Li2O SiO2 Research Articles

Effect of Li content in ion conductivity of lithium silicate glasses

We present the electrical and the phonon vibrational properties of Li2O–2SiO2 (LS12) and Li2O–SiO2 (LS11) glasses to exploit for lithium ion transport in the merits of solid electrolyte. Electrical impedance measurements are carried out in the frequency 100 Hz–30 MHz and temperature range 30–150 °C. Based on the theory of the modified fractional Rayleigh equation, we predict the number densities of the lithium ions in the lithium silicate glasses. As an increase in lithium content, the covalent interaction between the Li-cation and its local sites of network increases the number of the non-bridging oxygen (NBO) sites by the depolymerization of the silicate glass network. We find the fact that the number of NBOs in the LS11 glass increases a factor of two larger than the number of NBOs in the LS12 glass. A low conductivity of lithium oxide glasses is reflection of a long stay of the lithium ions in the NBO atoms. The partial Li+ ions in the lithium silicate glasses participate on the ac conduction through the NBO sites.

Influence of heat treatment regimes on crystalline phase formation and physical properties of Li2O–SiO2–Al2O3 glass system

The purpose of this research is to examine the influence of heat treatment regimes on crystalline phase formation and physical properties of Li2O–SiO2–Al2O3 glass system. The LAS glass samples with the composition 13.32 Li2O–65.98 SiO2–10.84 Al2O3–4.16 P2O5–2.35 Na2O–1.44 CaO–0.84 BaO–0.52 K2O–0.52 ZrO2–0.03 TiO2 (in wt%) were prepared via melt-quench method. The glass samples underwent triple-step heat treatment regimes according to the Differential Thermal Analysis (DTA) data. The glass sample composition and phase identification were determined using x-ray fluorescence spectroscopy and x-ray diffractometer (XRD) respectively. The average crystal size of the crystalline phases was determined using Debye–Scherrer equation. The hardness, compressional wave velocity, Elastic modulus, and density of the prepared glass and glass-ceramics samples were measured. Results of the analysis revealed β-spodumene (LiAlSi2O6), lithium disilicate (Li2Si2O5), lithium metasilicate (Li2SiO3), and lithium orthophosphate (Li3PO4) crystalline phases. β-spodumene shows dominance over other crystalline phases. The LAS glass-ceramics recorded an average hardness of 6.0 GPa, compressional wave velocity of 6882 m s−1, and Elastic modulus of 93.5 ± 0.42 GPa. The increasing crystallinity of LiAlSi2O6 and Li2Si2O5 phases and the reduction of the average crystal size of the Li2Si2O5 phase (from 72.56 nm–21.81 nm) guaranteed the improvement of the mechanical properties. The LAS glass-ceramics show higher bulk density compared to the parent glass. The results suggest that the developed LAS glass-ceramics can be used as dental restorative materials.

Quartz‐containing glass‐ceramics in the SiO2–Li2O–K2O–MgO–CaO–Al2O3–P2O5 system

AbstractVolume crystallization of quartz, triggered by adding P2O5, was investigated in the multicomponent SiO2–Li2O–K2O–MgO–CaO–Al2O3–P2O5 glass system. Glass‐ceramics comprising quartz as the main crystal phase besides lithium disilicate (Li2Si2O5) as a minor crystal phase were produced by controlled crystallization from the parent glass. According to quantitative crystal phase analysis by means of Rietveld refinement the mass fraction of the minor Li2Si2O5 phase decreased with increasing P2O5 content, while the fraction of quartz increased. Scanning electron microscopy revealed lath‐like Li2Si2O5 embedded in a matrix of rather globular quartz crystals forming an interlocking microstructure. Well machinable glass‐ceramics with a mean biaxial flexural strength of about 300 MPa and a fracture toughness of about 2.0 MPa × m0.5 could be realized. With mean values ≥13.6 × 10−6 K−1 the glass‐ceramics coefficient of thermal expansion is close to the one reported for low‐quartz crystals. The ease of production based on conventional glass melting and fabrication technology together with the good mechanical, optical, and machining properties enables the application of these materials in prosthodontics.

