Lithium Aluminosilicate Glass Research Articles

PROSPECTIVE LITHIUM ALUMINOSILICATE GLASS-CERAMIC MATERIALS FOR PULSE RANGEFINDERS

The relevance of creating multi-functional nanosecond pulsed laser devices with a generation wavelength that lies in the conditionally eye-safe region of the spectrum of 1.5÷1.6 μm has been established. The prospects of using the mode of passive Q-switching when receiving powerful nanosecond laser pulses with a radiation divergence close to the diffraction one have been determined. Materials for shutters that function in the mode of passive Q-switching were analyzed: solid-state nonlinear optical materials based on single crystals of yttrium-aluminum garnet doped with cations of neodymium, chromium, vanadium and other Nd- or Yb-doped crystals in the wavelength range of 0.8–1.2 μm. The promising use of oxide single crystals activated by Co2+ ions in four-coordinated oxygen positions for MgAl2O4, LiGa5O8, LaMgAl11O19 has been confirmed. The feasibility of developing transparent glass-ceramics based on aluminomagnesium and lithium gallium spinel for pulsed ranging was determined, taking into account its commercial availability, the simplicity of the production technology, as well as the homogeneity of the distribution of the activator in the volume. The feasibility of creating a new type of nonlinear optical materials based on nanostructured heat-resistant lithium aluminosilicate glass ceramics with spinel nanocrystals activated by Co2+ ions under low-temperature heat treatment conditions, has been determined. The purpose and tasks of the work are formulated, which consist in justifying the choice of the system and compositions of glasses for obtaining glass-ceramic materials as a passive laser shutter for powerful lasers that operate at a wavelength of 1.54 μm and are characterized by high heat resistance. The choice of the lithium aluminosilicate system R2O – RO – RO2 – P2O5 – R2O3 – SiO2 based on phase-forming SiO2, Al2O3, Li2O, modifying K2O is substantiated; RO – MgO, ZnO, CaO, SrO, BaO components and a complex crystallization catalyst of P2O5, CeO2, TiO2, SnO2, ZrO2 and ZnO. The structural criteria for the glass matrix were formulated. Compositions of model glasses were designed taking into account the calculated parameters fSi > 0.22, Kсr ≥ 3.5, Ktr ≥ 2.1, and the probability of obtaining transparent glass-ceramic materials with a sitallized structure for pulse rangefinders was established on their basis.

The effect of nucleating temperature on the crystallization, phase formation and properties of lithium aluminum silicate (LAS) glass-ceramics

To study the influence of the nucleation mechanism in lithium aluminosilicate glass, a composition similar to commercially produced glass was used. The glass-ceramics was obtained as a result of two-stage heat treatment, differing in the nucleation temperature and coinciding in the temperature and time of crystal growth. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to study the formed nanocrystals. It was shown that the change of nucleation temperature in the glass transition interval Tg ±15 °C significantly affects the coefficient of thermal expansion, which is due to the formation of a different number of nanocrystals of the general composition LixAlxSi1-xO2 with x = 0.33 with the size less than 50 nm.

Effect of Na+ Ions on the Mechanical Properties of Lithium Aluminosilicate Glass

Effect of Na+ Ions on the Mechanical Properties of Lithium Aluminosilicate Glass

Microstructure, Dielectric Properties and Bond Characteristics of Lithium Aluminosilicate Glass-Ceramics with Various Li/Na Molar Ratio

The advent of 5G technology presented new challenges regarding the high-frequency characteristics of electrical signals and their impact on the cover glass properties of electronic devices. This study aimed to analyze the effect of the Li/Na molar ratio on the dielectric and mechanical properties, as well as the structural characteristics, of lithium aluminosilicate glass-ceramics. Using the melting method, we prepared lithium aluminosilicate base glasses and subsequently crystallized them by adjusting the molar ratio. XRD and TEM analyses were employed to investigate the resultant structures and crystal formation in the five base glasses. It was observed that Li2Si2O5 and LiAlSi4O10 crystals precipitated, exhibiting varying degrees of crystallinity and crystal ratios. Through a comparison of dielectric properties before and after crystallization, it was found that the dielectric constants of the glass-ceramics were consistently reduced. This decrease can be attributed to the lower dielectric constants exhibited by both crystalline phases compared to the parent lithium aluminosilicate glasses. Furthermore, the presence of glass crystals effectively immobilized the alkali metal ions within the glass phase, impeding their movement under an electric field. Consequently, the dielectric loss value of the glass-ceramics decreased with the increasing amount of precipitated crystals. By carefully adjusting the composition and optimizing the crystallization process, we successfully produced lithium aluminosilicate glass-ceramics, demonstrating excellent mechanical and optical properties, coupled with low dielectric properties.

