Lithium Aluminosilicate Glass-ceramics Research Articles

Effect of striae on the high temperature dielectric and electrical properties of lithium aluminosilicate glass-ceramics

Lithium Aluminosilicate glass-ceramics with striae (LAS-WS) and without striae (LAS-WoS) were processed using melt casting technique. LAS-WS and LAS-WoS samples were characterized and found stress birefringence >10 nm/cm and <10 nm/cm, respectively. LAS-WS and LAS-WoS samples were subjected to structural, microstructural, high temperature dielectric and electrical characterization. The presence of striation did not significantly affected the formation of β-spondumene structure during crystallization heat treatment. TEM image confirms the formation of nanocrystals in the glass matrix of lithium aluminosilicate glass-ceramics. The homogeneous distribution of LAS nanocrystals of average size of 3–6 nm is evident from TEM results. Stress birefringence distribution in lithium aluminosilicate glass-ceramic clearly shows the striae formation. Shadowgraphy images confirmed the striae free and striae containing regions in the glass-ceramic. The effect of striae on dielectric properties and AC conductivity was analysed using impedance spectroscopy and it was found that the value of the relative permittivity decreased from 415 (1.2 Hz) to 9.76 (1.2 MHz) for LAS-WoS and from 401 (1.2 Hz) to 10.3 (1.2 MHz) for LAS-WS, respectively. It was found that striae in LAS glass-ceramics influence the electrical impedance and AC conductivity relaxation process rather than relative permittivity. The effect of striae on crystallization and morphology are presented. Both the samples have shown crystallinity of more than 75 %. The electrical conductivity of σ = 2.0 × 10−3 S/cm for LAS-WoS and 2.7 × 10−3 S/cm for LAS-WS at 300 °C as well as σ = 4.6 × 10−3 S/cm for LAS-WoS and 6.9 × 10−3 S/cm for LAS-WS at 700 °C are found to be in good agreement due to increase in the electrical conductivity with temperature. The ionic conductivity of the material due to Li-ion mobility with respect to temperature and electric field and possible mechanism of AC conductivity are discussed. The results presented indicates the potential application of this material that demands high temperature operation of lithium aluminosilicate glass-ceramics.

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 &gt; 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.

Ion-exchange induced mechanical properties enhancement and microstructural modifications of transparent lithium aluminosilicate glass-ceramics

Alkali-aluminosilicate glass and glass-ceramics can be effectively strengthened by ion-exchange if compression is introduced into the surface, which have been widely used in many electronic devices, especially for mobile phones. In this work, the transparent lithium aluminosilicate glass-ceramics with eucryptite crystalline phase were ion-exchanged in the mixed x NaNO3 + (100－x) KNO3 (wt%, x = 60, 70, 80, 90, 100) molten salts at 420 °C for 4 h. With the increase of NaNO3 concentration in the molten salts from 60 to 100 wt%, the depth of stress layer increase from 98 to 104 μm, and the surface compressive stress increase to the maximum ∼500 MPa at x = 80 and then decrease. In addition, there is also a K+-rich layer observed with the depth of ∼25 μm. The ion-exchange takes place in both crystalline and residual glassy phases, and thus leads to the microstructural modifications, including the amorphization of eucryptite and the presence of lithium phosphate. Upon ion-exchange, the Vickers hardness of glass-ceramics increase from 7.03 GPa to the maximum ∼7.62 GPa (x = 80), and the bending strength from 198 MPa to the maximum ∼510 MPa (x = 90). The improvement in mechanical properties is mainly related to the generation of surface compressive stress layer. Meanwhile, the amorphization and transformation of crystalline phase during the ion-exchange process are probably conductive for the reduction of surface cracks and defects, leading to the enhancement of mechanical properties, especially for the bending strength.

Tuning the Coefficient of Thermal Expansion of Transparent Lithium Aluminosilicate Glass-Ceramics by a Two-Stage Heat Treatment

Transparent glass-ceramics with a Li2O–Al2O3–SiO2 (LAS) system have been extensively utilized in optical systems in which thermal stability is of utmost importance. This study is aimed to develop thermal treatment routes that can effectively control the structure of transparent LAS glass-ceramics and tune its thermal expansion coefficient within a wide range for novel applications in photonics and integrated optics. The optimal conditions for the nucleation and crystallization of LAS glass were determined by means of differential scanning calorimetry and a polythermal analysis. XRD, Raman spectroscopy, and TEM microscopy were employed to examine the structural changes which occurred after heat treatments. It was found that the second stage of heat treatment promotes the formation of β-eucryptite-like solid solution nanocrystals, which enables effective control of the coefficient of thermal expansion of glass-ceramics in a wide temperature range of −120 to 500 °C. This work provides novel insights into structural rearrangement scenarios occurring in LAS glass, which are crucial for accurately predicting its crystallization behavior and ultimately achieving transparent glass-ceramics with desirable properties.

