Neo Materials / Materials / Aerogel
NANOPOROUS · SiO₂ · 2–50 nm PORE SIZE

Silica
Aerogel

99.8% air. Lighter than air per volume of network. R-value 39 per inch — ten times better than fibreglass. The best solid thermal insulator known. Used on Mars. Holds a brick. Blowtorch one side, touch the other.

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~1kg/m³Bulk Density
0.015W/m·KThermal Conductivity
99.8%Porosity
39R/inchInsulation R-Value
Interactive Laboratory · 10 Phenomena

INSIDE THE FROZEN SMOKE

3D SILICA NETWORK — FRACTAL PORE ARCHITECTURE · BET SURFACE 800 m²/g PORE SIZE 2–50 nm Knudsen regime Mean free path λ_air > pore size BET surface area: 500–1000 m²/g · Particle size: 2–5 nm SiO₂ clusters Si-O-Si bond angle: 144° · Network fractal dimension D_f ≈ 2.4 (SAXS)

FRACTAL SILICA NANOSTRUCTURE — PORES IN THE KNUDSEN REGIME

Aerogel consists of a 3D percolating network of 2–5 nm SiO₂ particles with pores of 2–50 nm diameter. BET surface area 500–1000 m²/g. Crucially, pore size < mean free path of air molecules (λ_air = 70 nm at atmospheric pressure) — this puts heat conduction into the Knudsen regime where gas thermal conductivity → 0. Network fractal dimension D_f ≈ 2.4 measured by SAXS. Si-O-Si bond angle 144° with Si-O length 1.62 Å creates a 3D open framework. Porosity P = 1 - ρ_aerogel/ρ_silica = 1 - 0.1/2.2 = 95–99.8%.

THREE HEAT TRANSFER MECHANISMS — ALL SUPPRESSED BY AEROGEL AEROGEL κ = 0.015 W/m·K 400°C 25°C ① SOLID CONDUCTION torturous path ② GAS CONVECTION Knudsen suppressed IR scattered Aerogel: κ=0.015 W/m·K vs Air: κ=0.025 W/m·K Fiberglass: κ=0.04 · Rock wool: κ=0.04 · EPS foam: κ=0.035

TRIPLE SUPPRESSION OF HEAT TRANSFER — κ = 0.015 W/m·K

Aerogel defeats all three heat transfer modes: (1) Solid conduction: SiO₂ network is tortuous with tiny contact areas — effective solid path is 1000× longer than direct path. (2) Gas convection/conduction: Knudsen effect — pore size (20 nm) < air mean free path (70 nm) → gas molecules hit walls before each other → gas κ → 0. Knudsen number Kn = λ/d > 1. (3) Radiation: SiO₂ nanoparticles scatter IR at λ = 3–8 µm. Net thermal conductivity κ = 0.015 W/m·K — 40% less than still air. R-39 per inch = 10× fiberglass.

SUPERCRITICAL CO₂ DRYING — WHY NORMAL DRYING COLLAPSES THE PORES NORMAL DRYING → COLLAPSE P_cap = 2γ/r = 300 MPa XEROGEL (collapsed) SUPERCRITICAL CO₂ → INTACT AEROGEL CO₂ PHASE DIAGRAM TEMPERATURE → PRESSURE CP: 31.1°C 73.8 bar SCCO₂ → drying path (no gas-liq interface) AEROGEL — pores intact, 99.8% void fraction Capillary pressure Pc = 2γcosθ/r: at r=5nm, Pc=300 MPa — destroys network. SCCO₂ eliminates meniscus entirely.

SUPERCRITICAL DRYING — BYPASSING THE LIQUID-GAS INTERFACE

Normal drying creates liquid-gas meniscus at pore openings: capillary pressure P_c = 2γ/r = 2×0.073/5×10⁻⁹ = 29 MPa — enough to collapse the silica network (Young's modulus ~20 MPa). Solution: supercritical CO₂ drying. Solvent exchanged to CO₂; temperature raised above T_c = 31.1°C at P > 73.8 bar. CO₂ transitions directly from supercritical → gas by depressurization at constant temperature. No liquid-gas interface ever forms. No capillary pressure. Pores remain intact. Yield: transparent or translucent aerogel monolith up to 1 m² panels.

