Effect of MgO/Al2O3 ratio on the crystallization behaviour of Li2O–MgO–Al2O3–SiO2 glass-ceramic and its wettability on Si3N4 ceramic

The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li₂O–MgO–Al₂O₃–SiO₂ glass-ceramic for the application of joining Si₃N₄ ceramics. We investigated the influence of the MgO/Al₂O₃ composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi₂O₆ and Mg₂SiO₄ were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg₂SiO₄. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10^?6/°C, which was very close to that of Si₃N₄ ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si₃N₄ ceramic surface was 32° and the interface was well bonded.     

Influence of heat-treatment protocols on mechanical behavior of lithium silicate dental ceramics

In this work, three different commercial lithium silicate (LS) glass-ceramics for computer aided design/computer aided machining systems, CeltraDuo-Dentsply (LS-C), E-MaxCAD-Ivoclar (LS-E), and Suprinity-Vita (LS-S), were comparatively characterized. Following the protocols recommended by the manufacturers, the glass-ceramics were heat-treated under low vacuum and characterized by X-ray diffraction, scanning electron microscopy, hardness, fracture toughness, Young's modulus, and flexural strength. Rietveld refinement indicated that the materials “as-received” present mostly amorphous phase and Li₂SiO₃ as secondary crystalline phase in LS-E and LS-S specimens, while LS-C specimens also present Li₂Si₂O₅ and Li₃PO₄ as crystalline phases. All “as-received” glass-ceramics present hardness, fracture toughness, and Young's modulus of around 647-678 HV, 1.15-1.40 MPa.m^1/2, and 82-92 GPa, respectively. After heat treatment, the LS-C and LS-S specimens presented decreasing of amorphous phase associated to Li₂SiO₃ and Li₂Si₂O₅ grains with low aspect ratio, while LS-E indicates a reduction of amorphous phase and Li₂Si₂O₅ elongated grains. Fracture toughness and Young's modulus increase about 10% due to the crystallization of residual amorphous phase for all materials. Moreover, crystallographic and microstructural characteristics are responsible for the higher flexural strength of LS-E (327 MPa), regarding LS-C and LS-S. However, the glass-ceramics LS-E present lower Weibull modulus (m = 5.4) comparatively to LS-C (m = 9) and LS-S (m = 6).     

Thermo-magnetic properties of Fe2O3-doped lithium zinc silicate glass-ceramics for magnetic applications

The crystallization behaviour and thermo-magnetic characteristics of glass-ceramic based on the 15Li₂O–20ZnO–10CaO–55SiO₂ system doped with varied Fe₂O₃ additions (0.0125, 0.025, and 0.05 mol) are described in this work. In some cases, Al₂O₃ was also added to the iron-containing sample. Glasses were successfully prepared by melt-quenching technique and converted into glass-ceramics by controlled heat-treatment, using DTA, SEM, XRD, and VSM techniques. The density, thermal expansion coefficients (TCE), and magnetic characteristics of the glass-ceramic were examined. XRD results confirmed characteristic peaks for various phases like quartz, Li₂ZnSiO₄, wollastonite, Li₂Si₂O₅, ZnFe₂O₄, and β-spodumene. By doping Fe₂O₃ and Al₂O₃ with lowering annealing temperature, the particle size was reduce, resulting in glass-ceramics with a more uniform and dense microstructure. The density of glass-ceramics rises from 2.74 g/cm³ to 3.45 g/cm³, whereas the TCE values in average 14–78 × 10⁻⁷/°C with temperature range of 25–500 °C. The doped glass-ceramics have superior magnetic properties with saturation magnetization (0.143–0.548 emu/g), the coercivity force (65.116–86.359 G), and remanence magnetization (0.074–0.436 emu/g). Under an alternating magnetic field, the presence of the Zn-ferrite phase in the glass-ceramics improves their magnetic properties and increases their heat-generating capability. Certain features of the doped glass-ceramics control the extensive variety of possibilities for their usage in various magnetic applications particularly for cancer hyperthermia treatment.     

