Li2O SiO2 Research Articles

High strength YSZ/YSZ joints bonded with a matching thermal expansion coefficient sealing glass

A novel CaO–Al2O3–SiO2–Li2O (CASL) glass was developed for bonding yttria–stabilized zirconia ceramics (YSZ). The CASL glass possessed a coefficient of thermal expansion (CTE) that matched with YSZ and exhibited outstanding wettability on the surface of YSZ substrate. During the bonding process, mutual dissolution and diffusion between YSZ and CASL glass took place, which ensured good interface bonding. Furthermore, the rapid cooling speed led to a completely amorphous seam, which allowed the CTE of the seam to correspond with that of the original glass. The optimal flexural strength of YSZ/YSZ joints could reach more than 90 % of that of the YSZ.

Decoding the role of bismuth oxide in advancing structural, thermal, and nuclear properties of [B2O3–Li2O–SiO2]-Nb2O5 glass systems

This paper investigates the pivotal role of bismuth oxide (Bi₂O₃) in the enhancement of nuclear safety, structural, and thermal properties of glasses, specifically in the BNLS system. BNLS system has the formula [B2O3–Li2O–SiO2]-Nb2O5(20-x)–(Bi2O3)x (where x = 0.0,5.0,10.0,15.0 and 20.0 mol%). Through a comparative study, the potential advantages, and limitations of integrating Bi₂O₃ in place of traditional elements are highlighted, emphasizing its importance in the field of advanced glass materials. FTIR analysis showed the presence of Bi–O vibrations of the tetrahedral [BO4] groups and the Bi–O–Bi linkages. DSC testified the glass formation with increasing thermal stability of the formed glass with the inclusion of Bi2O3 into the glass system. Through the quantification of the Gamma Linear Attenuation Coefficient (GLAC) and Gamma Mass Attenuation Coefficient (GMAC), the work identifies the attenuation behavior against varying photon energies. Notably, a concentration-dependent rise in attenuation characteristics is observed, with BNLS20 exhibiting the most potent radiation shielding. Glass Half-Value Layer (GHVL) parameters and Mass Gamma Photon Penetration (GMFP) were measured, reinforcing that glasses with higher Bi2O3 concentrations and lower GHVL are better attenuators. The transmission factor (ln(I/Io)) was also studied, confirming that BNLS20 possesses the most effective radiation shielding capabilities. This research establishes that adding Bi₂O₃ to the [B2O3–Li2O–SiO2]-Nb2O5 glass system markedly improves its thermal stability and radiation shielding capabilities. BNLS20, in particular, emerges as a standout for radiation protection, surpassing both other BNLS variants and conventional shielding materials, thereby positioning it as an exceptional choice for advanced nuclear safety applications.

Enhancing optical and radiation shielding properties: A dive into Bi2O3-Infused glasses

In the world of contemporary glass research, the subtle interplay between composition and resulting properties is of paramount importance. The structural, optical, and gamma-ray attenuation properties of BiNb(x) glasses having a formula xBi2O3–(20-x)Nb2O5–B2O3–Li2O–SiO2 (where x = 0,5,10,15 and 20 mol%) were investigated. This study delves deep into the transformative role of Bi2O3 when introduced into the glass matrix, a journey from opacity to enlightening transparency. The density of the BiNb glass system was found to increase from 4.579 g/cm3 for pristine to 5.439 gm/cm3 for BiNb20. XRD analysis testifies the transfer of a pristine sample from a crystalline to a fully amorphous, with Bi2O3 as the catalyst. UV–visible spectra were investigated, and optical parameters were extracted. The optical bandgap (Eg) was decreased from 4eV for BiNb0 to 3.83eV for BiNb20. In addition, Eg value was used to evaluate the refractive index of the prepared BiNb glasses using various theoretical models. The refractive index of the Moss model increases from 2.208 for BiNb0 to 2.229 for BiNb20, besides the Moss, Herve-Vandamme, and Kumar-Singh models are compatible. The studied glass samples show a metallization criterion within the range of 0.434–0.447, indicating the potential for new optical materials with good nonlinearity. Moreover, gamma rays with energy ranging from 0.015 MeV to 15 MeV are used to highlight the shielding capabilities of the glasses. As the Bi2O3 fraction increases and the Nb2O5 decreases, the shielding capability of the prepared BiNb glass system increases.

