New Glass-Ceramic of Li–Aegirine Composition Based on β-Quartz Solid Solution and Its Electrochemical Properties

The basic glass of Li2O-Al2O3-SiO2 system using P2O5 as nucleator was prepared by means of conventional melt quenching technology, and the heat-treatment process was determined by using differential thermal analysis. The crystalline phases and the microstructure of the glass-ceramics were investigated by using X-ray diffraction and scanning electron microscopy. The results show that the glass based on Li2O-Al2O3-SiO2 oxides using P2O5 as nucleator can be prepared at lower melt temperature of 1450°C and the glass-ceramics with lower thermal expansion coefficient of 21.6 × 10−7°C−1 can also be obtained at 750°C. The glass-ceramics contain a few crystal phases in which the main crystal phase is β-quartz solid solution and the second crystal phase is β-spodumene solid solution. When the heat treatment temperature is not higher than 650°C, the transparent glass-ceramics containing β-quartz solid solution can be prepared. β-quartz solid solution changes into β-spodumene solid solution at about 750°C. And the appearance of the glass-ceramics changes from translucent, part opaque to complete opaque with increasing temperature.

Crystallization of a glass having the composition SiO2 63.2, Al2O3 20.1, MgO 2.6, MgF2 8.2, Li2O 5.9% in weigt and some properties of the crystallized glass were investigated.The results are summarized as follows;1) Small unknown crystals of about 80 Å in size were already found in the original glass, which might have precipitated during cooling of the melt. Heat treatment of the glass caused first the precipitation of another kind of unknown crystal and subsequently the precipitation of the main crystal, that is, β-quartz solid solution. It was conjectured that the presence of the former crystals might have facilitated the crystallization of the latter crystal in the bulk of the glass.2) Crystallization of β-quartz solid solution at 680°C and 700°C was easier at the surface than in the interior of the samples. At 740°C, however, little difference was observed in the amount of the precipitated β-quartz solid solution between the surface and the interior supposedly because of a rapid in increase of the amount of the crystal throughout the sample. β-quartz solid solution precipitated at 700°C transformed into β-spodumene solid solution at higher temperatures than 950°C.3) The bending strength of the crystallized glass increased somewhat with time of heat-treatment at 680°C and 700°C, while no increase was observed at 840°C. The bending strength of the glass heated at 700°C for 5hours and then further heat-treated at 800°C, 900°C, 950°C or 1000°C for 3 to 8 hours was slightly smaller than that of the glass subjected to the only heat-treatment at 700°C. The bending strength decreased markedly upon heating up to 1050°C.4) The thermal expansion coefficient of the crystallized glass was relatively low (3-7×10-7/°C) when the glass was heat-treated at 800°C or 900°C after the heat treatment at 700°C for 5 hours and relatively high (23×10-7/°C) when heat treated at 950°C. The thermal expansion coefficient decreased again slightly (18×10-7/°C) when the glass was heat-treated at 1000°C and decreased markedly (0×10-7/°C) when heat-treated at 1050°C.

β-quartz solid solution consisting of zinc aluminocilicate was prepared from a Zn-exchanged zeolite A (Zn-A) as a precursor. In the thermal-transformation process of Zn-A, two kinds of β-quartz solid solutions were obtained. Zn-A became an amorphous material upon heating at 873K. The β-quartz solid solution (β-Qss (Z)), which has a composition close to that of Zn-A (ZnAl2Si2O8), formed with the presence of small amounts of gahnite and mullite from the amorphous material at temperatures above 1163K. The β-Qss (Z) decomposed at temperatures above 1223K and then another β-quartz solid solution (β-Qss (S)) formed. The composition of β-Qss (S) was richer in SiO2 than that of β-Qss (Z). The d value in the (101) plane of β-Qss (S) decreased with increasing heating temperature, which suggested that the amounts of Al and Zn in the specimen decreased and that β-Qss (S), formed above 1573K, has the composition of nearly pure SiO2.

Crystallization of lithium aluminosilicate and microstructure of a lithium alumino borosilicate glass designed for zero thermal expansion

The effect of addition of fluorine on the crystallization of the glass having the composition Li3Mg1.75Al3Si8O23.75-x/2Fx, where x=0 to 1.84, was studied. The results obtained are summarized as follows:1) For a small amount of fluorine content (x=0-1.34), the tendency of the glass to crystallization increased with addition of fluorine. For more amount of fluorine content (x=1.43-1.84), however, the tendency of the glass to bulk crystallization and surface crystallization at relatively low temperatures decreased with addition of fluorine and the crystallization occured throughout the samples at higher temperatures. The cause for this effect of the addition of the fluorine was considered as follows. If it is assumed that fluorine atoms exist in the form of SiFO3 in the glass, addition of fluorine would weaken the structure of the glass, promoting its crystallization. When the fluorine content is over a certain value (x=1.43), however, the process of the exclusion of fluorine from the formation of the crystalline lattice, and the formation of β-quartz solid solution might be suppressed at relatively low temperatures. It was inferred that the precipitation of tiny MaF2 crystals in this step might have facilitated the subsequent crystallization of β-quartz solid solution in the bulk of the glass.2) β-quartz solid solution precipitated in the glass at relatively low temperatures transformed to β-spodumene solid solution at relatively high temperatures. The stability of the former depended on the content of fluorine in the glass. When the glass was heated once at various temperatures, the temperature of transformation decreased with increasing fluorine content. When the glass was heated at a higher temperature after the heat-treatment at lower temperatures, however, β-quartz solid solution was more stable in the glass with richer fluorine content (x=1.84) than in the glass with smaller fluorine content (x=1.34, 1.59). This was attributed to the smaller fluorine content of the residual glass in the sample with x=1.84 than those in the samples with x=1.34 and 1.59.3) The effects of fluorine content on the bending strength and the thermal expansion coefficient of the crystallized glsses were explained in terms of the state and the thermal expansion coefficient of the precipitated crystals.

