Lithium Aluminosilicate Research Articles

Co-enhancement of oxidation resistance and mechanical properties of Cf/LAS composites: The effects of h-BN addition

Carbon fiber reinforced lithium aluminosilicate glass-ceramic composites have been extensively studied and widely used in industry applications, because of its good mechanical properties and low thermal expansion coefficient. However, further investigation is also need to improve its oxidation resistance and mechanical performance to meet higher requirements. In this work, Cf/LAS glass-ceramic composites were fabricated by a slurry impregnation and hot-pressing method with different amounts of h-BN. Results indicate that composites with 2 wt.% h-BN addition exhibit excellent flexural strength and fracture toughness, reaching 910 ± 22 MPa and 21 ± 1 MPa·m1/2, respectively, and that after oxidation at 600, 800 and 1000 °C for 1 h, their strength residual ratio can reach 47%, 35% and 32%, respectively. TEM analyses suggest the improvement of oxidation resistance and mechanical properties should be attributed to the unique interface of composites caused by h-BN addition.

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.

Sustainable geopolymer using lithium concentrate residues

Australia is a key player in the global supply of lithium products given its large resources of spodumene. This mineral occurs in pegmatite rocks and can be processed to extract lithium salts used to make valuable products such as lithium ion batteries, ceramics, lubricants along with specific by-products such as lithium aluminosilicate residue (LASR). This paper investigates, for the first time, the use of LASR as a geopolymer precursor. A total of ten mixes have been synthesised, comparing the performance of LASR, fly ash, ground granulated blust-furnace slag (GGBS), kaolin and metakaolin. Ranges of mechanical and chemical tests have been carried out to examine the hardening of the mixes. Our experimental results reveal that LASR has a good thermal stability up to 1000 °C. While it has a low reactivity in alkaline solutions, its presence significantly improves the efficiency of other binder materials. LASR particles bridge the gaps between the larger sand grains, resulting in reduced micro-cracking. Based on the hardening trends, pH measurements and XRD analysis, we noticed that LASR could effectively retard the setting of geopolymer mixtures. A high 28-day compressive strength of 84.8 MPa has been obtained in the mix with 50% LASR and 50% GGBS; this mix produces three times higher strength than conventional concrete. With the delayed reactions and lower extent of micro-cracks, our hardening tests suggest that the strength can continue to develop past 28 days.

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.

Boron-speciation and aluminosilicate crystallization in alkali boroaluminosilicate glasses along the NaAl1-xBxSiO4 and LiAl1-xBxSiO4 joins

The influences of boron on silicate glass dissolution behavior and crystallization have long been important in the nuclear waste glass and technical glass communities. Boron is a challenging component to model due to this ability to assume three- and four-fold coordinations with oxygen, as well as its ability to form complex structural units with silicate tetrahedra. Furthermore, the low atomic mass limits the available characterization techniques. In the present work, recent literature findings on the compositional influence on boron speciation are implemented to interpret new data on alkali boroaluminosilicate glasses studied with 11B nuclear magnetic resonance (NMR), synchrotron X-ray scattering (s-XRS), and chemical durability measurements. The purpose of this study is to understand the influence of boron on the crystallization behavior of sodium and lithium aluminosilicate systems, NaAl1-xBxSiO4 and LiAl1-xBxSiO4, as applied to problems in nuclear waste vitrification. Comparisons are drawn between the alkali coordination number and crystallization behavior as a function of boron addition, as obtained through modeling of synchrotron X-ray total scattering using Empirical Potential Structural Refinement.

Microstructures and mechanical properties of Cf/LAS composite and Ti60 alloy joints brazed with TiZrNiCu + Cf mixed powders

AbstractIn this paper, carbon fiber reinforced lithium aluminosilicate (LAS) glass‐ceramics matrix composites (Cf/LAS composites) are joined to Ti60 alloy using TiZrNiCu + Cf mixed powders by proper process parameters. The carbon fibers distribute uniformly in the brazing interlayer and react with Ti, Zr elements in the brazing alloy to form (Ti, Zr)C thin reactive layers, which are between the carbon fibers and the Ti, Zr elements. The effect of Cf content on the mechanical properties and microstructure of brazed joints are investigated. The microstructure of brazed joints varied obviously with the increasing of Cf content. The thickness of reactive layer between interlayer and Cf/LAS composites and Ti solid solution (Ti (s.s)) decrease gradually, and the volume of eutectic structure (Ti(s,s) + (Ti,Zr)2(Ni,Cu)) decrease gradually. The obtained brazed joints exhibit a maximum shear strength of 73.5 MPa at room temperature using TiZrNiCu + 0.3 wt% Cf mixed powders. The enhanced shear strength can be attributed to the reduction in thermal stress and the reinforcing effect originated from the carbon fiber addition.