Preparation of some selective glass–ceramics from nano-silica within the Li2O–SiO2 system with ZrO2 for future dental applications

Many recent studies have indicated that some modified silicate glass–ceramics are considered and recommended to be part of the process of dental applications. Examples from the recommended glass–ceramics include modified lithium silicate with various dopants (ZrO2, CeO2), mica-based glass–ceramics, and leucite-based glass–ceramics. The present study employs a new direction of research in the preparation of modified lithium silicate glasses containing varying dopant percents of ZrO2 to produce the parent glasses using nano-silica as an essential chemical component in comparison with silica. The ZrO2-doped glass–ceramic reveals the crystalline phase of lithium aluminosilicate (Li5AlSi2O8) due to the effect of ZrO2. The modified lithium silicate glasses doped with ZrO2 prepared from nano silica indicate their high mechanical properties and can be primarily recommended for dental applications.

Electrical properties of Lithium silicate-based glasses and their Glass-ceramics

Crystallization of lithium di- and meta-silicates were developed in the SiO2–Li2O–TiO2 glass system. Inclusion of TiO2 relatively reduced the crystallization temperature. Through the sintering process at 650 °C/2 h, lithium disilicate was devolved in the TiO2-free sample, whereas the incorporation of TiO2 catalyzed the appearance of lithium metasilicate phases. The microstructure of lithium disilicate glass-ceramics was studied using differential thermal analysis (DTA), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). At 650 °C/2 h, the microstructure consists of spherulitic growths with reasonably sorted nanosize particles in a glassy groundmass. The electrical characteristics of lithium silicate glasses and glass-ceramics having variable concentrations of TiO2 were tested in order to explore their electronic hopping process. To clarify the effects of composition and sintering on the electrical and dielectric behavior of glasses based on lithium silicate, a Broadband Dielectric Spectroscopy (BDS) was employed. While the matching-sintered glass-ceramic exhibits like an insulator with interfacial polarization that significantly lowers the density number of free ions, bulk glass nevertheless demonstrate high conductivity. Lithium oxide considerably increases the conductivity of the composite instead of titanium oxide.

In vitro biodegradation, blood, and cytocompatibility studies of a bioactive lithium silicate glass-ceramic

This study investigates a novel non-stoichiometric lithia-silica glass-ceramic (Bioactive LD) designed for bone tissue engineering applications. Incorporating SiO2–Li2O–CaO–P2O5–K2O–SrO–ZnO, the glass-ceramic underwent optimized thermal treatments resulting in a composition predominantly of lithium disilicate (Li2Si2O5 - 87 %) with a minor lithium phosphate phase (Li3PO4 - 13 %). Structural analysis using X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed a refined microstructure with Li2Si2O5 crystals in rod form with a high aspect ratio of around 4:1. Expanding on previous work, this study investigates the in vitro osteoblastic response of Bioactive LD compared to a commercial glass-ceramic (E-Max CAD®). The evaluation, employing live/dead assays, resazurin assays, and alkaline phosphatase activity measurements at different time points, demonstrated comparable cell viability and proliferation on both glass-ceramics. The chemical stability of the samples was tested, and the Bioactive LD showed a higher amount of leached ions in the solution, without significant mass loss, consistent with the standardized values for a class 4 material (ISO 6872), with no significant change in its microstructure. The chemical solubility tests were investigated employing SEM and energy dispersive X-ray analysis (EDS), giving insights into the role of leached ions in the microstructure and bioactivity of the materials. Notably, Bioactive LD exhibits higher alkaline phosphatase activity, indicating enhanced stimulation of osteoblastic cells. Additionally, the Bioactive LD promotes mineralization matrix production, as evidenced by alizarin red S staining. The study also employs SEM-EDS to evaluate the formation of apatite mineralized matrix. Bioactive LD exhibits a homogeneous mineralized matrix with increased Calcium and Sulfur signals, suggesting early hydroxyapatite formation after Alizarin Red S assay. In contrast, Commercial LD shows limited reactivity and bioactivity, with no substantial calcium deposition. An indirect cytotoxicity test indicates minimal cytotoxicity for Bioactive LD, while Commercial LD exhibits slight cytotoxicity, consistent with findings from the literature. The results highlight Bioactive LD's potential for bone regeneration, emphasizing its enhanced bioactivity and the formation of a complex mineralized matrix that could contribute to improved bone integration properties.

