*1.1.3. Stability towards light and weather*

When subjected to intense radiation or weathering, systems with incorporated TiO<sup>2</sup> show color or structural changes. Yellowing, chalking and loss of gloss occur due to photocatalytic activity of TiO<sup>2</sup> . Formation of extremely reactive radicals (˙ OH, HO2˙), that cause deterioration of the coating matrix can be suppressed by doping or coating the surface of the pigment [3, 19–21].

layer increases with the increase of the mole ratio of Na<sup>2</sup>

tant siliceous micelles anchor on the surface of TiO<sup>2</sup>

SiO<sup>3</sup>

powders is affected by the morphology of the SiO<sup>2</sup>

 *layer*

are anchored onto the TiO<sup>2</sup>

*1.2.2. Coating process of the SiO2*

Isoelectric point (IEP) of rutile TiO<sup>2</sup>

**Figure 2.** Silica surface treatment as a fluffy layer.

SiO<sup>3</sup>

micelles anchor on the surface of TiO<sup>2</sup>

**Figure 3.** Silica surface treatment as a dense, glass-like layer.

island-like coating layers.

The hydrolysis rate of Na<sup>2</sup>

TiO<sup>2</sup>

range 7–8, Na<sup>2</sup>

SiO<sup>3</sup>

coating [4].

surface by the Ti─O─Si bonding. Dispersibility of the SiO<sup>2</sup>

rapidly hydrolyzes to form a large number of siliceous micelles. The resul-

surface is negatively charged under conditions where the pH value of the reaction solution is greater or equal to 7. Under conditions where pH values of the reaction solutions are in the

results in the formation of small-sized or less aggregated siliceous micelles. Small-sized

micelles present in the solution and the anchored micelles condense via Si─O─Si bonding resulting in the formation of continuous and uniform coating layers. Over pH 10.5, silicon

to TiO<sup>2</sup>

TiO2 Applications as a Function of Controlled Surface Treatment

http://dx.doi.org/10.5772/intechopen.72945

is usually located around pH 3.5 [24, 25]. The rutile TiO<sup>2</sup>

should be lowered by increasing the pH value to 9–10. This

powders initially via Ti─O─Si bonding. Later, the

. The SiO<sup>2</sup>

powders via Ti–O–Si bonding to obtain

coating layers


425
