Yellow, Cadmium

Inorganic yellow oxide combinations may contain lead, antimony, tin, nickel, or chromium. They are classed as yellows rather than brown, but they are dull compared with the cadmium yellows. 

Cadmium chloride (CdCy, a soluble crystal, is formed when cadmium metal is treated with hydrochloric acid (Cd + 2HC1 — CdCl + H ). CdCl is used in dyeing and printing textiles, in electroplating baths, in photography, and as the ingredient for cadmium yellow in artists oil paint. 

James Elkins underscores the importance of the tide of an important book by Hubert Damisch, The Cadmium Yellow Window. For while the window is an opening for tight into the interior space of a painted room, it is, in acmal-ity, an opaque deposit of minerals on a canvas. This paradox has a significant impact on the matrix of alchemy, painting, clarity, and the composition type of the alchemist in his study. Hollander elaborates on the presence of the window ... 

Pure semi-conductors e.g. cadmium yellows and oranges)... 

Cepria G, Garcia-Gareta E, Perez-Arantegui J (2005) Cadmium yellow detection and quantification by voltammetry of immobilized microparticles, Electroanalysis 17 1078-1084. 

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. 

Production. The raw material for the production of cadmium yellow pigments is high-purity cadmium metal (99.99 %), cadmium oxide, or cadmium carbonate. If the metal is used it is first dissolved in mineral acid. A zinc salt is then added to the solution the amount added depends on the desired shade. The zinc salt is followed by addition of sodium sulfide solution. An extremely finely divided cadmium sulfide or cadmium zinc sulfide precipitate is formed, which does not possess any pigment properties. This intermediate product can also be obtained by mixing the cadmium or cadmium-zinc salt solution with sodium carbonate solution. An alkaline cadmium carbonate or cadmium zinc carbonate precipitate is formed which reacts in suspension with added sodium sulfide solution. 

The crude precipitated cadmium yellow is washed and then calcined at approx. 600 °C, at which temperature the cubic crystal form changes to the hexagonal form. This process determines the particle size distribution, which is essential for the pigment properties. 

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. 

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. 

Cadmium chloride is used in photography in dyeing and calico printing in radio valve manufacture in the manufacture of cadmium yellows and reds in galvanoplasty in mirror manufacture. 

The principal red and yellow pigments are Lead chromate chrome yellow, orange and red), zinc chromate zinc or buttercup yellow), barium chromate lemon yellow or yellow ultramarine) various products based on jerric oxide, hydrated (yellow) or anhydrous (red), both natural yellow and red ochres) and artificial Mars yellow, English red, etc.) red oxide oj lead minium or red lead) mercuric sulphide cinnabar, vermilion) antimony oxysulphide antimony cinnabar) cadmium sulphide cadmium yellow) basic lead antimonate Naples yellow). 

These common uses only hint at all the things that transition metals can do. The copper penny, for instance, is mostly made of zinc, another transition metal. Chromium provides the shiny, mirror-like metal coating on chrome car bumpers, but is also added to some lasers to make their light shine red. Nickel and chromium combine in an alloy that can be coiled into the wires that heat toasters and hair dryers. Titanium dioxide is a very white reflective compound used in toothpaste and paints. The transition metal cadmium is used in brilliant and permanent colors such as cadmium yellow, red, and orange. Artists have used cadmium-based paints for hundreds of years, and manufacturers used the colors more recently in plastic products. However, the colors are rarely used now that scientists have discovered that cadmium pollution can cause cancer and other health problems. 

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