A new perspective for nucleation and nanocrystallization from interfacial energy and nanoscale composition fluctuations in glasses

AbstractNucleation behaviors in glasses/supercooled liquids (SCLs) such as lithium disilicate Li2O–2SiO2, cordierite Mg2Al4Si5O18, fresnoite Ba2TiSi2O8, and K2O–Nb2O5–GeO2/TeO2 glasses were analyzed and discussed from the interfacial energy γ at SCL–nucleus interfaces and nanoscale composition fluctuations. Based on the fragility concept for SCLs and the intrinsic origin of γ, the magnitude order of γ(fragile SCL) < γ(strong SCL) was proposed to be a crucial guide for an understanding of high homogeneous nucleation rates and prominent nanocrystallization. The role of nucleating agent TiO2/ZrO2 in accelerating the nucleation rate in cordierite‐based and β‐spodumene‐type Li2O–Al2O3–SiO2‐based glasses was discussed from the new perspective of γ(homoepitaxial‐like nucleation) < γ(heteroepitaxial‐like nucleation). Ferroelectric nanocrystals such as SrxBa1–xNb2O6 in borate glasses and fluoride nanocrystals such as CaF2 are also well understood from the proposed guidelines. The present article provides a new perspective for nucleation in glasses/SCLs, contributing to the comprehensive composition design of new innovative glass‐ceramics.

Influence of fluorine content on crystallization and mechanical properties of SiO2–Li2O glass-ceramics

The effect of fluorine content on the crystallization, microstructure and mechanical properties of SiO2–Li2O glass-ceramics was investigated. Four parent glass samples with different fluorine content were prepared by melt quenching method. The glass-ceramic samples are obtained by heat treatment including nucleation and crystallization process. It was found that lithium disilicate (Li2Si2O5) is the main phase crystallizing in the course of heat treatment, while lithium metasilicate (Li2SiO3), petalite (LiAlSi4O10), and fluorapatite (Ca5(PO4)3F) appear in some of the samples as minor phases. The addition of fluorine increases the crystallinity and promotes the formation of Li2Si2O5 and Ca5(PO4)3F crystals, and thereby regulates the microstructure and mechanical properties. A proper amount of fluorine significantly enhanced mechanical properties. The SiO2–Li2O glass-ceramic sample with 0.5 mol% fluorine content has the highest Vickers hardness HV value of 6.64 GPa and highest fracture toughness KIC value of 0.932 MPa m1/2 after crystallization process at 670 °C for 8 h. The SiO2–Li2O glass-ceramic sample with 1.0 mol% fluorine content has the highest Young’s moduli E value of 102.1 GPa after crystallization process at 670 °C for 8 h.

