3D-Printed SiC Aerogel Functional Materials

Abstract

With the rapid advancement of electronic and communication technologies, the demand for materials possessing thermal management ability and electromagnetic microwave absorption (EMA) capability has surged significantly in high-end industrial applications. Aerogels, as nanostructured porous solid materials with high porosity, low density, excellent compressive strength, tunable thermal insulation properties, and electromagnetic wave absorption capabilities, have emerged as a research focus in the fields of mechanics, thermodynamics, electronics, optics, and acoustics in recent years. However, traditional aerogels face challenges such as high production costs, insufficient mechanical strength, a lack of adequate multi-functional uses, and limitations in processing technologies, which hinder their widespread application. To address these issues, the presence of aerogel composites brings forward a suitable solution. By introducing specific ceramic reinforcement phases purposefully, the mechanical and functional properties of the material can be enhanced, while advanced manufacturing techniques can be employed to allow the composite to work effectively in complex and extreme environments.

In this work, two types of SiC-based aerogel composites with remarkable integrated performance were produced by employing a 3D printing method: direct ink writing (DIW), alongside a two-step heat treatment approach. On one hand, additive manufacturing methods make near-net shaping of complex geometries possible. The fabricated multi-scale hierarchical structures enhance the functional performance of the material. At the microscopic level, in-situ formation of core-shell structured SiC nanowires (SiCNWs) occurs; at the macroscopic level, DIW achieves periodic alternation between open and closed spaces at the millimeter scale. On the other hand, the optimization of the printing ink could be realized by introducing ceramic phase. Compared with the original one, which only provides C and Si sources, the addition of mullite helps to construct a stronger support framework while enriching the interface structure. The resulting mullite-reinforced SiC-based aerogel composite (MR-SiC AC) demonstrated significant improvements in compressive strength, thermal insulation, and EMA property compared to the original SiC-based aerogel composite (SiC AC).

In terms of mechanical properties, MR-SiC AC exhibited an excellent Young’s modulus (24.4 MPa) and compressive strength (1.65 MPa), both surpassing traditional aerogels by an order of magnitude. The substantial boost in performance stems from the refined architecture of the supporting framework, the addition of the mullite phase, and the in-situ growth of SiC nanowires. These factors collectively form a high-strength, multi-scale reinforced structure, enabling MR-SiC AC to maintain its lightweight characteristics while possessing load-bearing capability, making it suitable for mechanical support in complex structural applications.

In terms of thermal insulation properties, MR-SiC AC demonstrated an extremely low thermal conductivity (0.021 W·m⁻¹·K⁻¹) and a porosity as high as 90.0%. The low-density structure minimized solid conduction, while the pores formed during sintering guaranteed a high still air layer content, which afforded the sample extraordinary thermal resistance and low density. Additionally, the SiC nanowires, with abundant stacking faults and boundary effects, enhanced phonon scattering, which could significantly reduce the thermal conductivity. At the same time, the high-temperature stability of SiC expands the application scenarios of MR-SiC AC. These factors collectively contributed to making MR-SiC AC an ideal thermal insulation material. Furthermore, it overcame the load-bearing limitations of traditional aerogels, providing new solutions for lightweight thermal management systems.

In terms of EMA properties, MR-SiC AC significantly improved impedance matching through multi-scale hierarchical designs. The material allowed more electromagnetic waves (EMW) to enter and undergo multiple internal reflections, extending propagation paths and time, thus increasing attenuation. The formation of a conductive network through SiC nanowires led to considerable energy attenuation, while interfacial polarization relaxation at the nanowire interfaces further enhanced absorption performance. Results from the experiments indicated that MR-SiC AC demonstrated a reflection loss as low as -69.66 dB and an absorption bandwidth of 1 GHz under room temperature conditions. Additionally, it maintained excellent absorption performance at elevated temperatures (800 °C), demonstrating its potential for using in extreme conditions. Compared to traditional EMA materials, such as ferrites, polymer-based composites and carbon-based materials, MR-SiC AC exhibited superior thermal stability and EMA properties, overcoming the performance degradation issues of conventional absorbers at high temperatures. This makes it a promising material for efficient signal transmission in future communication technologies and smart devices.

In conclusion, this study successfully fabricated MR-SiC AC with outstanding mechanical, thermal management, and EMA properties through 3D printing and subsequent heat treatment. The adopted fabrication method offers high design flexibility and manufacturing freedom, providing a promising pathway for the development of aerogel composites with complex geometries. In the future, further optimization of structural designs and functional exploration is expected to enable the development of multi-functional SiC-based aerogel composites capable of adapting to more complex environments, offering efficient and reliable solutions for aerospace, defense, electronics, and communication technologies.

Date of Award	6 Aug 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Jian LU (Supervisor)