Polyimide foam is used for sound and heat insulation in rail transit carriages.

Polyimide foam is a high-performance, open-cell foam plastic made from polyimide resin. It inherits the outstanding properties of polyimide polymers while also boasting the lightweight and porous characteristics typical of foam materials.

Characteristics of polyimide foam:

1. Exceptional High-Temperature Resistance: Polyimide foam can maintain long-term stability across an extreme temperature range of -269°C to +300°C (and even higher for short periods, such as 400°C), without melting or undergoing significant decomposition. Its glass transition temperature (Tg) and thermal decomposition temperature are significantly higher than those of common foam materials like polyurethane and polystyrene.

Excellent thermal and heat-insulating performance: Featuring an exceptionally low thermal conductivity, it serves as a highly effective thermal and acoustic insulator. Even under extreme temperatures—whether high or low—its insulation properties remain consistently stable.

2. Excellent flame retardancy and low smoke toxicity:

The limiting oxygen index is high—typically above 40%—indicating that combustion in air is highly difficult.

Fire self-extinguishes: It can quickly go out on its own once the ignition source is removed.

Low smoke density: Produces very little smoke when burned.

Low toxicity: The gases produced during combustion have relatively low toxicity.

3. Excellent chemical stability: It exhibits strong resistance to most organic solvents, oils, aviation fuel, hydraulic fluids, acids, alkalis, and more, making it highly resistant to corrosion or swelling.

Low moisture absorption: Exhibits low water uptake, maintaining stable performance even in humid environments, and its insulation properties remain resistant to degradation.

Radiation Resistance: Exhibits good tolerance to radiation types such as ultraviolet light, gamma rays, and electron beams.

Good electrical insulation: Maintains excellent dielectric properties even in high-temperature and high-humidity environments.

Machinability: It can be processed into complex shapes through methods such as cutting, milling, and thermoforming (at a specific temperature).

4. Good mechanical properties:

It exhibits a high specific strength (strength-to-density ratio) in foam materials.

Good toughness and impact resistance (compared to other high-performance foams such as phenolic foam).

Excellent dimensional stability (low thermal expansion coefficient, resistant to shrinkage or deformation at high temperatures).

Applications of polyimide foam:

1. Aerospace field

Airplane:

Thermal/Acoustic Insulation: Thermal and sound insulation layers used for fuselages, bulkheads, ceilings, floors, equipment compartments, and piping systems (air conditioning, hydraulics, fuel lines). Effectively blocks extreme external temperatures (such as low-altitude cold and high engine compartment heat) and reduces noise levels (from engines and airflow).

Fire Barrier: Serving as firewalls, partitions, and sealing materials, it creates fire-resistant barriers around engine compartments, auxiliary power units, and high-temperature pipelines, effectively preventing the spread of flames and toxic smoke.

Lightweight structural filling: Used to fill honeycomb sandwich structures or other cavities, enhancing structural stiffness, damping vibrations, and preventing core collapse—while maintaining a lightweight design (crucial for fuel efficiency).

Electronic device thermal insulation/insulation: Protects critical electronic equipment such as avionics compartments and flight recorders from high temperatures while providing electrical insulation.

Spacecraft (satellites, spacecraft, launch vehicles):

Extreme Temperature Protection: Withstands the frigidly low temperatures of space (deep cryogenic conditions) as well as the intense heat during atmospheric re-entry or in close proximity to engines—temperatures that can briefly exceed 1000°C, thanks to its charred protective layer.

Thermal insulation for cryogenic propellant tanks: Provides highly efficient insulation layers for ultra-low-temperature propellant tanks such as those storing liquid hydrogen, liquid oxygen, and liquid helium, minimizing evaporation losses to the greatest extent.

Payload Protection: Safeguarding sensitive instruments from launch vibrations, extreme temperature fluctuations in space, and radiation effects.

Flame Retardancy and Low Smoke Toxicity: In the confined environment of a spacecraft cabin, the fire safety and low smoke toxicity of materials are critical to life support systems.

2. High-end Industrial and Energy Sectors

High-temperature pipe and equipment insulation: Used for insulating high-temperature reactors, cracking furnaces, steam pipelines, and thermal oil lines in refineries and chemical plants, this insulation can withstand sustained exposure to temperatures exceeding 200°C—or even up to 300°C—far surpassing the performance of conventional insulation materials.

Liquefied Natural Gas Transportation and Storage: Insulation layers for LNG carriers, land-based storage tanks, and tank trucks. These materials maintain exceptional thermal insulation performance, dimensional stability, and mechanical strength even at the ultra-low temperature of -162°C, preventing "cold shrinkage" cracking and ensuring safe transportation.

Semiconductor Manufacturing:

Thermal Insulation for High-Temperature Process Equipment: Thermal insulation components designed for high-temperature semiconductor manufacturing equipment such as CVD, PVD, and diffusion furnaces, capable of withstanding process-induced heat while maintaining cleanliness (low outgassing and excellent chemical corrosion resistance).

Wafer carrier/thermal insulator: Supports the wafer during thermal processing and isolates it from the heat source.

Electricity and Nuclear Power:

High-temperature motor/transformer insulation: Enhances equipment heat resistance and reliability.

Nuclear facilities: Used for insulation and sealing areas requiring radiation resistance, high-temperature tolerance, and fire protection.

3. Rail Transit (Subway, High-Speed Rail, etc.)

Vehicle fireproof, soundproof, and heat-insulating: Applied in the sandwich layers of车厢 wall panels, roof panels, flooring, and equipment compartments, providing excellent:

Fire Safety: Meets railway vehicle fire standards (high LOI, low smoke toxicity, self-extinguishing upon removal from flame).

Soundproofing and noise reduction: Significantly lowers both interior and exterior cabin noise, enhancing ride comfort.

Thermal insulation and heat preservation: Maintain cabin temperature while reducing air conditioning energy consumption.

Cable Channel Fire Sealing: Used for fire-stopping cable conduits that pass through the vehicle body.

4. Specialized Vessels and Vehicles

Warships/Submarines: Fireproof, soundproof, and heat-insulated (with enhanced spatial sealing), as well as corrosion-resistant.

Fire truck: Fire-resistant and heat-insulating layers in high-temperature areas such as the engine compartment and pump compartment, protecting personnel and equipment.

Armored vehicles: Lightweight thermal and sound insulation enhance crew comfort and equipment protection.

Racing/High-Performance Sports Cars: Engine compartment insulation, lightweight components (such as seat padding and interior trim), all aimed at achieving ultimate performance.

5. Special Buildings and Safety Protection

High-fire-rated buildings: Wall and ceiling thermal, acoustic, and fire-resistant insulation layers for spaces with extreme fire protection requirements, such as data center server rooms, archives, museums, laboratories, and the core shafts of high-rise buildings.

Fire door core material: Enhances the fire resistance rating and thermal insulation performance of fire doors.

Safety protective equipment: Liner insulation layers (high-temperature resistant and flame-retardant) used in fire-fighting suits and specialized workwear.

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