Manufacturing and characterization of a 3D printed lithium disilicate ceramic via robocasting: A pilot study

ObjectiveThe objective of this study was to manufacture and to evaluate the physico-mechanical properties of the Lithium disilicate (Li2O5Si2) ceramic structures fabricated using additive manufacturing (3D printing). MethodsLi2O5Si2 samples were divided into (n = 30/group): SM (subtractively manufactured) and AR (additive/robocasting). For the AR group, Li2O5Si2 powder was combined with ammonium polyacrylate, hydroxypropyl methylcellulose, and polyelectrolyte to create a colloidal gel, which was then used for printing. A digital CAD model of a disc was designed, and the G-code transferred to a custom built DIW 3D printer. The control group samples were prepared using pre-crystallized ceramic blocks, which were cut to obtain discs with same dimensions as the AR group. Disc-shaped specimens from both groups were crystallized at 840 °C. Mechanical properties were evaluated using biaxial flexural strength test (BFS) and Vickers hardness test. Representative fractographic images of the specimens were acquired using scanning electron microscopy (SEM) to analyze the fracture origin and crack propagation. Energy-dispersive X-ray spectroscopy (EDS) and attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) were used for chemical analysis, and X-ray diffractometry (XRD) was performed to analyze the crystalline phases. ResultsAR group yielded lower values of BFS (120.02 MPa ±33.91) and hardness (4.07 GPa ±0.30), relative to the SM group, (325.09 MPa ±63.98) and (5.63 GPa ±0.14), respectively. For EDS analysis, AR and SM groups showed similar elemental composition. In FTIR-ATR analysis, higher peaks referring to the crystalline structure were found for SM group. XRD analysis indicated a decreased formation of Li2O5Si2 from Lithium metasilicate (Li2O–SiO2) in the AM group. SEM micrographs showed a more porous microstructure associated with the 3D printed samples. SignificanceThe viability of fabricating Li2O5Si2 ceramic constructs using the Robocasting technique was successful. However, the samples prepared using subtractive manufacturing presented higher mechanical properties compared to the 3D printed constructs. The difference in properties between the manufacturing may be correlated to the decreased formation of Li2O5Si2 crystals and higher degrees of porosity.

Search for Lithium Ion Conducting Oxides Using the Predicted Ionic Conductivity by Machine Learning

A machine learning method was developed, which predicts ionic conductivity based on chemical composition alone, aiming to develop an efficient method to search for lithium conductive oxides. Under the obtained guideline, the material search was focused on the Li2O–SiO2–MoO3 pseudo-ternary phase diagram, which is predicted to have high ionic conductivity (>10−4 S·cm−1). We investigated the formation range, ionic conductivity, and crystal structure of the lithium superionic conductor (LISICON) solid solution on the Li4SiO4–Li2MoO4 tie line. The ionic conductivity of the LISICON phases is about 10−7 S·cm−1, which is higher than that of the end members; however, two orders of magnitude lower than that of the analogous LISICON materials. In addition, the experimental values were two or three orders of magnitude lower than the predicted conductivity values by machine learning. However, the developed prediction model can be used as an initial guideline for material exploration since the predicted values follow the trend of practical conductivity in the phase diagram. The crystal structure analysis indicated that the distance between the lithium sites and the occupancy of each lithium site in the crystal structure contributed to the decrease in ionic conductivity. This strong correlation between crystal structure and ionic conductivity was one of the reasons for the discrepancy between the predicted ionic conductivity based on chemical composition alone and the experimental value.

Radiation shielding capacity of Li2O-SiO2/GeO2 glasses doped with rare earth oxides: Nuclear security applications

In the present work, the ionizing radiation (namely, gamma-rays, charged particles, and neutrons) attenuation parameters of Li2O–SiO2 (denoted as LS) and Li2O–SiO2–GeO2 glasses doped with Y2O3 and In2O3 (LGY and LGI) glasses were estimated and analyzed with the aim of exploring their shielding potentials. The gamma-ray transmission attenuation coefficient was simulated by the FLUKA code and also estimated by XCOM. Also, the stopping powers and ranges of electrons, protons, α-particles, and carbon ions were estimated for particle kinetic energies within 15–15000 keV. The fast and thermal (25 meV) neutron cross-sections were estimated for the three glasses. At 15 MeV, the mass attenuation coefficient is 0.019, 0.021 and 0.022 cm2/g while the linear attenuation coefficient magnitude varied within the range of 0.047–11.564 cm−1, 0.061–32.008 cm−1 and 0.068–38.122 cm−1 for LS, LGY, and LGI, respectively. The effective atomic number varied from 8.21 to 12.00 for LS, 8.71–22.71 for LGY, and 8.78–26.37 for LGI. Likewise, the charged particle shielding ability of the glasses was in the order: LS < LGY < LGI. This trend was conserved for the neutrons’ cross-sections. Compared to conventional and recently researched shields, LS, LGY, and LGI present viable alternative glass shields in nuclear radiation applications.

