In aerospace, advanced equipment, and extreme-protection applications, lightweight construction, thermal insulation, high-temperature resistance, and electromagnetic compatibility have become essential material requirements.

Traditional insulation materials often suffer from serious limitations. They may crack at high temperatures, exhibit relatively high thermal conductivity, offer insufficient ablation resistance, or provide only a single function. As a result, they struggle to meet the demands of increasingly complex service environments.

As a new generation of lightweight porous functional materials, ceramic aerogels have overcome many of these limitations through their ultralow thermal conductivity, extremely high specific surface area, and precisely tunable pore structures. They are becoming key materials for extreme thermal protection and electromagnetic stealth applications.

The development of polysilazane polymer-derived ceramics has introduced a new molecular-design approach to ceramic aerogel development. Instead of relying solely on conventional formulation or filler modification, researchers can regulate performance at the molecular-chain, crosslinking, and microstructure levels, enabling coordinated improvements in thermal insulation, high-temperature resistance, mechanical strength, and electromagnetic absorption.

1. Molecular Engineering for Lower Thermal Conductivity

Earlier ceramic aerogel research focused mainly on macroscopic formulation adjustments and composite fillers, resulting in limited performance gains. Polysilazane precursors offer a different approach: molecular engineering can be used to precisely modify linear, branched, and curled chain structures, enabling the pore network to be redesigned from the source and reducing heat-transfer efficiency.

Research by Wang and colleagues demonstrated that molecular structure directly influences the thermal-insulation limit. By changing the structure of the polysilazane precursor, the researchers converted linear molecular structures into branched structures.

As the proportion of branched molecules increased, the internal pore structure evolved from large pores toward a more uniform mesoporous network. Large pores intensify convective heat transfer and increase thermal losses, while dense and evenly distributed mesopores effectively interrupt gas-phase heat-transfer pathways and suppress thermal diffusion.

Through molecular-structure optimization, the resulting SiCN(O) ceramic aerogel achieved a minimum thermal conductivity of only 0.046 W/(m·K).

The research team also adjusted the solvent ratio to 95 wt%, further optimizing the pore structure. The material achieved a specific surface area of 255.9 m²/g and a pore volume of 0.36 cm³/g. Higher porosity and more uniform pore channels delivered a second improvement in thermal-insulation performance and provided a practical route for designing low-conductivity ceramic aerogels.

2. Curled Molecular Chains for High-Temperature Stability

Volume shrinkage and structural collapse at high temperatures have long been major challenges in the commercialization of ceramic aerogels. During pyrolysis, molecular-chain breakage and framework collapse can destroy the pore structure and cause thermal-insulation performance to deteriorate.

To address this problem, Zheng and colleagues proposed a strain-energy-storage strategy based on curled molecular chains.

Using polysilazane as the precursor, the researchers synthesized precursor microspheres with curled molecular chains through a solvothermal process. These microspheres were then grafted and crosslinked to produce a new type of precursor-microsphere aerogel.

The key innovation is that the curled molecular chains store structural strain during synthesis. When exposed to high-temperature pyrolysis, the stored strain is released to offset the volume shrinkage caused by ceramic conversion. At the same time, the three-dimensional support provided by the microsphere skeleton and the interconnected channels for gas release further improve structural stability at elevated temperatures.

The performance results confirmed these advantages. After pyrolysis, the aerogel retained its porous framework and achieved a thermal conductivity of only 0.0463 W/(m·K). During a 1,300°C butane-torch ablation test, the temperature on the rear surface was only 120.5°C, demonstrating outstanding insulation under extreme heat.

The researchers further adjusted the water content in the mixed solvent to increase the degree of polysilazane-chain curling while improving ceramic yield and shrinkage resistance. The optimized SiCN microsphere aerogel achieved a linear shrinkage of only 13.7% after sintering at 1,200°C, with a density of 0.091 g/cm³. Its minimum thermal conductivity reached 0.0357 W·m⁻¹·K⁻¹, setting a new benchmark for similar materials.

Molecular-dynamics simulations and finite-element analysis were also used to clarify how curled molecular chains influence thermal insulation and mechanical performance, establishing a theoretical foundation for designing high-performance, high-stability ceramic aerogels.

3. Composite Modification for Strength and Ablation Resistance

Pure ceramic aerogels are often brittle and mechanically weak. They may also be damaged under extreme flames, making them unsuitable for high-speed applications and high-heat-flux environments.

