Titanium Dioxide Pigment

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. 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. Electronics industry 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 transform into rutile type titanium dioxide at high temperature. Only rutile type has a melting point and boiling point. The melting point of rutile titanium dioxide is 1850 ℃. 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%.

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.

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 will 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.  The water adsorbed on the surface dissociates easily forms hydroxyl groups due to polarization. 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 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. It 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.

Sulfuric acid method

Subject ferro-Titanium powder and concentrated sulfuric acid to an acid hydrolysis reaction to produce titanyl sulfate, which is hydrolyzed to produce metatitanic acid. And then calcine and crush to obtain a titanium dioxide product. This method can produce both rutile titanium dioxide and anatase titanium dioxide pigment.

Advantages.  It take ilmenite and sulfuric acid with the features of low price and easy availability as raw materials. The technology is mature, the production equipment is simple and the anti-corrosion material is easy to solve.

Disadvantage. The process is so long and it can only adopt intermittent operation. Sulfuric acid and water consumption are high. The produced waste and by-products are more. Thus causing great environment pollution.

Chlorination Method

Use materials containing titanium. Make the chlorinated high-titanium slag, or artificial rutile, or natural rutile react with chlorine gas to generate titanium tetrachloride. Purify it by rectification and then subject to gas-phase oxidation. After rapid cooling, TiO2 is obtained through gas-solid separation. Because the TiO2 adsorbs a certain amount of chlorine, it needs to be removed by heating or steam treatment.

The process is simple, but it is chlorinated at 1000℃ or higher temperature. There are many chemical engineering problems, such as, high corrosion of chlorine, oxychloride and titanium tetraloride that need to be solved. In addition, the raw materials used are special, which is more costly than the sulfuric acid method.

Chlorination production is continuous production. The operation flexibility of the production equipment isn’t large, and it isn’t easy to adjust the the start or stop of the process and production load. However, its continuous process production is simple, the process control points are few, the product quality is easy to achieve optimal control. In addition, without the sintering process formed by rotary kiln calcination, the primary TiO2 particles are easy to depolymerize. So apparently people are accustomed to believe that the quality of the chorinated titanium dioxide is much better.

Advantages. Short process, easy expansion of production capacity, high degree of continuous automation, relatively low energy consumption less “three wastes”. Meanwhile, it can obtain high quality products.

Disadvantages. Large investment, complex equipment structure, high requirements on materials, high temperature resistance and corrosion resistance, difficult maintenance of the device, and difficulty in research and development.

• Used in solvent-based coatings and water-borne coatings, titanium dioxide powder not only plays the role of covering and decoration. The most importantly, it can improve the physical and chemical properties of the coatings, enhance the chemical stability, improve hiding power, decolorization power, corrosion resistance, light resistance and weather resistance. Meanwhile, it can enhance the mechanical strength and adhesion of the coating film, prevent cracking and shedding, prevent the penetration of ultraviolet rays and moisture, as well as extend the service life of objects.
• Compared to other commonly used pigments, such as, zinc white, zinc barium white, titanium dioxide pigment has more advantages, for that its particles are small and uniform with high optical stability. Whether in terms of hiding power or achromatic power, the performance of rutile titanium dioxide and anatase titanium dioxide are far superior to zinc white and zinc barium white.
• Used in plastic, titanium dioxide pigment has the characteristics of high whiteness, great achromatic power, good opacity and chemical stability. If it is used instead of lithopone, the consumption of white pigment can be reduced by 50% to 70%.