Mordants, Chrome

Chromates and dichromates are used in industry as oxidising agents, for example in the coal tar industry, in the leather industry (chrome taiming), and in the dye industry as mordants. Some chromates are used as pigments, for example those of zinc and lead. Chromates and dichromates are poisonous. 

Other compounds are of industrial value lead chromate is chrome yellow, a valued pigment. Chromium compounds are used in the textile industry as mordants, and by the aircraft and other industries for anodizing aluminum. 

Chrome-tanned leather has chromium bonded to the leather fibers. This chromium can act as a mordant for acid dyes resulting in fast colors and intense shading at the surface of the leather. 

Mordant Dyes. MetaUizable azo dyes are appHed to wool by the method used for acid dyes and then treated with metal salts such as sodium chromate [7775-11-5] sodium dichromate [10588-01-9] and chromium fluoride [1488-42-5] to form the metal complex in situ. This treatment usually produces a bathochromic shift ia shade, decreases the solubUity of the coloring matter, and yields dyeiags with improved fastness properties. The chromium salts can be appHed to the substrate before dyeiag (chrome-mordant or chrome-bottom method), together with the dye ia a single bath procedure (metachrome process), or as a treatment after dyeiag (afterchrome process). 

Around 1800, the attack of chromite [53293-42-8] ore by lime and alkaU carbonate oxidation was developed as an economic process for the production of chromate compounds, which were primarily used for the manufacture of pigments (qv). Other commercially developed uses were the development of mordant dyeing using chromates in 1820, chrome tanning in 1828 (2), and chromium plating in 1926 (3) (see Dyes and dye intermediates Electroplating Leather). In 1824, the first chromyl compounds were synthesized followed by the discovery of chromous compounds 20 years later. Organochromium compounds were produced in 1919, and chromium carbonyl was made in 1927 (1,2). 

Mordant or chrome dyes metallic salt or lake formed directly on the fiber by the use of aluminum, chromium, or iron salts that cause precipitation in situ. 

Like the analogous chrome alums they find use as mordants in dying processes. The sulfate is the cheapest salt of Fe and forms no less than 6 different hydrates (12, 10, 9, 7, 6 and 3 mols of H2O of which 9H2O is the most common) it is widely used as a coagulent in the treatment not only of potable water but also of sewage and industrial effluents. 

Absud, m. decoction, extract (Dyeing) specif., iron or chrome mordant. 

Chrom bad( n. chrome bath. beizet /. chrome mordant. 

Elderberries yield a violet color. In times past, not only were the berries used to color hair and wine, but also to enliven fabric and basket materials. Elder-berries have also been used to make beautifully colored inks and to tint paper blue. With alum used as a mordant to fix the dye, the berries give a purple color, used best on wool and silk. Elderberries mixed with alum and salt produce a lilac hue, and mixed with alum and cream of tartar they make a lovely crimson shade. Chrome used as a mordant with elder-berries produces a blue dye and tin used as a mordant produces blue gray. 

Elder leaves combined with alum or chrome as a mordant dyes fabric green. When the leaves are mixed with alum and salt, a lilac color emerges. Adding elder leaves to copper and acetic acid yields a... 

Chrome-magnesite brick, 6 495 Chrome Manganese Zinc Brown, pigment for plastics, 7 369t Chrome-mordant dyeing, 9 399 Chromenes... 

Mordant dyes are notoriously troublesome from the viewpoint of colour matching because the hue of the chromium complex usually differs greatly from that of the unmetallised parent dye (section 5.4.1). If other metal ions are present in the treatment bath or on the fibre during chroming, the colour obtained is likely to differ from that of the pure chromium complex. Certain important chrome dyes, including Cl Mordant Black 11 (3.29) and Black 17 (3.30), are particularly sensitive to traces of iron or copper. The hue of the black dyeings obtained is redder in the presence of copper and browner with iron contamination. The fastness to light and wet treatments may also prove inferior under these conditions. Even certain 1 2 metal-complex acid dyes show similar effects in the presence of these impurities,... 

There are problems of definition with the term mordant dye (section 1.6.8) and it is often more precise to refer to those chelatable dyes, mostly o.o -dihydroxyazo ligands, that are applied to wool at low pH and fixed by dichromate aftertreatment as chrome dyes. Nevertheless, mordant dyeing is a convenient way to describe this two-stage process that has become the focus of substantial development work in recent years because of increasing concern about the environmental hazards associated with residual chromium in dyehouse effluent. 

By far the most widely used chroming agent is sodium dichromate, although the potassium salt has occasionally been preferred. The dichromate may be applied before the dye (mordant method), simultaneously with the dyeing process (metachrome method) or as an aftertreatment (afterchrome method), but only the afterchrome process remains of practical significance. The theoretical aspects of chroming have been reviewed [72,73] and the mechanism of the reactions may be represented as follows ... 

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