Cai Xincheng,Li Xiaoqiang,Lu Tiecheng,Jia Zhuoying,Yu Shengquan,Kang Bin,Shi Qiwu,Qi Jianqi
Transparent ceramics are critical for advanced optics and armor, but shaping them into highly curved geometries without degrading their optical and mechanical properties remains a formidable challenge. Here, we introduce a force-driven sintering strategy that harnesses force-induced creep to dynamically control microstructure and curvature through continuous stress release. A hallmark of this process is a dynamic curvature reversal phenomenon, governed by cyclic stress accumulation and release. Using force-driven sintering, we fabricated large-scale (0.5*2*22 cm 3 ) curved MgAl 2 O 4 ceramics exhibiting a high curvature (>5.36 m −1 ), and exceptional transmittance exceeding 85% (approaching the theoretical limit), while matching the best-reported mechanical properties. We also demonstrate the versatility of force-driven sintering by producing curved Al 2 O 3 transparent ceramics. This method synchronizes external mechanical forces with intrinsic material creep and stress relaxation, enabling the single-step fabrication of complex-shaped, high-performance transparent components. force-driven sintering establishes a scalable and versatile manufacturing paradigm for transparent ceramics in demanding applications.
High-entropy Mg(Mg 0.25 Zn 0.25 Ga 0.5 Ti 0.5 Al 0.5 )O 4 ceramics with disordered spinel structure were prepared at 1420-1500 °C. When sintered at 1480 °C, Mg(Mg 0.25 Zn 0.25 Ga 0.5 Ti 0.5 Al 0.5 )O 4 ceramics exhibited extremely high Q×f of 105,800 ± 300 GHz, improved τ f of –45.3 ± 0.01 ppm/°C, and low ε r of 11.5 ± 0.1, with favorable H v and flexural strength of 11.43 ± 0.01 GPa and 128.1 ± 0.1 MPa, respectively, which were 23.3% and 31.7% higher than those of MgAl 2 O 4 . The measured ε r of Mg(Mg 0.25 Zn 0.25 Ga 0.5 Ti 0.5 Al 0.5 )O 4 ceramics was substantially higher than the calculated εᵣ (C-M) (9.9), due to the underestimated Ti 4+ polarizability and rattling effect. The improved τ f was caused by the decreased τ ε and increased Gibbs free energy. The 1.5 times increase in Q × f stemmed from the increased packing fraction and lattice energy, lowered σ AC , enhanced E a and covalency factor. A cylindrical dielectric resonator antenna was designed with Mg(Mg 0.25 Zn 0.25 Ga 0.5 Ti 0.5 Al 0.5 )O 4 high-entropy ceramic, which can fulfill the communication demands of high-frequency and high-power applications.
This study fabricated translucent alumina ceramics with varying MgAl 2 O 4 doping concentrations using vat photopolymerization (VPP) additive manufacturing combined with vacuum sintering. The influence of MgAl 2 O 4 content on the microstructure, mechanical properties, and optical characteristics was comprehensively investigated. Results demonstrate that optimal MgAl 2 O 4 doping (0.2 wt%) significantly enhances material densification, achieving superior mechanical performance with a flexural strength of 510 ± 30 MPa and fracture toughness of 3.7 MPa m 1 / 2 after sintering at 1700 °C, alongside improved optical transmittance. Microstructural characterization demonstrates that the MgAl 2 O 4 sintering additive promotes densification and grain refinement through effective suppression of abnormal grain growth and pore formation.
Zhang Wenlong,Wang Bin,Xu Yuxin,Chen Xiao,Zhang Kuibao,Hao Yan
To enhance the thermal stability of SiO 2 aerogels at high temperature, this study proposes a method involving the incorporation of MgAl 2 O 4 nanoparticles into SiO 2 aerogels to improve their high-temperature stability. By comparing the performance of MgAl 2 O 4 -SiO 2 aerogel with pure SiO 2 aerogels after heat treatment at high temperatures, it is demonstrated that the MgAl 2 O 4 nanoparticles significantly enhances the thermal stability of SiO 2 aerogels at elevated temperatures while almost no effect on thermal conductivity, about 0.0312 and 0.0322 W/(m·K). The MgAl 2 O 4 -SiO 2 aerogels exhibit superior thermal stability and insulation performance compared to pure SiO 2 aerogels at temperatures exceeding 800 ℃. Notably, even after heat treatment at 1100℃, a condition that causes pure SiO 2 aerogels to nearly lose their porous structure, the MgAl 2 O 4 -SiO 2 aerogels retain a specific surface area of 81.95 m 2 /g and thermal conductivity of 0.0584 W/(m·K).
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