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.

The study of near-net shape lithium aluminosilicate glass-ceramics by direct ink writing

3D printing, a competitive manufacturing technology, has opened up new possibilities for fabricating complex structure ceramic components, but near-net forming is still difficult. This work presented a kind of near-net forming lithium aluminosilicate (LAS) glass-ceramics using direct ink writing (DIW) method by controlling thermal shrinkage. To achieve this goal, a high solid-loading ink was prepared using low thermal expansion LAS glass-ceramic powder containing β-spodumene as raw material. And we comprehensively evaluated the effects of the rheological properties of the slurry and sintering process on the thermal and mechanical performances. Attributed to the restricted sintering activity and thermal deformation of LAS glass-ceramic particles, the 3D-printed samples sintered at 1300 ◦C for 2 h showed an average linear shrinkage of 0.84% with a flexural strength of 45.59 ± 2.82 MPa and a compressive strength of 65.58 ± 3.99 MPa, respectively. The results suggested that LAS glass-ceramics were excellent candidate materials for near-net forming 3D printing.

Optical and Mechanical Properties of Lithium Aluminosilicate Glass-ceramics

Lithium aluminosilicate glass-ceramics has many uses in high-tech applications. Beta quartz or spodumene solid solution phase in the Li2O-Al2O3-SiO2-P2O5 glass system has been precipitated by controlled heat-treatment of the parent glass. These glasses prepared by melt-quench technique. High transparency (&gt;80%) in the visible wavelength range has been observed in the material by UV-VIS-NIR spectrometry. FTIR spectra indicated the presence of Si-O as well as Al-O bonds in the glass-ceramics. The LAS glass ceramics showed moderate flexural strength (~80 MPa) and young’s modulus (~50 GPa). Microstructural characterization of the heat-treated glass ceramics by FESEM and TEM showed nano-crystalline spherical particles of 30-40 nm, which provided a rationale for its high transparency and good mechanical properties that may open up possibilities for newer applications.

Mechanochemical removal of lithium aluminosilicate glass-ceramics

In this study, the material removal behaviors of diamond and SiO2 tips on lithium aluminosilicate (LAS) glass-ceramics surface were investigated in vacuum and deionized water using atomic force microscope. Two types of mechanochemical removal, stress corrosion and tribochemical removal were identified depending on counter-surface chemical activity. Their mechanisms were revealed using Fourier transform infrared spectroscopy (FTIR) and Density functional theory (DFT) calculations. In addition, combined with Raman spectra detection and thermal annealing experiments of removal areas, it was confirmed that compared with stress corrosion removal which reduced the removal energy threshold, tribochemcial removal was dominated by mechanochemical interaction without structural damage. The findings enrich the mechanochemical removal theory and furnish theoretical guidance for nano-precision machining of LAS glass-ceramic surface.

Light-Transmitting Lithium Aluminosilicate Glass-Ceramics with Excellent Mechanical Properties Based on Cluster Model Design.

In this study, for the first time, a cluster-plus-glue-atom model was used to optimize the composition of lithium aluminosilicate glass-ceramics. Basic glass in glass-ceramics was considered to be a 16-unit combination of three-valence {M2O3} and one-valence {Li2O} units. By adjusting the ratio of {M2O3} and {Li2O}, the composition of basic glass could be optimized. After optimization, the average cation valence of the base glass was increased to 2.875. After heat treatment of the optimized base glass, it is found that the crystal size, proportion, and crystallinity changed obviously compared with that before optimization. The main crystalline phases of all the lithium aluminosilicate glass-ceramics prepared in this work were Li2Si2O5 and LiAlSi4O10. All optimized glass-ceramics had an obvious improvement in the crystallinity, with one of the largest having a crystallinity of over 90%. Furthermore, its bending strength was 159 MPa, the microhardness was 967 Hv, and the visible light transmission rate exceeded 90%. Compared with the widely used touch panel cover glass, the optical properties were close, and the mechanical properties were greatly improved. Due to its excellent performance, it could be used in microelectronics, aerospace, deep-sea exploration, and other fields.

