Mixed crystal pigments

Spietschta, E. and Troster, H. (1988a). Mix-crystal pigments based on perylenete-tracarbamides, process for preparing and their use. Hoechst AG Patent DE 3 436... 

Sicotherm . [BASF BASF AG] Cadmium sulfid zinc sulfide or cadmium sulfide/selenide mixed crystals pigments for coloring plastics and paints. 

The crystallography of iron oxides is complex because there are two oxides, FeO and Fe203, as well as a-FeOOH, which can occur in mixed crystals. Kittel [34] has given a full account of the chemistry and Feitknecht [35] has discussed the theory of the colours of these pigments. 

Another phenomenon to be detected by X-ray crystallography is the formation of mixed crystals, as observed in the mixed coupling of azo pigments or the solid solutions of quinacridone pigments. A change in the angles of the reflected X-rays of a mixed crystal indicates a transition from one crystal phase to another. If, how-... 

P.R.206 is a mixed crystal type and consists of unsubstituted quinacridone and quinacridone quinone. The ratio between the two components as well as the crystal modification is not yet known. P.R.206 affords a very dull, yellowish shade of red, referred to as maroon. The pigment is considerably weaker than perylene pigments. All commercially available types of P.R.206 are more or less transparent and are used mostly in metallic finishes for automobiles, to which they lend reddish shades of copper. The pigment is often found to be difficult to disperse. The finishes frequently exhibit rheological problems, especially at high pigment concentration. 

A number of other members of this class are also available, although not all are listed in the Colour Index. Their exact chemical and physical properties remain to be published. The list includes mixed phase pigments made of unsubstituted quinacridone with dimethylquinacridone or other substituted quinacridones. Recently mixed crystal phase pigments of two substituted quinacridones have been published [28]. These pigments are considered specialty products for automotive finishes, especially for metallic finishes. 

DPP/Quinacridone Mixed Crystal Phase ( Solid Solutions ) Pigments... 

Cadmium yellow consists of pure cadmium sulfide (golden yellow color) or mixed crystals of zinc and cadmium sulfide [8048-07-5], (Cd, Zn)S, in which up to one-third of the cadmium can be replaced by zinc. The density of this pigment is 4.5-4.8 g/cm3 and its refractive index is 2.4-2.5. The prevalent parcticle size is approx. 0.2 pm with cubic to spheroidal habits. Cadmium yellow is practically insoluble in water and alkali, and of low solubility in dilate mineral acid. It dissolves in concentrated mineral acid with generation of hydrogen sulfide. 

Molybdate red and molybdate orange [12656-85-8], C.I. Pigment Red 104 77605, are mixed-phase pigments with the general formula Pb(Cr,Mo,S)04 [3.131]. Most commercial products have a Mo03 content of 4-6 % (refractive index 2.3-2.65, density 5.4-6.3 g/cm3). Their hue depends on the proportion of molybdate, crystal form, and particle size. 

Molybdenum salts used as catalysts include cobalt molybdate for hydrogen treatment of petroleum stocks for desulfurization, and phospho-molybdates to promote oxidation. Compounds used for dyes are sodium, potassium, and ammonium molybdates. With basic dyes, phosphomolyb-dic acid is employed. The pigment known as molybdenum orange is a mixed crystal of lead chromate and lead molybdate. Sodium molybdate, or molybdic oxide, is added to fertilizers as a beneficial trace element. Zinc and calcium molybdate serve as inhibitory pigments in protective coatings arid paint for metals subjected to a corrosive atmosphere. Compounds used to produce better adherence of enamels are molybdenum trioxide and ammonium, sodium, calcium, barium, and lead molybdates. 

There are still challenges BrUUant, inorganic, nontoxic, stable and cheap green or blue pigments are amongst these. Probably, the mixed crystal systems are promising fields for new discoveries. 

Variation of the hue of yellow cadmium sulfide pigments hy mixed-crystal formation ... 

Fe, Co, Ni. This provides a range of colours in which the excellent durability characteristics of the host crystal structures are retained. An important commercial example of a mixed oxide pigment based on the spinel lattice is cobalt aluminate blue (Cl Pigment Blue 28), which is usually represented as C0AI2O4,... 

Solid solution formation, where two or more components form one crystal lattice over a continuous range of compositions, is frequently observed in dye and pigment chemistry l As a consequence, the X-ray diffraction pattern of such a solid solution is the same or very similar to that of one of the components, the host. In analogy to liquid solutions, the guesf molecules are dissolved into the crystal lattice of the hosf. In some cases this can also lead to a variation of the coloristic and other properties compared to a physical mixture of the individual pigments. A special case of solid solutions is a mixed crystal, where a specific composition containing two components results in a unique diffraction pattern different from the XRD of either of the components. In this case, a loose analogy can be drawn to the formation of azeotropes in the liquid state. Both cases have been observed within DPP chemistry. 

Figure 11-10 illustrates both a ternary and a binary solid solution. The ternary solid solution of AA, AB and BB accomodates the lattice of the asymmetric DPP AB. A binary combination of equimolar amounts of the DPP AA (C.I. Pigment Red 255) and the symmetrical DPP BB (C.I. Pigment Red 254) can be combined and form an entirely new binary mixed crystal in the lattice of the asymmetrical DPP AB. The asymmetric DPP AB and the mixed crystal show a hypsochromic shift compared to the single components AA and BB. 

Synthesis of Peiylene Pigments and Mixed Crystals by Condensation of PTCA with Amines... 

Mixed Crystals and Solid Solutions of Perylene Diimide Pigments... 

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