Dielectric constant. Because of its high dielectric constant, titanium dioxide pigment has excellent electrical properties. In the determination of some physical properties of titanium dioxide, the crystallization direction should be considered. For example, the permittivity of rutile type titanium dioxide pigment varies with the direction of the crystal. When it is parallel to the C axis, the measured dielectric constant is 180, and it is 90 when it is at a right angle to this axis. The average value of the powder is 114. The permittivity of anatase type is relatively low, which is only 48.
Conductivity. Titanium dioxide has the properties of a semiconductor, and its conductivity increases rapidly with temperature rise, and it is also very sensitive to hypoxia. Rutile titanium dioxide pigment is still an electric insulator at 20℃. But when heated to 420℃, its electrical conductivity increases by a factor of 107. Slightly reducing the oxygen content will have a special affect on its electrical conductivity. The dielectric constant and semiconductor properties of rutile titanium dioxide are very important to the electronics industry, which uses the conductivity characteristics to produce ceramic capacitors and other electronic components.
Hardness. According to the Mohas hardness scale of 10 points, the rutile type is 6 to 6.5, and the anatase type is 5.5 to 6.0. Therefore, in order to avoid abrasion of the spinneret in chemical fiber extinction, the anatase type is used.
Melting point and boiling point. Since both anatase and brookite titanium dioxide will be transformed into rutile type titanium dioxide at high temperature, the melting point and boiling point of the brookite and anatase titanium dioxide actually doesn’t exist. Only rutile type has a melting point and boiling point. The melting point of rutile titanium dioxide is 1850 ℃, the melting point in air is 1830±15℃, and the melting point in oxygen-rich is 1879 ℃. The melting point is related to the purity of titanium dioxide. The boiling point of rutile titanium dioxide is (3200 ± 300) K. At this high temperature, titanium dioxide is slightly volatile.
Hygroscopicity. Although titanium dioxide is hydrophilic, its hygroscopicity isn’t very strong. The hygroscopicity of rutile type if smaller than the anatase type. The hygroscopicity has a certain relationship with its surface area, the higher the surface area is, the higher the hygroscopicity is. Meanwhile, it is also related to surface treatment and properties.
Thermal stability. Titanium dioxide pigment is a substance with good thermal stability, and the general dosage is 0.01% to 0.12%.
Granularity. The particle size distribution of titanium dioxide is c comprehensive index, which seriously affects the performance of titanium dioxide pigment and product application performance. Therefore, the discussion on covering power and dispersion can be directly analyzed from the particle size distribution.
The factors that affect the particle size distribution of titanium dioxide powder are more complicated. The first is the size of the original particle size of hydrolysis. By controlling and adjusting the hydrolysis process conditions, the original particle size is within a certain range. The second is the calcination temperature. During the calcination of metatitanic acid, the particles undergo a crystal transformation period and growth period. The appropriate temperature is controlled so that the growing particles are within a certain range. The last is the crushing of the product. The modification of the Raymond mill and the adjustment of the analyzer speed are usually used to control the quality of the crushing. Other crushing equipment can also be used, such as, universal mill, air jet mill and hammer mill.
Surface properties
Superhydrophilic surface. Research suggests that the superhydrophilicity of the TiO2 surface results from changes in its surface structure under light conditions. Under the irradiation of ultraviolet light, TiO2 valence band electrons are excited to the conduction band, electrons and holes migrate to the TiO2 surface, electron hole pairs are generated on the surface, the electron react with Ti and the hole react with surface bridge oxygen ions to form separately positive trivalent titanium ions and oxygen vacancies. At this time, the hydrolytic ions in the air is absorbed in the oxygen vacancy and becomes chemically adsorbed water. The chemically adsorbed water can further adsorb moisture in the air to form a physical adsorption layer.
Surface hydroxyl. Compared with the metal oxides of other semi-metallic materials, the polarity of Ti-O bonds in TiO2 is relatively large, and the water adsorbed on the surface dissociates due to polarization and easily forms hydroxyl groups. This surface hydroxyl group can improve the performance of Tio2 as an adsorbent and various monomers, and provide convenience for surface modification.
Surface acid-base property. When TiO2 is modified, oxides such as AI, Si and Zn are often added. When the oxides of AI or Si exist alone, there is no obvious acidity or alkalinity. However, when they are combined with Tio2, solid superacid can be prepared.
Surface electrical behavior. TiO2 particles in a liquid, especially polar medium will adsorb opposite charges due to the charge on the surface to form a diffused electric double layer, which increases the effective diameter of the particles. When the particles are close to each other, they are repelled due to the same charge, which is beneficial to the stability of the dispersion system. For example, the surface of Al2O3 coated TiO2 has a positive charge, while TiO2 treated with SiO2 has a negative charge.