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.

Fractographic strength estimations of 1- and 2-step, ion-exchanged glass plates fractured in bending

Fractography is routinely applied to estimate the fracture strength of annealed brittle materials, however, it is rarely used in chemically strengthened (CS) glasses displaying significant residual stress. This work expands and improves upon a recently proposed fractographic strength estimation method applicable to CS glass plates with deep, 1-step residual stress profiles and no stress relaxation. In particular, the current work considers both CS soda-lime silicate glass with significant stress relaxation and 2-step, ion-exchanged lithium aluminosilicate glass plates. The proposed methodology and its limitations are discussed in light of extensive testing and analysis carried out on numerous CS glass plates. The accuracy of the proposed correlation between non-dimensional strength and mirror radius was validated on both 1-step and 2-step ion-exchanged glass plates with a relatively small case depth and relatively large, induced surface damage.

Repair bond strength of different CAD-CAM ceramics after various surface treatments combined with laser irradiation.

The aim of this study was to evaluate the effect of different surface treatments combined with laser irradiation on the shear bond strength of different CAD-CAM ceramics to composite resin. A total of hundred forty-seven ceramic specimens with thicknesses of 2.5mm were prepared from three different CAD-CAM ceramics (an yttrium oxide partially stabilized tetragonal zirconia polycrystal (Y-TZP); a zirconia-reinforced lithium silicate glass ceramic (ZLS); and a lithium disilicate-strengthened lithium aluminosilicate glass ceramic (LD-LAS)) and subjected to seven groups of treatment (n = 7): (1) control (no treatment), (2) Er:YAG laser irradiation, (3) Nd:YAG laser irradiation, (4) etching with hydrofluoric acid (HFA), (5) Er:YAG + HFA, (6) Nd:YAG + HFA, and (7) sandblasting. After surface treatment procedures, a ceramic primer (Clearfil Ceramic Primer Plus, Kuraray, Japan) was applied to the ceramics. Bonding agent (Single Bond Universal Adhesive, 3M ESPE, USA) was then applied, and the composite resin (Estelite Sigma Quick, Kuraray, Japan) was layered on the ceramic surfaces. The shear bond strength test was performed using a universal testing machine at a load of 0.5mm/min. Data were analyzed by 2-way analysis of variance (ANOVA), and the Bonferroni correction was used for pairwise comparisons (α = 0.05). Compared to the bond strength of the control group, irradiation by Er:YAG and Nd:YAG lasers alone improved the bond strength of the composite resin to the Y-TZP (P < 0.001) but did not change the bond strength of composite resin to the ZLS and LD-LAS (P > 0.05). Compared to the bond strength of the control group, etching with HFA alone increased the bond strength of the composite resin to the ZLS and LD-LAS (P < 0.001) but did not affect the bond strength of the composite resin to the Y-TZP (P > 0.05). The highest bond strength of ZLS was obtained using HFA + Er:YAG, and the highest bond strength for LD-LAS was obtained using HFA + Nd:YAG. It was concluded that Er:YAG and Nd:YAG laser treatments presented the highest repair bond strength between the composite resin and Y-TZP ceramics. Er:YAG and Nd:YAG laser treatments in conjuction with HFA presented the highest repair bond strength between the composite resin and the glassy ceramics, ZLS, and LD + LAS.