Preliminary Study on the Development of New Composition Lithium Aluminosilicate Glass Ceramic

Abstract Lithium aluminosilicates (LAS) glass ceramic is well known for its excellent coefficient of thermal expansion. LAS has commonly been used in an application that requires the ability of controlling thermal expansion at high temperature such as in cookware application. Previous research often studied on the behaviour of coefficient thermal expansion of LAS glass ceramic however research on improving thermal shock resistance on cooktop panel is rarely discussed. Hence, this study purposely to develop a new composition of LAS glass ceramic with improved thermal shock resistance which was motivated by the renowned cookware brand, CERAN®. Moreover, for better understanding on the process of fabricating LAS glass ceramic, powder route involving melt-quench and sintering process was carried out. The amorphous phase was identified before sintering and transformed into crystalline phase after LAS was sintered at 900 °C where this temperature was selected based on crystallization temperature (Tc) obtained from differential thermal analysis (DTA). Major crystalline phase of β-spodumene (LiAlSi2O6) was observed and functional group of silica-oxygen-silica bonding was appeared in fourier-transform infrared spectroscopy (FTIR) analysis. This result has also supported by X-ray fluorescence (XRF) analysis where most of the LAS glass ceramic composition was dominated by SiO2. Therefore, LAS glass ceramic with higher thermal shock resistance would be fabricated through this method for cooktop panel application.

Quantitative determination of the phosphorus environment in lithium aluminosilicate glasses using solid-state NMR techniques.

We investigated using solid-state NMR spectroscopy the short-range structural features in lithium aluminosilicate glasses with the addition of P2O5 and considering various Al2O3/Li2O ratios. The phosphorus environment is determined quantitatively using 31P Magic Angle Spinning NMR constrained by results obtained from 31P-27Al Multiple-Quantum Coherence-based NMR techniques. Phosphorus is mainly located as orthophosphate and pyrophosphate species in glasses with a low amount of Al2O3. These depolymerized units disappear with increasing Al2O3 content and a strong affinity of PO4 tetrahedra for aluminum is revealed, which reduces phase separation. The local environments of framework (Si and Al) and charge-balancing (Li) cations are also studied through NMR experiments to assess the influence of P2O5 addition. The Si environment is mostly modified by the presence of P2O5 in glasses containing a low amount of Al2O3, with an increase of Q4Si species in relation to phase separation phenomena observed in these compositions. Conversely, P2O5 addition does not have a significant influence on the 27Al NMR response. 7Li NMR spectra reflect a change in the structural role of Li when P2O5 or Al2O3 is added. The observed structural changes can be rationalized to improve our knowledge of the structure-property relationships, focusing, in particular, on phase separation and nucleation/crystallization processes that are strongly affected by the presence of P and the evolution of its local environment with composition.

Microstructural evolution of Ti–6Al–4V/UD-Cf/LAS composites joint brazed by graphene nanosheets reinforced composite filler

A graphene nanosheets reinforced Ag-Cu composite filler (Ag-Cu + GNSs) was developed by introducing GNSs into Ag-Cu powder filler. Unidirectional carbon fiber reinforced lithium aluminosilicate matrix composites (UD-Cf/LAS composites) and Ti–6Al–4V alloy were brazed with Ag-Cu + GNSs composite filler. The typical interfacial microstructure of joint was Ti–6Al–4V/Ti(s,s)/Ti2Cu/TiCu/Ag(s,s)/Ti3Cu4/Cu(s,s)+TiCu + TiC/Ti3Cu4/TiC + TiSi2/UD-Cf/LAS composites. The in situ synthesized TiCu + TiC composite from the reaction between Ti and GNSs had the following benefits: 1) refined the microstructure of the joint; 2) reinforced the joint; 3) alleviated the thermal stress of the joint by constraining the growth of continuous Ti3Cu4 intermetallic layers. Moreover, with the increase of GNSs content, the amount of TiCu + TiC phases increased. Ag(s,s) and Ti3Cu4 became uniform and fine in the interlayer. Both the thickness of reaction layers and the size of granular Ti3Cu4 and TiCu + TiC phases firstly increased and then decreased with the rise of the brazing temperature. On the contrary, the content of Ag based composite decreased at first and then increased. The highest shear strength of joints reached 45.5 MPa with 0.5% GNSs addition when brazed at 900 °C for 10 min. Based on the experimental results, the interface evolution mechanism of the Ti–6Al–4V/Ag-Cu + GNSs/UD-Cf/LAS composites joint was investigated.