Effects of Oxide Ions on the Electrodeposition Process of Silicon in Molten Fluorides

We studied the effects of O2− ions on the coordination structure of Si ions and the electrodeposition process of Si films in molten fluorides using SiO2 powder (as a source of Si) and Li2O (as a source of O2−). High-temperature Raman spectroscopic data revealed that the dissolution of SiO2 in molten KF, LiF-KF, and LiF-NaF-KF without Li2O was proceeded by the formation of silicate ions, with the [Si2O5]2− ion acting as the dominant species. On the other hand, when 3.0 mol% Li2O was added to molten LiF-KF and LiF-NaF-KF, the intensity of Raman band due to [SiO3F]3− ion was increased compared to that without Li2O system, which indicated that the O2− ions could cause breakage of Si-O-Si bonds of SiO2 or [Si2O5]2− ions. Furthermore, the reduction currents, attributed to the reduction of Si ions, increased significantly by the addition of Li2O; moreover, the thickness and current efficiency of the electrodeposited polycrystalline Si layer prepared by potentiostatic electrolysis was improved. These results indicated that the O2− ions can change the coordination structure of Si ions in molten fluorides and that the design of the molten salts bath is a key technology for fabricating high-quality Si layers with high current efficiency.

Study of the Non-Isothermal Crystallization Kinetics of Lithium Disilicate Glass Ceramic

The glass ceramic with the crystals of lithium disilicate Li2O · 2SiO2 (LS2) as the main crystal phase is one of the prospective materials in the field of restorative dentistry. In this study, the crystallization kinetics of LS2 glass ceramic obtained from the base glass of the system SiO2–Li2O–Al2O3–K2O–P2O5 were investigated by the non-isothermal method using differential thermal analysis at four different heating rates. The DTA curves showed different exothermic crystallization peaks over the temperature ranges of 645–683 and 807–845°C. The lithium metasilicate, Li2O · SiO2 (LS), and the lithium disilicate, crystallized over these respective temperature ranges, was established by XRD technique. The crystallization kinetic parameters were calculated by the Kissinger plot and Augis-Bennett equations for non-isothermal analysis. The calculated activation energy of crystal growth, EC1= 236 kJ/mol, EC2 = 340 kJ/mol, and the Avrami parameters, n1 = 1.46–1.67, n2 = 2.73–2.91, together with the results from SEM observations, indicated that the crystallization mechanism of LS was substantial surface crystallization while the crystallization mechanism of LS2 was dominant bulk crystallization. The calculated activation energy of glass transition was also determined EV = 516 kJ/mol.

Effect of Heat Treatment Temperature on the Microstructure and Mechanical Properties of Li2O–SiO2–P2O5–Al2O3–K2O–CaO Glass-Ceramics

Effect of Heat Treatment Temperature on the Microstructure and Mechanical Properties of Li₂O–SiO₂–P₂O₅–Al₂O₃–K₂O–CaO Glass-Ceramics

Homogeneous and Heterogeneous Crystal Nucleation in Glass of the Li2O–SiO2 System

The results of studying the kinetics of homogeneous (spontaneous) and heterogeneous (catalyzed) crystal nucleation in silicate glass is presented for glasses in the Li2O–SiO2 system. Nucleation is catalyzed via the photosensitive mechanism by adding poorly soluble impurities, shifting the glass composition towards the higher content of one of the components (autocatalysis), and by passing steam through the glass melt. The fundamental characteristics of crystal nucleation are obtained. The composition ranges with the maximum and minimum steady-state crystal nucleation rates are identified.

Properties investigation of CaO–Al2O3–SiO2–Li2O–B2O3–Ce2O3 mould flux with different w(CaO)/w(Al2O3) for heat-resistant steel continuous casting