Role of MgO in lowering glass transition temperature and increasing hardness of lithium silicate glass and glass-ceramics

The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li₂O–K₂O–Na₂O–CaO–MgO–ZrO₂–Al₂O₃–P₂O₅–SiO₂ glass system has been reported here. Increased amount of MgO enhanced the participation of Al₂O₃ as a glass network former along with [SiO₄] tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (～10 GPa) and elastic modulus (～127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.     

Influence of Al2O3/SiO2 ratio in multicomponent LNAS glasses and glass-ceramics on the crystallization behavior,microstructure and mechanical performance

Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al₂O₃ for SiO₂. The relationships between glass network structure and crystallization behavior of Li₂O–Na₂O–Al₂O₃–SiO₂ (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al₂O₃. LNAS glasses with the addition of Al₂O₃ from 16 to 18 mol% exhibited increasing Q⁴ (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al₂O₃ content increasing to 19–20 mol%, the formation of highly disordered (Li, Na)₃PO₄ phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al₂O₃ showed high transparency ～84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m^1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays.     

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.     

Persistent luminescence of Eu/Dy-doped Sr2MgSi2O7 glass-ceramics processed by aerodynamic levitation

Glass beads of the Sr₂MgSi₂O₇ stoichiometric composition and a non-stoichiometric composition with higher SiO₂/SrO ratio doped with Eu₂O₃/Dy₂O₃ were prepared through aerodynamic levitation coupled to CO₂ laser heating. The glass beads were subsequently treated at 1100 ºC to produce glass-ceramics with Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ as the main crystalline phase. The doped glasses exhibit red emissions; after crystallisation, the corresponding glass-ceramics emit blue light under UV excitation. The starting glass composition considerably affects the crystallisation process, resulting in Sr₂MgSi₂O₇ glass-ceramics with very different microstructures which, in turn, have a significant influence on the luminescence properties. The photoluminescence emission spectra of the glass-ceramics under UV light show a broadband emission (λ = 400–500 nm) with a main peak assigned to the typical Eu²⁺ transition under excitation at 365 nm. Both the intensity of the emission and the persistence time significatively increase on decreasing temperature. Glass-ceramics from the non-stoichimetric glass composition co-doped with 1Eu₂O₃/0.5Dy₂O₃ (mol%.) provided the longest persistence times.     

Effect of metastable phase on the crystallization and mechanical properties of MgO-Al2O3-SiO2 glass-ceramics without nucleating agents

Glass-ceramics without nucleating agents usually undergo surface crystallization, which deteriorates the overall performance of the products. In this paper, we evaluated the effects of the metastable MgAl₂Si₃O₁₀ crystalline phase on the crystallization behavior of a MgO–Al₂O₃–SiO₂ (MAS) glass without nucleating agents and mechanical properties of the glass-ceramics obtained. The results demonstrated that the precipitation of metastable MgAl₂Si₃O₁₀ crystallites promotes the crystallization mechanism transformed from surface crystallization into volume crystallization with two-dimensional crystal growth. Furthermore, the grain size of MgAl₂Si₃O₁₀ near the surface of the prepared glass-ceramics was larger than that of MgAl₂Si₃O₁₀ inside, which helps to generate compressive stress and improves its mechanical properties. The glass-ceramics containing metastable MgAl₂Si₃O₁₀ phase exhibited an enhanced hardness in the range of 7.6 GPa–9.5 GPa for indentation loads ranging from 2.94 N to 98 N, and indentation size effect behavior was observed in Vickers hardness tests of both MAS glass and glass-ceramics. The load-independent hardness values for MAS glass and glass-ceramics were reliably evaluated by the modified proportional specimen resistance (MPSR) model of 7.1 GPa and 7.6 GPa, respectively, with a high correlation coefficient of more than 0.9999. This work reveals the unexploited potential of the metastable phase in improving the crystallization ability and mechanical properties of glass-ceramics.     

