Crystallization Behavior Of Glass-ceramics Research Articles

Optimization of heat treatment of glass-ceramics made from blast furnace slag

AbstractCaO–MgO–Al2O3–SiO2 glass-ceramics with diopside as the main crystalline phase were prepared by melting blast furnace slag obtained from Baotou Iron and Steel Company. The effect of heat treatment on the crystallization behavior of glass-ceramics, containing a large proportion of melted blast furnace slag, was studied by means of differential thermal analysis and scanning electron microscopy. The optimum heat-treatment regime was obtained by orthogonal experimental results for glass-ceramics in which blast furnace slag comprised 70% of the composition and 1% Cr2O3 and 4% TiO2 were used as nucleating agents. The nucleation temperature was 750°C for 2.5 h and the crystallization temperature was 930°C for 1 h. Under this regime, the performance of the glass-ceramic was better than that of other groups in the orthogonal experiment.

Influence of Cr2O3 on the viscosity and crystallization behavior of glass ceramics based on blast furnace slag

CaO–MgO–Al2O3–SiO2 glass-ceramics with various Cr2O3 contents are successfully prepared from blast furnace slag as the main raw material using a conventional melting method. The influence of Cr2O3 addition on the viscosity, crystallization kinetics, structure, and properties of the obtained materials are systematically determined by viscometry, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray powder diffraction, thermal-field-emission environmental scanning electron microscopy, and corrosion-resistance property tests. The results showed that the obtained glass-ceramics is composed of dendritic diopside (main crystalline phase) and bulk spinel (second crystalline phase). With increasing amount of Cr2O3, the viscosity of the slag glass melt increases. In addition, the samples exhibit crystallization activation energies in the range 378–454 kJ/mol, with slight fluctuations. Moreover, the crystallization index increases from 0.84 to 2.80. The obtained glass-ceramics exhibit a maximum density, bending strength, and acid and alkali resistances of 2.97 g/cm3, 196.69 MPa, 97.61%, and 98.04% respectively, demonstrating their wide application potential for various industrial applications.

Feasibility of Producing Glass-Ceramics from a Mixture of Glass Cullet-Eggshell and Perlite

Feasibility of producing glass-ceramics from cullet, eggshell and perlite was investigated. In this study, a nucleating agent was synthesized from calcined eggshell and expanded perlite prior to blend with soda-lime waste glass, and then sintered at temperatures ranging from 850 to 1050°C at a heating rate of 10°C/min for 30 - 180 minutes. The crystallization behavior of glass-ceramics was investigated by means of X-ray diffraction analysis and surface morphology, and the chemical compositions were evaluated by scanning electron microscopy and energy dispersive X-ray spectroscopy. Results showed that crystalline phase embedded in the glass phase were needle-like crystal of wollastonite, cristobalite and quartz. According to the chemical resistance test, the obtained glass-ceramics showed acceptable corrosion resistance particularly in acidic environment. The weight loss for glass-ceramics immersed in 1wt% of sodium hydroxide solution was 0.28 - 0.50 wt%, while weight loss due to 1vol% of sulfuric acid solution was 0.04 - 0.16 wt%.

Characterization of Glass Ceramics Produced from Natural and Waste Raw Materials

Glass ceramics were prepared from fly ash, waste window glass and fluorite rawmaterials. Mixtures of raw materials were melted at 1300, 1400 and 1500 °C for 4 h and quenchedin cold water. The crystallization behavior of glass ceramics was investigated by differentialthermal analysis-thermogravimetry (DTA-TG). Crystallization at various temperatures (700, 800,900 and 1000 °C) for 30 min was used to obtain the glass ceramics. The obtained glass ceramicswere characterized by X-ray diffraction (XRD), light microscopy and hardness test. XRD studyrevealed that the crystallized phases were plagioclase-type minerals (diopside and albite). TheVickers hardness of the glass ceramics increased from 0.80±0.19 GPa to 6.35±0.35GPa and densityranged from 1.44 g/cm3 to 2.42 g/cm3 depending on the treatment temperature. Glass ceramicsprepared from fused glass melted at 1500 °C temperature showed the highest hardness comparedwith those melted at lower temperatures.

Lithium ion-conducting glass-ceramics in the system Li2O–TiO2–P2O5–Cr2O3–SiO2

Conductive glass-ceramics based on Li2O–TiO2–P2O5–Cr2O3–SiO2 system were fabricated by heat-treatment at the crystallization peak temperature for 2h. The crystallization behavior of glass-ceramics was identified by differential thermal analysis (DTA), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) methods and their conductivity behavior was investigated by complex impedance techniques. The glass-ceramics were mainly composed of LiTi2(PO4)3 in which Ti4+ ions were partially replaced by Cr3+ ions. A considerable enhancement in conductivity was observed by partial substitution of Ti4+ by Cr3+ ions. 100 part [Li1.5Cr0.5Ti1.5(PO4)3] and 5 part SiO2 glass-ceramics in the 100 part [Li1+xCrxTi2−x(PO4)3] and 5 part SiO2 system, where x=0–0.8, exhibited the highest ambient conductivity value of 2.14×10−2S/cm with an activation energy as low as 15.1kJ/mol.

