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Q

XII.What types of aerogels exist today? How silica aerogel differs from other aerogel types.

A

1. Main Types of Aerogels Known Today

(1) Silica Aerogel (SiO?? Aerogel) ?? the Most Mature and Widely Used

路 The world's most common and commercially mature aerogel

路 Based on a Si??O??Si nano-porous structure

路 Applications: building insulation, EV battery thermal protection, industrial insulation, architectural glazing, aerospace

(2) Carbon Aerogel

Includes RF-carbon aerogels, graphene aerogels, CNT aerogels, etc.

Key traits:

路 Excellent electrical conductivity

路 Ultra-low density

路 Used in supercapacitors, energy storage, adsorption materials

(3) Polymer Aerogel

Includes:

路 Polyurethane (PU) aerogel

路 Polyimide (PI) aerogel

路 Epoxy aerogel

Traits:

路 Flexible

路 Better mechanical integrity

路 Thermal resistance typically 200??400掳C

路 Used in aerospace, lightweight insulation, flexible components

(4) Metal Oxide Aerogel

Examples:

路 Alumina (Al??O??) aerogel

路 Zirconia (ZrO??) aerogel

路 Titania (TiO??) aerogel

Traits:

路 High-temperature resistance (up to 1000??1200掳C)

路 Often used in catalysts, aerospace heat shields, extreme-temperature insulation

(5) Biomass / Bio-Based Aerogel

Examples:

路 Cellulose aerogel

路 Alginate aerogel

路 Chitosan aerogel

Traits:

路 Biodegradable, environmentally friendly

路 Used in medical, filtration, adsorption

路 Still mainly semi-industrial or research-stage

2. Differences: Silica Aerogel vs Other Aerogel Types

Below is the version most useful for customer education and sales discussions:

(1) Material Structure & Stability

Aerogel Type	Structure	Stability
Silica Aerogel	Si??O??Si network	Extremely stable, chemically inert
Carbon Aerogel	Carbon framework	Oxidizes above ~400掳C in air
Polymer Aerogel	Organic polymer matrix	Degrades at high temperature
Metal Oxide Aerogel	Metal oxide network	High-temperature stable but heavier

Notably, silica aerogel stands out for its unparalleled long-term structural stability paired with complete chemical inertness??attributes that make it indispensable in harsh environments where material degradation risks are unacceptable.

(2) Performance Differences

Indicator	Silica Aerogel	Other Aerogels
Thermal Conductivity	Lowest (0.013??0.020 W/m路K)	Generally higher
Fire Resistance	A1 non-combustible	Organic aerogels cannot reach A1
Thermal Stability	600掳C (up to 1000掳C in composites)	PI: 300??400掳C; Carbon: 400掳C (air); Oxides: 1000掳C
Weight	Extremely low	Similar or heavier (oxides)
Cost	Best cost??performance ratio	Higher, less scalable

For most industrial and consumer scenarios, silica aerogel delivers the optimal balance of insulation performance, non-combustibility, and cost-effectiveness??addressing the core requirements of safety and efficiency simultaneously.

(3) Commercial Readiness

Aerogel Type	Commercial Maturity
Silica Aerogel	猸?猸?猸?猸?猸? Most mature
Polymer Aerogel	猸?猸?猸?
Carbon Aerogel	猸?猸?
Metal Oxide Aerogel	猸?猸?
Bio-Based Aerogel	猸? (early-stage)

Silica aerogel is the only type already used at global industrial scale.

(4) Application Suitability

Application	Best Aerogel Type	Reason
Building insulation, heritage retrofit, glazing	Silica	Lowest thermal conductivity + non-combustible
EV battery thermal runaway protection	Silica	High-temperature stability + fire safety
Industrial furnaces >1000掳C	Metal oxide	Extreme heat resistance
Supercapacitors, energy storage	Carbon aerogel	Conductive, high surface area
Aerospace insulation	PI/oxide aerogel	High strength + heat resistance
Biomedicine, filtration	Biomass aerogel	Biodegradability

3. Summary: Why Silica Aerogel Is Unique

(1) Best insulation performance

World's lowest thermal conductivity among solids.

(2) Fully non-combustible (A1)

Essential for EV safety, building fire safety, and industrial. applications.

(3) Most commercially scalable

Silica aerogel has a mature, global supply chain.

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Q

XI.Is silicon dioxide (SiO??) aerogel toxic?

A

1. Chemical Composition
Silica aerogel is primarily composed of silicon dioxide (SiO??) ?? the same material found in glass and quartz sand.

