Synthesis and Characterization of Hydroxyapatite Nanocoatings by Sol–Gel Method for Clinical Applications - Biological and Biomedical Coatings: Processing and Characterization - page 49

(a) M(OR) n + M'(OR) n or M(OR) n + M'(O 2 CR) n + ....

Solvent
(alcohols)

Additives-prevent precipitation
(acetylacetone, glycols, amines)

Imprortant factors-
solution viscosity,
rate of dipping, etc.

Dip-coating of substrate

Linkage of metal centers via
hydroxide (M-OH-M), oxide
(M-O-M) or alkoxide bridges

Hydrolysis,
polymerization

Sol forms on substrate

Dispersion of discrete colloidal
particles (10-1000 Å) Destabilization of sol

Gel

(b)

Gel

Drying

Monoliths -minimize
stress caused by
volume change
Films -faster drying
rates possible

Dry gel

Firing

Many processes-
combustion of organics,
dehydration
(polymerization), etc.

Oxide film (<1 µm)

FIGURE 2.6
(a) Chemistry of sol-gel process based on alkoxide route, (b) process covering the process from gel formation to
the final oxide nanocoating.