AlO1.5/SiO2 substitution effect on the viscosity of alkali silicate melts

The effect of alumina addition on the viscosity of silicate melts is strongly related to the type of non-framework cations; however, the origin of these interactions is not well understood. In this study, we measured the viscosity change in selected alkali disilicate (R2O·2SiO2, R: Na or Li) melts by varying the AlO1.5/SiO2 molar ratio (AlO1.5 = 0–16.8 mol%) within the 1373–1823 K temperature range. We observed that as the molar ratio increased, sodium silicate viscosity increased, whereas lithium silicate viscosity was not affected. Aluminum-27 nuclear magnetic resonance spectra of the quenched glasses indicated that the aluminum cations in both types of alkali silicate melts were mostly present as AlO4 tetrahedra. In contrast to sodium-containing systems, the shear strain on the AlO4 tetrahedron was greater for lithium aluminosilicate glass. Our findings indicated that the degree of shear strain on AlO4 plays an essential role in controlling the viscosity of aluminosilicate systems.

Network Structure and Properties of Lithium Aluminosilicate Glass.

Based on lithium aluminosilicate glass, the composition of glass was optimized by replacing SiO2 with B2O3, and the influence of glass composition on structure and performance was studied. With the increase in B2O3 concentrations from 0 to 6.5 mol%, Al2O3 always existed in the form of four-coordinated [AlO4] in the network structure, and B2O3 mainly entered the network in the form of four-coordinated [BO4]. The content of Si-O-Si linkages (Q4(0Al)) was always dominant. The incorporation of boron oxide improved the overall degree of polymerization and connectivity of the lithium aluminosilicate glass network structure. An increase in the degree of network polymerization led to a decrease in the thermal expansion coefficient of the glass and an increase in Vickers hardness and density. The durability of the glass in hydrofluoric acid and NaOH and KOH solutions was enhanced overall.

High-Strength Glass-Ceramic Material with Low Temperature Formation

Prospects for development of glass-ceramic materials on the lithium aluminosilicates base in order to increase the reliability of armor protection elements have been analyzed. Compositions of lithium aluminosilicate glasses with low content of lithium oxide have been developed, spodumene glass-ceramic materials were obtained on their base in conditions of low-temperature thermal treatment. Formation of structure of glass-ceramic materials based on model glasses after thermal treatment has been investigated and the influence of phase composition on mechanical properties has been established. It was determined that the developed glass-ceramic materials are feasible for the application against the action of high-energy munitions with significant penetrating ability, especially when used in combination with ceramic elements.

Effect of ZnO on the structural, physio-mechanical properties and thermal shock resistance of Li2O–Al2O3–SiO2 glass-ceramics

The composition of lithium aluminosilicate (LAS) with different zinc oxide-magnesium oxide (ZnO–MgO) contents that ranged from 0 to 1.45 wt percent (wt%) was investigated to determine the thermal shock resistance properties of the glass-ceramics. The LAS glasses were melted in an alumina crucible at 1550 °C for 5 h, and the green compact samples were then heat-treated at 1100 °C for 3.5 h. The presence of zinc oxide (ZnO) in the compositions did not change the major crystal phase of β-spodumene. However, the addition of ZnO shifted the pronounced peak to a lower angle and increased the percentage of crystallinity from 55% to 59%. Additionally, the function of ZnO in LAS glass-ceramics as the network modifier was confirmed through Fourier Transform Infrared Spectroscopy (FTIR) analysis. The physio-mechanical properties were improved when 1.45 wt% ZnO was added to the LAS glass-ceramics. The results showed increased density (2.42 g/cm3), low porosity (0.85%), high flexural strength (125.23 MPa), and low coefficient of thermal expansion (25–800 °C) (CTE(25–800 °C)) value of 1.73 × 10−6 °C−1. Meanwhile, the thermal shock resistance properties evaluation of the LAS glass-ceramics at different ZnO contents were conducted at different thermal shock temperatures of 200 °C, 500 °C, and 800 °C. The critical temperature of the LAS specimens with 1.45 wt% ZnO demonstrated the ability to withstand a thermal shock at 800 °C while preserving 87% of their initial strength of 108.40 MPa, exemplifying the best LAS glass-ceramics properties for rapid high-temperature change applications.