It is chemically stable, non-toxic, odorless, and non-corrosive. Its internal structure is a silica??oxygen network that does not react with moisture or release harmful substances.

2. Health and Safety Considerations

Although silica aerogel is non-toxic, it is important to recognize that certain forms or handling conditions may pose minor physical risks:

(1) Dust Inhalation

路 During cutting, crushing, or processing, fine silica dust may be released.

路 These particles are extremely light and small, and long-term inhalation could irritate the respiratory tract ?? similar to silica dust exposure in industrial environments.

路 Protective masks (N95 or higher) and goggles are recommended when handling loose or powdered aerogel.

(2) Skin Irritation

路 Dry silica aerogel has a highly adsorptive surface that can draw moisture from the skin.

路 Prolonged contact may cause dryness, mild itching, or irritation.

路 Use protective gloves and apply moisturizer after handling.

(3) Environmental and Toxicological Safety

路 Silica aerogel is environmentally friendly, non-radioactive, and does not emit toxic gases.

路 It contains no formaldehyde, benzene, or asbestos, and is widely certified under REACH, RoHS, and MSDS standards for safety and sustainability.

3. Summary Table

Aspect	Toxicity	Description
Chemical Composition	?? Non-toxic	Chemically inert SiO?? network
Dust Inhalation	??锔? Risk	Use masks and ventilation when processing
Skin Contact	??锔? Minor irritation	Wear gloves and clean after contact
Environmental Impact	?? Safe	No pollution, recyclable, green material

Conclusion锛?Silica aerogel itself is non-toxic and environmentally safe, but proper protective measures should be taken when handling its powder or dust form. It is widely recognized as a green, sustainable, and high-performance insulation material.

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Q

??What Is the Knudsen Effect? How It Works in Aerogels

A

1. Origin of the Knudsen Effect

The Knudsen Effect is named after Martin Hans Christian Knudsen (1871??1949), a Danish physicist who made pioneering contributions to the study of rare gas dynamics and molecular transport phenomena.In the early 20th century, Knudsen investigated how gas behavior changes when confined in narrow capillaries or pores, where the size of the channels is comparable to the mean free path of gas molecules.Through his experiments between 1909 and 1911, Knudsen discovered that:

路 When the pores or tubes are extremely small, gas molecules collide more frequently with the walls than with each other.

路 This changes gas flow and heat transfer behavior dramatically, deviating from classical continuum (Navier??Stokes) theory.

These discoveries led to two famous phenomena bearing his name:

Phenomenon	Description
Knudsen Flow	Gas flow in micro/nano channels dominated by molecule??wall collisions (free molecular regime)
Knudsen Effect	Suppression of gas-phase thermal conduction when pore size ?? mean free path of gas molecules

Knudsen's findings laid the foundation for modern microfluidics, vacuum technology, and nanoporous material science ?? including aerogels.

2. What Is the Knudsen Effect?

The Knudsen Effect refers to the phenomenon that occurs when the pore size of a material becomes comparable to or smaller than the mean free path of gas molecules.In such a situation, gas molecules collide more frequently with the pore walls than with each other, which significantly reduces the thermal conductivity of the gas phase inside the pores.

路 The mean free path (位) is the average distance a gas molecule travels between two collisions.

o For air at room temperature and atmospheric pressure, 位 ?? 70 nm.

3. Knudsen Number (Kn)

The strength of the Knudsen effect is represented by the Knudsen number, defined as: Kn=位/r ,where:

路位 = mean free path of gas molecules

路 r = pore radius

Depending on the value of Kn, heat transfer behavior changes:

Regime	Kn Range	Dominant Heat Transfer Mechanism
Continuum	Kn<0.01	Molecular collisions dominate (normal gas conduction)
Transition	0.01	Collisions with pore walls start to matter
Free Molecular	Kn>1	Wall collisions dominate; gas thermal conduction drops sharply

4. How It Works in Aerogels

In silica aerogels, the pore sizes are typically 10??100 nm, which are comparable to or smaller than the mean free path of air molecules.
This means ( Kn>1 ), so the system is in the free molecular regime, where the Knudsen effect is very strong. As a result:

路 Gas molecules are trapped in nanopores and mostly collide with the solid silica walls, not with each other.

路 These wall collisions are mostly random reflections, transferring very little energy.

路 Therefore, the gas-phase thermal conductivity is greatly suppressed ?? often 1/10 or less of that of free air.

