What are the Factors Affecting the Whiteness of Titanium Dioxide ?
Titanium dioxide as a high-quality white pigment for coatings, its whiteness is crucial, is one of the key quality indicators of coating requirements, titanium dioxide whiteness is poor, will directly affect the appearance of the coating film.
(1) Impurities
The main factor affecting the whiteness of titanium dioxide is the type and content of harmful impurities, because titanium dioxide is very sensitive to impurities, especially rutile titanium dioxide, so even a trace of impurities, will have a significant impact on the whiteness of titanium dioxide. In the titanium dioxide process, especially the sulfuric acid titanium dioxide process, most of the operations are to remove the impurities from the product, because the impurities seriously affect the application performance of titanium dioxide, especially the whiteness.
Usually the whiteness of titanium dioxide produced by the chloride method is often better than that of titanium dioxide produced by the sulfuric acid method, mainly because the raw materials used in the production of titanium dioxide by the chloride process titanium tetrachloride has been distilled and purified, itself less impurity content, while the high impurity content of raw materials used in the sulfuric acid method, can only be removed through washing and bleaching and other process technologies to remove impurities
(2) Titanium dioxide crystal type
Rutile crystalline titanium dioxide is easier to absorb short-wave light than anatase, if there are too many rutile crystals mixed in the anatase titanium dioxide, titanium dioxide absorption coefficient K value of light will increase, the whiteness and gloss of the finished product will become poor.
(3) Particle size and particle size distribution
Particle size and particle size distribution is the main factor affecting the whiteness of titanium dioxide, it is mainly through the reflection of titanium dioxide particles on the light, scattering and other phenomena. According to the available measurement data, within a certain particle size range, the smaller the particle size of titanium dioxide, the higher the whiteness value, which is mainly due to the smaller the particle size of titanium dioxide, the increase in surface area, light reflection, diffuse reflection strong.
(4) Particle shape
Particle shape refers to the state of existence of titanium dioxide particles, can be divided into spherical, rod-shaped and laminar. According to the available measurement data show that the whiteness of laminated titanium dioxide is slightly lower, spherical and rod-shaped whiteness is very close, so the shape of titanium dioxide particles can slightly affect the whiteness though.
(5) Titanium content
Titanium content refers to the total content of titanium dioxide in titanium dioxide powder, for pigment grade titanium dioxide content is generally above 90%, specifically in 92% to 98%, other substances are mainly coating agents with a small amount of impurities. According to the available measurement data show that with the increase in titanium dioxide content, the whiteness value also increases.
(6) Various additives
In the production, often use to many additives, such as filtering aids, lubricants, etc., which may contain long carbon chains of organic compounds, high temperature will be carbonized, so that the titanium dioxide color becomes dull, even with obvious red-brown.