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.

Enhanced mechanical properties of carbon fibre/lithium aluminosilicate composites modified by SiB6 addition

ABSTRACTCarbon fibre-reinforced lithium aluminosilicate matrix composites (Cf/LAS) with different SiB6 contents were prepared by the hot pressing method to assess their mechanical properties and oxidation resistance. Composite that was incorporated with 2 wt-% SiB6 exhibited the highest flexural strength of 500 ± 22.3 MPa. Weight loss and residual strength of Cf/LAS modified by SiB6 were analysed. The results indicated that the addition of SiB6 had a remarkable effect on improving the oxidation resistance for Cf/LAS. To establish a direct relationship among interfacial microstructure, mechanical and oxidation behaviour of the studied composites, their connection was examined and discussed.

Different roles of phosphorus in the nucleation of lithium aluminosilicate glasses

Glasses in the Li2O–Al2O3–SiO2 (LAS) system with different Al2O3Li2O ratio and with or without addition of P2O5 have been synthesized and characterized by thermal analysis. The glass structure and the phosphorus environments in the glasses and their evolutions with annealing have been studied by 31P Solid-State Nuclear Magnetic Resonance (NMR) and 27Al{31P} D-HMQC (Dipolar Hetero-nuclear Multiple-Quantum Coherences) NMR correlation technique. The crystallization behavior has been studied by X-ray diffraction, NMR and Raman spectroscopy. The results showed a different role for P2O5 depending on the Al2O3Li2O ratio. For low alumina content, P2O5 plays a nucleating role while it acts as crystallization inhibitor for high alumina content. These different roles are related to different local environments of the phosphorus in the as-cast glasses. Our study emphasizes the importance of POAl complexes in the crystallization of aluminosilicate glasses.

Evidence of epitaxial growth of high-quartz solid solution on ZrTiO4 nuclei in a Li2O-Al2O3-SiO2 glass

The early stage of crystallization of a glass with the composition 7.6 Li2O – 0.2 Na2O – 0.1 K2O – 1.9 MgO – 0.3 BaO – 1.2 ZnO – 12.7 Al2O3 – 69.6 SiO2 – 4.2 TiO2 – 1.8 ZrO2 – 0.4 Sb2O3 (mol %), suitable for the production of zero thermal expansion glass-ceramics is reported. Thermal treatment at 740 °C for 24 h resulted in the formation of Zr1-xTi1+xO4 crystals and close to them, high-quartz solid solution crystals (lithium aluminosilicate solid solution of high-quartz structure) were formed. TEM studies showed tetragonal Zr1-xTi1+xO4 crystals with a puck-like shape, and on their flat sides, high-quartz solid solution crystals were precipitated, squeezing the “Zr1-xTi1+xO4 patty” in-between two halves of the “lithium-alumosilicate bun”. Selected area electron diffraction showed a distinct crystallographic relationship between these two crystal lattices. High resolution TEM micrographs indicate that the lattice planes observed in the Zr1-xTi1+xO4 crystal continue into the high-quartz solid solution crystal. This is evidence for epitaxial growth of the lithium-alumosilicate with high-quartz structure on the Zr1-xTi1+xO4 crystal. Epitaxial growth within glass-ceramics has hardly been shown up to now.

A Li K-edge XANES study of salts and minerals.

