Β-eucryptite Solid Solution Research Articles

Study on crystallization and microstructure of Li 2O-Al 2O 3-SiO 2 glass ceramics

Lithium aluminosilicate (LAS) glasses are generally difficult to prepare because of their high melting temperature. In this study, the preparation of LAS glasses was achieved at a relatively low melting temperature. The batch containing MgO-ZnO-Li 2O-Al 2O 3-SiO 2 was melted in a platinum crucible at 1550°C for 2 h and was then followed by two- or three-step heat treatment processes for nucleation and crystal growth. The characterizations were carried out by differential thermal analysis, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and UV-Vis-NIR scanning spectrophotometry. The hexagonal stuffed β-eucryptite solid solution crystallized at 840–960°C. Most of the hexagonal β-eucryptite solid solution transformed into the tetragonal β-spodumene solid solution at 1100°C. Almost all the aluminum atoms entered into the tetrahedral sites in the aluminosilicate network of the β-eucryptite/β-quartz solid solution. All of the Al atoms did not belong to the aluminosilicate network of the β-spodumene solid solution. The glass ceramic with a mean grain size of 10–20 nm is transparent, the transmittance reaches ∼85% in the visible light wavelength.

Preparation of transparent lithium-mica glass-ceramics

In order to fabricate transparent and machinable mica-type glass-ceramics, parent glasses having chemical compositions corresponding to Li(1+x)Mg3AlSi3(1+x)O10+6.5xF2 (x=0.15, 0.5, 0.65, 1.0 and 1.2) were crystallized. Lithium-micas were precipitated in all the specimens as the main crystal at 650°C though the content was little. And the micas were changed from trisilicic type to tetrasilicic type as the x increased. After the precipitation of the micas, a large amount of β-eucryptite solid solution was precipitated as the main crystal at higher temperatures and even at 650°C after a certain period of time. The parent glasses having the spinodal phase separation, of which the x was 1.0 and 1.2, were transparent and colored in light blue. And at 650°C, the fine mica crystals with size of about 20nm were precipitated in one continuous glass phase of the spinodal phase separation, which made the phase separation structure become finer. Consequently, the heated specimens showed higher transmittance of visible ray and became colorless. Moreover, because the mica crystals formed the continuous phase, the specimens showed the machinability.

Effect of Crystallization of Li 2O-Al 2O 3-SiO 2 Glasses on Luminescence Properties of Nd 3+ Ions

Generally the preparation of lithium aluminosilicate (LAS) glasses is difficult on account of their high melting temperature. This research managed to prepare LAS glasses doped with Nd 3+ ions by the conventional melting and quenching technique, at a relatively low melting temperature and by the use of some additives. Lithium aluminosilicate glasses were transformed to glass-ceramics by controlled nucleation and the crystallization process. The characterizations were performed by differential thermal analysis, X-ray diffraction, UV-Vis-NIR scanning spectrophotometry, and fluorescence spectrometry. The research focused on the photoluminescence spectra of the initial glass and the glass-ceramics under different heat-treatment schedules. Three main fluorescence bands centering at about 890, 1065, and 1330 nm were observed, which corresponded to the transitions of 4F 3/2→ 4I 9/2, and 4F 3/2→ 4I 11/2, and 4F 3/2→ 4I 13/2, respectively. Phase compositions of glass-ceramics were found to affect their fluorescent characteristics considerably. The fluorescent intensity increased markedly when Nd 3+ ions entered the Li x Al x Si 1- x O 2 β-eucryptite solid solution (SS). Quenching occurred when Nd 3+ ions located at Li x Al x Si 3- x O 6 β-eucryptite SS. Quenching disappeared after Li x Al x Si 3- x O 6 β-eucryptite SS recrystallized into β-spodumene SS. The effectively induced cross section σ in of Nd 3+ ions located at the Li x Al x Si 1- x O 2 β-eucryptite SS was 1.931 × 10 −21 cm 2 at 1065 nm.

