Β-quartz Solid Solution Research Articles

Preparation of low thermal expansion, transparent LAS glass-ceramics via simplified heat-treatment method

Li2O–Al2O3–SiO2 (LAS) glass-ceramics are commercially significant due to their unique microstructure and exceptional properties, including near-zero thermal expansion coefficient, making them suitable for a wide range of applications. However, the content of SiO2 and Al2O3 in the composition of LAS glass is very high, which leads to high viscosity and very difficult melting of this type of glasses. In order to reduce the melting temperature of the glass, use of relatively high Na2O in the basic glass composition allows high-quality glass to melt. Employing a simplified heat-treatment method, LAS glass-ceramics are prepared with Australian spodumene as the primary material. By exploring the effect of crystallization temperature on the structures and properties of the resulting LAS glass-ceramics, samples with excellent comprehensive properties are achieved. The prepared glass-ceramics are thoroughly characterized using DSC, XRD, FTIR, SEM, and TEM, along with assessments of their viscosity, thermal, optical, and mechanical properties. Relatively more Na2O is introduced into the glass compositions, which can lower the melting temperature of the glass to below 1600 °C. The basic glass is annealed at 700 °C for 2 h, nucleation phenomenon Nucleation phenomenon can be generated in the LAS glasses. When the microcrystalline temperature of glasses increases from 835 °C to 910 °C, the main crystalline phase of glass-ceramics changes from β-quartz solid solution to β-spodumene solid solution. The change in the main crystal phase has significantly affected the properties of glass-ceramics. When the crystallization temperature is below 860 °C, the glass-ceramics exhibit a low negative expansion coefficient (<-0.5 × 10−6 K−1), high visible light transmittance (>85 %), and excellent average flexural strength (173.3 MPa).

Synthesis of Spherical β-Quartz Solid-Solution Particles Derived from Cordierite Using a Flame Process

Synthesis of Spherical β-Quartz Solid-Solution Particles Derived from Cordierite Using a Flame Process

Phase Transformations upon Formation of Transparent Lithium Alumosilicate Glass-Ceramics Nucleated by Yttrium Niobates

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.

A comprehensive approach to crystallization sequence in novel MgO/CaO-Al2O3-SiO2 glass-ceramics by Ostwald's step rule and composition fluctuation model

An understanding of the crystallization sequence (the formation order of crystalline phases) of glasses is crucial for the processing and composition design of novel glass-ceramics. A comprehensive approach to the crystallization sequence in novel MgO/CaO-Al2O3-SiO2 (MAS/CAS) glass-ceramics was performed from the Ostwald's step rule and the model of the distribution of nanoscale composition fluctuations (DNCF) for the first time. The stoichiometric cordierite Mg2Al4Si5O18 glass exhibits the crystallization sequence predicted by the Ostwald's step rule and a narrow DNCF model, i.e., metastable β-quartz solid solutions (β-QSSs) → high-temperature type indialite → low-temperature type α-cordierite. A broad DNCF model was proposed to present in osumilite Mg2Al4Si11O30 and pyrope Mg3Al2Si3O12 glasses, resulting in the initial formation of β-QSSs or forsterite 2MgO.SiO2 prior to α-cordierite formation. The crystallization sequence in stoichiometric anorthite CaAl2Si2O8 glass was also understood along the Ostwald's step rule and a narrow DNCF model. The importance of nanoscale composition fluctuations, in particular the formation of MgO/CaO-rich fragile regions, was emphasized in the crystallization of MAS and CAS-based glasses having strong Al-O-Si linkages between AlO4 and SiO4 tetrahedra. The present article will contribute to the comprehensive design of new innovative aluminosilicate-based glass-ceramics.