Preparation and characterization of alkali-free glass substrates with enhanced properties for TFT–LCDs applications

To obtain an alkali-free glass substrate with enhanced properties for thin-film transistor–liquid crystal displays (TFT–LCDs) applications, we chose a base glass composed of 3B₂O₃-15Al₂O₃-58SiO₂-22MgO-0.5SrO-1.5MgF₂ (mol%) for nucleation–crystallization. The results show that when the nucleation–crystallization processes of the base glass are 810 °C/6 h + 880 °C/6–9 h, the prepared GC/6–GC/9 glass-ceramics exhibit enhanced properties because of the precipitation of nano-sized cordierite. The transmittances in the visible range of the GC/6–GC/9 glass-ceramics exceed 85%, the densities are 2.564–2.567 g/cm³, thermal expansion coefficients are 2.934–3.059 × 10^-6/°C (25–300 °C), compressive strengths are 417–589 MPa, bending strengths are 141–259 MPa, Vickers hardnesses are 6.8–7.8 GPa, and strain points are approximately 735 °C. Considering these properties, the prepared GC/6–GC/9 glass-ceramics have good potential as candidate materials for alkali-free glass substrates. Additionally, these results demonstrate that it is feasible to improve the properties of alkali-free glass substrates by nucleation–crystallization.     

A novel high-strength lithium disilicate glass-ceramic featuring a highly intertwined microstructure

To achieve long-term clinical performance and wider application of glass-ceramic dental restorations, it is urged to enhance the mechanical properties of glass-ceramic materials. In this study, a high-strength lithium disilicate glass-ceramic was developed in a SiO₂–Li₂O–Al₂O₃–MgO–P₂O₅–ZrO₂ related glass system, which demonstrates a high flexural strength of 562 ± 107 MPa. In this high-strength glass-ceramic, the microstructure features highly intertwined colonies of lithium disilicate. This novel microstructure effectively contributes to the improvement of flexural strength. The minor crystalline phases (β-quartz, MgAl₂Si₄O₁₂, and Li₃PO₄) embedded within the Li₂Si₂O₅ (LS₂) crystal colonies and residual glass matrix could further strengthen the glass-ceramic. The development process of such a novel microstructure and its possible formation mechanism are proposed. This material could be an excellent candidate for restorative dental applications up to three-unit posterior bridges.     

Effect of substitution of ZrO2 by SnO2 on crystallization and properties of environment-friendly Li2O–Al2O3–SiO2 system (LAS) glass-ceramics

In this study, a transparent and environmentally friendly Li₂O–Al₂O₃–SiO₂ (LAS) glass-ceramic was prepared by melt-quenching and two-step heat treatment. The influence of the substitution amount of ZrO₂ by SnO₂ on the crystallization, microstructure, transparency, and mechanical properties of LAS glass and glass-ceramics was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible Spectrophotometer, three-point bending strength test, and microhardness test. The results indicate that the main crystalline phase of LAS glass ceramics was a β-quartz solid solution when heat treated at 780 °C for 2 h and 870 °C for 1.5 h. When the substitution amount of ZrO₂–SnO₂ increased from 0.4 mol% to 2.5 mol%, the grain size and thermal expansion coefficient of LAS glass-ceramics first decreased and then increased, and the crystallinity first increased and then decreased. When the substitution amount of ZrO₂–SnO₂ was 0.8 mol%, the transparency of the LAS glass-ceramics was maximum, the bending strength was 96 MPa, and the Vickers hardness was 10.9 GPa.     

