| 摘要 |
<p>1491697 Ferrocyanide blue DEUTSCHE GOLD-UND SILBER-SCHEIDEANSTALT 10 Dec 1974 [8 Nov 1974] 53320/74 Heading CIA Ferrocyanide blue (ferric ferrocyanide; Berlin blue) is produced by simultaneously introducing into water an aqueous solution containing ferrocyanide ions and an aqueous ferrous salt solution, provision being made for optimum mixing (i.e. stirring with an intensity which is not high enough to damage the precipitated product) during precipitation, after which the precipitate formed (white paste; ferrous ferrocyanide; Berline white) is aged in the reaction medium itself at elevated temperature in the presence of salts produced during the reaction and is subsequently converted into ferrocyanide blue by oxidation in acid medium. Either the ferrocyanide or the ferrous solution may be used in slight excess in order to adjust colouring strength. The ferrocyanide used may be sodium or calcium ferrocyanide. A calcium ferrocyanide solution which also contains about I mole of calcium chloride per mole of calcium ferrocyanide may be used. Use of potassium ferrocyanide results in a higher quality product containing potassium ions. When other ferrocyanides are used, including mixtures of potassium and sodium ferrocyanides, a potassium or ammonium salt may be added during or after precipitation in order to improve the colour properties of the pigment. The ferrous salt solution may be a pickling solution. Ageing of the precipitate may take place under elevated pressure.</p> |
