Cadmium red

FIGURE B.l Samples of common elements. Clockwise from the red-brown liquid bromine are the silvery liquid mercury and the solids iodine, cadmium, red phosphorus, and copper. 

The terminology of the elements suffuses our language, sometimes divorced from the questions of composition to which it once referred. Plumbing today is more likely to be made from plastic pipes than from the Romans (lead) the lead in pencils is no such thing. Cadmium Red paints often contain no cadmium at all. Tin cans have no more than the thinnest veneer of metallic tin it is too valuable for more. The American nickel contains relatively little of that metal. And when was the last time that a Frenchman s pocketful of jingling argent made of real silver ... 

Cadmium red consists of cadmium sulfoselenide [12656-57-4], [58339-34-7], Cd(S,Se), and is formed when sulfur is replaced by selenium in the cadmium sulfide lattice. With increasing selenium content, the color changes to orange, red, and finally dark red. The density of these pigments increases correspondingly from 4.6 to 5.6 g/cm3 and the refractive index from 2.5 to 2.8. The crystals have cubic or spheroidal habits, the prevalent particle size is 0.3-0.4 pm. 

Production. Cadmium red pigments are produced in a similar way to the cadmium yellow pigments. The cadmium salt solution is prepared by dissolving the metal in mineral acid and then sodium sulfide is added. A certain amount of selenium powder is dissolved in the sodium sulfide solution to obtain the desired color shade. In an alternative procedure, the cadmium solution is mixed with sodium carbonate solution to precipitate cadmium carbonate which is reacted with the selenium-containing sodium sulfide solution. 

The cadmium red pigment intermediate is obtained as a precipitate which is filtered off, washed, and calcined at approx. 600 °C. As with cadmium yellow, calcination yields the red pigment and determines the particle size, particle size distribution, and color shade. Analogously to the cadmium yellow process, cadmium red can be produced by direct reaction of cadmium oxide or cadmium carbonate with sulfur and the required amount of selenium at approx. 600 °C. 

Cadmium pigments, especially cadmium red, are very sensitive to intensive grinding, which causes loss of brilliance due to an increase in the number of irregular lattice defects. A brilliant red shade may become a dirty brownish red. 

The cadmium pigments are lightfast but, like all sulfide pigments, are slowly oxidized to soluble sulfates by UV light, air, and water. This photooxidation is more pronounced with cadmium yellow than with cadmium red and can still be detected in the powder pigment which normally contains 0.1 % moisture. 

Use of red iron oxide in plastics has increased as cadmium reds and lead molybdate oranges have been restricted in their use. In combination with the appropriate organic red toners, red iron oxide can be used to cover some of the same color space formerly occupied by cadmium- or molybdate-containing formulations. The red iron oxide component of the organic-inorganic approach also lowers the cost of the formulation, opacifies the formulation, and offers an increment of UV stability to the formulation. 

Antimony oxide White lead Lead sulfate Cadmium red Lead silicochromate Lead chromates Zinc chromates Cadmium yellow Calcium plumbate Chromium oxide Prussian blue Ultramarine blue Lead Barytes whiting China clay Mica Talc... 

Both the metre and the yard have now been measured in terms of the cadmium red spectral line (p. 308). 

Until a few years ago, the red pigment for coloring containers, toys, household wares, plastic crates, etc. was Cadmium Red. This is Cadmium sulfoselenide red, C9Hi3CdN204SSe (CAS 58339-34-7), also known as Pigment Red 108 (see Chemnet 2015). The cadmium compound is now considered environmentally undesirable, so it is being replaced by the non-toxic Cerium(III) sulphide (Cc2S3 CAS 12014-93-6). This compound gives a rich red color and is stable up to 350 °C (Emsley 2001). 

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. 

Cadmium compounds are a cumulative type of poison, and they are used as the common bright pigment (cadmium yellow) in the form of cadmium sulfide in paints, and also in rubber and plastics as an additive. Until recently, cadmium red was widely used for containers, toys and household wares (which have been completely phased out now). From March 2001, sales and use of any cadmium-containing stabiliser was harmed in EU. 

Cadmium oxide brown. See Cadmium oxide Cadmium pigment. See Cadmium sulfide Cadmium red... 

Pigment red 105. See Lead oxide, red Pigment red 107. See Antimony trisulfide Pigment red 108. See Cadmium red Pigment red 112 CAS 6535-46-2... 

Cadmium Cadmium red Cobalt tungstate (ous) DSiC Red No. 34 Pigment red 81 Pigment red 104 Pigment red 122 Pigment violet 19... 

Basic red 1 Cadmium red Chrome antimony titanium buff D C Red No. 34 Diarylanilide yellow... 

Aminotrimethylene phosphonic acid Arsenic disulfide Arsenic pentasulfide Barium molybdate Barium sulfate Basic violet 1 Basic violet 10 Bone black Cadmium red Cadmium sulfide Calcium fluoride Calcium phosphate dibasic Calcium sulfate Chrome antimony titanium buff Cobalt... 

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