Physical and structural characteristics of sol–gel derived CaO–B2O3–SiO2 glass-ceramics and their dielectric properties in the 5G millimeter-wave bands

In this study, sol–gel derived CaO–B₂O₃–SiO₂ glass-ceramics with a set B₂O₃ content of 22.2 mol% and CaO/SiO₂ ratios ranging between 0.15 and 0.27 were used for low-temperature cofired ceramic applications in the 5G millimeter-wave bands. X-ray diffraction analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy data indicated that, unlike the typical CaO–B₂O₃–SiO₂ glass-ceramics prepared via melting resulted in the presence of calcium silicates, the CaO–B₂O₃–SiO₂ glass-ceramics in this study comprised only an amorphous phase containing different amounts of CaB₂O₄ crystallites depending on the CaO/SiO₂ ratio. Among the formulations evaluated, the 14.5CaO?22.2B₂O₃?63.3SiO₂ glass-ceramic sintered at 950 °C exhibited a dielectric constant of 4.33 and a dielectric loss of 0.0012 at 60 GHz, which conferred its low signal propagation delay and low signal attenuation in applications. In addition, the electrical resistivity, breakdown strength, thermal conductivity, and coefficient of thermal expansion of the 14.5CaO?22.2B₂O₃?63.3SiO₂ glass-ceramic were 1.72 × 10¹² Ω cm, 15.49 kV/mm, 1.70 W/mK, and 4.1 ppm/°C, respectively. The 14.5CaO?22.2B₂O₃?63.3SiO₂ glass-ceramic exhibited excellent insulating properties, facilitating its use as substrate material; moreover, its thermal properties matched those of Si and GaAs.     

Effect of Ta2O5 addition on the structure,crystallization mechanism,and properties of CaO–B2O3–SiO2 glasses for LTCC applications

CaO–B₂O₃–SiO₂–Ta₂O₅ (CBST) glass-ceramics, with different Ta₂O₅ content, (up to 6 mol%), have been prepared by using glass melt quenching followed by heat treatment between 800 and 880 °C. The Fourier Transform Infrared (FTIR) results showed that the stronger the attraction of Ta⁵⁺ to the oxygens in the BO₃^3? and SiO₃^2? structures, the more easily the B–O and Si–O bonds will be destroyed. The underlying reason is most probably the high field strength of Ta⁵⁺, which results in a weakening of the vibration intensities of the [BO₃] and [SiO₄] units. Moreover, the Differential Scanning Calorimetry (DSC) results showed that the softening point (T_g), crystallization starting temperature (T_c1), and exothermic crystallization peak temperature (T_p1), of the CaSiO₃ phase, shifted to higher values with the addition of Ta₂O₅. Also, the crystallization activation energy (E_a) and the glass stability factor (ΔT) of the CaSiO₃ phase increased, which indicated that the CaSiO₃ phase of the glass became inhibited by the addition of Ta₂O_5. It was, thus, obvious that there was a need of glass characterization. The results of the crystallization kinetics showed that the critical cooling rate decreased with the addition of Ta₂O₅, which indicated that the viscosity of the system had increased. The CBST glass-ceramics, containing 1 mol% Ta₂O_5, that were sintered at 875 °C for 15 min showed excellent dielectric properties: ε_r = 6.22 and tanδ = 1.19 × 10^?3 (1 MHz). To sum up, CaO–B₂O₃–SiO₂–Ta₂O₅ glass-ceramics are potential low temperature co-fired ceramic substrate materials.     

Effects of Y2O3 addition on structure and properties of LZAS vitrified bond for CBN grinding tools application