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

A glass with the composition 7.9 Li2O∙2.0 MgO∙1.4 ZnO∙10 Al2O3∙2.7 B2O3∙72.6 SiO2∙0.9 ZrO2∙2.1 TiO2∙0.4 Sb2O3 was thermally treated at temperatures in the range from 650 to 750 °C. During thermal treatment, at first, nearly spherical Zr1-xTixO4 crystals with sizes of 5–20 nm were formed. On these nanocrystals, elongated particles consisting of TiO2 were observed to grow. Subsequently hexagonal β-quartz solid solution was formed at temperatures ≥650 °C. In this β-quartz solid solution, Zn as well as Mg and excess Al were incorporated. At temperatures >690 °C, the formation of tetragonal β-spodumene solid solution was observed. In the microstructure of the formed glass-ceramics, a volume concentration of around 12% spherical aggregates with a diameter of 1.5–2 μm composed of β-spodumene solid solution and areas enriched in Al and Zn occur. These heterogenous structures were formed by the transformation of β-quartz solid solutions to β-spodumene solid solution. At the same time, Zn(Mg) and excess Al were expelled from the aluminosilicate phase and a cubic spinel type phase Zn(Mg)Al2O4 was formed. These aggregates did not contain a glassy phase. In-between these spherical aggregates, i.e. in around 88% of the volume, tiny Zr1-xTixO4 crystals, aluminosilicate crystals with diameters of around 200 nm, and a glass phase shoved away by these growing crystals consisting of oxides of Mg, Zn, Al, Si, and Sb happened to occur.

Effects of Ti Containing Cu-Based Alloy on Sintering Mechanism, Element Diffusion Behavior and Physical Properties of Glass-Ceramic Bond for Cubic Boron Nitride Abrasive Tool Materials

Ti containing Cu-based (TC) alloy reinforced glass-ceramic bond was fabricated for cubic boron nitride (CBN) abrasive tool materials, and its crystal composition, phase transformation, sintering activation energy, microstructure, element diffusion mathematical model, physical properties, and the bonding mechanism between the TC alloy reinforced glass-ceramic bond and the CBN grains were systematically investigated. The results showed that the structure, composition and sintering behavior of glass-ceramic were influenced by TC alloy adding. The generated TiO2 affected obviously the precipitation of β-quartz solid solution Li2Al2Si3O10, thus improving the relative crystallinity, mechanical strength and thermal properties. By establishing the mathematical model for element diffusion, the element diffusion coefficients of Ti and Cu were 7.82 and 6.98 × 10-11 cm2/s, respectively, which indicated that Ti diffused better than Cu in glass-ceramic. Thus, Ti4+ formed a strong Ti-N chemical bond on the CBN surface, which contributed to improving the wettability and bonding strength between CBN and glass-ceramic bond. After adding TC alloy, the physical properties of the composite were optimized. The porosity, bulk density, flexural strength, Rockwell hardness, CTE, and thermal conductivity of the composites were 5.8%, 3.16 g/cm3, 175 MPa, 90.5 HRC, 3.74 × 10-6 °C-1, and 5.84 W/(m·k), respectively.

Effect of substitution of ZrO2 by SnO2 on crystallization and properties of environment-friendly Li2O–Al2O3–SiO2 system (LAS) glass-ceramics

In this study, a transparent and environmentally friendly Li2O–Al2O3–SiO2 (LAS) glass-ceramic was prepared by melt-quenching and two-step heat treatment. The influence of the substitution amount of ZrO2 by SnO2 on the crystallization, microstructure, transparency, and mechanical properties of LAS glass and glass-ceramics was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible Spectrophotometer, three-point bending strength test, and microhardness test. The results indicate that the main crystalline phase of LAS glass ceramics was a β-quartz solid solution when heat treated at 780 °C for 2 h and 870 °C for 1.5 h. When the substitution amount of ZrO2–SnO2 increased from 0.4 mol% to 2.5 mol%, the grain size and thermal expansion coefficient of LAS glass-ceramics first decreased and then increased, and the crystallinity first increased and then decreased. When the substitution amount of ZrO2–SnO2 was 0.8 mol%, the transparency of the LAS glass-ceramics was maximum, the bending strength was 96 MPa, and the Vickers hardness was 10.9 GPa.

