SOL-GEL TECHNIQUE

A SOL IS A DISPERSION OF THE SOLID PARTICLES (~ 0.1-1 ΜM) IN A LIQUID

A GEL IS A STATE WHERE BOTH LIQUID AND SOLID ARE DISPERSED IN EACH OTHER, WHICH

PRESENTS A SOLID NETWORK CONTAINING LIQUID COMPONENTS. THE SOL-GEL COATING PROCESS

USUALLY CONSISTS OF 4

STEPS:

(1) THE DESIRED COLLOIDAL PARTICLES ONCE DISPERSED IN A LIQUID TO FORM A SOL.

(2) THE DEPOSITION OF SOL SOLUTION PRODUCES THE COATINGS ON THE SUBSTRATES BY SPRAYING, DIPPING OR

SPINNING.

(3) THE PARTICLES IN SOL ARE POLYMERIZED THROUGH THE REMOVAL OF THE STABILIZING COMPONENTS AND PRODUCE A

GEL IN A STATE OF A CONTINUOUS NETWORK.

(4) THE FINAL HEAT TREATMENTS PYROLYZE THE REMAINING ORGANIC OR INORGANIC COMPONENTS AND FORM AN

AMORPHOUS OR CRYSTALLINE COATING[1-4]

COLLOIDS=MICROSCOPIC MATERIALS+DISPERSION PHASE

• A COLLOID IS A SUBSTANCE MICROSCOPICALLY DISPERSED THROUGHOUT ANOTHER SUBSTANCE.

• THE DISPERSED-PHASE PARTICLES HAVE A DIAMETER OF BETWEEN APPROXIMATELY 1 AND 1000 NANOMETERS.[2] SUCH PARTICLES ARE NORMALLY INVISIBLE IN AN OPTICAL MICROSCOPE, THOUGH THEIR PRESENCE CAN BE CONFIRMED WITH THE USE OF AN ULTRA MICROSCOPE OR AN ELECTRON MICROSCOPE.

LIGHT BEING SHINED THROUGH WATER AND MILK. THE LIGHT IS NOT REFLECTED WHEN PASSING THROUGH THE WATER BECAUSE IT IS NOT A COLLOID. IT IS HOWEVER REFLECTED IN ALL DIRECTIONS WHEN IT PASSES THROUGH THE MILK, WHICH IS COLLOIDAL.

PRECURSOR ORGANOMETALLIC COMPOUND

(M-OR)

ORGANOMETALLIC COMPOUND(M-OR) +WATER (H20)

METAL-OXIDE SOLUTION M-OH +R-OH

COATING XEROGEL

GELLING WET GEL

PRECIPITATING UNIFORM PARTICLES

Sol

SOL-GEL FOR NORMAL COATING

SOL GEL FOR SPIN COATING

ADVANTAGES OF SOL-GEL METHOD

( SIMPLE , ECONOMIC & EFFECTIVE )

HIGHLY PURE PRODUCTS

UNIFORM NANOSTRUCTURE &EASILY SHAPEABLE

HAVE LOW TEMP. SINTERING CAPABILITY

DISADVANTAGES OF SOL-GEL TECHNIQUE

SUBSTRATE dependentNON_UNIFORM THERMAL EXPANSION

APPLICATIONS

CAPACITORS IN PIEZOELECTRICITY APP.

TRANSPARENT SEMICONDUCTORS

GLASSES ,LENSES

NANOPOWDER FOR DENTAL &BIOMEDICAL APP.

PROTECTION WITH HARD COAT