Chemical strengthening of lithium aluminosilicate glass-ceramic with different crystallinity

The chemically strengthened lithium aluminosilicate glass-ceramic with petalite phase has excellent performance and can be used in electronic mobile devices such as electronic display substrates, cover plates and light guide plates. The role of petalite crystals in Li+-Na+ ion exchange is elucidated. The effect of different crystallinity on Li+-Na+ ion exchange in lithium aluminosilicate glass-ceramics was investigated by differential scanning calorimeter (DSC), X-Ray Diffraction (XRD), field emission scanning electron microscope (FESEM), Raman spectroscopy, electron probe micro-analysis (EPMA) and other performance test. The results show that when the glass-ceramic crystals are exchanged with Li+-Na+ ions for more than 10 h, part of the crystals in the exchange layer will decrystallize. The surface stress, Vickers hardness and flexural strength of lithium aluminosilicate glass-ceramic with a crystallinity of 73.6%±3% after Li+-Na+ ion exchange at 450 °C for 6 h reach 418±3 MPa, 7.45±0.1 GPa and 450±3 MPa, respectively.

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%.

The structure and properties of chemical strengthened transparent lithium disilicate glass ceramics with various P2O5 contents

Transparent lithium aluminosilicate glass-ceramics with P2O5 and ZrO2 as nucleating agents were prepared, and the effects of P2O5 contents on the glass network structure, crystallization behavior, and properties were investigated. A small amount of P2O5 addition can improve the Q3 tetrahedral proportion in the glass network. When the amount of P2O5 is 0.8 mol%, the Q3 content increase to 65.6%, facilitating the conversion of Li2SiO3 to Li2Si2O5. The transmittance of glass-ceramics with the main crystalline phases of LiAlSi4O10 and Li2Si2O5 was ∼85% in the visible wavelength range. The transparent glass-ceramics were chemically strengthened by ion-exchanged with NaNO3 and KNO3 mixed molten salt. Their Vicker's hardness and fracture toughness reached 8.87 GPa and 2.87 MPa · M1 / 2, respectively.

Lithium aluminosilicate glass-ceramics for low-temperature anodic sealing of MEMS sensors

The results of a study of the anodic bonding parameters of transparent glass-ceramics based on lithium aluminosilicates which are promising as structural materials of MEMS and MOEMS sensors are presented. A comparison of the optical transmittance of these materials and classical for MEMS industry glasses has been carried out. The glass-ceramics electrical conductivity in a wide temperature range has been measured. The procedure of hermetic sealing of glass-ceramics by the anodic bonding at temperatures of 150 – 250 °C has been worked out. A prototype of glass-ceramic atomic cell has been fabricated.

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.

Green extraction of lithium from waste lithium aluminosilicate glass-ceramics using a water leaching process

An acid-free leaching process for lithium extraction from waste lithium aluminosilicate (LAS) glass-ceramics was investigated. Lithium was extracted by a water leaching process after calcination with CaO or a CaO-CaCl2 mixture. Compared to extraction using only CaO calcination, the addition of CaCl2 to CaO can significantly reduce the Si:Ca mixing ratio as well as the thermal treatment temperature. A drastic decrease in thermal treatment and leaching time was observed during the experiments. Based on thermodynamics calculations and X-ray diffraction analysis, the crystalline phase that determined the lithium extraction mechanism was investigated. In substituting CaO with CaCl2, the lithium leaching rate initially decreased or remained constant due to a decrease in the LiAlO2 phase. However, the lithium leaching rate gradually increased with increasing CaCl2 substitution rate, caused by an increase in the formation of the LiCl phase. In addition to lithium, calcium and chloride were also observed during the water leaching process. The leaching rate was independent of the thermal treatment and leaching time. Considering conventional lithium purification techniques, a green process for lithium extraction, purification, and recovery from waste LAS glass-ceramics is proposed.

Direct laser writing of depressed-cladding waveguides in extremely low expansion lithium aluminosilicate glass-ceramics

We report on direct femtosecond laser writing of depressed-cladding optical waveguides in extremely low expansion lithium aluminosilicate glass-ceramics. The waveguide cladding was formed by space-selective vitrification of nanocrystals in laser-modified regions of glass-ceramics responsible for the negative refractive index change up to 0.005. The optical properties of the laser-written waveguides were evaluated in terms of near-field and far-field intensity distribution and propagation losses at the wavelength of 1064 nm. The possibility of single-mode waveguiding with the upper limit of propagation losses 2.4 or 2.7 dB/cm for vertically or horizontally polarized light, respectively, was demonstrated. The obtained results open up new frontiers in the laser-assisted fabrication of 3D optical waveguide circuits in the media with outstanding thermal stability.