ABSTRACTThe new CaO–Al2O3–SiO2–Li2O–B2O3–Ce2O3 mould flux was devised to realise smooth continuous casting of Ce-bearing heat-resistant steel. The new devised mould flux was based on calcium-aluminate system, so the w(CaO)/w(Al2O3) has great influence on the properties of the slag, which is similar to the basicity in the silicate system. The melting temperature, viscous properties, slag structure and crystalline phases with different w(CaO)/w(Al2O3) were investigated. The melting temperature of the mould flux could remain relatively steady with w(CaO)/w(Al2O3) in the range of 1.0–1.82. The main network former in the new slag was [AlO4]-tetrahedron. The network formed by [AlO4]-tetrahedron was destroyed by increasing w(CaO)/w(Al2O3), the viscosity decreased consequently. The mould flux show weaker crystallisation tendency with increasing w(CaO)/w(Al2O3). When the temperature decreased to 1100°C, the change of the fully crystallised phases with increasing w(CaO)/w(Al2O3) was as follows: Li2O·Al2O3 + 2CaO·Al2O3·SiO2 → Li2O·Al2O3 → Li2O·Al2O3 + 3CaO·Al2O3 + CaCeAlO4.

Crystallization of a high-strength lithium disilicate glass-ceramic: An XRD and solid-state NMR investigation

The phase evolution of a high flexural strength lithium disilicate (Li2Si2O5: LS2) glass-ceramic in a complex SiO2–Li2O–Al2O3–MgO–P2O5–ZrO2 glass system has been investigated as a function of temperature using in situ and ex situ X-ray diffraction (XRD) and 31P and 29Si solid-state nuclear magnetic resonance (SSNMR) spectroscopy. In the base glass, lithium metasilicate (Li2SiO3: LS) crystallizes (at 525°C) before LS2 (at 675°C). 29Si NMR shows that LS is not only formed from the Q(2)glass species, but also by disproportionation of the Q(3)glass units. The XRD data demonstrate the formation of a minor phase of MgAl2Si4O12 from the reaction of SiO2 with minor components of Al2O3 and MgO. Diffraction peaks of Li3PO4 are firstly detected at 675°C, and they become evident at 750°C and above. The evolution of phosphorus species in the glass as a function of temperature has been revealed by 31P NMR spectroscopy. Two 29Si T1 relaxation components were observed in samples across all temperatures, suggesting the presence of glass-in-glass phase separation in the base glass. A plot of 29Si T1 relaxation measurements shows discontinuity at 750°C, indicating microstructural changes. A detailed crystallization mechanism of high-strength LS2 glass–ceramics is proposed.

A novel high-strength lithium disilicate glass-ceramic featuring a highly intertwined microstructure

To achieve long-term clinical performance and wider application of glass-ceramic dental restorations, it is urged to enhance the mechanical properties of glass-ceramic materials. In this study, a high-strength lithium disilicate glass-ceramic was developed in a SiO2–Li2O–Al2O3–MgO–P2O5–ZrO2 related glass system, which demonstrates a high flexural strength of 562±107MPa. In this high-strength glass-ceramic, the microstructure features highly intertwined colonies of lithium disilicate. This novel microstructure effectively contributes to the improvement of flexural strength. The minor crystalline phases (β-quartz, MgAl2Si4O12, and Li3PO4) embedded within the Li2Si2O5 (LS2) crystal colonies and residual glass matrix could further strengthen the glass-ceramic. The development process of such a novel microstructure and its possible formation mechanism are proposed. This material could be an excellent candidate for restorative dental applications up to three-unit posterior bridges.

Sealing Glass‐Ceramics with Near‐Linear Thermal Strain, Part II: Sequence of Crystallization and Phase Stability

The sequence of crystallization in a recrystallizable lithium silicate sealing glass‐ceramic Li2O–SiO2–Al2O3–K2O–B2O3–P2O5–ZnO was analyzed by in situ high‐temperature X‐ray diffraction (HTXRD). Glass‐ceramic specimens have been subjected to a two‐stage heat‐treatment schedule, including rapid cooling from sealing temperature to a first hold temperature 650°C, followed by heating to a second hold temperature of 810°C. Notable growth and saturation of Quartz was observed at 650°C (first hold). Cristobalite crystallized at the second hold temperature of 810°C, growing from the residual glass rather than converting from the Quartz. The coexistence of quartz and cristobalite resulted in a glass‐ceramic having a near‐linear thermal strain, as opposed to the highly nonlinear glass‐ceramic where the cristobalite is the dominant silica crystalline phase. HTXRD was also performed to analyze the inversion and phase stability of the two types of fully crystallized glass‐ceramics. While the inversion in cristobalite resembles the character of a first‐order displacive phase transformation, i.e., step changes in lattice parameters and thermal hysteresis in the transition temperature, the inversion in quartz appears more diffuse and occurs over a much broader temperature range. Localized tensile stresses on quartz and possible solid‐solution effects have been attributed to the transition behavior of quartz crystals embedded in the glass‐ceramics.