SOUND SPEED IN AEROGEL: 100 m/s (vs 343 m/s AIR) AIR — 343 m/s AEROGEL AEROGEL — 100 m/s ACOUSTIC IMPEDANCE: Z = ρ·c Aerogel: Z = 100 kg/m³ × 100 m/s = 10 kPa·s/m (vs air: 415 Pa·s/m) Transmission loss TL = 20 log₁₀[(Z₁+Z₂)²/(4Z₁Z₂)] ≈ 15 dB/cm Applications: acoustic tiles, sonar dampening, ultrasonic transducer coupling

ACOUSTIC PROPERTIES — SOUND SPEED 100 m/s, EXTREME IMPEDANCE MISMATCH

Aerogel sound speed c = √(E/ρ) = √(0.2×10⁶/1) ≈ 100 m/s — lowest of any solid (normal glass: 5640 m/s). Acoustic impedance Z = ρ·c = 100 Pa·s/m vs air (415 Pa·s/m) — close impedance match to air enables coupling. Aerogel between two media creates strong reflection due to huge Z-mismatch with solids. Transmission Loss TL = 20 log₁₀[(Z_a+Z_b)²/4Z_aZ_b]. Sound attenuation 15 dB/cm. Applications: LIDAR coupling layers (Z-match to air), submarine sonar tiles, anechoic chambers, and ultrasonic NDT coupling.

RAYLEIGH SCATTERING — WHY AEROGEL LOOKS BLUE (I ∝ λ⁻⁴) WHITE LIGHT BLUE scattered (450nm) RED transmitted (700nm) I_scattered ∝ λ⁻⁴ (Rayleigh regime: particle size << λ) Blue (450nm): I = 1 · Red (700nm): I = (450/700)⁴ = 0.17 → blue 6× more scattered Same reason sky is blue. Aerogel scattering coefficient β = 32π⁴a⁶|m²-1|²/3λ⁴V

RAYLEIGH SCATTERING — THE SKY IN A BLOCK OF SOLID

Aerogel's 2–5 nm SiO₂ particles are in the Rayleigh scattering regime (particle size ≪ wavelength). Scattering intensity I ∝ λ⁻⁴ — blue light (450 nm) is scattered (450/700)⁻⁴ = 5.8× more than red. Result: aerogel appears blue when backlit (scattered blue) and orange/red when transmitted (red passes through). Identical physics to sky color — same reason the sky is blue. Scattering coefficient depends on particle size: smaller SiO₂ clusters → cleaner blue. High-purity aerogels approach optical window clarity (85–95% transmittance) for solar collector applications.

TMCS HYDROPHOBIZATION — CONTACT ANGLE 150° (SUPERHYDROPHOBIC) BEFORE: Si-OH (hydrophilic) OH OH OH OH OH Contact angle ~20° (water absorbs in) +TMCS Si(CH₃)₃Cl AFTER: Si-CH₃ (superhydrophobic) CH₃ CH₃ CH₃ CH₃ CH₃ CH₃ Contact angle 150° (superhydrophobic) Water rolls off — no absorption Young equation: cosθ = (γ_SV - γ_SL)/γ_LV → Cassie-Baxter state at θ=150° TMCS reaction: Si-OH + ClSi(CH₃)₃ → Si-O-Si(CH₃)₃ + HCl (complete in 2h at 60°C)

TMCS HYDROPHOBIZATION — REPLACING SILANOL WITH METHYL GROUPS

Native aerogel contains Si-OH (silanol) groups — strongly hydrophilic, absorbs moisture and collapses over time. TMCS (trimethylchlorosilane) replaces Si-OH with Si-O-Si(CH₃)₃: reaction Si-OH + ClSi(CH₃)₃ → Si-O-Si(CH₃)₃ + HCl at 60°C in hexane or supercritical CO₂. Methyl groups (-CH₃) are non-polar, repel water. Contact angle increases from ~20° (hydrophilic) to 150° (superhydrophobic). Young equation: cosθ = (γ_SV-γ_SL)/γ_LV. Water droplets bead and roll off. Hydrophobic aerogel stable at 95% humidity for years. Essential for building insulation applications.

MECHANICAL BEHAVIOUR — BRITTLE IN TENSION, ELASTIC IN COMPRESSION COMPRESSION TEST RECOVERY STRESS-STRAIN (COMPRESSION) STRAIN ε (0 → 80%) STRESS σ (MPa) elastic plateau densification ~70% Compressive modulus E ≈ 1–10 MPa · Spring-back from 80% compression · Tensile strength <0.1 MPa

SPRING-BACK COMPRESSION — 80% STRAIN RECOVERY

Aerogel has unique mechanical duality: brittle in tension (σ_tensile < 0.1 MPa), yet remarkably elastic in compression due to the hierarchical network. Stress-strain shows three regimes: (1) Linear elastic (E ≈ 1–10 MPa), (2) Plateau — network buckles and collapses progressively (σ_y ≈ 0.01–0.1 MPa), (3) Densification at 70–80% strain. Polymer-reinforced aerogels (crosslinked with diisocyanate) increase tensile strength to 1.2 MPa and flexural strength 0.8 MPa while maintaining 95% porosity. Compressive spring-back makes aerogel blankets self-seating against rough surfaces.