Wetting and joining of surface-oxidized SiC ceramic with calcium lithium aluminosilicate glass filler

A novel strategy was developed to join SiC ceramics via a two-step method (i.e., SiC surface was modified by pre-oxidation treatment before bonding) using CaO-Li2O-Al2O3-SiO2 (CLAS) glass as the joining material. The wetting behavior, joint microstructure, bonding strength, fracture characteristics, and joining mechanism were investigated. Due to the formation of the SiO2 layer on the SiC surface by the pre-oxidation, the wettability of CLAS glass solder on the SiC matrix was significantly improved and the interfacial bonding was also enhanced. The microstructure of the joint revealed that the nanoscale eutectic structure composed of wollastonite and spodumene and the rod-shaped anorthite with micron-size were the main products in the joint seam. Besides, the content and size of anorthite in the joints increased with the increase of the joining temperature. Compared with one-step joining, the two-step method can obtain more reliable SiC/SiC joints due to the strong interfacial bonding. As a result, the optimal shear strength of 127 MPa was achieved at a joining temperature of 1240 °C, which was 119% higher than that obtained by the one-step joining method.

The Structure of Gd3+-Doped Li2O and K2O Containing Aluminosilicate Glasses from Molecular Dynamics Simulations

Understanding the atomic structure of glasses is critical for developing new generations of materials with important technical applications. In particular, the local environment of rare-earth ions and their distribution and clustering is of great relevance for applications of rare earth-containing glasses in photonic devices. In this work, the structure of Gd2O3 doped lithium and potassium aluminosilicate glasses is investigated as a function of their network modifier oxide (NMO–Li2O, K2O) to aluminum oxide ratio using molecular dynamics simulations. The applied simulation procedure yields a set of configurations, the so-called inherent structures, of the liquid state slightly above the glass transition temperature. The generation of a large set of inherent structures allows a statistical sampling of the medium-range order of the Gd3+ ions with less computational effort compared to other simulation methods. The resulting medium-range atomic structures of network former and modifier ions are in good agreement with experimental results and simulations of similar glasses. It was found that increasing NMO/Al ratio increases the network modifier coordination number with non-bridging oxygen sites and reduces the overall stability of the network structure. The fraction of non-bridging oxygen sites in the vicinity of Gd3+ ions increases considerably with decreasing field strength and increasing concentration of the network modifier ions. These correlations could be confirmed even if the simulation results of alkaline earth aluminosilicate glasses are added to the analysis. In addition, the structure predictions generally indicate a low driving force for the clustering of Gd3+. Here, network modifier ions of large ionic radii reduce the probability of Gd–O–Gd contacts.

The effects of a Li2O excess on the crystallization sequence of lithium aluminosilicate glass powders

The surface crystallization of melt-quenched lithium aluminosilicate (LAS) glasses with SiO2-contents between 77 and 79 mol% was investigated by high-temperature X-ray diffractometry. Glasses possessing a ratio Li/Al > 1 underwent far earlier crystallization (starting from 750°C) than their stoichiometric counterparts, developing solely quartz solid solution (Qss) and keatite solid solution (Kss) crystals during a heat treatment up to 1200°C. In turn, samples with Li/Al = 1 devitrified only above 900°C and exhibited the transient formation of cristobalite, whose lattice constants hint at a slight Li+Al stuffing. The composition, structural parameters and critical inversion temperature Tc of the obtained Qss crystals were analyzed and compared with the available literature sources, reaffirming the established mutually linear dependence between these properties.

Effect of Soaking Time on Crystal Structure of Lithium Aluminosilicate Glass Ceramic

Formation of crystal structures in glass ceramic is influenced by the heat treatment of parent glass. Most of research often studied on the important of sintering temperature and its soaking time. In this study, the effect of soaking time (3, 4 and 5 hours) during melting process (1550 °C) on crystal structures of Lithium Aluminosilicate (LAS) glass ceramic was conducted. All samples were then sintered at 900 °C for 30 minutes. The amorphous phase was identified prior to sintering process and transformed into crystalline phase for all samples after sintering process in XRD analysis. Major crystalline phase of high quartz solid solution and β-spodumene (LiAlSi2O6) were observed and higher intensity peak is found as the soaking time is longer. The microstructure of the sintered samples was observed under SEM and the particles were displayed an evidently growth of the grain as function to the soaking time. The functional groups of Si-O-Si and Si-O(Si, Al) bonding were appeared in fourier-transform infrared spectroscopy (FTIR) analysis corresponding to the silicates and aluminosilicate bonding. The results achieved present 5 hours soaking time during melting process was the optimum soaking time for melting LAS glass at 1550 °C.

Measurement of stress build-up of ion-exchange strengthened lithium aluminosilicate glass.

