The important physical and mechanical properties of sintered titania are summarized in Table 7.10. Today, the predominant application of titania is still in pigments, owing to its optical properties and stability against ultraviolet ( UV ) radiation. However, other applications have emerged including oxygen sensors, antimicrobial coatings, photocatalysts to clean waste gases and liquids, and potential photovoltaic cells with a high degree of energy conversion.
2.3.2 Processing of Titania
Pure primary titanium dioxide does not occur naturally, but is derived by weathering from ilmenite (FeTiO3 ), perovskite (CaTiO3 ), and titanite (sphene) (CaTiSiO5 ). The weathering products form leuxocene ores with up to 68% rutile content. The most prevalent occurrence of titania is in rutile or ilmenite mineral sands mined in Canada, Australia, the USA, and South Africa.
These ores are the principal raw materials used in the manufacture of titanium dioxide pigment. The first step to purify the ore is basically a refinement, using either sulfuric acid (sulfate process) or chlorine (chloride process) as an extraction agent.
Sulfate process. The sulfate process yields both anatase and rutile grades, depending on the particular processing routes. Ilmenite or titanium slag is first digested with sulfuric acid, and the product is diluted with water or dilute acid. This causes most of the titanium dioxide from the ore to be dissolved as a titanium oxosulfate, TiO(SO4), and the iron is present in its two - valent oxidation state. The resultant liquor is clarified by sedimentation to remove any insoluble residues, such as silica. The iron is removed by crystallization as its sulfate salt (FeSO4.7H2O), followed by filtration. To produce the anatase form, a small portion of the clarified liquor is neutralized with alkali to produce anatase microcrystals; these microcrystals are then introduced into the mother liquor, which is hydrolyzed under carefully controlled conditions to produce crystals of anatase. The crystals are subsequently filtered, washed, calcined, and micronized. During calcination, the final temperature reaches about 800 – 850 °C.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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