Effect of heat-treatment condition on crystallization behavior and thermal expansion coefficient of Li 2O–ZnO–Al 2O 3–SiO 2–P 2O 5 glass–ceramics

Metastable phase separation and crystallization of Li 2OAl 2O 3SiO 3 glasses: Determination of miscibility gap from the lattice parameters of precipitated β-quartz solid solution

Microstructure and ion-exchange properties of glass-ceramics containing ZnAl2O4 and β-quartz solid solution nanocrystals

Crystallization and mechanical properties of MgO/Al 2O 3/SiO 2/ZrO 2 glass-ceramics with and without the addition of yttria

Li2O-MgO-Al2O3-SiO2(LMAS) system glass-ceramics had been prepared by sintering method. The effect of different nucleating agents on the phase composition, microstructure and properties of LMAS system glass-ceramics were investigated by DTA, XRD and SEM. The results indicate that the introduction of nucleating agents could contribute to decreasing the crystallization temperature of the glass-ceramics, the effect of the nucleating agent TiO2 is most obvious, and the crystallization temperature is the lowest(798.9°C). Main crystal phase of the glass-ceramics without the nucleating agents is β-quartz solid solution, while main crystal phase of the glass-ceramics with different nucleating agents changes into β-spodumene solid solution. The glass-ceramics with composite nucleating agents (TiO2+ZrO2+P2O5) are the lowest coefficient of thermal expansion (0.86×10-6/°C)and the highest flexural strength (95MPa). Composite nucleating agents have the best effect of crystallization, and contribute to the formation of a large number of short columnar crystals, which is the main reason for obtaining glass-ceramics with low expansion coefficient and high flexural strength.

Contribution of some divalent oxides replacing Li2O to crystallization characteristics and properties of magnetic glass–ceramics based on Li2O–Fe2O3–Al2O3–SiO2

Li2O-Al2O3-SiO2 glass-ceramics doped with Nd2O3 were prepared by the melting method. The effects of Nd2O3 on the crystallization behavior of Li2O-Al2O3-SiO2 glass-ceramics were studied by DTA, XRD and SEM. With the increase of Nd2O3 content, the glass crystallization temperature arised. The SEM result indicates that the main crystal phase of Li2O-Al2O3-SiO2 glass-ceramics doped with Nd2O3 is β-quartz solid solution, for without doping Nd2O3 it is β-spodumene solid solution. These results shows that the crystallization temperature increases significantly by doping Nd2O3, and phase transition from β-quartz to β-spodumene is suppressed. The grain size increases with the increase of Nd2O3 content.

Phase transformations in the lithium aluminosilicate glass nucleated by a mixture of yttrium and niobium oxides and doped with cobalt ions were studied for the development of multifunctional transparent glass-ceramics. Initial glass and glass-ceramics obtained by isothermal heat-treatments at 700–900 °C contain YNbO4 nanocrystals with the distorted tetragonal structure. In samples heated at 1000 °C and above, the monoclinic features are observed. High-temperature X-ray diffraction technique clarifies the mechanism of the monoclinic yttrium orthoniobate formation, which occurs not upon high-temperature heat-treatments above 900 °C but at cooling the glass-ceramics after such heat-treatments, when YNbO4 nanocrystals with tetragonal structure undergo the second-order transformation at ~550 °C. Lithium aluminosilicate solid solutions (ss) with β-quartz structure are the main crystalline phase of glass-ceramics prepared in the temperature range of 800–1000 °C. These structural transformations are confirmed by Raman spectroscopy and illustrated by SEM study. The absorption spectrum of the material changes only with crystallization of the β-quartz ss due to entering the Co2+ ions into this phase mainly in octahedral coordination, substituting for Li+ ions. At the crystallization temperature of 1000 °C, the Co2+ coordination in the β-quartz solid solutions changes to tetrahedral one. Transparent glass-ceramics have a thermal expansion coefficient of about 10 × 10−7 K−1.

Lithium aluminosilicate glass-ceramics (LAS GCs) are ideal shell materials for mobile phones; however, the mechanical properties of LAS GCs are comparatively lower than that of other shell materials. In this work, the impact of TiO2/(TiO2 + ZrO2) ratio on properties of LAS GCs was studied and the ion-exchange methods were applied to improve the mechanical properties of LAS GCs. The results show that LAS GCs with TiO2/(TiO2 + ZrO2) = 1/2 exhibit the best flexural strength (109 MPa) and Vickers hardness (525 Kg/mm2). The as-prepared glass was nucleated at 560 °C for 1 h and crystallized at 720 °C for 0.5 h. The main crystalline phases of LAS GCs are β-quartz solid solution, β-spodumene solid solution, and Li2SiO3. Moreover, the flexural strength and Vickers hardness of LAS GCs with TiO2/(TiO2 + ZrO2) = 1/2 further increased to 356 MPa and 838 Kg/mm2 after an ion-exchange at 420 °C for 6 h in pure KNO3 molten salt. The LAS GCs with enhanced mechanical strength have the potential to be applied as mobile phone back panels.

The effects of MgF2 in four complex nucleating agents on the performance and crystallization of lithium aluminum silicate glasses