Li2O Al2O3 SiO2 Glass Research Articles

Effect of SiO2/Li2O content on structure and physicochemical properties of photosensitive glass-ceramics

Easy-to-manufacture photosensitive glass ceramics are vital for wide applications due to their superior thermal, mechanical and chemical properties from an industrial point of view, while their commercialization is strongly limited by the complex effect of material compositions and thermal treatments. Here, the effect of SiO2/Li2O content on structure and physicochemical properties of photosensitive glass-ceramics was systematically investigated. The photosensitive glass-ceramics were prepared using a melting method based on the Li2O–Al2O3–SiO2 glass system. The effect of each component content on dielectric constant, dielectric loss and etching properties of the basic glass was studied. The relationship between the structure and properties of photosensitive glass-ceramics before and after crystallization were investigated via differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Raman spectroscopy measurements. The results show that when the SiO2/Li2O ratio is 76.5/9, the chemical stability of the basic glass is the highest, whereas the etching loss rate is the lowest. After UV exposure and heat treatment, acid-soluble Li2SiO3 crystals were formed inside the glass-ceramic matrix. Compared with the unexposed part, the etching ratio of the photosensitive glass-ceramic reaches its maximal value of 16/1. It is worth mentioning that after heat treatment, the dielectric constant and dielectric loss of the unexposed photosensitive glass-ceramic are slightly higher than those of the basic glass, reaching 6.67 and 5.78 × 10−3 (@1 GHz), respectively. Finally, after acid etching, photosensitive glass-ceramic is exposed via mask exposure and heat treatment to obtain holes with a diameter of 50–60 μm, which can be used as a substrate material in many fields such as communication, aerospace, biomedical and so on.

Effect of Y2O3/La2O3 on structure and mechanical properties of Li2O–Al2O3–SiO2 glass

Effect of Y2O3 and La2O3 substitution for SiO2 on the structure and mechanical properties of Li2O-Al2O3-SiO2 (LAS) glass was investigated. The structural changes were characterized by 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR), Fourier transform infrared spectrometer (FTIR) and viscosity-temperature tests. The results showed that LAS glass network structures depolymerized firstly and then polymerized with increasing Y2O3 or La2O3 content. Atomic packing density of LAS glasses monotonically increased as the addition of Y2O3 or La2O3 and its best measurement value is 0.5824 with the Y2O3 and La2O3 doping content are 4 mol% and 2 mol% (denoted as LAS-42). Simultaneously, Vickers hardness, elastic modulus and bending strength were measured and their best values corresponded to 712.80 HV, 99.72 GPa and 140.47 MPa when the glass is LAS-42, with the increases of 13.1%, 14.9% and 59.9%, respectively. This study revealed that high dissociation energy oxides, in terms of Y2O3 and La2O3, have obvious effects on improving mechanical properties of LAS glass.

High efficiency near infrared emission from Pb1-xSrxSe Quantum dots in lithium aluminosilicate glass-ceramics

Pb1-xSrxSe quantum dots (QDs) were prepared in Li2O-Al2O3-SiO2 (LAS) glass-ceramics with 0–2.0 mol% SrO by conventional melt-quenching method. The near-infrared photoluminescence and photodarkening properties of Pb1-xSrxSe QDs in LAS glass-ceramics were studied. Upon the heat treatments of 490–550 °C for 10 h, there are LiAlO2 nanocrystals and PbSe QDs co-existed in the glassy matrix without SrO, and 1024–1745 nm near infrared emission from PbSe QDs were realized. With the increasing of SrO concentration from 0 to 2 mol%, the absorption wavelengths blue-shifted from 1738 to 1380 nm at 540 °C, the PL peak wavelengths blue-shifted from 1788 to 1538 nm at 540 °C. The blue-shifts are attributed to the increasing bandgap by incorporation of Sr2+ ions into PbSe crystalline lattice. Pb1-xSrxSe QDs display better photoinduced anti-darkening properties than pure PbSe QDs with the increasing of pumping power, and the Pb1-xSrxSe QDs embedded in the LAS glass with 2.0 mol% SrO shows the highest photoluminescence quantum yield of ∼36.9%.

