Replacement pigment

The banning of lead chromate pigments has resulted in an enormous demand for yellow azo pigments as replacements. Pigment Yellow 74 (XXX) has become important as such a replacement in the past 10 years. The structure is written in the hydrazone form. There has been evidence over recent years that this is the preferred tautomeric form of these types of pigments in the solid state (39-41) versus the more commonly shown azo form (XXXl). 

Until recently, cadmium red was the preferred choice of red pigment for containers, toys, and household items, replacing pigments derived from toxic heavy metals such as lead and mercury, but cadmium is now considered totally undesirable and its pigments are being phased out, probably to be replaced with cerium sulfide, which gives a rich red colour, is stable up to 350 °C, and is completely non-toxic. 

Because of price restrictions, there are attempts to replace titanium dioxide with less expensive pigment. Figure 3.24 shows results of such an attempt in which magnesium oxide was used as a replacement pigment. It is clear that the attempt was not successful because material elongation was drastically decreased even by small additions of magnesium oxide. 

In the yellow-red region of the visible spectrum, traditional lead pigments such as chrome yellow and moly orange have been replaced with a variety of organic alternatives. In general, the replacement pigments are ... 

Alkali or alkaline-earth salts of both complexes are soluble in water (except for Ba2[Fe(CN)g]) but are insoluble in alcohol. The salts of hexakiscyanoferrate(4—) are yellow and those of hexakiscyanoferrate(3—) are mby red. A large variety of complexes arise when one or more cations of the alkah or alkaline-earth salts is replaced by a complex cation, a representative metal, or a transition metal. Many salts have commercial appHcations, although the majority of industrial production of iron cyanide complexes is of iron blues such as Pmssian Blue, used as pigments (see Pigments, inorganic). Many transition-metal salts of [Fe(CN)g] have characteristic colors. Addition of [Fe(CN)g] to an unknown metal salt solution has been used as a quaUtative test for those transition metals. 

Although white lead was the oldest white hiding pigment ia paints, it has been totally replaced by titanium dioxide, which has better covering power and is nontoxic (see Pigments). Nevertheless, basic lead carbonate has many other uses, including as a catalyst for the preparation of polyesters from... 

Production. Zinc sulfide production started in the United States and in Europe in the 1920s. Starting in the early 1950s, 2inc sulfide, like most white pigments, was slowly replaced by the more superior titanium white. Zinc sulfide can be prepared by a process similar to the one used to manufacture Hthopone. In the first step, barium sulfide reacts with sodium sulfate to produce sodium sulfide solution ... 

In the Bnchamp process, nitro compounds are reduced to amines in the presence of iron and an acid. This is the oldest commercial process for preparing amines, but in more recent years it has been largely replaced by catalytic hydrogenation. Nevertheless, the Bnchamp reduction is still used in the dyestuff industry for the production of small volume amines and for the manufacture of iron oxide pigments aniline is produced as a by-product. The Bnchamp reduction is generally mn as a batch process however, it can also be mn as a continuous (48) or semicontinuous process (49). 

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