TANG Yong ¹, TANG Weizhao ¹, XIA Peizong ¹, GAO Cundong ¹, WANG Weidong ¹,

ZHANG Chao ¹, GAO Cunji ¹, XIAO Zhuohao ², QIU Riliang ²

(1. Shandong Jingyao Glass Group Co., Ltd., Linyi 276624, Shandong, China;

2. Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended abstract:

[Significance] MgO-Al₂O₃-SiO₂ (MAS) glass and glass-ceramics are high-performance inorganic non-metallic materials with critical application value in aerospace, electronic communication optical engineering and heat-resistant products. Fabricated via controlled crystallization of base glasses, they consist of uniformly dispersed micro-nano crystalline phases embedded in a residual glass matrix. Through compositional design and heat treatment optimization, type, size and volume fraction of precipitated crystals can be precisely tailored, delivering unique property combinations, including ultra-low thermal expansion, excellent dielectric performance and high mechanical strength unachievable by conventional glasses or ceramics. The MAS system has drawn extensive research interest primarily for its dominant cordierite phase (2MgO·2Al₂O₃·5SiO₂). The anisotropic thermal expansion of cordierite yields an extremely low coefficient of thermal expansion (CTE) of ~1.5×10⁻⁶ ℃⁻¹, which can even be adjusted to be near-zero via structural control. Coupled with low dielectric constant, low loss and favorable thermal stability, MAS materials well satisfy the demands of 5G/6G communication, high-reliability aerospace equipment and precision optical systems. This review was aimed to systematically summarize research progress in compositional design, preparation technologies, property regulation and practical applications of MAS glass and glass-ceramics, providing a comprehensive reference for further development and industrialization of high-performance MAS materials.

[Progress] The MAS system is composed with SiO₂ as the network former, A₂O₃ as the network stabilizer and MgO as the network modifier. The stoichiometric ratio of the three oxides dominates phase separation, crystallization behavior and final properties, while optimized MgO content and MgO/A₂O₃ ratio can be used to produce high-crystallinity α-cordierite with uniform grains and low CTE. Nucleating agents are essential for achieving uniform bulk crystallization. Single agents, such as TiO₂, ZrO₂, P₂O₅ and fluorides, function via distinct mechanisms, including network depolymerization, heterogeneous nucleation and liquid phase separation. Composite nucleating agents exhibit remarkable synergistic effects. For example, the sample with 1:1 TiO₂/ZrO₂ exhibited 93.8% crystallinity with 134 nm refined grains, delivering a Vickers hardness of 9.70 GPa and flexural strength of 312 MPa. The P₂O₅/ZrO₂/TiO₂ ternary system triggered transformation from surface-dominated crystallization to bulk crystallization, shortened full crystallization time from 10 h to 5 h and achieved a low CTE of 1.4×10⁻⁶ ℃⁻¹, with excellent dielectric properties. Modifiers, including B₂O₃, ZnO and rare earth oxides, further lowered melting temperature, optimized thermal conductivity and adjusted CTE matching with different substrates. Four main preparation routes have been developed for MAS glass-ceramics. The melting method, the most widely used industrial approach, produces highly dense, homogeneous bulk materials with isotropic properties, but requires high melting temperatures (~1600 ℃) and faces challenges in formation of large-size component. The sintering method involved glass powders as raw materials, suitable for complex-shaped products with lower energy consumption. Spark plasma sintering (SPS) allowed rapid full densification at low temperatures, with superior mechanical performances to hot pressing and pressureless sintering. The sol-gel method ensured molecular-level mixing and nanoscale grains, ideal for optical-grade transparent products, which is limited to small components, due to the large shrinkage and cracking risk. Emerging 3D printing broke traditional structural limitations, successfully fabricating honeycomb components with 0.6 mm wall thickness and favorable mechanical strength. For thermal expansion, the CTE of MAS glass-ceramics was tunable over a wide range by controlling the purity of α-cordierite, crystallinity and grain size. Doping with B₂O₃, TiO₂ or rare earth oxides enabled precise CTE matching with silicon or GaAs substrates for advanced electronic packaging. For microwave dielectric properties, element doping and second-phase composite strategies effectively reduce dielectric loss and adjust frequency temperature coefficient, with optimized samples achieving high quality factors and tunable dielectric constants suitable for 5G/6G low temperature co-fired ceramic substrates. For optical properties, transparent MAS glass-ceramics with over 80% visible transmittance are obtained by controlling grain size below 50 nm and matching refractive indices between crystalline and glass phases. Rare earth ion doping further expanded their applications in solid-state lighting and near-infrared spectroscopy. For mechanical properties, surface crystallization-induced compressive stress and ion exchange significantly resulted in enhancement in flexural strength and crack resistance, while high-hardness nanocrystalline phases, such as spinel and ZrO₂, would raise intrinsic hardness and fracture toughness.

[Conclusions and prospects] MAS glass and glass-ceramics have achieved remarkable progress in compositional design, process innovation and multi-dimensional property regulation, demonstrating great application potential in aerospace, electronic communication, optical engineering and heat-resistant fields. Nevertheless, several bottlenecks still restrict their large-scale application, such as the transformation kinetics from μ-cordierite to α-cordierite remains difficult to control precisely, transparent products still lagging behind pure glasses in transmittance, high production cost for industrial popularization and the current dielectric properties that cannot satisfy the requirements of 6G and terahertz communication for ultra-low dielectric loss. Looking forward, future research will focus on revealing the atomic-scale cordierite phase transformation mechanism to develop efficient regulation strategies, exploring novel low-scattering nucleation systems to improve optical transmittance, optimizing preparation processes and utilizing low-cost raw materials to reduce production costs, developing ultra-low-loss dielectric materials for terahertz bands and constructing multi-phase composite structures to achieve multifunctional integration for next-generation high-end equipment.

Key words: MgO-Al₂O₃-SiO₂; glass-ceramics; cordierite; crystallization behavior; thermal expansion