Study of the material removal mechanism of glass-ceramics based on consecutive incremental loading in ductile-regime grinding

Glass-ceramics have many excellent properties and are widely used in various fields. During the grinding process, the workpiece surface is typically subject to material removal by grit of incremental heights, which has rarely been the focus of research. As such, it is necessary to study the material removal mechanism of glass-ceramics under consecutive incremental loading, which more closely reflects the actual grinding process. In this paper, to analyze the plastic deformation and residual stress of lithium aluminosilicate (LAS) glass-ceramics, a finite element model is established based on the Drucker–Prager yield criterion for ductile regimes. A nano-scratch test was also conducted and the test results show that both the residual depth and residual stress increase with an increase in the number of increments, and that consecutive incremental loading promotes the plastic deformation of glass-ceramics and increases the residual stress of the material in the ductile-regime process. These findings provide guidance for achieving higher dimensional accuracy in the actual grinding of glass-ceramics parts.

Clinical Evaluation of Three Types of CAD/CAM Inlay/ Onlay Materials After 1-Year Clinical Follow Up.

To evaluate the clinical performance and the marginal adaptation of inlay/ onlay restorations made of lithium of a new lithium disilicate strengthened, lithium alumino-silicate glass-ceramic (LAS) material compared with a conventional lithium-disilicate glass-ceramic (LDS) and new-generation polymer-based CAD/CAM resin composite (CS) materials over one year. Seventy-five inlay-onlay restorations were placed in 35 patients. The restorations were assigned and randomized to three groups as LDS, LAS, and CS. Clinical evaluations were performed after one week, six months, and one year after the cementation, according to the modified United States Public Health Services (USPHS) criteria. The marginal quality analyses of 21 samples (n=7) were assessed under a scanning electron microscope. The data were analyzed by using Friedman, Wilcoxon Signed Ranks, Chi-square and Paired t-tests (p⟨0.05). No statistically significant difference (p⟩0.05) was found between groups in the modified USPHS, gingival index, and plaque index evaluations, and the total success rate was 100% for three groups after one year. Following SEM evaluations in all groups, continuous margin percentages were decreased, but these results were not statistically significant (p⟩0.05). Lithium disilicate-strengthened lithium aluminosilicate glass-ceramics can be considered a reliable material for an option for posterior onlay/inlay restorations.

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.

Effect of Added Mullite Whisker on Properties of Lithium Aluminosilicate (LAS) Glass-Ceramics Prepared for Dental Restoration.

In this work, lithium aluminosilicate (LAS) glass-ceramics were prepared from lithium disilicate glass powder and mullite whiskers. Lithium disilicate glass powder (28.6Li-68.6Si-2K-0.8La, mol.%) with contents of 5, 10 and 15 wt.% mullite whiskers were hot-pressed at 860 °C for 1 h. The effects of added mullite on phase composition, microstructure, mechanical properties, coefficient of thermal expansion (CTE) and translucency were systematically studied. Also, the mechanism for phase transformation and grain growth was discussed. The LAS glass-ceramic samples exhibited relative densities above 98% with main crystalline phases of lithium disilicate (Li2Si2O5, LD), lithium silicate (Li2SiO3, LM), and β-spodumene (LiAlSi2O6). The β-spodumene whiskers were in-situ synthesized through the reaction between mullite whiskers and glass matrix. As β-spodumene fraction rose, lithium disilicate crystals content decreased and that of lithium silicate increased, resulting in declined bending strength and improved fracture toughness. The composite containing 10 wt.% mullite whisker showed optimal performance with bending strength above 300 MPa and fracture toughness of 2.7 MPa·m1/2. The formation of β-spodumene in the obtained composite declined CTE, with values ranging from 10.5×106 °C-1 for LD glass-ceramic to 6.03×10-6 °C-1 for LAS glass-ceramic doped with 15 wt.% mullite whiskers. Finally, though the real in-line transmission of obtained glass-ceramic composites declined as β-spodumene content rose, the specimens containing less than 10 wt.% mullite whiskers showed favorable translucency, which would suit applications in dental restoration.