Ionic conductivity and microstructural evaluation of Li2O–TiO2–P2O5–SiO2 glass-ceramics

Conductive glass-ceramics based on the Li2O–TiO2–P2O5–SiO2 system were fabricated by heat-treatment at the temperature interval of 700–1000°C for 2h. Based on the obtained results, the prepared glasses showed a tendency for bulk crystallization of LiTi2(PO4)3 and TiO2 as the major and minor crystalline phases, respectively. The crystallization behavior of glass-ceramics was monitored by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods; and their conductivity behavior was evaluated by complex impedance technique. It was shown that, the ionic conductivity of the glass-ceramic was enhanced by increasing the heat treatment temperature from 700 to 950°C. This tendency was attributed to the growth of LiTi2(PO4)3 crystals. The highest room temperature conductivity of 7×10−4S/cm was obtained after crystallization at 950°C for 2h. By increasing the heat treatment temperature above 950°C, the conductivity was decreased, probably due to the microcracking of the specimen as the result of grains growth.

Influence of amorphous phase separation on the crystallization behavior of glass-ceramics in the BaO–TiO2–SiO2 system

The possible role of a prior amorphous phase separation on the subsequent crystallization has been the topic of vigorous debates over the last decades and has not yet been clarified, especially regarding the role of the interfaces created by the phase separation. This study proposes to focus on the interplay between a prior amorphous phase separation and the crystallization of fresnoite in the BaO–TiO2–SiO2 system. The crystallization behavior of a non-stoichiometric composition inside the miscibility gap (called APS) is compared with the stoichiometric composition (called FRES) and a non-stoichiometric composition outside the miscibility gap (called NoAPS). The crystallization mechanisms are compared using differential thermal analysis (DTA) by calculating the Avrami parameters and the activation energies as a function of the particle size. The DTA study shows that the two non-stoichiometric compositions exhibit a pronounced surface crystallization behavior whereas FRES undergoes bulk nucleation. This is supported by a multi-scale microstructure characterization. Furthermore, this study demonstrates that the amorphous phase separation and the associated interfaces do not play any significant role in the nucleation step. Moreover, transmission electron microscope (TEM) and local orientation measurements show that the growth of the dendrites is not hindered by the SiO2-rich droplets. The final stage of crystallization of APS is tentatively explained by two composition effects that must be further investigated: the viscosity effect and the formation of a eutectic.

The Occurrence of Special Components in Blast Furnace Slag of Baotou Iron and Steel Company

The mineral composition of the solidified blast furnace slag and the occurrence of special components CaF2, K2O, Na2O, RexOy and ThO2 were researched by optical microscope analysis, X-ray diffraction analysis and scanning electron microscopy and energy spectrum analysis. The results showed that the major minerals in solidified furnace slag are akermanite and gehlenite; the special component CaF2 is not hosted in the cuspidine (3CaO•2SiO2•CaF2), but in the magnesium and aluminum silicate mineral; the special components K2O，Na2O is hosted in akermanite, magnesium and aluminum silicate mineral and perovskite; the element thorium cannot form an independent mineral, but coexist with the rare earth element Ce in the perovskite. The results will lay a foundation for further study on the influence of these special components on the crystallization behavior of glass-ceramics.

Crystallization behavior of glass ceramics prepared from the mixture of nickel slag, blast furnace slag and quartz sand

The purpose of this paper was to investigate the crystallization process of glass ceramics prepared from a mixture which was composed of nickel slag, blast furnace slag and a small amount of quartz sand. First, the parent glass of the mixture was prepared. Then, the glass ceramics were obtained by heat-treating for the parent glass. The crystallization behavior was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). A large number of tiny spherical crystals were observed when the glass was heated up to 700 °C. Subsequently, the radial crystals were observed when the glass was heated up to 820 °C. By XRD analyzing, the spherical crystals and radial crystals were likely to be the crystals of diopside (CaMg(Si,Al,Fe) 2O 6) and hedenbergite (CaFe(Si,Al,Fe) 2O 6). The crystallization temperature was 860 °C and the final crystalline phases were identified to be diopside and hedenbergite. In addition, the activation energy of crystallization was evaluated by Kissinger method.