Лако-красочные материалы — производство

X-ray and infrared spectroscopy show that iron blue pigments have the formula MIFeIIFeIII(CN)6 • x H2O [3.171]. MI represents sodium, potassium or ammonium, ofwhich potassium and ammonium ions are preferred in industrial manufacture be­cause they produce excellent hues; ammonium is the most common one.

The crystal structure of the Fen FenI (CN)6 grouping is shown in Figure 3.19. A face — centered cubic lattice of Fen (ferrous ion) is interlocked with another face-centered cubic lattice of FenI (ferric ion), to give a cubic lattice with the corners occupied by ferrous ions. The CN ions are located at the edges of the cubes between each Fen ion and the neighboring Fem; the carbon atom of the cyanide is bonded to the Fen ion and the nitrogen atom is coordinatively bonded to the FeIII ion. The alkali-metal ions and water molecules are inside the cubes formed by the iron ions.

The presence of coordinative water is essential for stabilization of the crystal struc­ture. Removal of this water, however carefully carried out, destroys the pigment properties. Many investigations helped to elucidate the structure of iron blue [3.172­3.175].

Fig. 3.19 Crystal structure of iron blue [3.172].

3.6.2