Nanoscale composition fluctuations and crystallization process: Case study in Li2O–SiO2‐based glasses

AbstractNanoscale composition fluctuations in Li2O–SiO2‐based glasses were analyzed and discussed from the data on the structure and crystallization process reported so far to enter deeply into the medium‐range ordered structure of multicomponent oxide glasses. Li2O is proposed to have a strong tendency for dynamical heterogeneous structure, that is, the formation of fragile Li2O‐rich regions with small SiO2 contents, resulting in the initial crystallization of metastable Li2SiO3 prior to the formation of stable Li2Si2O5 in Li2O–2SiO2‐based glasses. Li2O–Ga2O3/Nb2O5–SiO2 glasses are proposed to have nanoscale composition fluctuations of Li2O–Ga2O3/Nb2O5‐rich regions, resulting in the initial formation of LiGa5O8 and LiNbO3 nanocrystals. In Li2O–Al2O3–SiO2 glasses, the distribution width of composition fluctuations is proposed to be narrow, resulting in the initial crystallization of metastable β‐quartz solid solutions Li2O·Al2O3·nSiO2 (n = 6–8). Additive P2O5 and NiO leading to an enhanced nucleation are proposed to be present in fragile Li2O‐rich regions.

Investigation on crystallization behavior, structure, and properties of Li2O–Al2O3–SiO2 glasses and glass-ceramics with co-doping ZrO2/P2O5

Li2O–Al2O3–SiO2 (LAS) glasses and glass-ceramics with co-doping ZrO2/P2O5 were prepared by the traditional melt quenching method and nucleation-crystallization process in this study. The effect of ZrO2/P2O5 co-doping on crystallization behavior, structure, and properties of the LAS glasses and glass-ceramics was discussed. The results show that the LAS glass ZP/0.5 exhibits better properties as compared to the other LAS glasses. As for the LAS glass-ceramics, ZrO2/P2O5 with mass ratios of 0–1 have little effect on the crystallization behavior. However, with the ZrO2 content increases to 4 wt% (ZrO2/P2O5 with a mass ratio of 2), an effective crystallization promotion behavior is found. Under a crystallization temperature of 950 °C, the LAS glass-ceramic ZP/2 shows improved properties, including lower density (2.526 g/cm3), higher Vickers hardness (7.23 GPa) and bending strength (94 MPa), and excellent acid and alkali-resistance (4.12 and 5.32 × 10−5 g/cm−2 h).

Mechanical behavior of the joints between carbon/carbon composites and Li2O–Al2O3–SiO2 glass ceramics with YAS interlayer at high temperature

YAS (Y2O3–Al2O3–SiO2) glass ceramics were selected to join carbon/carbon (C/C) composites and Li2O–Al2O3–SiO2 (LAS) glass ceramics through vacuum hot-pressing sintering, due to the corresponding excellent compositional and structural stability at high temperature. Microstructures, mechanical properties and fracture features of the C/C-LAS joints were investigated. The joints with YAS interlayer exhibited more favorable results than the joints with MAS (MgO–Al2O3–SiO2) interlayer subsequently to shear testing at 300 and 600 °C. Strength retention of 70% for YAS joints was achieved at 600 °C, while for MAS joints the strength retention was only 28%. The joining properties amount decrease of YAS joints was due to degradation of the intrinsic properties of YAS and LAS glass ceramics. Regarding MAS joints, the poor structural stability of MAS interlayer at high temperature was the reason for the corresponding decrease. As a result, the mechanical behavior of joints at elevated temperatures was not only related to wettability and interfacial bonding, but it was also related to the intrinsic properties as well as to high-temperature stability of the interlayer and the joined substrates.

The formation of nanocrystalline ZrO2 nuclei in a Li2O-Al2O3-SiO2 glass \u2013 a combined XANES and TEM study

The high economic importance of glass ceramics based on Li2O/Al2O3/SiO2 (LAS) is mainly due to their low coefficients of thermal expansion (CTE), which make these materials suitable candidates for a number of applications. The exact mechanism of the crystallization processes in LAS glasses is still not fully understood. The present work focuses on the formation and development of nanocrystalline ZrO2 within an LAS base composition which contains only ZrO2 as nucleating agent. Using a combination of transmission electron microscopy and X-ray absorption spectroscopy techniques, the temporal evolution of the ZrO2 nanocrystal formation is described. It is found that the formation of ZrO2 is initiated by liquid-liquid phase separation droplets with high Zr content, which eventually evolve into the nanocrystalline ZrO2 precipitations. This process is accompanied by a gradual change of the coordination of the tetravalent Zr ions from sixfold in the glass to eightfold in the crystals. The diameters of the ZrO2 crystals stay well below 4 nm, even at late stages. The degree of crystallization at each step of the crystallization process is deduced, and from that, the Avrami coefficient n is determined to be n ≈ 1, which describes a barrier-limited crystal growth process.