Synthesis of high purity Li8SiO6 using a citric acid-assisted route

Lithium oxosilicate has the highest proportion of lithium among lithium silicates, which is desirable for applications. Although Li8SiO6 is a stable phase, its obtention as a polycrystalline pure phase is not reported yet, probably because of the high sensitivity of the system Li2O–SiO2 to the synthesis conditions. In this work, we adapted a citrate-based route used for the synthesis of Li4SiO4 as a novel approach to the obtention of Li8SiO6. We found that the lowest amount of impurities is achieved by using a Li:C6H8O7 molar ratio of 2.8:1, a pH value of 8.5, and a lithium excess of 20%. In a complementary way, we used the solid-state reaction method as a function of the excess of lithium and optimized the conditions that lead to a minimum amount of impurities. We found that the purest Li8SiO6 phase is obtained with low or no lithium excess. Samples obtained by both methods exhibited a higher purity compared to the reports available in literature. The crystal structure for this phase is confirmed by selected area electron diffraction.

252Cf -induced luminescence of cerium-doped lithium silicate glasses

In addition to the total attenuation of ionizing radiation, photoluminescence has been conventionally recognized to affect radiation-induced luminescence. In this study, we examined the optical and luminescence properties of Ce3+ in lithium silicate-based glasses with different optical basicities. The existence of Ce4+ was confirmed based on the optical absorption, Ce L3-edge X-ray absorption near edge structure (XANES), and optical coefficients of the calculated Ce4+ using the optical absorption and XANES data of Ce4+ species from a previous report. Compared to other multicomponent glasses, there was a slight deviation in the decay constant and quantum yield (QY) of the stoichiometric Li2O–2SiO2 glass. In addition, the light yields calculated from the pulse height spectra with 252Cf irradiation depend on the QY of the glasses. Considering the energy conversion process, the dependence of the light yield agreed with that of the conventional energy conversion process of neutron-induced luminescence.

Investigation of indentation size effect and R-curve behaviour of Li2O–SiO2 and Li2O–2SiO2 glass ceramics

Indentation size effect (ISE) and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics are investigated using micro-indentation and indentation-strength (IS) techniques, respectively. Vickers micro-indentations were applied on both materials at the load of 0.10-19.6N to determine the load influence on the measured hardness. For the IS-measured fracture toughness, the load ranged from 1.96 to 19.6N. The hardness decreased with increasing load by 20% and 18% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, indicating the ISE behaviour on both materials. The fracture toughness increased with the load by 27% and 59% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, signifying the R-curve behaviour. The ISE behaviour of both materials was analysed using the Meyer's, Hays-Kendall (HK), proportional specimen resistance (PSR), Nix-Gao (NG), modified PSR (MPSR) and elastic plastic deformation (EPD) models while the R-curve behaviour was analysed by the fractional power law. The Meyer's index of both materials was less than 2, strongly confirming the ISE existence. The HK, PSR and NG models were only suitable to determine intrinsic Vickers hardness for Li2O-2SiO2 glass ceramic while the MPSR and EPD models were successful for both materials. The fractional power law gave higher R-curve steepness for Li2O-2SiO2 than Li2O-SiO2 glass ceramics. Also, material and brittleness indices predicted, respectively, higher quasi-plasticity and better machinability for Li2O-2SiO2 than Li2O-SiO2 glass ceramics indicating superior performance in the former to the latter. Finally, this study presents a new significant insight into the micro-mechanisms of fracture tolerance behaviour of these glass ceramics which is critical to their functional performance as structural ceramics.

