Sulfuric acid in terms of calcined, or titanium white powder produced from the chlorination after the oxidation product is very pure, but does not use a filler such as a pigment product is generally different market purposes such as coatings, plastics and paper needs to be in accordance with Post processing. Its purpose is to improve its application performance, such as improving the weather resistance of titanium dioxide; improving the dispersibility of titanium dioxide in different medium solvents, plastics, water-soluble latex; improving the wettability of titanium dioxide; improving hiding power and gloss.
Post-treatment mainly includes wet grinding, inorganic coating, washing, drying, jet milling, organic coating and product packaging.
In order to improve the weather resistance of titanium dioxide, the purpose of the inorganic coating is to shield the ultraviolet light and prevent the photocatalytic activity of the titanium white powder, so it is necessary to understand the principle of photocatalysis.
1. Photocatalytic properties of Ti0 2 Regardless of the sulfuric acid method or the chlorination method, lattice defects (Schottky Defect, "oxygen defect") exist in the formation and growth of titanium dioxide crystals. Due to the lattice defects of titanium dioxide, there are many photoactivation sites on the surface, and under the action of ultraviolet light (UV), the following photocatalytic reaction occurs, as shown in FIG.
In the first step, the titanium dioxide particles absorb ultraviolet light, and charge separation occurs in the particles, and the negatively charged electrons e - in the conduction band and the positively charged holes P + in the valence band form an excited state. [next]
It is precisely because of this special photocatalytic property of Ti0 2 that titanium dioxide is used as a pigment to accelerate aging in applications such as plastics and coatings. Therefore, in addition to taking measures to compensate for and reduce the lattice defects during crystal formation and growth, it is necessary to carry out post-inorganic coating treatment to shield the photocatalysis caused by ultraviolet light. Here it is necessary to be noted that, due to the sharp differences in titanium dioxide polymorphic structure and the rutile structure of titania, the surface active sites of the light more, more photocatalysis; coupled, and no coating treatment, no matter in It is not wise to paint or plastic (as for hiding power, waste of resources, etc., I will not repeat them here).
2. The wet-milled to obtain sulfuric acid from the production process by the rotary kiln or calcining Ti0 2 obtained from the production of chlorinated oxidation process after Ti0 2, wet grinding in the presence of an inorganic or organic dispersant. The wet grinding equipment mainly uses medium grinding, and has a ball mill , a bead mill, a sand mill, a heavy medium mill and the like. The Ti0 2 aggregated particles are finely deagglomerated into primary particles to facilitate the inorganic coating. This process began to be used in large quantities in the 1990s with the aim of obtaining a better coated titanium dioxide with better pigment properties.
3. Inorganic coating and drying After the wet grinding and depolymerization, Ti0 2 needs to be coated with inorganic material to shield ultraviolet light and improve the weather resistance of titanium dioxide. Common inorganic coating agents are silicon, aluminum oxides and hydrated hydroxides. The silicon and aluminum coatings improve the weatherability of the titanium dioxide, but the opposite effect on the gloss of the application. Therefore, in recent years, a mixed coating film has been used to achieve a high weathering and high gloss pigment application. Inorganic coating agents often deposited in the form of oxides and hydroxides, and according to its final use of the product, using the form of loose or dense film is coated on the particle surface Ti0 and 2, the appearance shown in Figure 2. The reaction principle is as follows: [next]
During the coating treatment, the reaction temperature, pH value and time are strictly controlled to achieve the best use. The coated slurry is then filtered and washed with deionized water to a certain conductivity. Drying is carried out by various drying methods such as a belt dryer, a spray dryer or the like.
4. Organic Coating and Jet Milling The purpose of jet milling is to obtain a final process of post-treatment of titanium dioxide with a narrow particle size range and excellent pigment properties. Most of the pulverizers currently used are flat jet mills, which have a gas source of 16 kg of superheated steam and add a certain organic coating agent depending on the product. Its purpose is twofold: First, because the surface energy of the pulverized titanium dioxide is high, it is easy to re-agglomerate, it needs to neutralize its energy (or surface potential), and also helps the grinding effect; the second is to change the surface of its titanium dioxide. Physical and chemical properties, so that it can be used in coatings, plastics and other materials for better compatibility and compatibility. The organic coating agent is used for coatings with amines, alcohol amines, silanes; for plastics, there are dimethylsilane, polyethanol, triethanolamine and the like. Due to the complexity of the organic structure and the easy change and continuous synthesis of new products, to meet the needs of new coatings and new plastic products. The variety of coating agents is also constantly innovating, and new products and technologies with various organic coatings have emerged.
5. Product packaging Commercially available titanium dioxide is usually packaged in 25kg paper bags or woven composite paper bags. Large-scale use can be 500kg or 1000kg large package. Product grades, specifications, suitable standards, uses, manufacturers, and production lot numbers are indicated on the package. Most of the titanium dioxide sold in the domestic market is general-purpose, and can be used in water-based paints, oil-based paints, plastics, and even rubber or elastomers. When using, you should carefully read the manufacturer's instructions, or ask the manufacturer's instructions, the user's purchase of titanium dioxide is best for what product to use; otherwise, Zhang Guan Li Dai, the resources are used in the wrong place, the titanium dioxide cargo becomes waste.
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