Effect of the concentrations of nucleating agents ZrO2 and TiO2 on the crystallization of Li2O–Al2O3–SiO2 glass: an X-ray diffraction and TEM investigation

In order to study the effect of ZrO2 and TiO2 on the nucleation mechanism in a lithium aluminosilicate glass, a composition similar to that of the commercially available ROBAX™ glass (Schott AG) was modified. Glasses with different concentrations of ZrO2 and TiO2 were melted and studied using differential scanning calorimetry measurement. The glasses are thermally treated for different periods of time and at various temperatures and then investigated by X-ray diffraction and electron microscopy. Both scanning electron microscopy and transmission electron microscopy were applied to study size and shape of the formed crystal phases and possibly to obtain lattice plane distances. Increasing the concentration of the nucleation agents led to the spontaneous formation of Zr1−x Ti1+x O4 nano crystals during cooling. In any case, the nuclei contain much more titania than zirconia, possess an elongated shape, and are embedded in a shell enriched in alumina.

Effects of TiO2 on microstructures and properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC substrates

In order to increase the flexural strength and to adjust the coefficient of thermal expansion (CTE), TiO2 was introduced into Li2O–Al2O3–SiO2 (LAS) glass–ceramics to satisfy LTCC applications. The effects of TiO2 addition on the microstructure, thermal, mechanical and electrical properties were studied. The results showed that the crystal phases were composed of Li2OAl2O37.5SiO2 (major), as well as TiO2 and CaMgSi2O6 (minor). The crystal phase TiO2 having higher CTE value could appropriately increase the CTE value of LAS to fit the silicon and remarkably improve the flexural strength of LAS glass–ceramic with low CTE. The dielectric and insulating properties also strongly depended on the amount of TiO2. LAS glass–ceramic sintered at 800 °C with high performances was achieved in the case of 1 wt% TiO2: α = 2.56 × 10−6/°C, σ = 151 MPa, e = 6.8, tanδ = 1.731 × 10−3, ρ = 8.29 × 1010 Ω cm.

Microstructure and properties of ZnO doped Li2O–Al2O3–SiO2 glass–ceramic for LTCC applications

Microstructure and properties of ZnO doped Li2O–Al2O3–SiO2 glass–ceramic for LTCC applications

Influences of ZrO2 on microstructures and properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

In this work, Li2O–Al2O3–SiO2 (LAS) glass–ceramics for LTCC applications were prepared by the melt quench technique, and the influences of ZrO2 content on the microstructure, thermal, mechanical and electrical properties were investigated. XRD showed that the major crystalline phase was Li2OAl2O37.5SiO2 and the minor crystalline phases were ZrO2 and CaMgSi2O6. The formation of ZrO2 crystal phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of LAS glass–ceramics, which was favorable for matching with silicon (3.1 × 10−6/°C). Moreover, it was found that the mechanical property enhanced markedly when the high thermal expansion phases generated in the glass–ceramic system with low CTE. The results indicated that the addition of ZrO2 was beneficial to promote the mechanical, thermal and dielectric properties. 3 wt% ZrO2-added LAS glass–ceramic sintered at 800 °C exhibited excellent properties: a high bulk density of 2.567 g/cm3, a high linear shrinkage of 20.08 %, a low CTE value (2.68 × 10−6/°C), a high flexural strength of 157 MPa, a low dielectric constant of 7.1, a low dielectric loss (tan δ) of 1.884 × 10−3 at 1 MHz, and a high resistivity (ρ > 1010 Ω cm).

Glass–ceramics of LAS (Li2O–Al2O3–SiO2) system enhanced by ion-exchange in KNO3 salt bath

The paper describes a low-temperature ion-exchange process on specially designed Li2O–Al2O3–SiO2 glass–ceramics (LAS). Due to thermal treatment, two main crystalline phases: lithium di-silicate and lithium alumina-silicate were obtained in glass–ceramic materials. As a result of proper time/temperature profile treatment of precursor glasses, flexural strength of final materials increased up to 300–450MPa.Crystallized samples were immersed in KNO3 molten salt, at temperatures of 400–420°C for 9 or 16h. The final materials achieved almost 100% greater mechanical resistance than glass–ceramics before ion-exchange.We claim that the process of ion-exchange improved flexural strength significantly. Furthermore, it resulted in some changes of the surface layer structure. We noticed that chemical tempering process leads to decrystallization of the multiphase LAS glass–ceramic surface layer consisting of lithium di-silicate and lithium alumina-silicate phases.