MARS INSIGHT LANDER — AEROGEL THERMAL BARRIER · -80°C OUTSIDE, +20°C INSIDE MARS -80°C AEROGEL 2.5 cm -80°C +20°C LANDER ELECTRONICS +20°C MAINTAINED THERMAL CALC: Q = κ·A·ΔT/d κ = 0.015 W/m·K ΔT = 100°C d = 0.025 m Q = 60 W/m² Fiberglass equiv.: needs 18 cm for same CO₂ atm 6 mbar Also: Stardust mission (comet particle capture) · Hubble cryocooler · Spacesuit insulation

NASA MARS INSIGHT — AEROGEL KEEPS ELECTRONICS ALIVE ON MARS

Mars surface temperature cycles -80°C to +20°C. InSight lander electronics must stay near +20°C. 2.5 cm aerogel blanket (κ = 0.015 W/m·K) limits heat loss to Q = κ·A·ΔT/d = 60 W/m² — manageable by RTG heater. Alternative fiberglass would need 18 cm (4× heavier, 7× volume). Aerogel mass advantage: 2 kg/m² vs 14 kg/m² fiberglass for same insulation. Stardust mission (1999): aerogel tiles captured Comet Wild 2 particles at 6 km/s by gentle deceleration through 10 cm thick aerogel. Track lengths in aerogel = direct measure of impact energy.

FIRE BARRIER — SiO₂ STABLE TO 1600°C · BLOWTORCH ONE SIDE, TOUCH THE OTHER 1200°C FLAME AEROGEL 3cm 1200°C 47°C 47°C — touchable 1200°C hot face 47°C cold face SiO₂ m.p. = 1600°C No organic binders needed Fire resistance: ASTM E-119 rated · 3cm aerogel ≡ 18cm fiberglass in fire barrier performance

INORGANIC FIRE BARRIER — SiO₂ STABLE TO 1600°C

Pure silica aerogel is non-combustible (ASTM E136). SiO₂ melting point 1600°C. No organic binders in pure silica — no fuel source. 3 cm aerogel sustains 1200°C flame on hot face while cold face reaches only 47°C — fully touchable. Fire barrier mechanism: extremely low thermal conductivity (κ = 0.015 W/m·K) and high specific heat (750 J/kg·K) limit heat flux. Fire resistance class: ASTM E-119, 2-hour fire wall performance in 25 mm thickness (vs 150 mm drywall). Applications: cryogenic pipe insulation, LNG tanker insulation, building fire walls, battery thermal runaway protection.

SOL-GEL SYNTHESIS: TEOS + H₂O + NH₃ → GEL → SUPERCRITICAL DRYING → AEROGEL STEP 1: TEOS Si(OC₂H₅)₄ + H₂O + NH₃ Hydrolysis: Si-OR + H₂O → Si-OH STEP 2: SOL Si-OH + Si-OH → Si-O-Si + H₂O Condensation colloidal particles 2-5nm STEP 3: GEL Particles cluster Network percolates Gelation point: η→∞ Pores filled with solvent STEP 4: AEROGEL SCCO₂ drying Solvent removed Pores preserved ρ ~ 1 kg/m³ LIVE: SOL → GEL TRANSITION (condensation)

SOL-GEL CHEMISTRY — FOUR STAGES TO FROZEN SMOKE

TEOS (Si(OC₂H₅)₄) + H₂O + base catalyst (NH₄OH): (1) Hydrolysis: Si-OR + H₂O → Si-OH + ROH, rate ∝ [H⁺] or [OH⁻]. (2) Condensation: Si-OH + Si-OH → Si-O-Si + H₂O; oligomers form 2–5 nm particles (Sol). (3) Gelation: fractal clusters grow until network percolates (gel point: viscosity → ∞). (4) Supercritical drying: solvent replaced with CO₂, depressurized above Tc = 31°C, Pc = 73.8 bar. Total time: 3–7 days for monolith. Continuous manufacturing: ambient pressure drying (with TMCS) = 1–2 days for granular aerogel.

Key Properties

AEROGEL — REWRITING THE LIMITS OF INSULATION

Thermal

  • κ = 0.015 W/m·K
  • R-value 39 per inch
  • Fire stable to 1600°C
  • 10× better than fiberglass

Physical

  • Density ~1–200 kg/m³
  • 99.8% porosity
  • BET surface 800 m²/g
  • Pore size 2–50 nm

Surface

  • Contact angle 150°
  • Superhydrophobic (TMCS)
  • Optically translucent
  • Sound speed 100 m/s

NEED AEROGEL INSULATION?

We supply aerogel blankets, granules, and custom monoliths. Hydrophobic or hydrophilic. Fire-rated for building applications. Space-qualified for cryogenic systems.

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