Titanium Dioxide:
Titanium is the ninth most abundant element in the earth’s crust.  TiO2 is the most important white pigment produced commercially.  TiO2 exists in three crystal forms: rutile, anatase, and brookite.  Only anatase and rutile forms are important as pigments.  TiO2 is not perfectly white and absorbs a certain amount of radiation in the 400-500 nm region, giving a yellowish undertone.  The rutile crystal has a more compact structure than anatase and hence higher density, higher refractive index, greater opacifying power, and greater exterior durability.  TiO2 has the highest refractive index of all colorless substances known.  TiO2 is capable of developing highest hiding power in paint when the particles are within the size range of half the wavelength of light (0.2-0.4um).

Zinc Oxide:
Zinc oxide particles may be spherical, acicular or nodular depending on the manufacturing process.  TiO2 has therefore replaced zinc oxide in most coating formulations.  Zinc oxide absorbs virtually all ultraviolet light radiation at wavelengths below 360 nm and provides binders outstanding protection.  Zinc oxide reacts with acidic components of coatings and forms zinc soaps.  Zinc soaps improve the flexibility and hardness of coatings.

Antimony Oxide:
Pigmentary grades have particle sizes in the range of 1.0-1.5um and have high tint strength.  Increasing the particle size results in a significant decrease in tint strength (65% at 2um and 15% at 12um).  In presence of a halide, antimony oxide forms antimony halide which is a fire retardant.
 
 

Pigment	Refractive Index	Reflecitivty (F x 100)	Relative Opacity
TiO2 (rutile)	2.71	8.26	100
TiO2 (Anatase)	2.55	6.72	81
Antimony Oxide	2.20	3.58	43
Zinc Oxide	2.01	2.11	26
Calcium Carbonate	1.65	0.23	2.8
Fumed Silica	1.45	0.03	0.4

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