The first comprehensive Li K-edge XANES study of a varied suite of Li-bearing minerals is presented. Drastic changes in the bonding environment for lithium are demonstrated and this can be monitored using the position and intensity of the main Li K-absorption edge. The complex silicates confirm the assignment of the absorption edge to be a convolution of triply degenerate p-like states as previously proposed for simple lithium compounds. The Li K-edge position depends on the electronegativity of the element to which it is bound. The intensity of the first peak varies depending on the existence of a 2p electron and can be used to evaluate the degree of ionicity of the bond. The presence of a 2p electron results in a weak first-peak intensity. The maximum intensity of the absorption edge shifts to lower energy with increasing SiO2 content for the lithium aluminosilicate minerals. The bond length distortion of the lithium aluminosilicates decreases with increasing SiO2 content, thus increased distortion leads to an increase in edge energy which measures lithium's electron affinity.

Influencing the Crystallization of Glass-Ceramics by Ultrashort Pulsed Laser Irradiation after Nucleation

An ultra-fast laser with central wavelength at 1064 nm and 10 ps pulse duration was used to tightly focus laser radiation with a microscope objective inside the volume of nucleated Lithium Aluminosilicate (LAS) glass-ceramic. The nonlinear absorption of the LAS glass-ceramic was measured for different laser parameters and a thermal simulation was performed to determine the temperature field inside the laser-modified area. After laser processing, the samples were crystallized in a furnace and the effect of the laser-induced modifications on the microstructure was analyzed with SEM. The SEM analysis shows an increase in the length and size of whisker-shaped β-spodumene crystals in the laser-modified area. By increasing the dimension of these whisker-shaped crystals, the flexural strength of LAS can be improved locally. First four-point bending flexural tests were performed to examine the influence on the mechanical properties.

In vitro performance and fracture resistance of novel CAD/CAM ceramic molar crowns loaded on implants and human teeth

PURPOSETo investigate the fatigue and fracture resistance of computer-aided design and computer-aided manufacturing (CAD/CAM) ceramic molar crowns on dental implants and human teeth.MATERIALS AND METHODSMolar crowns (n=48; n=8/group) were fabricated of a lithium-disilicate-strengthened lithium aluminosilicate glass ceramic (N). Surfaces were polished (P) or glazed (G). Crowns were tested on human teeth (T) and implant-abutment analogues (I) simulating a chairside (C, crown bonded to abutment) or labside (L, screw channel) procedure for implant groups. Polished/glazed lithium disilicate (E) crowns (n=16) served as reference. Combined thermal cycling and mechanical loading (TC: 3000×5℃/3000×55℃; ML: 1.2×106 cycles, 50 N) with antagonistic human molars (groups T) and steatite spheres (groups I) was performed under a chewing simulator. TCML crowns were then analyzed for failures (optical microscopy, SEM) and fracture force was determined. Data were statistically analyzed (Kolmogorow-Smirnov, one-way-ANOVA, post-hoc Bonferroni, α=.05).RESULTSAll crowns survived TCML and showed small traces of wear. In human teeth groups, fracture forces of N crowns varied between 1214±293 N (NPT) and 1324±498 N (NGT), differing significantly (P≤.003) from the polished reference EPT (2044±302 N). Fracture forces in implant groups varied between 934±154 N (NGI_L) and 1782±153 N (NPI_C), providing higher values for the respective chairside crowns. Differences between polishing and glazing were not significant (P≥.066) between crowns of identical materials and abutment support.CONCLUSIONFracture resistance was influenced by the ceramic material, and partly by the tooth or implant situation and the clinical procedure (chairside/labside). Type of surface finish (polishing/glazing) had no significant influence. Clinical survival of the new glass ceramic may be comparable to lithium disilicate.

The effects of B2O3 on the microstructure and properties of lithium aluminosilicate glass-ceramics for LTCC applications

Lithium aluminosilicate glass-ceramics were prepared using melt-quenching method. B2O3 was added into glass-ceramics as sintering aids. The effects of B2O3 addition and sintering temperature on the microstructure, phase composition, dielectric properties, thermal and mechanical properties and densification of glass-ceramics were investigated. The addition of B2O3 lowered the sintering temperature of the glass-ceramics from 950 to 800 °C, and improved the bending strength from 97 to 195 MPa. The coefficient of thermal expansion of materials increased with the increasing sintering temperature and B2O3 content. The results show that B2O3 is helpful to densification sintering of glass-ceramics. The samples with 3 wt% B2O3 sintered at 800 °C showed εr of 7.2, tanδ of 1.4 × 10−3, bending strength of 195 MPa, and CTE of 2.67 × 10−6 K−1. The results indicated that the LAS glass-ceramic can be a possible candidate for LTCC substrate applications.