Thermodynamic modelling of M2O-SiO2 (М – Li, Na, K) melts as applying to mixed alkali systems

A Gibbs energy minimisation approach is used to study silicate melts of Li2O–SiO2, Na2O–SiO2, K2O–SiO2 and Li2O–K2O–SiO2 systems. The list of possible components includes 0.5M2Si2O5, M2SiO3, 0.5M6Si2O7 and M4SiO4, where М = Li, Na, K. The thermodynamic functions are assumed to be equal to those of silicon-oxygen tetrahedra Q3–Q0. The structural unit Q4 corresponds to the thermodynamic functions of pure SiO2. Li2O–K2O–SiO2 melts containing 33 and 40 mol.% of alkali oxide are studied according to a mixed alkali system model. The correspondence of the developed models with actual systems was determined by comparing the results of thermodynamic modelling with experimental Raman spectroscopy melt data along with the limits of their applicability.

Study of crystallization, microstructure and mechanical properties of lithium disilicate glass-ceramics as a function of the sintering temperature

Objective: The purpose of the present study was to synthesize and characterize lithium disilicate glass-ceramics through the Li2 O-SiO2 system for determining the most satisfactory sintering parameter by evaluating the crystalline composition, microstructure and mechanical properties. Material and methods: The glass-ceramics were prepared from a glass precursor by means of the melting/cooling technique with a composition of 33.33 Li2 O and 66.67 SiO2 (mol.%). The specimens were compressed by the uniaxial pressing technique and three different thermal treatments were used for sintering: 850 °C (Group 1), 900 °C (Group 2), and 950 °C (Group 3), which were determined based on the differential scanning calorimetry (DSC) result. The glass-ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes method, microhardness and biaxial flexural strength analyses. Results: The results regarding XRD predominantly showed lithium disilicate phase for all the heat treatments performed. Moreover, grains with a needle form were more predominantly observed in the SEM images for Group 3, as well as a higher densification and consequently higher mechanical properties. In contrast, Group 1 presented the lowest mechanical properties and densification, as well as the highest porosity. Conclusion: The present study demonstrated how extremely important it is to follow the heat treatment recommended by the manufacturers of ceramics, including time and temperature, which possess direct effects in the crystalline phase formation, as well as in the material’s microstructure and mechanical properties. Keywords Crystallization; Glass-ceramics; Lithium disilicate.

Insight into Electrical and Dielectric Relaxation of Doped Tellurite Lithium-Silicate Glasses with Regard to Ionic Charge Carrier Number Density Estimation.

We investigate the role of tellurite on a lithium-silicate glass 0.1 TeO2 − 0.9 (Li2O-2SiO2) (LSTO) system proposed for the use in solid electrolyte for lithium ion batteries. The measurements of electrical impedance are performed in the frequency 100 Hz–30 MHz and temperature from 50 to 150 °C. The electrical conductivity of LSTO glass increases compared with that of Li2O-2SiO2 (LSO) glass due to an increase in the number of Li+ ions. The ionic hopping and relaxation processes in disordered solids are generally explained using Cole–Cole, power law and modulus representations. The power law conductivity analysis, which is driven by the modified Rayleigh equation, presents the estimation of the number of ionic charge carriers explicitly. The estimation counts for direct contribution of about a 14% increase in direct current conductivity in the case of TeO2 doping. The relaxation process by modulus analysis confirms that the cations are trapped strongly in the potential wells. Both the direct current and alternating current activation energies (0.62–0.67 eV) for conduction in the LSO glass are the same as those in the LSTO glass.

