Type and content of impurities In the titanium dioxide process, especially the sulfuric acid process, most of the operations are to remove impurities in the product. The mature process route of the sulfuric acid process requires very low equipment configuration and low raw material requirements. Both titanium ore and titanium slag are acceptable. Moreover, this method can produce both rutile titanium dioxide and anatase titanium dioxide. Low requirements and short production time. In the titanium dioxide industry, especially my country's titanium dioxide industry still occupies a very important position. The titanium solution obtained by sulfuric acid hydrolysis is an extremely complex suspension system, which contains not only undecomposed ilmenite, but also some fine particles that have not participated in the reaction, and colloidal impurities formed by elements such as silicon and aluminum. There are a lot of soluble impurities such as sulfates. Even if the content of some impurities is very small, it has obvious adverse effects on its whiteness. These impurities are mainly oxides, and the whiteness reduction of titanium dioxide caused by oxides can be divided into two situations, one is the color of impurity oxide pollution, and the other is the coloring caused by lattice doping. Color metal oxide impurities can affect whiteness at very low content. These elements include iron, manganese, chromium, copper, etc. These impurities have their own color, and they are easily developed in white titanium dioxide. The impurities and color concentration are shown in the table below.
In actual production, the limit content of impurity pollution of titanium dioxide is lower than the above, and the impurity can develop color at a lower concentration. Take iron as an example. When the red Fe3+ enters the Ti4+ position, it deforms due to polarization, which absorbs more red than normal iron. In addition to the impurities caused by the above process, the impurities caused by mechanical wear, for example, in Raymond, gas powder and other equipment, due to severe friction, the material on the surface of the machine will fall off, and the impurities will also be brought into the titanium dioxide, thereby increasing the effect of titanium dioxide. The absorption of light reduces its whiteness. 2. Particle size and particle size distribution Particle size and particle size distribution are also the main factors affecting the whiteness of titanium dioxide, which are mainly affected by the reflection and scattering of light by titanium dioxide particles. Within a certain particle size range, the size of the titanium dioxide particles decreases, the surface area increases, and the light scattering ability increases, and the whiteness becomes higher. From the perspective of optical effects, when the light scattering force is maximum, the relationship between the diameter of the pigment and the wavelength of incident light λ, the refractive index of the pigment n1, and the refractive index of the paint n2 can be calculated by the formula: D=2λ[π(n1-n2) ]To represent. In the above formula, the wavelength of visible light is 400-700nm, the refractive index of rutile titanium dioxide is 2.71, and the refractive index of most paints (resins) in the coating is 1.45-1.60, so the particle size of rutile titanium dioxide is controlled within 0.2~0.3 μm is the best, the pigment has the greatest scattering power to visible light in this particle size range, and higher hiding power, decolorizing power and pure whiteness can be obtained. However, when the particle size is less than 0.1μm, due to light diffraction, the light passes through the pigment particles without reflection, but the hiding power decreases and even tends to be transparent. This kind of ultrafine titanium dioxide is transparent and can be used Manufacture of transparent sunscreen skin care cream, this kind of skin cream cream is delicate and has a natural skin feel. It is currently very popular in Japanese skin care products.
This popular model of Nissan's "Any Sunscreen Gold Bottle", which is loved by women, is the main sunscreen ingredient is zinc oxide and titanium dioxide. Third, the refractive index of the titanium dioxide coating agent of titanium dioxide is very different from that of titanium dioxide, which has great hiding power. The improvement of the titanium dioxide is limited, which affects the whiteness of the titanium dioxide. Generally, the covering power will be worse if the coating dose is large. The content of titanium dioxide in pigment-grade titanium dioxide is generally above 90%, specifically between 92% and 98%. Other substances are mainly coating agents and a small amount of impurities. At present, different types of coating agents can be selected according to different applications. Commonly used coating agents include aluminum coating, silicon coating, zirconium coating, etc. There are also two or more coating agents used together, such as zirconium aluminum coating The dosage of these coating agents varies from manufacturer to manufacturer. 4. Defects in the crystal lattice of titanium dioxide particles. The ratio of Ti to O of titanium dioxide is 1:2, but due to changes in manufacturing conditions and other factors, the final titanium dioxide product may have insufficient O, that is, oxygen defects, and it is pure Titanium dioxide can also cause oxygen atoms to break away from the crystal due to external energy such as ultraviolet radiation or heating (TiO2→Ti2O3+1/2O2). The O atom in the Ti4+O22+ crystal leaves two electrons to leave the system, and the remaining two electrons reduce the two Ti4+ to Ti3+. Ti4+ is colorless, while Ti3+ is bluish purple. Ti3+ in the crystals caused by lack of oxygen has a strong polarization effect, and the shell electrons are very tilted, which absorbs more light than Ti3+ without polarization, so the pigment has a heavier blue-gray phase. 5. The dispersibility of dispersible titanium dioxide has a great influence on the hiding power, especially when the amount of addition is small, the same 100g titanium dioxide can not see obvious particles when dispersed to 10um and 20um, but the finer the The particle size will have more particles to occupy the position in the resin, and the light refraction effect will be much improved. If the dispersibility of the titanium dioxide is poor, the powder is agglomerated and bonded together, and the fine powder becomes coarser, which will naturally reduce the whiteness and hiding power of the titanium dioxide.
