Aerogel

INTRODUCTION AEROGEL IS A SYNTHETIC POROUS ULTRALIGHT MATERIAL DERIVED FROM A GEL. IN WHICH THE LIQUID COMPONENT OF THE GEL HAS BEEN REPLACED WITH A GAS. THE RESULT IS A SOLID WITH EXTREMELY LOW DENSITY & THERMAL CONDUCTIVITY.

IT RESEMBLES A HOLOGRAM AND AN EXCELLENT INSULATOR. IT WAS DISCOVERED IN THE LATE 1930S BY CHEMIST SAMUEL STEPHENS KISTLER IN 1931. NICKNAME INCLUDES “ FROZEN SMOKE”, “SOLID SMOKE”, “SOLID AIR” OR “BLUE SMOKE”. ONE FORM OF THIS SUBSTANCE IS ACTUALLY 99.8 PERCENT AIR AND 0.2 PERCENT SILICA DIOXIDE (BY VOLUME). AEROGEL HAVE OPEN-PORE STRUCTURE AND HAVE PORES IN THE RANGE OF (1-100) NANOMETERS IN DIAMETER AND ACTUALLY (20NM) SIMILAR TO HONEYCOMB.

THE FIRST AEROGEL WERE PRODUCED FROM SILICA GELS. CARBON AEROGELS WERE FIRST DEVELOPED IN THE LATE 1980S.

DESCRIPTION

 IN GENERAL AEROGEL ARE PRETTY FRAGILE  INORGANIC AEROGELS ARE FRIABLE AND WILL SNAP WHEN BENT  IN THE CASE OF VERY LOW DENSITY AEROGELS WHEN POKED CLEAVING WITH AN IRREGULAR FRACTURE DEPENDING ON THEIR DENSITY

 AEROGEL CAN USUALLY HOLD A GENTLY APPLIED LOAD OF UP TOO 2000 TIMES THEIR WEIGHT AND SOMETIMES MORE, FIG. (1)

 ORGANIC POLYMER AEROGELS ARE LESS FRAGILE THAN INORGANIC AEROGELS

FIG. (1) ( A 2.5 Kg brick is supported by a piece of Aerogel with a mass of only 2 grams )

MANUFACTURING

• AEROGELS CAN BE MADE OF A WIDE VARIETY OF SUBSTANCES, INCLUDING:

SILICA, FIG. (2) MOST OF THE TRANSITION METAL OXIDES MOST OF THE METAL OXIDES SEVERAL MAIN GROUP METAL OXIDES ORGANIC POLYMERS BIOLOGICAL POLYMERS SEMICONDUCTOR NANOSTRUCTURES CARBON CARBON NANOTUBES METALS

FIG. (2) ( A classic silica aerogel )

PROPERTIES DESPITE THEIR NAME , AEROGELS ARE SOLID , RIGID AND DRY MATERIALS THAT DO NOT RESEMBLE A GEL IN THEIR PHYSICAL PROPERTIES.

A PROPERTY KNOWN AS FRIABILITY : IF WE PRESS SOFTLY ON AEROGEL TYPICALLY DOES NOT LEAVE EVEN A MINOR MARK , PRESSING FIRMLY WILL CAUSE A PERMANENT DEPRESSION , PRESSING EXTREMELY FIRMLY WILL CAUSE IT TO SHATTER LIKE GLASS .

DESPITE THE FACT THAT IT IS PRONE TO SHATTERING , IT IS VERY STRONG STRUCTURALLY. AEROGELS ARE VERY GOOD THERMAL INSULATORS BECAUSE THEY ALMOST NULLIFY TWO OF THE THREE METHODS OF HEAT TRANSFER (CONVECTION, CONDUCTION , AND RADIATION)

AEROGELS ARE POOR RADIATIVE INSULATORS BECAUSE INFRARED RADIATION (WHICH TRANSFERS HEAT) PASSES RIGHT THROW SILICA AEROGEL.

THE SLIGHT COLOR IT DOES HAVE IS DUE TO THE SCATTERING OF SHORT WAVELENGTHS OF VISIBLE LIGHT BY NANO-SIZED DENDRITIC STRUCTURE , THIS CAUSES IT TO APPEAR SMOKY BLUE AGAINST BLACK BACKGROUNDS AND YELLOWISH AGAINST BRIGHT BACKGROUNDS, FIG. (3)

COLORED AEROGEL

FIG. (3) (COLORED AEROGEL)

TABLE This Table Demonstrates The Difference Between Silica Aerogel & Silica Glass Property

Silica Aerogel

Silica Glass

5-200

2300

Specific Surface Area (m2 /g)

500-800

0.1

Refractive Index At 632.8 nm

1.002 - 1.046

1.514 – 1.644

Optical Transmittance at 632.8 nm

90 %

99 %

Coefficient Of Thermal Expansion 1/C At 20 – 80 Deg c Thermal Conductivity (W/mK) At 25 Deg c Sound Velocity (m/s)

