Core Conclusions
Fumed silica (silicon dioxide, SiO₂) exhibits excellent high-temperature resistance. Its thermal stability is primarily determined by three factors: preparation method, surface chemical state, and composite structure. Fumed silica prepared by the gas-phase method, due to its high purity (>99.8%), small particle size (8–19 nm), and absence of crystalline water, can withstand temperatures up to 1000°C for long-term use.  Precipitated silica, however, contains crystalline water (SiO₂·nH₂O) and impurities, resulting in significantly lower heat resistance compared to gas-phase fumed silica. Above 800°C, pure fumed silica materials are prone to volume shrinkage and structural deformation, but its high-temperature stability can be significantly improved through surface silanization modification or compounding with alumina.

Key Parameters of High-Temperature Resistance
Performance Indicator | Gas-Phase Fumed Silica | Precipitated Silica | Description
Chemical Composition | Anhydrous SiO₂ | Hydrated SiO₂·nH₂O | Crystalline water is removed at >200°C, leading to structural degradation
Purity | >99.8% | 87%–95% | Higher purity leads to stronger thermal stability
Average Particle Size | 8–19 nm | 11–100 nm | Nanoscale structure increases specific surface area and thermal resistance
Thermal Decomposition Temperature | 400–1000°C | 250–900°C | At high temperatures, mainly surface hydroxyl dehydration and structural densification occur
Long-Term Use Limit | ≤1000°C | ≤800°C | A safety margin is recommended in practical applications
Note: 1000°C is the theoretical limit for maintaining the structural integrity of the material; in industrial applications, it is usually controlled below 800°C to ensure long-term reliability.

High-Temperature Stability Mechanism
Structural Stability: Fumed silica is amorphous silicon dioxide, without grain boundaries, and is not prone to phase transitions at high temperatures. Its nanoscale chain-like aggregates can effectively suppress thermal expansion. Antioxidant properties: The surface is rich in silanol groups (Si–OH), which can adsorb and stabilize oxygen molecules, slowing down the oxidative aging of the organic matrix.
Low thermal conductivity: The porous structure hinders heat conduction, making it an excellent high-temperature thermal insulation filler.
Cutting-edge modification technologies to improve high-temperature performance:
1. Surface silanization modification
Through the condensation reaction between silane coupling agents (such as KH-560, KH-570) and the hydroxyl groups on the surface of fumed silica, Si–O–Si–R organosilicon bonds are formed, achieving:

Reduced surface energy, improving dispersibility in polymers;
Shielding of active hydroxyl groups, reducing structural collapse caused by dehydration at high temperatures;
Enhanced interfacial bonding force, improving the mechanical and thermal stability of composite materials.
Detection methods: The enhancement of the Si–O–Si peak (1000–1100 cm⁻¹) in infrared spectroscopy (IR), the shift of the Si 2p peak in XPS, and the increase in contact angle (improved hydrophobicity) can verify the success of the modification.

2. Ceramic composite material reinforcement
Compositing fumed silica with fumed alumina (Al₂O₃) can significantly inhibit high-temperature volume shrinkage:

At 1000°C, the volume shrinkage rate of pure fumed silica composite material reaches 10.49%;
After adding 5 wt% fumed alumina, the shrinkage rate drops to 3.47%, and the thermal insulation performance remains stable.
The high melting point (2050°C) and low thermal expansion coefficient of alumina form a "skeleton support," effectively stabilizing the silica network structure. Applications and High-Temperature Performance
Application Area | High-Temperature Mechanism | Actual Performance
High-Performance Tires | High specific surface area enhances rubber cross-linking, reducing rolling heat generation | Tire temperature ≤ 150°C under high-speed driving, no softening or deformation
Electronic Packaging Materials | Low thermal conductivity + high insulation, buffering thermal stress | Used in IC packaging, withstands reflow soldering peak temperature (260°C)
High-Temperature Coatings/Coatings | Forms a dense SiO₂ network, blocking oxygen diffusion | Used in engine components, withstands continuous operation at 600–800°C
Thermal Insulation Composites | Porous structure reduces heat conduction | After compounding with gas-phase alumina, thermal conductivity < 0.05 W/(m·K) @ 800°C
High-Temperature Catalyst Support | High specific surface area provides active sites | Maintains structural stability at 800°C, catalytic efficiency decay < 10%
Current Research Challenges and Limitations
High-Temperature Shrinkage Problem: Pure fumed silica undergoes irreversible densification at >800°C, leading to volume shrinkage and cracking, limiting its independent use in ultra-high temperature environments (>900°C).
Dispersion Bottleneck: Nanoparticles are prone to agglomeration, affecting the uniformity of composite materials, requiring surface modification or ultrasonic dispersion processes.
Cost Constraints: The preparation of fumed silica by the gas-phase method is energy-intensive (>1000°C flame reaction), and its price is 3–5 times that of the precipitation method, limiting large-scale applications.
Lack of Standardized Testing: The definition of "high-temperature resistance" varies in different studies (weight loss rate, modulus retention rate, deformation threshold), lacking a unified evaluation system.
Frontier Research Directions
Interfacial Heat Transfer Regulation: Reducing the thermal boundary resistance (TBC) between gas-phase silica nanoparticles through surface chemical functionalization to achieve better thermal insulation performance^[2006.12758v3]^.
Multilevel Structure Design: Constructing hollow, core-shell, or hierarchical pore structures to improve thermal stability and mechanical toughness. In-situ characterization techniques: High-temperature in-situ SEM, Raman spectroscopy, and TGA-MS are used to simultaneously monitor structural evolution and gas release behavior.