Research progress of aerogel thermal insulation materials

**Advanced Thermal Protection Systems for Hypersonic Vehicles: Aerogel Composites and Stitched Structural Solutions**

**Abstract**

Hypersonic vehicles operating at speeds exceeding Mach 5 face significant aerodynamic heating challenges, necessitating lightweight thermal protection systems (TPS) that account for approximately 20% of total vehicle mass. This paper examines recent advancements in oxide aerogel composites and stitched structural materials for integrated thermal protection, addressing both insulation performance and mechanical stability requirements.

**1. Oxide Aerogel Insulation Materials**

**1.1 Fundamental Characteristics**

Inorganic oxide aerogels (SiO₂, Al₂O₃, ZrO₂) have emerged as superior insulation materials due to their nanoporous architecture (<100 nm pore size), ultralow density (0.01-0.33 g/cm³), and exceptional thermal resistance (0.021-0.081 W/m·K). These materials demonstrate synergistic enhancements when combined with fibrous reinforcements, overcoming inherent brittleness while maintaining thermal stability up to 1,400°C.

**1.2 Material Innovations**

- **Silica-Based Composites**:

Recent developments employ cellulose fibers (354.9 m²/g surface area), mullite felts (88.5% elastic recovery), and ZrO₂ fibers (0.82 MPa compressive strength) to enhance mechanical properties. Ambient pressure drying techniques using MTMS precursors achieve 0.037 W/m·K conductivity, comparable to supercritical drying outputs.

- **Alumina Systems**:

SiO₂-Al₂O₃ hybrids exhibit improved infrared shielding, with mullite-fiber composites demonstrating 0.065 W/m·K at 1,100°C. Fly ash-derived composites maintain amorphous structure after 900°C/2h treatment, suggesting cost-effective production routes.

- **Zirconia Advancements**:

PAZ precursor-derived ZrO₂ aerogels show enhanced network stability, while SiO₂-modified versions achieve record-low 0.021 W/m·K conductivity. Fiber-reinforced composites maintain 0.063 W/m·K at 1,200°C, with zirconia foam ceramics showing 0.712 W/m·K at 1,000°C.

**2. Stitched Composite Structures**

The integration of through-thickness stitching (carbon/glass/aramid fibers) addresses delamination issues in conventional laminates:

- 8× improvement in tensile strength (vs. unstitched CFRSA)

- 3.3× enhancement in shear resistance

- Maintained structural integrity at 1,600°C with 80°C cold-face temperatures

- Optimized needle spacing (5×15 mm) and 23mm felt thickness achieve optimal thermal performance

**3. Challenges and Future Directions**

Key development areas include:

1) **Temperature Resilience**: Extending operational limits beyond current 1,400°C thresholds through nanoscale architecture engineering

2) **Manufacturing Optimization**: Transitioning from supercritical to ambient drying processes without compromising porosity

3) **System Integration**: Addressing thermal expansion mismatch in multilayer assemblies via parametric stitching studies

4) **Cost Reduction**: Scaling production using industrial waste streams (e.g., fly ash) and automated stitching technologies

**Conclusion**

The synergistic combination of fiber-reinforced oxide aerogels with 3D stitching architectures presents a viable pathway for next-generation TPS. These materials simultaneously achieve ultralow conductivity (0.021-0.712 W/m·K across 25-1,600°C), mechanical robustness (0.36-0.82 MPa compressive strength), and mass efficiency (0.01-0.6 g/cm³), meeting critical demands for aerospace, personal protective equipment, and architectural applications.