2 × 10-6

10 × 10-6

0.016 – 0.03

1.2

70 – 1300

5000 – 6000

Density (kgm3 )

Acoustic Impedance (Kg.S/ m2) Electric Resistivity (ohm-cm)

104

107

1 × 1018

1 × 10157

Dielectric Constant At 3-40 GHz

1.008 – 2.27

4.0 – 6.75

RELATIONSHIP WITH OTHER MATERIALS & TYPES OF AEROGEL 1 SILICA AEROGEL: IT’S THE MOST COMMON TYPE OF AEROGEL, AND THE MOST EXTENSIVELY STUDIED AND USED IT IS SILICABASED , DERIVED FROM SILICA GEL. FIG (4)

IT HAS REMARKABLE THERMAL INSULATIVE PROPERTIES HAVING AN EXTREMELY LOW THERMAL CONDUCTIVITY FROM (0.03TO 0.004) W/M.K IN ATMOSPHERIC PRESSURE,

UNTIL 2011, SILICA AEROGEL HELD 15 ENTRIES IN GUINNESS WORLD RECORDS FOR MATERIAL PROPERTIES INCLUDING BEST INSULATOR AND LOWEST-DENSITY SOLID.

CARBON AEROGEL: THEY ARE COMPOSED OF PARTICLES WITH SIZES IN THE NANOMETER RANGE, COVALENTLY BONDED TOGETHER. FIG (5)

THEY HAVE VERY HIGH POROSITY ( OVER 50 % WITH PORE DIMETER UNDER 100 NM ) THEY ARE OFTEN MANUFACTURED AS COMPOSITE PAPER CARBON AEROGELS ARE USED TO CREATE SUPERCAPACITORS, WITH VALUES RANGING UP TO THOUSANDS OF FARADS.

RELATIONSHIP WITH OTHER MATERIALS & TYPES OF AEROGEL 2 CARBON AEROGELS ARE ALOSO EXTREMELY “BLACK” IN THE INFRARED SPECTRUM , REFLECTING ONLY 0.3 % OF RADIATION BETWEEN 250 NM AND 14.3µICRO METER.

ALUMINA AEROGEL : ALUMINIUM OXIDE ARE KNOWN AS ALUMINA AEROGELS THESE ARE USED AS CATALYSTS , ESPECIALLY WHEN “DOPED” WITH A METAL OTHER THAN ALUMINIUM (NICKLE- ALUMINA) AEROGEL IS THE MOST COMMON COMBINATION. FIG (6).

ALUMINA AEROGEL ARE ALSO BEING CONSIDERED BY NASA FOR CAPTURING HYPERVELOCITY PARTICLES. OTHER AEROGELS : ( SEAGEL : IS A MATERIAL SIMILAR TO ORGANIC AEROGEL MADE OF AGAR ). CHALCOGEL : IS AN AEROGEL MADE OF CHALCOGENS SUCH AS SULFUR, SELENIUM AND OTHER ELEMENTS.

TYPES OF AEROGEL

FIG. (4) SILICA AEROGEL

FIG. (5) CARBON AEROGEL

FIG. (6) ALUMINA AEROGEL

USES IN THEIR EARLIEST DAYS AEROGEL WERE MARKTED AS THICKENING AGENTS AND USED IN EVERYTHING FROM MAKEUP AND PAINT TO NAPALM.

THEY WERE ALSO USED AS CIGARETTE FILTERS AND INSULATORS FOR FREEZERS. SILICON MANUFACTURES, HOMEBUILDING MATERIALS MANUFACTURES AND SPACE AGENCIES HAVE ALL PUT AEROGEL TO USE.

ALSO AEROGEL CAN BE FOUND IN THE RANGE OF PRODUCTS: ( WETSUITS, FIREFIGHTER SUITS, SKYLIGHTS, WINDOWS, ROCKETS, PAINTS, COSMETICS AND NUCLEAR WEAPONS )

APPLICATIONS • AT NASA’S JET PROPULSION LABORATORY (JPL) AEROGEL HAS FOUND TWO PRIMARY APPLICATION : THE FIRST ONE IS : THE CAPTURE OF THE DUST PARTICALS FROM COMET WILD 2 BY THE STARDUST SAMPLE RETURN MISSION, FIG. ( 7 ).

THE SECOND ONE IS : AEROGEL SPACECRAFT INSULATION BECAUSE AEROGEL IS MOSTLY AIR AN EFFECTIVE THERMAL INSULATOR . THIS PRESENT AS EXCELLENT THERMAL BARRIER TO PROTECT THE SPACECRAFT AGAINST THE EXTREME COLD DEEP SPACE.

• JBL IS CURRENTLY INVESTIGATING A VARIETY OF FUTURE APPLICATION FOR AEROGEL.

THE STARDUST COLLECTOR

FIG. (6) (THE STARDUST COLLECTOR)

A LOOK AT AEROGEL IN VIDEO :

THANK YOU…