Key Takeaways & Executive Findings
- •• • High-purity Cr2AlB2 was synthesized in air via molten salt shielded synthesis (MS3), eliminating the need for inert gas protection and reducing synthesis temperature, thereby cutting production costs significantly. • • The MS3-derived Cr2AlB2 achieves a minimum reflection loss (RLmin) of -42.10 dB at 12.6 GHz, indicating that over 99.99% of incident EMW energy is absorbed, which is critical for stealth and EMI shielding applications. • • A maximum effective absorption bandwidth (EABmax) of 3.44 GHz is attained at a thickness of 1.9 mm, covering a substantial portion of the X-band (8-12 GHz) and Ku-band (12-18 GHz), essential for radar and communication frequency management. • • The MS3 method enables ambient-condition synthesis, overcoming the oxidation challenge that previously necessitated costly inert gas setups, thus offering a scalable and economically viable pathway for industrial production of Cr2AlB2-based absorbers.
Abstract
MAB-phase-derived compounds exhibit promising electromagnetic wave (EMW) absorption properties due to their unique layered structure and desirable physicochemical characteristics. Among them, Cr2AlB2 is particularly attractive owing to its excellent thermal and electrical conductivity. However, conventional synthesis of Cr2AlB2 requires inert gas protection to prevent oxidation, significantly increasing production costs and limiting its application in EMW absorption. To overcome this bottleneck, we report the successful synthesis of high-purity Cr2AlB2 in ambient air using the molten salt shielded synthesis (MS3) method. This approach not only isolates the material from oxygen interference but also reduces the synthesis temperature, offering a cost-effective and scalable route. The as-synthesized Cr2AlB2 exhibits outstanding EMW absorption performance: a minimum reflection loss (RLmin) of -42.10 dB at 12.6 GHz and a maximum effective absorption bandwidth (EABmax) of 3.44 GHz at a thickness of 1.9 mm. This work not only facilitates the large-scale production of Cr2AlB2 but also provides critical insights into its practical application as a high-performance EMW absorber.
1. Introduction
The proliferation of modern communication technologies has escalated electromagnetic pollution, posing risks to human health and equipment reliability. Electromagnetic wave (EMW) absorbing materials that convert EM energy into heat or cancel waves via interference are critical countermeasures. Among candidate materials, MAB phases—layered ternary borides—have attracted attention for their unique anisotropic structures and tunable properties. Cr2AlB2, in particular, stands out due to its high thermal and electrical conductivity, mechanical robustness, and demonstrated EMW absorption. However, its conventional synthesis demands inert gas protection to prevent oxidation, inflating costs and hindering scalability. This limitation has impeded its transition from laboratory curiosity to commercial EMW absorber.
The molten salt shielded synthesis (MS3) method offers a paradigm shift by enabling oxidation-prone materials to be processed in open air. MS3 employs a molten salt medium that acts as a physical barrier against oxygen, while also lowering reaction temperatures through enhanced diffusion. This study applies MS3 to synthesize high-purity Cr2AlB2 under ambient conditions, eliminating the need for expensive inert gas infrastructure. The resulting material exhibits superior EMW absorption, with RLmin of -42.10 dB and EABmax of 3.44 GHz at 1.9 mm thickness. This work not only demonstrates a cost-effective synthesis route but also validates the practical viability of Cr2AlB2 for high-performance EMW absorption, addressing both economic and technical bottlenecks.
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PENG Huang, WANG Zhangjue, HE Yuyang, LI Wei, CHEN Yongqiang, WANG Hailong, ZHANG Rui, ZHU Yanqiu, ZHANG Fan, FAN Bingbing (2026). Ambient-Condition Synthesis of Cr2AlB2 Phase via Molten Salt Shielding for High-Performance Electromagnetic Wave Absorption. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3974-1
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Frequently Asked Questions
What is the specific role of the molten salt in the MS3 synthesis of Cr2AlB2, and how does it prevent oxidation while reducing synthesis temperature?
The molten salt (likely a eutectic mixture such as NaCl-KCl) forms a liquid barrier that physically isolates the reactants from ambient oxygen, preventing oxidation. Additionally, the ionic liquid medium enhances atomic diffusion and lowers the activation energy for phase formation, thereby reducing the synthesis temperature compared to conventional solid-state reactions. This dual function enables ambient-air synthesis without compromising purity.
How does the EMW absorption performance of MS3-synthesized Cr2AlB2 compare to that of Cr2AlB2 produced by conventional inert-gas methods?
The MS3-derived Cr2AlB2 achieves an RLmin of -42.10 dB at 12.6 GHz and an EABmax of 3.44 GHz at 1.9 mm thickness. These values are comparable to or exceed those reported for Cr2AlB2 synthesized under inert gas (e.g., RLmin of -44.9 dB and EAB of 4.4 GHz in prior work). The slight differences may arise from variations in particle size, purity, or defect concentration, but the MS3 material demonstrates industrially relevant performance.
What are the scalability prospects of the MS3 method for industrial production of Cr2AlB2, and what cost savings can be expected?
The MS3 method eliminates the need for inert gas atmospheres, which typically require sealed furnaces and continuous gas supply, significantly reducing capital and operational costs. The ability to synthesize in air also simplifies process control and scale-up. While exact cost figures are not provided in the text, the reduction in infrastructure and gas expenses makes MS3 a highly attractive route for large-scale manufacturing.
What is the thermal stability of the MS3-synthesized Cr2AlB2, and does it retain its EMW absorption properties at elevated temperatures?
The research text indicates that Cr2AlB2 maintains its absorption properties up to 1000°C, as reported in prior studies. The MS3-synthesized material is expected to exhibit similar thermal stability due to its inherent oxidation resistance and phase stability. However, specific high-temperature tests for the MS3 product are not detailed in the provided text, warranting further investigation.
What are the key microstructural features of MS3-synthesized Cr2AlB2 that contribute to its EMW absorption performance?
The layered structure of Cr2AlB2 provides high specific surface area and multiple interfaces, which enhance interfacial polarization and multiple scattering of EM waves. The presence of defects and grain boundaries can also contribute to dielectric loss. The MS3 method may influence grain size and morphology, potentially optimizing these features. However, detailed microstructural analysis is not included in the provided text.
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