were identified by X-ray diffraction analysis. Infrared reflection spectroscopy was performed on the glassy and crystalline derivative samples before and after immersion in simulated body fluid for different time periods of 1 week, 2 weeks or 1 month. The main crystalline phase formed in the undoped and TM-doped samples are solid solutions of sodium calcium silicates (1Na.2Ca.3Si and 3Na.3Ca.6Si). Infrared reflectance spectra reveal the formation of the two layers of SiO2-gel and CaO-P2O5 and the transition metal ions seem to act as nucleating catalysts initiating the ease of formation of an apatite layer and hence promoting bioactivity in the doping level.

Precipitation of ZnO in Al 2O 3-doped zinc borate glass ceramics

Crystallization behavior of the oxide semiconductor ZnO in zinc borate glass was investigated. The precipitated crystalline phase of glass ceramics containing a small amount of Al 2O 3 was α-Zn 3B 2O 6 whereas that of the glass ceramics containing a large amount of Al 2O 3 was ZnO. It was found that the c-oriented precipitation of ZnO in a glass ceramic was brought about by the in-plane crystal growth of needle-like ZnO crystallites along the a-axis. Amount of Al 2O 3 that can make glass network affected the coordination state of B 2O 3 in the glass, and a three-coordinated BO 3 unit was preferentially formed in the glass containing a higher amount of Al 2O 3. The present results suggest that crystallization of ZnO from multi-component glass is dominated by the local coordination state of the mother glass.

Surface crystallization of Fresnoite-type crystallized glasses with large thickness

Transparent crystallized glass with a surface crystallization layer of sub-millimeter thickness was found in the glass compositions of 35BaO–15TiO2–50GeO2 (BTG50), 28BaO–18TiO2–54SiO2 (BTS54), and 35SrO–20TiO2–45SiO2 (STS45), and the precipitated fresnoite-type crystalline phase showed nonlinear optical properties. XRD measurements confirmed that BTS54 and STS45 crystallized glasses precipitate as a single phase of the fresnoite-type crystallites Ba2TiSi2O8 and Sr2TiSi2O8, respectively. On the other hand, BTG50 crystallized glass precipitated two phases with mainly fresnoite-type BTG, Ba2TiGe2O8 and BaGe4O9. The results of the XRD analysis of STS45 crystallized glass demonstrated high crystal orientation in the (002) direction from the glass surface.

Radiative Heat Transfer Behavior of Mold Fluxes for Casting Low and Medium Carbon Steels

An investigation was carried out to study the radiative heat transfer behavior of two typical mold fluxes for casting low (Flux1) and medium (Flux2) carbon steels. By using an infrared radiation emitter, a radiative heat flux was applied to a copper mold covered with solid mold flux disk to simulate the heat transfer phenomena in continuous casting. The effective thermal conductivities were determined by measuring the temperature gradient in the copper mold system. It was found that the solid crystalline mold Flux2 for casting medium carbon steel has a better capability to transfer heat than that of solid crystalline Flux1, while their glassy fluxes behave similar capability. The DHTT (Double Hot Thermocouple Technique) was employed in this paper to study the heat transfer capability of the crystalline mold fluxes. DHTT measurements suggested that the thermal diffusivity of crystalline sample of Flux2 is higher than that of Flux1. The XRD and SEM results were indicated that the precipitated crystalline phase for Flux1 is only granular cuspidine, Ca4Si2O7F2, while those for Flux2 are consisted of dendritic cuspidine, Ca4Si2O7F2 and gehlenite, Ca2Al2SiO7.

Eu3+ photoluminescence enhancement due to thermal energy transfer in Eu2O3-doped SiO2–B2O3–PbO2 glasses system

In this work, Eu3+-doped lead borosilicate glasses (SiO2–B2O3–PbO2) synthesized by fusion method had their optical properties investigated as a function of temperature. Atomic Force Microscopy images obtained for a glass matrix annealed at 350 and 500°C show a precipitated crystalline phase with sizes 11 and 21nm, respectively. Besides, as the temperature increases from 350 to 300K a strong Eu3+ photoluminescence (PL) enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from nanocrystals and charged intrinsic defects states to Eu3+ energy levels. In addition, the PL peaks in this temperature range were assigned to the Eu3+ transitions 5D0→7F2, at 612nm, 5D0→7F1, at 595nm, and 5D0→7F0, at 585nm. It was also observed that the 5D0→7F3 and 5D0→7F4 PL bands at 655 and 700nm, respectively, show a continuous decrease in intensity as the temperature increases.