5. Components of Aerogel Thermal Conductivity

The total thermal conductivity of aerogel (k_total) has three parts: k_total=k_solid+k_gas+k_radiation

路 k_solid: heat conduction through the silica skeleton (very low due to its sparse structure)

路 k_gas: heat conduction through the air in pores (strongly reduced by the Knudsen effect)

路 k_radiation: heat transfer by thermal radiation (significant only at high temperature)

The Knudsen effect mainly reduces (k_gas), which is why aerogels have extremely low total thermal conductivity (typically 0.012??0.018 W/m路K).

6. Summary

Aspect	Description
Definition	Suppression of gas-phase thermal conductivity when pore size??mean free path of gas molecules
Key Parameter	Knudsen number (Kn=位 / r)
In Aerogel	Nanopores cause gas??wall collisions to dominate over gas??gas collisions
Result	Dramatically reduced gas thermal conductivity and ultra-low overall heat transfer

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Q

??Why silica aerogel is so fragile?

A

1. Structural Nature ?? Extremely Porous 3D Network with Ultra-high porosity (>90%)

Silica aerogel typically has a porosity between 90% and 99.8%, meaning:

路 Only 1??10% of its volume is solid material;

路 The rest is air-filled voids.

As a result:

路 The load-bearing cross-sectional area is extremely small;

路 Stress concentrates on the thin silica necks connecting nanoparticles;

路 Once one link breaks, a cascade collapse occurs through the network.

Analogy: It??s like a 3D scaffold made of glass needles ?? extremely light, but very easy to break.

2. Chemical Bond Nature ?? Strong but Brittle Si??O??Si Bonds

The silica skeleton is built from Si??O??Si covalent bonds, which are:

路 Strong (bond energy ?? 450 kJ/mol), but

路 Directional and non-ductile ?? they cannot deform plastically like metallic bonds.

Therefore, when external stress exceeds the critical point, the bonds fracture suddenly instead of yielding.

In other words: Once a Si??O??Si chain is overstressed, it snaps instantly rather than absorbing energy by deformation.

3. Microstructural Fragility ?? Stress Concentration at Nanoscales

路 Primary particle size: 10??50 nm

路 Particles are linked by thin ??neck-like?? bridges

路 Each node has a low coordination number, so load transfer paths are few

When force is applied:

路 Local bonds break first,

路 The network collapses locally,

路 Microcracks propagate into macroscopic fractures.

4. Drying Process Effects ?? Capillary Forces Create Microcracks

During the sol??gel process, the drying stage can introduce residual damage:

路 In non-supercritical drying, capillary pressure can crush the delicate gel network;

路 Even in supercritical drying, minor shrinkage or microcracks may remain;

路 These become stress initiation sites under later mechanical loading.

5. Macroscopic Mechanical Properties ?? Very Low Modulus and Fracture Toughness

Property	Silica Aerogel	Ordinary Glass	Aluminum Alloy
Density (g/cm鲁)	0.003??0.2	2.5	2.7
Young??s Modulus (GPa)	0.001??0.1	70	69
Fracture Toughness (MPa路m鹿??虏)	0.01??0.1	0.75	25??35

These values show: Silica aerogel??s fracture toughness is about 1/10 of glass and 1/1000 of metals,making it almost incapable of resisting bending, compression, or impact.

6. Methods to Improve Toughness

Researchers and manufacturers are developing several strengthening strategies:

(1)Fiber Reinforcement

路 Introduce glass, aramid, or polymer fibers;

路 Create aerogel blankets or composite panels;

路 Greatly improves flexural and compressive strength.

(2)Organic??Inorganic Hybridization

路 Graft flexible polymer chains (e.g., PDMS, PVA, PMMA) onto silica skeletons;

路 Increases elasticity and crack resistance.

(3) Nanostructure Optimization

路 Control particle size, neck thickness, and pore size distribution;

路 Build hierarchical porous networks to enhance energy absorption.

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Q

VIII. Why Does Aerogel Shrink During Drying?

A

1. Core Physics: Capillary Pressure (Laplace Pressure)
路 During drying, liquid??gas interfaces form menisci inside nanopores, exerting negative capillary pressure on the fragile skeleton:

P=2纬cos?∥?P = \frac{2 \gamma \cos \theta}{r}
路纬\gamma: surface tension of solvent
路胃\theta: contact angle (for hydrophilic surfaces, 胃??0??\theta \approx 0^\circ, cos?∥糕??1\cos \theta \approx 1)
路 rr: pore radius (smaller pore ?? higher stress)
路 Magnitude example (hydrophilic case):
o Ethanol: 纬??0.022 N/m,r=10 nm??P??4.4 MPa\gamma \approx 0.022\ \text{N/m}, r=10\ \text{nm} \Rightarrow P \approx 4.4\ \text{MPa}
o Water: 纬??0.072 N/m,r=10 nm??P??14.4 MPa\gamma \approx 0.072\ \text{N/m}, r=10\ \text{nm} \Rightarrow P \approx 14.4\ \text{MPa}

Such stress is far above the yield strength of the ??wet?? silica skeleton, leading to elastic??plastic deformation, pore collapse, shrinkage, densification, or even cracking.