Sealing Glass‐Ceramics with Near Linear Thermal Strain, Part I: Process Development and Phase Identification

A widely adopted approach to form matched seals in metals having high coefficient of thermal expansion (CTE), e.g. stainless steel, is the use of high CTE glass‐ceramics. With the nucleation and growth of Cristobalite as the main high‐expansion crystalline phase, the CTE of recrystallizable lithium silicate Li2O–SiO2–Al2O3–K2O–B2O3–P2O5–ZnO glass‐ceramic can approach 18 ppm/°C, matching closely to the 18 ppm/°C–20 ppm/°C CTE of 304L stainless steel. However, a large volume change induced by the α‐β inversion between the low‐ and high‐ Cristobalite, a 1st order displacive phase transition, results in a nonlinear step‐like change in the thermal strain of glass‐ceramics. The sudden change in the thermal strain causes a substantial transient mismatch between the glass‐ceramic and stainless steel. In this study, we developed new thermal profiles based on the SiO2 phase diagram to crystallize both Quartz and Cristobalite as high expansion crystalline phases in the glass‐ceramics. A key step in the thermal profile is the rapid cooling of glass‐ceramic from the peak sealing temperature to suppress crystallization of Cristobalite. The rapid cooling of the glass‐ceramic to an initial lower hold temperature is conducive to Quartz crystallization. After Quartz formation, a subsequent crystallization of Cristobalite is performed at a higher hold temperature. Quantitative X‐ray diffraction analysis of a series of quenched glass‐ceramic samples clearly revealed the sequence of crystallization in the new thermal profile. The coexistence of two significantly reduced volume changes, one at ~220°C from Cristobalite inversion and the other at ~470°C from Quartz inversion, greatly improves the linearity of the thermal strains of the glass‐ceramics, and is expected to improve the thermal strain match between glass‐ceramics and stainless steel over the sealing cycle.

Sol–Gel Synthesis and Crystal Nucleation of Photosensitive Au/Ag- Containing Glasses of Lithium Silicate System

A sol–gel method has been proposed for obtaining the sintering mixture used in the preparing of a photosensitive Au/Ag-containing glasses of the Li2O - SiO2 system. It has been established that the use of sol–gel method for the production of the batch for synthesizing photosensitive Au/Ag-containing glasses gives more homogeneous distribution of Au/Ag metals in the bulk of the glass. Crystal-nucleation main characteristics have been defined in a large area of compounds of photo-structured compositions of a lithium-silicate system (23.4–46.0 Li2O mol % by analysis) both for spontaneous and catalyzed nucleations. The spontaneous (homogeneous) nucleation happened in the samples without any photosensitive metals and with photosensitive gold–silver additives (0.05 wt % above 100%) without irradiation; the catalyzed (heterogeneous) nucleation happened in the samples with photosensitive silver ore gold additives under x-ray CuKa irradiation. The ranges of the compositions of the glasses in which the effect of catalyzing irradiation is reversed (suppressing nucleation in accordance with the autocatalytic mechanism) under certain conditions. The spontaneous and catalyzed nucleation of crystals in the glasses of Li2O–SiO2 system caused by the addition of photosensitive impurities and X-ray irradiation was analyzed in glasses with a very wide range of compositions in Li2O–SiO2 system. Composition ranges with positive (+) and negative (-) differences in the rates of catalyzed and spontaneous steady-state nucleation were established. This finding point is favorable for obtaining photostructured (photosensitive) materials. The concentration limit was determined to be 37.98 mol % Li2O. About this value, we observe a modification of the mechanism of nucleation of crystals. The behavior of crystal nucleation in photostructured glasses under X-ray irradiation changes to the reverse: autocatalytic nucleation is suppressed rather than induced by x-ray CuKa irradiation. These peculiarities of crystallization mechanism in glasses under study give one the possibility to choose the correct composition range depending on the problems facing researchers.

