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Just a regular Wikipedia user that corrects errors and adds text as I come across them. |
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I am PhD in chemistry and my thesis was about titanium dioxide. I know very well titanium dioxide and its manufacturing processes. I am specialist in inorganic and material chemistry. I am working with cellulose. Also other areas of chemistry interests me. |
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Titanium dioxide is very important substance, while it is the best white pigment. That is because of its high refraction index. It has high opacity and therefore it is used in most paints. Titanium dioxide crystals should be about 220 nano meters, when it is used as pigment. TiO2 pigment must be extremely pure in order to have really good optical properties. As little as a few parts per million (ppm) of certain metals (Cr, V, Cu, Fe, Nb) can disturb the crystal lattice so much that the color change from whiteness can be detected by human eyes. |
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TiO2 is produced in two crystal structures anatase and rutile. Rutile is mostly used in paint and plastic applications and anatase in paper and fiber applications. |
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Micro-crystalline titanium dioxide has crystal structure rutile and crystal size about 10-50 nano meters. It is not any more white but transparent. It is after treated as pigment with aluminium and silicon substances to prevent photo catalytic reactions. Micro crystalline titanium dioxide is both UV-A and UV-B blocker, and therefore it is used in sunscreens; nowadays in all cosmetic lotions. |
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Photocatalytic titanium dioxide has crystal structure anatase and crystal size 2-30 nano meters. It is transparent. It is very good photocatalytic substance because of its electro chemical structure, its band gap between the valence and the conductivity bands is wider than of many other substances. The band gap could be made even wider with impurities in crystal lattice. Photocatalytic TiO2 could keep window glasses clean, if there is a TiO2 film on the glass. |
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Scientifically TiO2 is very interesting substance. It could be utilized in solar cells, etc. Therefore it is important to know TiO2 better. I recently heard one professor telling that he had ordered to university TiO2 and they had made their experiments which failed. The TiO2 was not pure, but had contaminants more than 1 ppm. |
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Ilmenite is a black iron-titanium oxide with a chemical composition of FeTiO<sub>3</sub>. Ilmenites contain 37-54 % TiO2, when they are suitable for sulfate process to produce TiO2. Ilmenite or titanium slag reacts with concentrated sulfuric acid at 150 – 220 °C. Iron sulfate is removed. Relatively pure TiO<sub>2</sub> dihydrate is precipitated by hydrolysis of the sulfate solution, which contains colored heavy metal sulfates, sometimes in high concentration. The impurities are largely removed in further purification stages. The hydrate is then calcined, ground, and further treated. |
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In the ''chloride process,'' the titanium-containing raw materials ilmenite, leucoxene, natural and synthetic rutile, titanium slag, and anatase are chlorinated at 700 – 1200 °C. Titanium tetrachloride is separated from other chlorides by distillation. Vanadium tetrachloride (VCl<sub>4</sub>) and vanadium oxychloride (VOCl<sub>3</sub>) must, however, first be reduced to solid chlorides. The TiCl<sub>4</sub> is burnt at temperatures of 900 – 1400 °C to form TiO<sub>2</sub>. This extremely pure pigment undergoes further treatment depending on the type of application |
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