The sol-gel technique involves creating a sol by dispersing colloidal particles in a liquid. This sol is then used to deposit coatings on substrates via spraying, dipping, or spinning. The particles in the sol are polymerized to form a continuous gel network. Finally, heat treatment forms an amorphous or crystalline coating. This technique allows for highly pure and uniform products to be formed at low temperatures and is used to create materials for applications like capacitors, transparent semiconductors, glasses, lenses, and nanopowder for dental and biomedical uses.
2. A SOL IS A DISPERSION OF THE SOLID PARTICLES
(~ 0.1-1 M) 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:
3. (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]
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.
5. 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.