Method of Improving the Whiteness of Titanium Dioxide during Production
It is expected that the whiteness of titanium dioxide could be higher during the process of both production and customer using. According to the empirical analysis, when the whiteness of the titanium dioxide increased, the opacity and the lightening power index will also rise respectively, therefore, to achieve the same effect, the quantity of titanium dioxide will decrease and the cost will reduce. In order to improve whiteness during production (for sulfuric acid method), there are several methods.
Raw material is the first step of production. To produce qualified products, qualified raw material is needed. Titanium dioxide is extremely sensitive to impurity content which needs to accurate to 1 ppm sometimes, therefore, choosing a good mineral source is the top priority. Iron, manganese and vanadium niobium are important impurities, and their content needs to be strictly tested and accurately controlled.
Hydrolysis technology is an important process during the production of Titanium dioxide and it is also an important factor that will influence the whiteness of titanium dioxide powder
. Normally, the pressured hydrolysis products have a poor uniformity, slow washing speed, and poor product whiteness, while the normal pressure hydrolysis can overcome this shortcoming. Normal pressure hydrolysis can make the particle shape more even and increase the whiteness at the same time.
Calcining is the process of dehydration, desulphurization, crystalline transformation and crystalline growth, which is directly related to the whiteness of the finished product. So remember not to under burning or over burning. Usually, a combustion chamber is set up in front of the rotary kiln to prevent the high temperature flame from contacting the material directly, and control the temperature, speed and calcining time, which is based on the parameters according to the experience.
Sanding is the first task in the post-processing stage. The main task is to break the material to use in the later coating processing. When the material is too thick, the envelope will be nonuniform, and if it is too thin, it can lead to the decrease of the covering ability of finished products and waste the grinding resources. Therefore, the average particle size should generally controlled between 0.3~0.6μm.
5) Coating Process
Coating method, coating amount and the coating uniformity, etc. will all affect the whiteness of the product, in general, coating phosphorus, aluminum and zirconium will increase the whiteness, while coating silicon can have an adverse effect that the whiteness has no change or even decline, and uneven coating will also seriously affect the whiteness of the finished product.
(6) Gas Powder Condition
The gas powder is to crush titanium white powder to a suitable particle size. The larger the particle size is, the worse the evenness is, and the lower the white degree is. Otherwise, whiteness will increase. Therefore, according to the common experience, the finished particle size can be crushed between 0.2~0.35μm.