Titanium Dioxide
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Titanium Dioxide
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Color Index
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Pigment White 6 CI 77891
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Formula
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TiO2
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Structure
Titanium dioxide exists in three crystal forms:
- brookite that is not used as a pigment,
- anatase that is used occasionally
- and rutile, the most commonly used crystal form.
Two different processes are used to manufacture the rutile grade: the sulphate method
(the older one) and the chloride process (more modern).
Pigments produced by the sulphate method used to be slightly stained by the iron
salt, giving it a slightly yellow color.
Properties
Titanium Dioxide contains most of the properties of an ideal white pigment ie. clarity
of color, high resistance to most chemicals, organic solvents and heat, and most
importantly, a high refractive index. This last property allows the production of
highly opaque coatings. Further, titanium dioxide has good durability
and is unaffected by industrial atmospheres, however, its photoreactivity reduces
the light fastness of some colored pigments and nearly all organic pigments. Despite
its excellent properties TiO2 is reasonably priced. Nevertheless, attempts are made
to replace or partially replace it with cheaper pigments or semi-opaque extenders.
Because of its tighter network, rutile has in general better properties than anatase.
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Compared properties of rutile and anatase
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Property
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Rutile
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Anatase
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Refractive Index
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2.72
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2.55
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Density
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4.2
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3.9
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Surface Area
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12-17 m2/g
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10 m2/g
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Oil Absorption
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13-24
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19-20
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Heat Stability
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> 1000°C
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< 700°C
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Hiding power
The hiding power is influenced by the refractive index and the granulometry. Rutile
has a higher refractive index and is therefore more opaque.
The hidding power of TiO2 is superior to that of other white pigments.
Whiteness
Anatase is softer in texture and has a slightly better white color. Indeed,
there is a good diffusion of the visible spectrum of light except in blue where
there is an absorption. This phenomenon is more marked for rutile than for anatase.
Therefore, the rutile appears yellower than the anatase.
However, rutile has much less tendency to chalk. Modern grades have much better
chalk resistance imparted by treating the photoreactive sites on the surface of
the crystals with inorganic oxides, such as those of aluminium, silicon and zinc.
Chemical Stability
It is the most chemically inert pigment. It has a neutral pH, a good resistance
to alcali solutions
Uses
The balance between dispersibility and durability generally requires products that
are specific to a range of applications, such as water-based paints or solvent based
stoving finishes. TiO2 has favorable physiological properties due to its inert composition.
This makes it suitable for use in food packaging, toys, and other sensitive applications,
provided that it meets purity criteria.
Titanium Dioxide can be used in all coatings formulations for building and industry.