2. Structural & Chemical Factors
路 Smaller pores / narrow distribution ?? stronger capillary stress.
路 Insufficient neck growth (weak skeleton) due to poor aging ?? prone to irreversible plastic shrinkage.
路 Surface state: hydrophilic Si??OH surfaces (low 胃\theta) ?? high stress; hydrophobic surfaces (high 胃\theta) reduce stress.
路 Solvent: high 纬\gamma (e.g., water) increases stress.
路 Sample geometry: thick monoliths develop drying gradients ?? cracks; thin films/felts are less prone.
路 Pre-shrinkage (syneresis) during gelation/aging can set the stage for further collapse.

Summary: Shrinkage mainly comes from capillary pressure; small pores, hydrophilic surfaces, high-纬\gamma solvents, weak skeletons, and thick parts all worsen it.

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Q

VII. How is the pore structure of aerogel formed? If we use 3D printing to create a similar porous structure, is it also considered an aerogel?

A

1. How is the pore structure of aerogel formed?

Aerogels are typically produced using the sol??gel process, and their pore structure develops through three main steps:

(1)Sol Formation

a. A precursor (e.g., tetraethyl orthosilicate, TEOS) undergoes hydrolysis and condensation reactions in solution.

b. This generates a large number of uniformly dispersed silica nanoparticles.

(2) Gelation

a. As condensation continues, these nanoparticles connect via chemical or hydrogen bonds, forming a 3D interconnected network.

b. The pores are still filled with solvent (alcohols or water) ?? this is called a "wet gel."

(3) Drying

a. The critical step is to remove the solvent without collapsing the fragile network.

b. Simple evaporation causes capillary forces and collapse.

c. Therefore, supercritical drying or surface modification + controlled drying is used to replace liquid with gas while retaining the network.

d. The result is a solid with a nanostructured porous network (pore size ~10??100 nm, porosity 80??99%).

In summary: the aerogel's pore structure is formed by a nanoparticle network from sol??gel chemistry, preserved by a special drying process.

2. If we use 3D printing to create a similar porous structure, is it also an aerogel?

Strictly speaking, no.

(1) Essential difference

a. Aerogel pores are naturally self-assembled at the nanoscale via chemical reactions.

b. Most 3D printing technologies today can only fabricate pores at the microscale or larger, not true nanostructures.

c. The printed object would be a porous scaffold, but not classified as an aerogel.

(2) Definition issue

a. The widely accepted definition of aerogel is: a material derived from a sol??gel process, dried to preserve its nanostructured porous network.

b. If a material does not come from this process, even if it looks similar, it usually isn't considered an aerogel.

3. Interesting frontier

路 If future 3D printing technologies can build structures with nanoscale precision, high porosity, and ultralow density, then we might achieve ??aerogel-like?? materials.

路 Some researchers are already combining 3D printing inks with sol??gel precursors to print wet gels and then dry them into true 3D-printed aerogels.

Conclusion

路 Aerogel pore structures are formed by sol??gel chemistry + special drying methods.

路 Simply 3D printing a porous structure ?? aerogel; it would be called a porous material.

路 But if 3D printing is combined with sol??gel methods, then 3D-printed aerogels are possible.

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Aerogel Forum

XII.What types of aerogels exist today? How silica aerogel differs from other aerogel types.

XI.Is silicon dioxide (SiO??) aerogel toxic?

??What Is the Knudsen Effect? How It Works in Aerogels

??Why silica aerogel is so fragile?

VIII. Why Does Aerogel Shrink During Drying?

VII. How is the pore structure of aerogel formed? If we use 3D printing to create a similar porous structure, is it also considered an aerogel?

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Aerogel Forum

XII.What types of aerogels exist today? How silica aerogel differs from other aerogel types.

XI.Is silicon dioxide (SiO??) aerogel toxic?

??What Is the Knudsen Effect? How It Works in Aerogels

??Why silica aerogel is so fragile?

VIII. Why Does Aerogel Shrink During Drying?

VII. How is the pore structure of aerogel formed? If we use 3D printing to create a similar porous structure, is it also considered an aerogel?

This website uses cookies

Product Consultation

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