Fabrication and properties of Li2O–Al2O3–SiO2 glass/Al2O3 composites for low temperature co-fired ceramic applications

The Al2O3 filler was added to a Li2O–Al2O3–SiO2 glass–ceramic in order to increasing the bending strength and coefficient of thermal expansion of these composites for low temperature co-fired ceramic applications. The influence of the Al2O3 filler on the sintering, microstructure and characteristics was investigated. When the content of Al2O3 increases from 0 to 20 wt%, the bending strength increases from 104 to 155 MPa and the coefficient of thermal expansion increases from 1.26 to 2.65 ppm/°C. The Al2O3 filler also plays an important role for obtaining desired sintering, microstructure and dielectric properties. But the linear shrinkage, microstructure, mechanical and dielectric properties would deteriorate because of the excessive Al2O3 and the decrease of glass content. The composite with 20 wt% Al2O3 filler exhibits excellent properties: a low sintering temperature of 800 °C, a good density of 2.78 g/cm3, a dense microstructure, an high bending strength of 155 MPa, good dielectric properties (er: 8.0 and tan δ: 2.4 × 10−3) and a low CTE of 2.65 ppm/°C.

Microstructure and properties of ZnO doped CaO–Al2O3–SiO2 ceramic for LTCC applications

The effects of ZnO content and sintering temperature on the microstructure, bending strength, coefficient of thermal expansion and dielectric properties of Li2O–Al2O3–SiO2 glass–ceramic are presented. The prepared Li2O–Al2O3–SiO2 glass–ceramic could be used for the application of LTCC substrate. Glass powders were produced by conventional melt-quenching technique. The sintering and crystallization behavior of glass powders was explored using scanning electron microscopy, differential thermal and X-ray diffraction analyses. The crystalline phase formation in the calcination of Li2O–Al2O3–SiO2 samples has shown a major phase of Li2OAl2O37.5SiO2 and two minor phases ZrO2 and CaMgSi2O6. Increasing ZnO content at the expense of SiO2 was shown to not only promote the densification and lower the linear shrinkage, but also enhance the bending strength and the coefficient of thermal expansion of the glass–ceramic. The linear shrinkage and density of samples will decrease with the increasing sintering temperature.

Effect of SiC nanowires on the thermal shock resistance of joint between carbon/carbon composites and Li2O–Al2O3–SiO2 glass ceramics

Abstract In order to improve the bonding property of joint between SiC modified carbon/carbon (C/C) composites and Li2O–Al2O3–SiO2 (LAS) glass ceramics, SiC nanowires were attempted as the reinforcement materials in the interface region of SiC transition layer and Li2O–MgO–Al2O3–SiO2 (LMAS) gradient joining interlayer. The C/C–LAS joint with SiC nanowire-reinforced interface layer was prepared by a three-step technique of pack cementation, in situ reaction and hot-pressing. The microstructure and thermal shock resistance of the as-prepared joints were examined. The average shear strength of the joined samples with SiC nanowires increased from 24.9 MPa to 31.6 MPa after 40 thermal cycles between 1000 °C and room temperature, while that of the joined samples without SiC nanowires dropped from 21.4 MPa to 8.3 MPa. The increase of thermal shock resistance of the C/C–LAS joints was mainly attributed to the toughening mechanism of SiC nanowires by pullout, bridging and crack deflection.

Thermal and spectroscopic characterization of glasses and glass–ceramics of Li2O–Al2O3–SiO2 (LAS) system

Research were focused on obtaining Li2O–Al2O3–SiO2 glass–ceramics where crystallization of both Li-di-silicate and Li-alumina-silicates occurs. DTA techniques were used to determine the basic glass temperature/time crystallization profile of the set chemical composition (wt%): SiO2 66.3%; Al2O3 10.2%; Li2O 12.1%; CaO 1.46%; K2O 0.53%; Na2O 2.59%; P2O5 4.28%; ZrO2 0.56%; CeO2 1.5%; V2O5 0.04%. In order to define in material the crystallization degree and phase composition after particular thermal treatments, XRD method was used. On this base the proportion of main, Li-di-silicate and Li-Al-silicates, crystalline phases was defined. As a complementary, the spectroscopic FTIR examinations has been performed. After temperature/time thermal treatment of basic glass, FTIR spectra were changing: bands correlated with crystalline phases became sharper and split. This indicated increase the crystallization in material after particular heat treatments. For the investigated glasses and glass–ceramics 27Al MAS NMR and 29Si MAS NMR spectra was also measured. These spectra indicated what was the local structure of the alumina Al and silica Si in examined glasses and glass–ceramics. On this base various Qn units of aluminum Al3+ and silicon Si4+ were identified.