Raman spectroscopy study of phase transformations in titania-containing lithium aluminosilicate glasses doped with CoO

The influence of small additions of CoO (0.05–2.0 mol%) on phase decomposition and further crystallization in glasses of the Li 2O–Al 2O 3–SiO 2–TiO 2 system were studied by comparison of variations in corresponding Raman scattering spectra, optical absorption spectra and X-ray diffraction patterns. It is found out that at early stages of phase decomposition at heat-treatment temperatures of 660–700 °C, cobalt oxide enters the alurninotitanate phase, increases temperature range of its existence and influences the kinetics of formation of crystalline phases with anatase and anosovite structure precipitated in this phase upon heat-treatment. Upon heat-treatments at higher temperatures (720–750 °C), crystallization of aluminocobalt spinel and of small amounts of cobalt titanate is revealed. Addition of CoO facilitates crystallization of β-eucryptite solid solution with β-quartz structure, which takes place at the same temperatures. With increasing heat-treatment temperature, anosovite, spinel, and cobalt titanate are decomposed. At 950 °C, a part of TiO 2 precipitates in the form of aluminum titanate, tialite, which leads to slowing down the crystallization of anatase.

Effect of LiF addition on the phase transition of sinterable β-spodumene precursor powders prepared by a sol-gel process

β-Spodumene (Li2O · Al2O · 4SiO2, LAS4) precursor powders were obtained through a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as starting materials and LiF as a sintering aid. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy with a wavelength dispersive spectrometer, and electron diffraction analysis were utilized to study the phase transition of the β-spodumene glass–ceramics prepared from the gel-derived precursor powders with LiF additive. For the LAS4 precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4.0 wt% LiF and sintered at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution and β-eucryptite (Li2O · Al2O3 · 2SiO2, LAS2) solid solution. When the LiF content was 5.0 wt% and the sintering process was carried out at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution, β-eucryptite solid solution (triclinic), and eucryptite [rhombohedral (hex.)]. When the LiF addition attains 3.0 wt%, the fully densified grains are formed, accompanied with an increase in grain size for LiF addition. At the triple junction of grain boundaries a second phase segregates which is identified to be β-spodumene solid solution. In the sintering period of LAS4 precursor powders with LiF additive, the grains converted to β-eucryptite solid solution and β-spodumene solid solution remains at the grain boundaries.

Structural transformations of nanometer sized crystals in CoO-doped β-eucryptite-based glass-ceramics

Structural transformations of nanometer sized crystals in CoO-doped β-eucryptite-based glass-ceramics were studied by optical spectra and X-ray diffraction analysis. Four types of Co(II) absorption spectra were revealed. In the course of amorphous phase separation Co(II) ions enter into the aluminotitanate amorphous phase. Nanometer sized crystals of CoAl 2O 4, TiO 2 and CoTiO 3 precipitate at elevated temperature. The temperature reversible order–disorder phenomenon was revealed in spinel crystals. Nanometer sized disordered crystals of β-eucryptite solid solution precipitate after heat treatment at 720°C. At a crystallization temperature higher than 900°C, an ordering of these crystals takes place which is confirmed by the absorption spectra and the temperature dependence of lattice parameters of the unit cell.

β-Eucryptite by a Sol-Gel Route

β-Eucryptite solid solution (LAS) Li2O : Al 2O3 : 3SiO2(113) was prepared via a sol-gel route. Complex solutions of lithium or aluminum salts in ethanol/water mixtures were catalysed by inorganic acids (catalyst/alkoxide ratio 0.1). Different ratios of H2SO4 catalyst were also used.

Lithia porcelains as promising breeder candidates — I. Preparation and characterization of β-eucryptite and β-spodumene porcelain