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

Glasses and glass-ceramics in the LAS system containing four complex nucleating agents (TiO2+ZrO2+P2O5+MgF2) were prepared by the traditional melt quenching technology and two-step (nucleation-crystallization) method. The effects of MgF2 contents on the performances and crystallization behavior of parent glass were examined using XRD, SEM, DSC, Fourier transform infrared, Transmittance, TEC, Density, Bending strength, Vickers hardness and the Quality loss of Alkali (Acid) resistance. The result reveals that when the complex nucleating agents (TiO2+ZrO2+P2O5+MgF2) in a ratio of 2: 2: 5: 3, the parent glass has the most prominent performance and optimal crystallization promotion. Fluoride has the better promotion effect on the formation of ZrTiO4 when the MgF2 content is 2 wt%, regardless of whether β-quartz or β-spodumene solid solution used as main crystalline phase. Besides, fluoride may be hinder the precipitation of AlPO4 (in β-quartz solid solution) and has the limit impact on the formation of AlPO4 (in β-spodumene).

Influences of Al2O3 content on crystallization and physical properties of LAS glass-ceramics prepared from spodumene

Low thermal expansion Li2O-Al2O3-SiO2 transparent glass-ceramics with low Li2O content and relatively high total content of Na2O and K2O (> 2.00 wt.%) were prepared from spodumene. And the influences of Al2O3 addition on structure and properties of such LAS glasses and glass-ceramics were investigated. The crystallization behavior and structure of the samples were explored by differential scanning calorimetry (DSC), X-ray diffraction (XRD), magic-angle-spinning (MAS) NMR, Fourier transform infrared spectrometer (FTIR), and scanning electron microscope (SEM). The results show that the addition of Al2O3 contributes to the precipitation and transition of β-quartz solid solution (s.s.) Besides, the smaller grains can be obtained in glass-ceramics with higher Al2O3 content, resulting in the higher visible transmittance. When the Al2O3 content is 21.00 wt.%, the transparent and low coefficient of thermal expansion (CTE) samples crystalized at 860 °C present the best mechanical properties.

Preparation and Characterization of High-Strength Glass-Ceramics via Ion-Exchange Method.

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.

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

Crystallization of glass has significant effects on glass structure and the resultant ion-exchange behaviors. In this work, transparent glass-ceramics (GCs) with sequential crystallization of ZnAl2O4 and β-quartz solid solution nanocrystals (NCs) were prepared, and effects of the crystallization on microstructure and ion-exchange properties were investigated. Compared with the specimen with simultaneous precipitation of ZnAl2O4 and β-quartz solid solution NCs, GCs with sequential crystallization of ZnAl2O4 and β-quartz solid solution NCs show smaller grain size and more uniform structure and higher transparency. Ion-exchange depth of layer (DOL) increases significantly with the crystallization of the specimens due to the reduction in content of zinc and five coordinated aluminum in the residual glass matrix. High residual compressive stress and Vickers hardness can be obtained after ion-exchange in KNO3 molten salt.

Mixed alkali effect in SiO2-CaO-Al2O3-TiO2-R2O (R = Li, Na) glass ceramics

The effects of Li2O/(Li2O + Na2O) ratio and temperature on structure, crystallization, microstructure and mechanical properties of SiO2-CaO-Al2O3-TiO2-9 mol% R2O glass ceramics were investigated by melting-sintering method. It was concluded that as substituting Li2O for Na2O, the degree of polymerization of glass first increased and then decreased by Raman spectra analysis. The activation energy of crystallization was in the range of 165–193 kJ/mol, and the crystallization behavior was dominated by bulk crystallization. When the glass samples were heat treated at 750 ℃, only glass containing 9 mol% Li2O crystallized, and the crystalline phases were β-quartz solid solution and wollastonite phases; while when heat treatment temperature increased to 800 ℃ or 850 ℃, the main crystal phase changed from granular wollastonite to fine-grained β-spodumene phase as replacing Na2O by Li2O. In addition, both the flexural strength and Vickers hardness first increased and then decreased with the increase of Li2O/(Li2O + Na2O) ratio.

