tailieunhanh - handbook of extractive metallurgy 1 Part 6

Tham khảo tài liệu 'handbook of extractive metallurgy 1 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 190 Handbook of Extractive Metallurgy Aqueous precipitation reactions are used for production of commercial Fe2O3-mica pigments starting from Fe2 or Fe31- with subsequent calcination at 700-900 C. Pigments can also be produced by a dứect CVD fluidized-bed process based on oxidation of iron pentacarbonyl and deposition of Fe2O3 on mica and other platelet substrates 476 477 Brilliant intense colors are obtained with 50-150 nm layers of Fe2O3 hematite on muscovite. Absorption and interference colors are produced simultaneously and vaiy with layer thickness. Especially the red shades are more intense than those of TiO2-mica pigments because interference and absorption enhance each other. An intense green-red flop with different viewing angles is possible at a Fe2O3 layer thickness producing green interference 478 . A theoretical investigation is given in 479 480 On account of their good hiding power high chemical inertness lack of toxicity and brilliant intense color in the bronze copper and red ranges these pigments are becoming increasingly important in sophisticated end uses such as automotive coatings and cosmetics. Transparent Iron Oxides Transparent yellow iron oxide has the a-FeO OH goethite structure on heating it is converted into transparent red ữon oxide with the a-Fe2O3 hematite structure. Differential thermogravrmetric analysis shows a weight loss at 275 C. Orange hues develop after brief thermal treatment of yellow iron oxide and can also be obtained by blending directly the yellow and red iron oxide powders. Production. Transparent yellow iron oxide . Pigment Yellow 42 77492 is obtained by the precipitation of iron II hydroxide or carbonate with alkali from iron II salt solutions and subsequent oxidation to FeO OH . On an industrial scale oxidation is usually carried out by introducing atmospheric oxygen into the reaction vessel Important factors for good transparency are high dilution during precipi tation a temperature of 25 C during .

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