β-Eucryptite, β-spodeumene and solid-solution porcelain were prepared by the conventional ceramic technique with three lithia:alumina:silica (LAS) ratios, 1:1:2, 1:1:3 and 1:1:4. The optimization of the ceramic parameters was assessed through measuring their vitrification parameters with firing temperatures in the range 1000–1350 °C. Structural characterization of the bodies obtained at optimum conditions were followed through X-ray diffraction (XRD) and infrared (IR) spectral analyses. Thermal dilation up to 1000 °C was measured. Morphological variations were examined through scanning electron microscopy (SEM) of fractured surfaces, as well as selected area electron diffraction (SAED). Results proved that the change from β-eucryptite with 1:1:2 LAS through its solid solution to β-spodumene with 1:1:4 LAS, i.e. from hexagonal to tetragonal structures, need a firing temperature of 1320 °C. Shifts in XRD lattice planes were complemented by parallel shifts in IR bands specific for silicates around 1100 cm −1. Unique negative thermal expansion up to 1000 °C for β-eucryptite changed to the positive value only after 600 °C for β-spodumene. Characteristic large grains were detected in both β-eucryptite and β-spodumene micrographs parallel with the polycrystalline rings of the SAED figures. On the other hand, the β-eucryptite solid-solution body has smaller grain size with higher glassy phase shown by the larger SAED halo. The present results illuminate the importance of assessing the detailed structural features for future radiation damage studies.

Structural states of Co(II) in β-eucryptite-based glass-ceramics nucleated with ZrO2

The structure of a Co(II) ion lithium aluminosilicate glass and glass-ceramics nucleated with ZrO2 was studied by optical spectra and X-ray diffraction analysis. Three types of Co(II) absorption spectra were revealed. A type I spectrum arises from the absorption of six-coordinated and four-coordinated Co(II) in an initial glass. A type II spectrum appears when, in the course of crystallization of β-eucryptite solid solution, Co(II) ions enter into microcrystals of this phase, mainly, in sixfold positions, isomorphously substituting for Li(I) ions. At crystallization temperature higher than 950°C, the ordering of microcrystals of β-eucryptite solid solution takes place, which leads to Co(II) coordination change to fourfold positions, which leads to a type III spectrum. The Co(II) structural change in β-eucryptite solid solution was confirmed by the temperature dependence of lattice parameters of the unit cell.

Strengthening of glass through surface crystallization of β-spodumene ss

Compositions close to spodumene with additional flux were investigated regarding surface crystallization for strengthening of glass articles. The influence of Au, TiO 2, P 2O 5 and ZnO was determined. After a general characterization, nucleation and crystallization rates and the activation energies for viscosity of the starting glasses were determined. Further, the activation energy for crystallization and the Avrami exponents were calculated from the results of differential thermal analysis. Transformation with time and temperature was investigated, showing that crystallization of the β-eucryptite solid solution starts at temperatures around Tg. At higher temperatures, the β-spodumene solid solution is the predominant crystalline phase. The base composition was chosen for further investigation of crystalline growth. Glass rods were drawn under industrial conditions. Due to a crystallized surface layer with an extremely low expansion coefficient, the flexural strength of the initial glass increased fourfold to a maximum of 800 MPa.

Glass-ceramics from fly ash with added Li2O

Abstract The effects of the addition of Li2O to fly ash on the devitrification behaviour of the derived glass are investigated with the aid of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The phases crystallizing first for the as-quenched glass and the glass sample previously nucleated are different. Solid solutions of lithium-magnesium silicate (Li(2 + 2x)Mg(1 − x)SiO4) and a small quantity of β-eucryptite (LiAlSiO4) solid solution are formed from the as-quenched glass, while only solid solutions of lithium-magnesium silicate are formed from the sample previously nucleated. In both cases, these crystalline phases are then converted, at higher temperatures, into a large amount of β-eucryptite solid solution together with small quantities of diopside crystals (CaMgSi2O6). Kinetic parameters for nucleation and crystal growth were estimated from the DTA curves. The temperature of maximum nucleation rate was 620°C and the activation energy for crystal growth E = 316 kJ mol−1. The crystal morphology was investigated by SEM, and the crystal shape was consistent with the morphological index n calculated by DTA. The glass-ceramic obtained from a previously nucleated glass showed a fine-grained texture.