The effects of Y₂O₃ addition on the structure and properties of Li₂O–ZnO–Al₂O₃–SiO₂ (LZAS) vitrified bonds were firstly investigated for CBN grinding tools application. Glasses and glass-ceramics were characterized using differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy and infrared spectroscopy. The thermal expansion coefficient (TEC), microhardness, bending strength and chemical durability of the obtained products were also evaluated. Results showed that Y₂O₃ acted as the network former in the track of SiO₄ tetrahedrals. Introducing Y₂O₃ in the glasses increased the glass transition temperature and crystallization temperature. The crystallization of the main β-quartz_ss phase increased with increase of Y₂O₃ content. The morphology of the crystals was dependent on the Y₂O₃ content. The TEC (5.15×10⁻⁶/°C) of vitrified bond containing 1.0 mol% Y₂O₃ (Y1.0) was very close to the TEC (5.0×10⁻⁶/°C) of CBN grains. Moreover, Y1.0 vitrified bond exhibits a high microhardness (5.98 GPa), a high bending strength (202 MPa) and a good chemical durability (20 days, DR=2.8×10⁻⁹ g/cm² min), suggesting that it would be a promising material for CBN grinding tool.     

Crystallization of LiNbO3 and NaNbO3 in niobiosilicate glass–ceramics

Although glass–ceramics have been widely explored for their thermal stability and mechanical properties, they also offer unique symmetry-dependent properties such as piezoelectricity and pyroelectricity through controlled crystallization of a polar phase. This work examines crystallization of LiNbO₃ in a 35SiO₂–30Nb₂O₅–35Li₂O mol% composition and crystallization of LiNbO₃ and NaNbO₃ in a 35SiO₂–30Nb₂O₅–25Li₂O–10Na₂O mol% composition. Crystallization kinetics are examined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory where the Avrami exponent, n, is calculated to be 1.0–1.5. Microscopical analysis shows dendritic morphology, which when combined with the JMAK analysis, suggests diffusion-controlled one-dimensional growth. Adding Na₂O to the glass composition increases the inter-diffusivity of ions which causes LiNbO₃ to crystallize faster and lowers the activation energy of transformation from 1054 ± 217 kJ/mol in the ternary composition to 882 ± 212 kJ/mol. Time-temperature-transformation diagrams are presented which show that the temperature for maximum rate of transformation for LiNbO₃ is ∼650°C and for NaNbO₃ is ∼715°C.     

The Role of GeO 2 and In 2 O 3 in the Glass-Ceramic Formation and Microstructure of Lithium Alumino-Silicate Glasses

The crystallization characteristics of the glasses based on the Li₂O–Al₂O₃–SiO₂ system have been investigated. The base glass composition was modified by partial replacement of GeO₂ for SiO₂ and In₂O₃ for Al₂O₃. The effect of the compositional variation on the crystallization products of the glasses and the type of the solid solution (ss) phases formed as well as the resulting microstructure were traced by differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). A decrease in the endothermic and exothermic temperatures was detected by the replacement processes. β -spodumene ss, β -eucryptite ss, lithium meta- and di-silicate, lithium aluminum germanate and two forms of indium-containing phases (LiInSi₂O₆ & In₂Si₂O₇ phases) were mostly developed in the crystallized glasses. The objective of the present work is to understand the role of the glass oxide constituents in determining the type of the crystalline phases formed, their solid solution formed and the microstructure of the resultant glass-ceramic materials.     

Characterization of Yb2Si2O7–Yb2SiO5 composite environmental barrier coatings resultant from in situ plasma spray processing

Plasma spraying of multicomponent materials produces shifts in coating composition associated with differential vaporization of constituent elements within the strong thermal gradients of the process. This effect is quite noticeable in rare-earth silicates which are now widely being employed as Environmental Barrier Coatings (EBCs) for SiC based ceramic components of turbine engines. Of particular interest is the preferential volatilization of SiO₂ during thermal plasma spraying Yb₂Si₂O₇ (ytterbium disilicate) coatings which leads to the deviation from stoichiometry of the desired disilicate composition resulting in a mixed phase coating consisting of Yb₂Si₂O₇ plus Yb₂SiO₅ (ytterbium monosilicate). Recent work has shown that presence of monosilicate can be beneficial as its evolution from amorphous, metastable to stable crystalline phase can lead to crack healing during high temperature exposure, however, careful control of the chemistry and architecture may be needed. In this work a 50/50 mol% Yb₂Si₂O₇–Yb₂SiO₅ composite coating has been targeted through in situ decomposition during plasma spray from stoichiometric Yb₂Si₂O₇ powder. The as sprayed amorphous coating reverts to crystalline upon thermal treatment passing through a metastable state identified by XRD and Raman spectroscopy. The transition to the final stable phases results in a mixed phase coating comprising of 46/54 mol% Yb₂Si₂O₇–Yb₂SiO₅ composite that is thermo-mechanically stable with the underlying bond coated silicon coated SiC substrate.     

