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The role of titanium dioxide

2018-10-25 13:22 View:
The role of titanium dioxide
 
Titanium dioxide has a good UV masking effect and is often incorporated into textile fibers as a sunscreen. Ultrafine titanium dioxide powder is also added to sunscreen creams to make sunscreen cosmetics.
 
Titanium dioxide can be extracted from rutile by acid decomposition or from titanium tetrachloride. Titanium dioxide is stable in nature and is used in large quantities as a white pigment in paints. It has good hiding power and is similar to lead white, but it does not turn black like lead white; it has the same durability as zinc white. Titanium dioxide is also used as a matting agent for enamels to produce a very bright, hard and acid-resistant enamel finish.
 
Surface properties
 
1, the surface is super hydrophilic
 
It is believed that the superhydrophilicity of TiO2 surface is caused by the change of surface structure under light conditions. Under ultraviolet light, the valence band electrons of TiO2 are excited to the conduction band, electrons and holes migrate to the surface of TiO2, electron-hole pairs are formed on the surface, electrons react with Ti, and holes react with surface bridge oxygen ions to form respectively. Positive trivalent titanium ions and oxygen vacancies.
 
At this time, the hydrolysis in the air is adsorbed in the oxygen vacancies to become chemisorbed water (surface hydroxyl group), and the chemisorbed water can further adsorb the moisture in the air to form a physical adsorption layer.
 
2, surface hydroxyl
 
Compared with the metal oxides of other semiconductor semimetal materials, the polarity of Ti-O bonds in TiO2 is large, and the water adsorbed on the surface is dissociated by polarization, and hydroxyl groups are easily formed. The surface hydroxyl group can improve the performance of TiO2 as an adsorbent and various monomers, and is convenient for surface modification.
 
3. Surface acidity and alkalinity
 
TiO2 is often added with oxides such as Al, Si, and Zn. When Al or Si oxides are present alone, there is no obvious acidity and alkalinity. However, when combined with TiO2, it exhibits strong acidity and alkalinity, and solid super acid can be prepared.
 
4, surface electrical properties
 
In the liquid (especially polar) medium, the TiO2 particles will absorb the opposite charges due to the charge on the surface to form a diffused electric double layer, which will increase the effective diameter of the particles. When the particles are close to each other, they will have the same charge. Repelling is conducive to the stability of the dispersion system. For example, the surface of TiO2 coated with Al2O3 has a positive charge, while the TiO2 treated with SiO2 has a negative charge.
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