To balance insulation, structural stability, and ablation resistance, You and colleagues developed a polysilazane-modified phenolic-resin/carbon-fiber composite aerogel using ambient-pressure drying.

The polysilazane modification produced a uniform and stable nanoporous matrix while significantly improving thermal stability. The composite maintained a thermal conductivity of approximately 0.126 W/(m·K).

Its ablation resistance was particularly notable. Under oxyacetylene-flame tests with different heat-flux levels, the linear ablation rates were as low as 0.112 mm/s and 0.018 mm/s.

During ablation, polysilazane converts in situ into dense SiC and Si₃N₄ ceramic protective layers. These layers tightly cover the carbon-fiber skeleton, isolating it from high-temperature flames and oxidizing gases. This mechanism significantly improves resistance to erosion and ablation, making the composite suitable for thermal-end protection in aerospace engines and high-speed vehicles.

Liu and colleagues developed another solution using eccentric coaxial electrospinning and precursor conversion. The resulting ordered aerogel featured a polysilazane shell, a Nomex core, and carbon-nanotube reinforcement.

Its ordered hierarchical structure combined flexibility with high-temperature resistance. The material achieved a thermal conductivity as low as 0.0349 W/(m·K) and maintained structural integrity and stable performance through repeated compression cycles at high and low temperatures. This approach addresses the brittleness, cracking, and poor stability associated with conventional ceramic aerogels and offers a solution for long-term thermal protection under fluctuating temperatures.

4. Integrated Thermal Insulation and Electromagnetic Absorption

As advanced equipment becomes lighter, more integrated, and increasingly focused on stealth performance, thermal insulation alone is no longer sufficient. Integrated thermal protection and electromagnetic stealth are becoming important material requirements.

Polysilazane-derived ceramic aerogels support multifunctional integration through their adjustable carbon content and dielectric properties.

Using a combined sol-gel, freeze-drying, and precursor-conversion process, You and colleagues prepared a high-performance SiCN ceramic aerogel for electromagnetic absorption. By precisely adjusting the C=C/Si-H molar ratio, the researchers controlled the carbon content and microstructure, thereby regulating the dielectric parameters and electromagnetic-loss capability.

When the molar ratio reached 1.25:1, the material achieved its best absorption performance. The minimum reflection loss reached −37.57 dB at 10.88 GHz, while the effective absorption bandwidth covered the entire X-band. This performance is suitable for electromagnetic-stealth and electromagnetic-shielding applications in defense equipment.

Wang and colleagues further expanded the material system through vinyl-addition and crosslinking reactions between polysilazane and phenolic resin. A multilevel porous PRVS aerogel was prepared and subsequently converted into a SiOCN quaternary ceramic aerogel through high-temperature pyrolysis.

By simply adjusting the pyrolysis temperature, researchers could regulate the material's phase composition, pore structure, and dielectric properties. This enabled independent control of thermal-insulation and electromagnetic-absorption performance in one material, reducing structural weight and development costs for advanced equipment.

5. Polysilazane as a Driver of Ceramic Aerogel Innovation

The overall research shows that polysilazane-derived ceramic technology is changing the development logic of ceramic aerogels.

The focus has shifted from conventional macroscopic filler modification to precise molecular-structure design. Through branched-chain regulation, curled-chain strain storage, multiphase composites, and multilevel pore construction, researchers are addressing five major industry challenges: excessive thermal conductivity, high-temperature shrinkage, brittleness, weak ablation resistance, and limited functionality.

Current material systems have achieved several key performance advantages:

• Ultralow thermal conductivity: as low as 0.0349 W/(m·K)

• Excellent high-temperature stability: extreme thermal insulation at 1,300°C with low shrinkage

• Strong ablation resistance: suitable for high-heat-flux flame and erosion environments

• Multifunctional integration: combined thermal protection and broadband electromagnetic absorption

• Lightweight and durable construction: low density, cyclic-fatigue resistance, and structural stability

With continued advances in molecular design and composite-processing technologies, polysilazane-based ceramic aerogels are expected to play an increasingly important role in aerospace thermal protection, stealth systems for advanced equipment, insulation under extreme conditions, and precision-instrument protection.

They are emerging as a core material platform for the next generation of multifunctional, lightweight protection systems.

This article was adapted from content published by the WeChat public account “Liquid Ceramic Precursors.” Please contact us if any reproduced material affects intellectual property rights or other lawful interests.