Influence of TiO2 amount on the interfacial wettability and relevant properties of vitrified bond CBN composites

The influence of TiO2 amount on the microstructure and relevant properties of SiO2-Al2O3-B2O3-Na2O-Li2O-BaO vitrified bond and vitrified bond CBN composites were systematically studied via SEM, EDS, FTIR, and XPS. Results indicated that adding TiO2 could regulate the quantity of β-quartz solid solution and rutile crystals in the vitrified bond and considerably affect the thermal properties and mechanical strength of this bond. Under sintering temperature, the dense B2O3 oxide layer on the CBN surface diffused into vitrified bond and reacted with Ti4+ enriched at the interface to form a strong chemical Ti-B bond. This reaction extensively improved the interfacial wettability between the CBN and the vitrified bond. When the TiO2 amount was 6wt.%, the interfacial wettability significantly improved, and the wetting angle decreased from 68° to 43°. The flexure strength and hardness of the composites were 116.18 MPa and 128 HRB, which were 48.49% and 34.74% higher than those of the basic-formula composites, respectively.

Sinterability and mechanical properties of glass-ceramics in the system SiO2-Al2O3-MgO/ZnO

The sintering, crystallization and mechanical behavior of three glass compositions in the SiO2-Al2O3-MgO/ZnO system were investigated. Partial substitution of MgO by ZnO causes a decrease in Tg, a slight increase in the crystallization temperature and improves sinterability. Cordierite and enstatite were crystallized in bulk glasses heat treated at 1000 °C. Addition of ZnO resulted in the crystallization of cordierite, willemite and gahnite for the heat treated bulk glasses and cristobalite, enstatite, gahnite and willemite for the sintered glass powders. The first phase to crystallize is the β-quartz solid solution at 850−900 °C for all compositions. The glass and glass-ceramic with ZnO had the lowest hardness and elastic modulus. There was no variation of fracture strength with composition. The glass-ceramic with ZnO had a similar wear resistance in comparison to the composition with higher MgO content.

Low Li2O content study in Li2O-Al2O3-SiO2 glass-ceramics

The price of lithium-containing minerals and other chemical materials continues to increase, resulting in an increase in the production cost of Li2O-Al2O3-SiO2 (LAS) system glass-ceramics. In the LAS glass-ceramics component, the reduction in the amount of Li2O used can reduce the cost of the product. It is worthwhile to study whether it is possible to prepare glass-ceramics with low expansion properties under low Li2O content. The effect of Li2O content on the glass-ceramics of LAS system was studied. In this paper, spodumene was used as the main raw material, and TiO2 and ZrO2 were added as crystal nucleating agents to prepare transparent glass-ceramics with low expansion coefficient. The effects of the change of Li2O content on the crystal phase and microstructure of glass-ceramics were investigated by XRD, DSC, FTIR and SEM. The results show that the main crystalline phase of the low expansion transparent glass-ceramics is β-quartz solid solution. When Li2O content is in the range of 2.99 wt% to 4.13 wt%, low expansion glass ceramics can be prepared by an appropriate method. With the increase of Li2O content, the average coefficient of thermal expansion (CTE) in the temperature range of 30 °C–300 °C shows a decreasing trend. When Li2O content is in the range of 3.51 wt% to 4.13 wt%, the thermal expansion coefficient of the glass ceramics is extremely small, and even a negative expansion coefficient occurs.

Transparent ultra-low expansion lithium aluminosilicate glass-ceramics: Crystallization kinetics, structural and optical properties

β-quartz solid solution phase in the Li2O-Al2O3-SiO2-P2O5 (LAS) glass system has been precipitated by controlled heat-treatment of the parent glass prepared by melt-quench technique. Detailed crystallization kinetics of LAS glass was studied which facilitated in determination of an optimized heat-treatment protocol in order to synthesize highly transparent glass-ceramics of extremely low thermal expansion coefficient. The crystallization kinetic studies indicated a bulk nucleation with linear growth event in the LAS glasses.The LAS glass-ceramics (GCs) containing the beta-spodumene crystalline phase shows extremely low to negative thermal expansion coefficient (K−1) ranging from −0.0029 × 10−6 to 0.3227 × 10−6 measured in the temperature range 223 to 423 K. The glass-ceramics exhibited visible light transmittance of nearly 90%, such high transparency was possible by restricting average crystal size to nanometric scale through controlled crystallization. Microstructural characterization of the heat-treated GCs using FESEM and TEM showed nano-crystalline spherical particles of 2–3 nm, which provided a rationale for its high transparency.