Effects of microstructures on the mechanical properties of lithium disilicate glass-ceramics for the SiO2–Li2O–P2O5–K2O–ZnO system

The effects of microstructures on the mechanical properties of lithium disilicate (Li 2 Si 2 O 5 :LS2) glass-ceramics (GCs) were carefully investigated for the SiO 2 –Li 2 O–P 2 O 5 –K 2 O–ZnO system. The microstructures of GC samples, having three different compositions but the same total 6 mol% of additives (P 2 O 5 , ZnO, K 2 O), could be controlled by varying heat treatment conditions of glass samples. In addition to major LS2 crystalline phase, two other minor crystalline phases of Li 3 PO 4 (LP) and cristobalite were detectable. Average crystal sizes of GC samples were in the region of 0.3–10 μm, and the volume fractions of crystalline phases were in the region of 0.70–0.73. The biaxial flexural strength was improved with decreasing the average crystal size from ~10 to ~1 μm by following the Hall-Petch relation, and the maximum flexural strength of 445.8 ± 7.2 MPa was obtainable from the GC samples with the additive compositions of 1.5 mol% P 2 O 5 , 2.75 mol% K 2 O and 2 mol% of ZnO which were nucleated at 540 °C for 1 h and grown at 850 °C for 4 h. When 8.4 vol% cristobalite was incorporated into the sample, however, there was a severe scattering in flexural strength data due to the formation of microcracks induced by the beta-to-alpha transition of cristobalite and also due to a micro tensile stress in the residual glassy phase induced by a large difference in thermal expansion coefficients between crystal and residual glassy phases. Meanwhile, the Vickers hardness was increased with decreasing the average crystal size down to ~0.3 μm, indicating that the factors for the deterioration of flexural strength have a negligible effect on hardness.

Highly translucent nanostructured glass-ceramic

Transparent and translucent glass-ceramics (GCs) are found in an increasing number of domestic and high-technology applications. In this paper, we evaluated and optimized the effects of two-stage heat treatments on the resulting crystalline phases and microstructure of a glass of the SiO2–Li2O–P2O5–TiO2–CaO–ZnO–Al2O3 system. The objective was to develop a transparent nanostructured glass-ceramic (GC). After numerous heat treatment trials, we found that a long nucleation period of 72 h at 455 °C followed by a crystal growth treatment at 660 °C for 2 h resulted in a highly translucent GC having homogenously distributed nanocrystals. The relatively high amount of P2O5 (2.5 mol%) induced the formation of lithium disilicate as the main crystal phase. We thus developed a GC having crystals under 50 nm, with a high crystallized fraction (52%vol. Li2Si2O5 and 26% vol Li2SiO3), transmittance of approximately 80% in the visible spectrum for 1.2 mm thick specimens, nano hardness of 8.7 ± 0.1 GPa (load of 400 mN), a high elastic modulus of 138 ± 3 GPa as measured by nanoindentation, and good flexural strength (350 ± 40 MPa) as measured by ball-on-3 balls tests. Due to its high content of Li+, this GC has the potential to be chemically strengthened and can be further developed to be used in a number of applications, such as on displays of electronic devices.

Crystallization-triggered bubbles in glass-ceramics

Bubbles appear sometimes in glass-ceramics and degrade most properties, especially light transmission and fracture strength. In this work, we deduced microstructural conditions that trigger bubble genesis during crystallization of bubble-free glasses. We related bubble formation to some microstructural parameters in two model glass compositions that exhibit internal crystallization: 1.07Na2O.2CaO.3SiO2 (1.07N2C3S) and Li2O.2SiO2 (L2S). In this way, we constructed bubble maps – experimental diagrams showing a region of bubble nucleation and growth in a crystal size versus crystallinity plot. Both glass-ceramics show bubbles having similar geometry that emerge from crystal/liquid interfaces and propagate into the residual liquid. These diagrams show that holes of the order of the crystal size tend to form in glass-ceramics containing a high-volume fraction crystallized (>50%) and relatively large crystal size (>10 μm). Mass spectroscopy experiments revealed that bubble formation in the 1.07N2C3S system is caused by O2. We believe the knowledge generated by this work and resulting maps provide a very useful tool for the design of bubble-free glass-ceramics.