A recently developed non-destructive method was used to investigate the stress build-up in chemically strengthened lithium aluminosilicate glass. We utilized an updated version of the gradient scattered light method, which now enables more precise determination of the depth coordinates, recovering a more detailed stress profile around the knee. The main motivation of the work was to characterize and optimize the development of the knee-shaped breaking point in stress profile in lithium aluminosilicate glass using Saunders-Kubichan method of 1-step strengthening in a mixture of KNO3+NaNO3 molten salt bath. In the industry, a 2-step process is still commonly used to build such a stress profile. 1-step strengthening will simplify the process as well as save the cost. Compared to previous studies, which used a destructive method based on transmitted light photoelasticity, we found that in the samples ion-exchanged for 24h the knee-shaped breaking points were situated two times deeper whereas the case-depths were 28% shallower. The measured stress profiles were validated by stress equilibrium and by comparison to Na+ ion concentration profiles.

Stress interaction and crack propagation behavior of glass ceramics under multi-scratches

The interaction between scratches has a significant influence on the material removal mechanism during scratching glass ceramic. To clarify the interaction mechanism, an analytical model of stress interference considering scratch distance is established based on the interaction features between scratches to analyse the relationship between stress distribution and crack propagation. A double scratch experiment with different scratch distances was conducted on lithium aluminosilicate (LAS) glass ceramics. Experimental and analytical results show that the crack is further extended by the enhanced maximum principal stress in the case of the scratch interference. In the interaction range, the maximum principal stress decreases with increasing scratch distance. Furthermore, larger scratch distance in the interaction range is prone to achieve ductile material removal while smaller scratch distance makes the brittle material removal occurring.

Crystallisation studies on site saturated lithium aluminosilicate (LAS) glass

Available sites for nucleation has to reach saturated condition that is a primary validity criterion for employing conventional thermo-analytical (TA) methods. Non-isothermal DSC and TA methods were employed to determine the crystallisation parameters of site-saturated lithium aluminosilicate (LAS) glass. Activation energy of crystallisation for a thermally stable LAS composition was determined after prenucleation process and it was found to be 371 ± 14 kJ/mol. A heat treatment programme for controlled crystallisation process was designed to result a transparent (>80%), nanocrystalline, low expansion (coefficient of thermal expansion −0.31 ppm/K between −60 to +60 °C) glass-ceramic. Crystal growth at 1048 K was determined to be in range 2.56–3.53 × 10−11 m/s and viscosity of glass near the growth front was predicted to vary between 1.28 × 105 and 2.82 × 105 N s m−2.

TiO2(B) nanocrystals in Ti-doped lithium aluminosilicate glasses

Abstract Three different compositions of TiO2-doped lithium aluminosilicate glass were annealed and analyzed to investigate their first stages of crystallization. After phase separation had occurred, monoclinic TiO2(B) was invariably observed as the first seed forming phase. Phase identification was confirmed by Raman spectroscopy and transmission electron microscopy, disproving its interpretation as pseudobrookite in previous literature sources. The phase was observed to undergo gradual transformation into anatase with increasing temperature, but its persistence was longer in the Si-richer samples. It disappeared right before the volume crystallization of high quartz solid solution and keatite solid solution.

Kinetics of crystallization in 13.2Li2O-67.6SiO2-14.49Al2O3-3.3TiO2-0.4BaO-0.97ZnO glass ceramic powder: Part I: A model-free vs. model-fitting approach

Crystallization kinetics of lithium aluminosilicate glass powder has been investigated by model-free and model–fitting methods. Non-isothermal experiments were carried out using differential scanning calorimetry (DSC) to monitor crystallization behavior. Model-free activation energy has been calculated based on Ozawa-Flynn-wall (OFW), Kissinger-Akahira-Sunose (KAS) and Friedman (FR) methods during crystallization progress. Although activation energy does not significantly differ between the models (400–470 kJ/mol), partial Avrami coefficient n(α) varies considerably with rate and crystallization progress. A better description of the crystallization behavior could be observed by the comparison of model-free and model fitting methods. The conformity of one model has been approved with comparison of theoretical DSC curve and experimental results. Finally, a model which can more accurately describe the crystallization behavior of this material was suggested.