Effects of MgO on properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

Li2O–Al2O3–SiO2 (LAS) glass–ceramics for low temperature co-fired ceramics (LTCC) application were prepared by melting method, and the effects of MgO on the sinterability, microstructure, dielectric property, thermal expansion coefficient (CTE) and mechanical character of this glass–ceramics have been studied. The X-ray diffraction images represent that the main phase is β-spodumene solid solutions. And some ZrO2 and CaMgSi2O6 phases in LAS glass–ceramics are detected. The LAS glass–ceramics without additive (MgO) sintered at 800° had the dielectric properties: dielectric constant (er) of 5.3, dielectric loss (tanδ) of 2.97 × 10−3 at 1 MHz, CTE value of 1.06 × 10−6 K−1, bulk density of 2.17 g/cm3, and flexural strength of 73 MPa. 5.5 wt% MgO-added LAS glass–ceramic achieves densification at 800° exhibited excellent properties: low dielectric constant and loss (er = 7.1, tanδ = 2.02 × 10−3 at 1 MHz), low CTE (2.89 × 10−6 K−1), bulk density = 2.65 g/cm3 as well as high flexural strength (145 MPa). The results indicate that the addition of MgO is helpful to improve the dielectric and mechanical properties. The formation of CaMgSi2O6 crystal phase with higher CTE leads to the increase of CTE value of LAS glass–ceramics due to the increasing MgO content, and the increase of CTE is favourable for matching with silicon (3.1 × 10−6 K−1). The prepared LAS glass–ceramics have the potential for LTCC application.

Effect of TiO2 content on the crystallization and the color of (ZrO2,TiO2)-doped Li2O–Al2O3–SiO2 glasses

Glass–ceramics formed by controlled crystallization of Li2O–Al2O3–SiO2 (LAS) parent glasses are well-known for their low thermal expansion and transparency. In order to promote bulk crystallization, it is necessary to add nucleating agents like TiO2 and ZrO2 to the glass composition leading to ZrTiO4 nuclei during heating, followed by the crystallization of a β-quartz phase that transforms into β-spodumene at higher temperature. Generally, these glass–ceramics present a yellowish-brown coloration whose intensity increases with the crystallization rate and that is partly due to coloring elements like titanium. In this study, we investigated the origin of the evolution of the color of LAS glasses and glass–ceramics by varying the TiO2 concentration. To do this, several TiO2-bearing LAS glasses (with TiO2 ranging from 0 to 4mol% and 1mol% ZrO2) were prepared and heat treated at a given temperature (925°C) to study the impact of the TiO2 concentration on their crystallization behavior and their color. The crystallization and microstructure of LAS glasses and glass–ceramics were studied by DTA, XRD and TEM whereas their structure was investigated by EPR, optical and X-ray absorption spectroscopies. From all the results obtained, the evolution of the optical absorption and coloration of LAS glasses and glass–ceramics was mainly explained by Ti4+–O2− charge transfer (glasses) and by gap absorption and Rayleigh scattering of nanocrystals (glass–ceramics).

Non-isothermal sinter-crystallization of jagged Li2O–Al2O3–SiO2 glass and simulation using a modified form of the Clusters model

We have tested a modified form of the Clusters model of sintering for the complex case of non-isothermal sintering with concurrent crystallization of a multicomponent lithium aluminum silicate (LAS) glass having a broad size distribution of jagged particles. We compared experimental and simulated densification data using a constant heating rate. Only one adjustable parameter was used: the particle shape factor (Ks). We discuss the results in light of some complicating factors, such as temperature gradients within the powder compacts and compositional shifts of the residual glass matrix due to crystallization, which lead to changes of viscosity. The modified Clusters model accurately predicted the temperature dependence of densification and the final (saturation) density of the glass particle compacts.

Effect of Neodymium on the Crystallization, Microstructure and Colorization of Li<sub>2</sub>O-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Glass Ceramics

The effect of single coloring agent Nd(NO3)3 on the crystallization, microstructure and colorization of Li2O-Al2O3-SiO2 (LAS) glass ceramics were investigated by differential thermal analysis (DTA), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The introduction of little neodymium has no effect on the crystallization manner and the formation of main crystallization phase, but more neodymium will weaken the crystallization of LAS glass. Little neodymium can increase the glossiness of LAS glass ceramic, while more neodymium can color LAS glass with light purple or red purple. The colorability of neodymium for LAS glass ceramic decreases with the increase of crystallization temperature.