Mechanical Properties of a Lithium Disilicate Strengthened Lithium Aluminosilicate Glass‐Ceramic

A glass composition in the Li₂O–Al₂O₃–SiO₂ (LAS)‐ternary phase diagram is presented, which enables the crystallization of Li₂Si₂O₅ as well as LiAlSi₂O₆ upon a well‐defined heat treatment. Li₂Si₂O₅ is the minor crystalline phase in the glass‐ceramic and generates through the bulk strengthening of the LAS glass‐ceramic. A flexural strength as higher as 400 MPa is measured in the proposed glass‐ceramic formulation, thus outperforming conventional LAS‐glass‐ceramics. A combination of the presence of those two crystalline phases of very different mechanical properties and coefficient of thermal expansion as well as the microstructure are believed to contribute largely to the enhancement of the measured properties.     

Microstructure evolution of Si3N4 ceramics with high thermal conductivity by using Y2O3 and MgSiN2 as sintering additives

Silicon nitride (Si₃N₄) ceramics were prepared by gas-pressure sintering using Y₂O₃–MgSiN₂ as a sintering additive. The densification behavior, phase transition, and microstructure evolution were investigated in detail, and the relevance between the microstructure and the performance (including thermal conductivity and mechanical properties) was further discussed. A significant change from a bimodal to a homogeneous microstructure and a decreased grain size occurred with increasing Y₂O₃–MgSiN₂ content. When the small quantity of preformed β-Si₃N₄ nuclei grew preferentially and rapidly in a short time, an obvious bimodal microstructure was obtained in the sample with 4 mol% and 6 mol% Y₂O₃–MgSiN₂. When more β-Si₃N₄ nuclei grew at a relatively rapid rate, the sample with 8 mol% Y₂O₃–MgSiN₂ showed a microstructure consisting of numerous abnormally grown β-Si₃N₄ grains and small grains. When more β-Si₃N₄ nuclei grew simultaneously and slowly, there was a homogeneous microstructure and smaller grains in the sample containing 10 mol% Y₂O₃–MgSiN₂. Benefitting from the completely dense, significant bimodal microstructure, low grain boundary phase, and excellent Si₃N₄–Si₃N₄ contiguity, the sample containing 6 mol% Y₂O₃–MgSiN₂ exhibited great comprehensive performance, with a maximum thermal conductivity and fracture toughness of 84.1 W/(m⋅K) and 8.97 MPa m^1/2, as well as a flexural strength of 880.2 MPa.     

Effects of different sintering additives on the synthesis of γ-Y2Si2O7 powders

Pure γ-Y₂Si₂O₇ powders were synthesized by the solid-liquid reaction method using Y₂O₃ and SiO₂ powders with Li₂O, MgO or Al₂O₃ additives. The effects of the metallic ions Li⁺, Mg²⁺ and Al³⁺ on the synthesis process were systematically investigated by X-ray diffraction and differential scanning calorimetry. The chemical kinetics of the Y₂Si₂O₇ synthetic process was calculated to illuminate the influences of the different metallic ions on the formation of silicate. The results indicate that the additives could effectively reduce the synthesis temperature by 100–300 °C. The apparent activation energy of the synthetic reaction was reduced by 79.75%, 65.16%, or 56.77% when 6 mol.% of Li₂O, MgO, or Al₂O₃ was added, respectively, and the reaction rate was also significantly increased.