Effect of Y2O3 content on the crystallization behaviors and physical properties of glasses based on MgO-Al2O3-SiO2 system

Different concentrations of Y2O3 doped MgO-Al2O3-SiO2 system glasses were prepared by melting method. The effects of Y2O3 content on the physical properties, crystallizability, and the resultant microstructures of the glass samples were investigated. With the increase of Y2O3 content, the glass transition temperature, dilatometric softening temperature and micro hardness all increased. Low concentrations of Y2O3 (0–1.0 mol%) favored the formation of quartz solid solution at 840 °C for 1.5 h, and phase transformation from β- to α-quartz solid solution happened after heat treatment at 1000 °C with subsequent cooling process. While high concentration of Y2O3 (1.5 mol%) inhibited the crystallization process, and quartz solid solution formed at a high temperature ~ 940 °C. The phase transformation from β- to α-quartz solid solution happened after heat treatment at 1060 °C with subsequent cooling process. Average crystal sizes were increased significantly with the crystallization temperature increasing from 940 °C to 1120 °C. The coefficient of thermal expansion of the glass treated at 1120 °C decreased obviously around temperature ~ 300 °C, which indicated that the phase transformation from α- to β-quartz solid solution happened in the heating process.

Transparent glass-ceramics with Yb3+,Ho3+:YNbO4 nanocrystals for green phosphors

We report on synthesis, structure, Raman and optical spectroscopy of transparent glass-ceramics (GCs) containing nanocrystals of rare-earth orthoniobates, Yb3+,Ho3+:YNbO4 and β-quartz solid solution. Under the near-IR excitation, the GCs exhibit intense upconversion luminescence which color properties can be tuned by the heat-treatment regime due to the structural changes in the orthoniobate nanocrystals. The developed GCs are promising as thermal shock resistant green phosphors.

Transparent glass-ceramics for optical applications

Abstract

Transparent glass–ceramics with (Eu3+,Yb3+):YNbO4 nanocrystals: Crystallization, structure, optical spectroscopy and cooperative upconversion

In the present work, we report on a comprehensive study of crystallization, structure and optical spectroscopy of transparent glass–ceramics with (Eu3+,Yb3+):YNbO4 nanocrystals synthesized by secondary heat-treatments of glass of the Li2O–Al2O3–SiO2 system, for the first time, to the best of our knowledge. Heat treatments result in volume crystallization of RENbO4 with the sizes of 4–15nm. Crystals of rare-earth niobates with disordered fluorite structure (T′) appear during heat-treatment at 720–740°C for 6h, crystals with tetragonal structure (T) appear at higher temperatures or longer durations of heat-treatment, and in samples heat-treated at 1000°C, the monoclinic form (M) is detected additionally. Rare-earth niobates act as nucleating agents for bulk crystallization of β-quartz solid solutions, the main crystalline phase of the glass–ceramics, which ensures their good thermo-mechanical properties. Optical spectroscopy confirms entering of both Eu3+ and Yb3+ ions into the RENbO4 nanophase and their specroscopic properties variation according to the T′→T→M phase transformations. Under UV excitation, glass–ceramics heat-treated at 900°C provide intense red emission with the color coordinates x=0.665, y=0.335 (CIE 1931). In the sample, heat-treated at 1000°C, a partial reduction of Eu3+ to Eu2+ is observed which allows for tuning the color properties of emission. When excited in the near-IR by an InGaAs diode, the initial glass and glass–ceramics show red cooperative upconversion due to the 2Yb3+→Eu3+ energy transfer. The efficiency of the latter is ~10%. The developed materials due to the good emission and thermo-mechanical properties are promising for the development of color-tunable red phosphors.