Surface treatment of titanium dioxide

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As a widely used high-grade white pigment, titanium dioxide has specific and strict requirements regarding physical and chemical parameters such as titanium dioxide content, pH value, resistivity, particle size, moisture content, and rutile content. At the same time, its pigment properties such as weather resistance, whiteness, coverage, and brightness are also receiving increasing attention from manufacturers and users. To improve its weather resistance, the crude titanium dioxide is usually first subjected to inorganic surface treatment, followed by organic surface treatment. Next, we will discuss the coating technologies for titanium dioxide one by one: 1. Inorganic coating: The inorganic coating of titanium dioxide is based on high-quality rutile-grade titanium dioxide. The diversification of rutile titanium dioxide products is achieved through inorganic coating technologies; such coatings must endow titanium dioxide with physical and chemical properties such as high weather resistance, high gloss, and good dispersion in application systems. Inorganic surface treatment involves forming a uniform layer of colorless or white inorganic oxide on the surface of TiO2 particles, in order to block the photoactivation sites of TiO2 and improve its weather resistance. To achieve this goal, actions can be taken from the following aspects: (1) Selection of inorganic coating agents. There are many inorganic coating agents used for rutile titanium dioxide, mainly including soluble compounds of titanium, hafnium, zinc, manganese, etc.; the most commonly used inorganic coating agents are soluble compounds of silicon, aluminum, zirconium, etc. The choice of coating agent depends on the specific application scenario of the product; for example, using zirconium compounds as a coating can improve the weather resistance of titanium dioxide ； (2) Inorganic coating parameters and control technology. The technical parameters of the inorganic coating process mainly include the concentration of the coating agent, the material injection rate, the temperature of the coating system, and the pH value of the system ； The control techniques for the inorganic coating process include the control of the temperature of the coating system, online monitoring of the system’s pH value, and the control of the material injection speed and method. The parameters of inorganic coating and the techniques for controlling them are directly related to the effectiveness of the inorganic coating; a good inorganic coating should involve uniform coverage of the titanium dioxide particle surface by the coating material ； (3) Design an inorganic coating scheme based on the specificity of the rutile titanium dioxide variety. The inorganic coating of rutile titanium white is a multi-layered composite coating. Different choices and combinations of factors such as the type of coating agent, the amount of coating, the order of coating, and the coating condition can yield various types of rutile titanium dioxide. The inorganic coating approach for rutile titanium dioxide must be determined based on the specific requirements of each type of rutile titanium dioxide. Technical features of titanium dioxide using zirconia coating technology and special organic surface treatment: uniform particle size with a narrow distribution, as well as excellent optical properties of the pigment: high whiteness and light-scattering ability ； It exhibits dispersibility, durability, and resistance to yellowing in both aqueous and non-aqueous systems. It has a low yellow light value, resulting in better whiteness. To improve the weather resistance and chemical stability of TiO2, as well as its dispersibility in various media, TiO2 is typically subjected to surface treatment. Generally, an inorganic surface treatment is carried out first, followed by an organic one. The purpose of such surface treatment is usually to keep the TiO2 particles in a dispersed state and to enable them to disperse uniformly and compatibly in organic media. Materials for inorganic coatings are generally SiO2 (silica), Al2O3 (alumina), and ZrO2 (zirconia). SiO2 is widely found in nature. Pure SiO2 is a colorless and transparent crystal known as \"quartz\"; it is an important material for optical instruments and a key component of rocks such as granite, gneiss, quartzite, and sandstone. SiO2 is insoluble in water and acids, but soluble in alkalis; it is used to manufacture chemical containers, glass, and refractory materials. Al203 (a white powder, insoluble in water, with different crystal forms). Among them is r-Al203. It dissolves in acids or bases; it is a typical amphoteric oxide, the main raw material for producing aluminum metal, and can also be used as an adsorbent. o1-Al203。 It is generally not corroded by chemicals and exists in nature in the form of corundum. Corundum has a hardness second only to diamond, and can be used to make drills, grinding wheels, files, and bearings. A1203。 It is also an important refractory material and filler. Zirconia (ZrO2) – the natural mineral sources of zirconia include mainly orthozirconite and zircon. Pure zirconia is a high-grade refractory material with a melting temperature of around 2900°C. Due to its high chemical inertness, it can also enhance the chemical stability and acid-base resistance of the glaze, as well as act as a opacifier. Zircon is commonly used in architectural ceramic glazes, with a typical usage level of 8%–12%. It is also a key ingredient in \"underglaze white\"; zirconium oxide serves as an excellent color enhancer for yellow-green pigments. To obtain high-quality vanadium-zirconium yellow pigments, it is necessary to use pure zirconium oxide. Pure zirconia is a white solid; it appears gray or pale yellow when impurities are present, and various other colors can be achieved by adding colorants. Due to its excellent physical and chemical properties such as high hardness, high strength, high toughness, extremely high wear resistance, and chemical resistance, zirconia material has been widely used in various fields including ceramics, refractory materials, machinery, electronics, optics, aerospace, biology, chemistry, and more. Titanium dioxide in the rutile form produced by the sulfuric acid method generally undergoes alumina/silica/zirconia treatment, with contents of 2.23%, 1.55%, and 0.77% respectively. Rutile TiO2 produced by the chlorination method can be treated only with an alumina/silica surface treatment. It has exceptional wear resistance, a high gloss level and good coloring power, along with high coverage and excellent weather resistance in outdoor conditions. Simply use Al203. Surface-treated TiO2 has good dispersibility, but lacks weather resistance. By bonding SiO2 to the Al2O3-treated surface, weather resistance can be **improved, but the TiO2 content decreases and the coloring intensity falls. Due to the relatively small particle size of zirconia, it can cover the rough rutile particles more effectively, thereby isolating them better from air and enhancing their weather resistance and luster. II: Organic treatment. The main function of organic surface treatment is to improve the wetting, dispersion, and rheological properties of TiO2 in various dispersion media; it also helps to reduce moisture absorption during storage and decreases agglomeration within the pigment. Organic surface treatment mainly involves the hydrophilic active groups in organic surfactants adsorbing onto the surface of TiO2, while the lipophilic non-polar groups interact with the organic dispersion medium on the outside. This not only enhances wettability with the dispersion medium but also improves the dispersion performance of TiO2 in the medium. Generally speaking, the coating treatment techniques for rutile titanium dioxide typically include single-silicon, single-aluminum, silicon-aluminum, and zirconium-aluminum types. Compared with the previous three types, products with a zirconium-aluminum coating possess properties such as high weather resistance and high dispersibility, and can be widely used in industries such as coatings, paints, inks, and plastics.