Phase relations of Li2O–FeO–SiO2 ternary system and electrochemical properties of Li x Si y O z compounds

Phase equilibria in the ternary Li2O–FeO–SiO2 system have been studied by means of X-ray powder diffraction. The experimental results show that no new lithium ferrous silicate compounds can be found in our experimental condition which may be a candidate cathode material for LIBs. The Li2O–FeO–SiO2 system can be characterized by the existence of 9 three-phase regions. In Li2O–SiO2 binary system, Li2SiO3 and Li4SiO4 are purely synthesized by solid-state reactions; other new information includes the electrochemical properties of Li2SiO3 and Li4SiO4 compounds, where the electrochemical test indicated that initial discharge-specific capacities can reach to 136 and 129 mAhg−1, respectively. Enhanced performance was exhibited after carbon coating. The initial discharge-specific capacities of carbon-coated Li2SiO3 and carbon-coated Li4SiO4 compound can reach to 230 and 220 mAhg−1 respectively. Our results show that Li2SiO3 and Li4SiO4 samples have better capacity retention except for the first discharge. No significant change can be seen in ex situ XRD patterns for Li2SiO3/C, while the lithium-ion insertion/extraction reaction may exist in Li4SiO4/C as forming solid solutions (nominated Li4+x SiO4).

Mechanical and X-band dielectric properties of vitrified bonded SiC composites

Vitrified bonded SiC composites were prepared from SiC powder and vitrified bond based on B2O3–Al2O3–SiO2–Li2O–Na2O–ZnO system. In the composites, SiC grains were well wetted and coated by the bonding glass, which is observed through a scanning electron microscope. The main crystal structure of the vitrified bonded SiC composites is SiC (3C) and SiO2 phases exist, according to X-Ray Diffraction analysis. The flexural strength of the vitrified bonded SiC composites was investigated and when the content of SiC was 70wt.% it reached up to 71.06MPa. The dielectric properties of the vitrified bonded SiC composites were characterized by the method of vector network analyzer. The real part of the complex permittivity ranges from 5.6 to 9.5 as SiC content changing. The sample incorporating 80wt.% SiC presented the highest dielectric loss tangent. The excellent mechanical and tailored dielectric properties make the vitrified bonded SiC composite a promising candidate for structural microwave shielding materials.

Lithium Disilicate Glass‐Ceramics by Heat Treatment of Lithium Metasilicate Glass‐Ceramics Obtained by Hot Pressing

Lithium disilicate glass‐ceramics are widely used as dental ceramics due to their machinability and translucency. In this study, lithium disilicate glass‐ceramic was fabricated through heat treatment of lithium metasilicate glass‐ceramics obtained by hot pressing of glass powder composed of SiO2–Li2O–P2O5–ZrO2–Al2O3–K2O–CeO2 at low temperature. The crystalline phase, microstructure, and mechanical properties were investigated. The results indicated that lithium metasilicate glass‐ceramic with a relative density of higher than 99% was obtained after hot pressing, and glass‐ceramic with interlocked rod‐like Li2Si2O5 crystals and good flexural strength (338 ± 20 MPa) was successfully obtained through heat treatment. The two‐step method was believed to be feasible in tailoring the microstructure and mechanical properties of lithium disilicate glass‐ceramics.

Siliconizing of iron and molybdenum by electrochemical reduction of silicon in molten SiO2–Li2O–MgO

Electrochemical reduction of silicon on metal electrodes in molten silicate was studied. An iron sheet was immersed in SiO2–Li2O–MgO at 1273K, and the electrode potential was controlled for 1h. Formation on the iron of a Si-containing layer about 10–30μm thick was observed after the electrolysis, depending on the potential. When a molybdenum electrode was used, α-MoSi2 layer about 5μm thick was formed on the surface. The results suggest the applicability of molten oxide electrolysis as a synthesis method of Si-containing alloy layers.

Trace phase formation, crystallization kinetics and crystallographic evolution of a lithium disilicate glass probed by synchrotron XRD technique.