Crystallization characteristics of iron-containing spodumene-diopside glasses

Abstract The crystallization characteristics of glasses based on a stoichiometric spodumene (LiAlSi2O6)-diopside (CaMgSi2O6) composition with addition of Fe2O3 replacing Al2O3 are described. The effects of compositional variation due to the Al2O3/Fe2O3 replacement and thermal treatment on the nature, type and stability fields of crystallizing phases as well as the resulting microstructure are traced by DTA, X-ray diffraction (XRD) and scanning electron microscopy (SEM). In most cases, intense uniform bulk crystallization with fine-grained microstructure were achieved on increase of iron oxide at the expense of alumina. The crystallizing phases, β-eucryptite solid solution (ss), β-spodumene ss, varieties of pyroxene solid solution of diopside, hedenbergite and augite nature are mostly formed together, in some cases, with α-quartz, lithium silicates, lithium ferrate (LiFeO2) and iron oxide. The type, stability and compatibility of the crystallized phases are discussed in relation to the compositional variation of the glass and thermal treatment.

Crystallization of spodumene-lithium magnesium orthosilicate glasses

The crystallization of some glasses in the LiAlSi 2O 6Li 2MgSiO 4 system with and without nucleation catalysts has been investigated using thermal, X-ray diffraction and microscopic techniques. Fine-grained glass-ceramic materials with good thermal properties were obtained. Different phase assemblages, including γ 0-lithium magnesium orthosilicate, β-eucryptite solid solution, β-spodumene, lithium metasilicate and forsterite, were formed under different conditions of heat treatment. The γ 0-phase showed a limited and narrow stability range and dissociated rapidly around 850°C. The β-eucryptite→ β-spodumene transformation was delayed with increase of the lithium magnesium component in the glass. The presence of TiO 2 enhanced the decomposition of the γ 0-phase, whereas ZrO 2 favoured its formation and stability. The type, stability and compatibility of the crystallized phases are discussed in relation to glass composition and thermal treatment.

Analysis of a Magnesium-containing: β-Eucryptite Solid Solution by the Lattice Constant Method and Its Application

Abstract An X-ray diffraction method has been developed for the determination of the composition of a magnesium-containing β-eucryptite solid solution which consists of a pseudo-ternary system, SiO2–Mg1⁄2AlO2–LiAlO2. Standard samples of the solid solution within the range of 60–75 mol% SiO2 and 0–15 mol% Mg1⁄2AlO2 were prepared from high-purity materials by the “glass-crystallization” technique. The diffraction angles of the (206) and (212) planes were measured from the center of gravity of the profile recorded on a chart by a counter diffractometer. After having been corrected for various systematic errors, both angles were used for the calculation of the lattice constants. It was found that Mg1⁄2AlO2 and LiAlO2 contributed similarly to a0, but in a different way to c0. The composition of the solid solution in a commercial glass-ceramic could be determined from the correlation between the composition and the lattice constants. The standard deviation of the determination from one measurement was about 0.2–0.4 mol%, and the time required for analysis was about 30 min.

Analysis of β-Eucryptite Solid Solution in Glass-Ceramics by Lattice Constant Method

Ari X-ray diffraction method has been developed for the determination of silica content of B--eucryptite solid solution precipitated in glass-ceramics. B-Eucryptite solid solytions.of Varioug silica content were prepared by the crystallization of glass technique, and d-spacings corresponding to (514), (406), (220), (206) and (114) lines were measured to obtain cali.braQon curvesMDThe Tocalibtation curves, showing the correlation between lattice constaRts and silica content of the solid solution had bent at the composition of Li20-A1203e3 SiO2 and Li20.A1203e 4SiO2.This phenomenon was explained on the basis of repulsive fore betwee-n lith um.iops, or litAium ion'and other cations in the lattice.On the low silica content region, the lattice constants also depended upon the crystallizing temperature and time. However, it was foupd that the calibrat- ocurve, showing .the correlation of (406) interplanar spacing against the silicacontent was linear irrespective of the crystallizing temperature over all solid solutiqn ladday eO1ule time required for ari analysis was dbout one hour w.hep the ayerage -of .thre.e time measurgments the interplanar spacing was used. The absolute values of the lattice constants 6Et5ihed in this woik can bMe also used for the determination anywhere it. is required, if correction is made for systematlc error