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Chrome alum. Chromium alum is produced from chromate salts or from ferrochromium alloys. Concentrated aqueous solutions of potassium dichromate can be reduced, usually with sulfur dioxide but also with alcohols or formaldehyde, in the presence of sulfuric acid at temperatures <40 °C.
For aluminum, the chromate conversion bath can be simply a solution of chromic acid. The process is rapid (1–5 min), requires a single ambient temperature process tank and associated rinse, and is relatively trouble free. [2] As of 1995, Henkel's Alodine 1200s commercial formula for aluminum consisted of 50-60% chromic anhydride CrO
The most common of these analogs is chrome alum KCr(SO 4) 2 ·12 H 2 O. In most industries, the name "alum" (or "papermaker's alum") is used to refer to aluminium sulfate, Al 2 (SO 4) 3 · n H 2 O, which is used for most industrial flocculation [1]: 766 (the variable n is an integer whose size depends on the amount of water absorbed into the alum).
(radius 50 pm), and they can replace each other in some compounds, such as in chrome alum and alum. Chromium(III) tends to form octahedral complexes. Commercially available chromium(III) chloride hydrate is the dark green complex [CrCl 2 (H 2 O) 4]Cl. Closely related compounds are the pale green [CrCl(H 2 O) 5]Cl 2 and violet [Cr(H 2 O) 6]Cl 3.
Predominance diagram for chromate. In aqueous solution, chromate and dichromate anions exist in a chemical equilibrium.. 2 CrO 2− 4 + 2 H + ⇌ Cr 2 O 2− 7 + H 2 O. The predominance diagram shows that the position of the equilibrium depends on both pH and the analytical concentration of chromium.
If anhydrous violet [35] chromium(III) chloride is dissolved in water, the violet solution turns green after some time as the chloride in the inner coordination sphere is replaced by water. This kind of reaction is also observed with solutions of chrome alum and other water-soluble chromium(III) salts.
Tawing is a method that uses alum and other aluminium salts, generally in conjunction with binders such as egg yolk, flour, or other salts. The hide is tawed by soaking in a warm potash alum and salts solution, between 20 and 30 °C (68 and 86 °F). The process increases the hide's pliability, stretchability, softness, and quality.
It is also used as a mordant for dyeing pigments, in manufacturing of alizarin, chrome alum, leather tanning and oil purification. [3] Photosensitive films containing PVA, ammonium dichromate, and a phosphor are spin-coated as aqueous slurries in the production of the phosphor raster of television screens and other devices. The ammonium ...
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