X-ray diffraction technique using a laboratory radiation has generally shown limitation in detectability. In this work, we investigated the in situ high-temperature crystallization of a lithium disilicate glass-ceramic in the SiO2–Li2O–CaO–P2O5–ZrO2 system with the aid of synchrotron radiation. The formation of lithium metasilicate and other intermediate phases in trace amount was successfully observed by synchrotron X-ray diffraction (SXRD). The crystallization mechanism in this glass was thus intrinsically revised to be the co-nucleation of lithium metasilicate and disilicate, instead of the nucleation of lithium disilicate only. The phase content, crystallite size and crystallographic evolutions of Li2Si2O5 in the glass-ceramic as a function of annealing temperature were studied by performing Rietveld refinements. It is found that the growth of Li2Si2O5 is constrained by Li2SiO3 phase at 580–700°C. The relationship between the crystallographic evolution and phase transition was discussed, suggesting a common phenomenon of structural response of Li2Si2O5 along its c axis to other silicon-related phases during glass crystallization.

Single-Component White Emitting Silicate Glass Triply Activated by Ce3+/Tb3+/Mn2+ for Organic-Resin-Free White LEDs

Thermal management is still a great challenge for high-power phosphor-converted white-light-emitting diodes (pc-WLEDs) intended for future general lighting. Luminescent glass based WLEDs (LG-WLEDs) are strongly expected to be an interesting and excellent alternative approach to traditional pc-WLEDs fabricated by combining InGaN based LED chips, with phosphor and organic resin. In the past years, many efforts have been made to develop luminescent glasses for LG-WLEDs. However, some of these glasses are poor in mechanical and chemical stability, some cannot be excited effectively owing to weak f-f absorption, and others are not very suitable for UV-LED chips ascribed to their maximum excitation wavelengths in deep UV. [1]In this paper, a series of single-component white emitting silicate SiO2–Li2O–SrO–Al2O3–K2O–P2O5: Ce3+, Tb3+, Mn2+(SLSAKP: Ce3+, Tb3+, Mn2+) glasses that simultaneously play key roles as a luminescent convertor and an encapsulating material for WLEDs were prepared via the conventional melt-quenching method. The as-synthesized SLSAKP: 0.3%Ce3+, 2.0%Tb3+, 2.0%Mn2+ glass shows good thermal stability, inconspicuous chromaticity shift, better high-temperature resistance, and higher thermal conductivity. These are rare but desirable characteristics that are not present in the phosphors used as luminescent convertor and the epoxy resin used as the encapsulating material in pc-WLEDs. Luminescent glass (LG-) WLEDs based on SLSAKP: 0.3%Ce3+, 2.0%Tb3+, 2.0%Mn2+glass and UV-COB was successfully fabricated. These results indicate that SLSAKP: Ce3+, Tb3+, Mn2+ glass may serve as a potential bifunctional white-light-emitting materialfor LG-WLEDs pumped by UV-LED chips, especially high-power UV-COB. Fig. 1. Photographic images of the mirror-polished (left) and rough-polished (right) SLSAKP: Ce3+, Tb3+, Mn2+glasses: (a) under white-emitting fluorescent lamp; (b) under 365 nm UV lamp. (c) The conceptual and actual fabrication process

Effect of heat treatment on the microstructure and properties of lithium disilicate glass-ceramics

The effect of heat treatment on microstructure and properties of SiO2–Li2O–K2O–Al2O3–ZrO2 glass-ceramics was investigated. The glasses were subjected to a multi-stage heat treatment. At the first stage at 650°C, Li2SiO3 was the main crystalline phase of all samples, which had a dimensional change with prolonging the heating time from 3h to 72h. After the second stage treatment at 830°C for 3h, all the Li2SiO3 crystals decomposed and Li2Si2O5 crystals formed with an opposite dimensional change from that of Li2SiO3. These Li2Si2O5 crystals were small, which could contribute to forming high translucency. The third stage at 550°C would release the internal strain and improve samples' bending strength, which could reach up to above 560MPa. The sample treated for 48h at the first stage had the smallest crystals and also obtained a highest real in-line transmission of 29% at 650nm with a thickness of 1.45mm and a bending strength above 581±25MPa.