Liquid-Liquid Phase Separation in Photo-Thermo-Refractive Glass

Photo-thermo-refractive (PTR) glass is an optical Na–Al–Zn–K–O–F–Br silicate glass doped with Ag, Ce, Sb, and Sn that undergoes photo-thermo-induced volume crystallization of nanosized NaF responsible for localized refractive index changes. PTR glass has found numerous commercial applications, but the intricate mechanism of photo-thermo crystallization is far from being understood. In this paper, we demonstrate that, additional to crystalline phase precipitation, liquid–liquid phase separation (LLPS), i.e. amorphous droplets embedded in the matrix glass, appears concurrently over a wide range of temperatures. The immiscibility temperature is 925°C. The droplet phase is richer in SiO2, rendering the alkali-rich remaining matrix glass a lower glass transition temperature and a higher electrical conductivity than the original glass. The droplet's surface does not catalyze NaF nucleation. Although the effects of LLPS on optical properties of PTR glass are still to be explored, it could contribute to unwanted scattering losses and/or uncontrolled refractive index change. The substantial change in the original glass composition resulting from LLPS should play an important role on NaF crystallization kinetics, and therefore must be considered for an overall understanding of the crystallization mechanism underpinning the refractive index change in PTR glass.

Crystallization and luminescence properties of Eu2+ doped diopside glass ceramics

Eu2+ doped glass ceramics have been prepared and characterized. The crystallization and optical properties of the glass ceramics were studied by XRD, SEM, and fluorescence spectra. The precipitated crystalline phase in the glass ceramics was prismatic diopside (CaMgSi2O6) and plate-like cristobalite (β-SiO2). As the heat treatment time increases, the content of crystals increases gradually. Fluorescence measurements showed that Eu2+ ions entered into the diopside crystalline phase and induced a much stronger emission in the glass ceramics than that in the corresponding glass. With increase of Eu2+ content, concentration quenching was observed.

Improving glass-forming ability and crystallization behavior of porous glass-ceramics in CaO–Al 2O 3–TiO 2–P 2O 5 system

Glass-forming ability and crystallization behavior of various compositions in the CaO–Al 2O 3–TiO 2–P 2O 5 system were investigated, using differential thermal analyzer (DTA), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) methods. According to our experiments, the precipitated crystalline phases were altered and the glass-forming and crystallization behaviors improved simultaneously, by addition of Al 2O 3 to the system. In the most promising composition, calcium pyrophosphate (Ca 2P 2O 7) and calcium titanium phosphate (CaTi 4(PO 4) 6) were formed during an ordinary short time heat treatment around the first DTA crystallization peak temperature of it. However, long-term heat treatment led to crystallization of calcium pyrophosphate (Ca 2P 2O 7) and titanium pyrophosphate (TiP 2O 7) phases. Chemical leaching of the optimum resulted glass-ceramic with HCl, caused that calcium pyrophosphate was selectively dissolved out and a porous skeleton of titanium pyrophosphate remained. Porous structure of final products seems to be conceivable for applications as filters, membranes, catalyst supports, etc.

Crystallization in glass: elucidating a realm of diversity by transmission electron microscopy

Glass ceramics, i.e. intentionally devitrified glasses, are used in manifold applications. This is due to the capability to precisely control the precipitation of crystalline phases possessing useful properties related to optics, mechanics, biocompatibility, piezoelectricity, machinability, etc. In order to control the nano and microstructure, transmission electron microscope imaging proves particularly useful. Illustrated by numerous examples, the diverse precipitate shapes and mechanisms at work upon crystallization of glasses are discussed. In addition, it is shown how useful cutting-edge transmission electron microscopy is in the field of nanoanalytics. The investigation of nanoscale processes controlling the precipitation of functional crystals evidences the need for more sophisticated theories describing the changes of composition accompanying crystallization in non-isochemical systems (precipitates possess compositions different from those of the host glasses).

Tb3+-activated SiO2–Al2O3–CaO–CaF2 oxyfluoride scintillating glass ceramics

In this paper, transparent glass ceramics containing CaF2 nanocrystals were synthesized by heat-treating as-made Tb3+/Gd3+-codoped 45SiO2–20Al2O3–10CaO–25CaF2 oxyfluoride glass. The precipitated crystalline phase in the glass ceramics is CaF2 nanocrystals identified by X-ray diffraction (XRD) patterns. Both photoluminescence (PL) and X-ray excited luminescence (XEL) results show that enhancement of Tb3+ 542nm emission intensity by a factor of about 2–3 is achieved in glass ceramics with respect to the as-made glass. XEL intensity of the investigated glass ceramics is comparable to that of the commercial glass sciltillatior (LHK-6 type), which suggests its potential for scintillation application.