Cadmium colors

For blood cleaned plastic collection tubes with stoppers and for urine high-density polyethene containers thoroughly cleaned with Suprapur (Merck, Germany) quality nitric acid and bidistilled water 1 + 10 must be used. The whole set (tube and stopper, or container) must be tested to deliver less than 10% extraneous amounts of cadmium. Colored stoppers and plastics with a Cd softener should not be used. Before starting the study six test tubes per tube production lot and during the study frequently blank tubes, e.g., for 1% of the total number of samples to study, must be tested. The test may be performed with a 1% v/v solution of nitric acid (e.g., Suprapur quality) in bidistilled water. Preferably vacuum collection tubes must be used. No special type of needle is requested. Needles of stainless steel are adequate. Other needles, e.g., siliconized or... 

Some of the reasons that certain colorants are more expensive than others are worth a little investigation. Copper phalocyanine (CPC) blues and greens are relatively nontoxic colorants, but they are manufactured overseas for the most part because the process has many byproducts that are hard on the environment. Cadmium colors (reds, oranges, and yellows) are manufactured from cadmium compounds that are highly toxic. The colorants (cadmium sulfos-elenides) are nontoxic but their products of incineration are toxic. All of these concerns and others apply to several classes of polymer additives and modifiers that themselves are only mildly toxic. 

Pigment color is determined by the ratio of Cd, and Zn or Hg if present, to S and Se in the product and can be changed all the way from primrose to maroon. Mercury substitution for cadmium yields (Cd, Hg)S pigments with ted and maroon shades similar to those obtained with selenium substitution. The Cadmium Association provides the simple diagram given in Figure 5 showing the color and composition correlation. 

Fig. 5. Color and composition correlation of cadmium-based pigments.

Chemical pigments or synthetics may be metal compounds. A good example is white titanium dioxide. Other chemical pigments include cadmium sulfide colors, iron blue, and several synthetic versions of iron oxides. 

Pigments and Glass. Tellurium has served as base for ultramarine-type cadmium sulfoteUuride (82) and cadmium teUuride pigments (83) (see Pigments, inorganic). In addition, smaU amounts of teUurium have been used in glass and ceramics to produce blue to brown colors (see Colorants for CERAMCS). 

Nitrite can be deterrnined by reaction with sulfanilamide to form the diazo compound, which couples with /V-(1-naphthyl)ethylenediamine dihydrochloride to form an intensely colored red azo dye. Nitrate can be deterrnined in a similar manner after reduction to nitrite. Suitable reducing agents are cadmium filings or hydrazine. This method is useful at a nitrogen concentration of 10 -lO " M. 

Although it is only slowly oxidized in moist air at ambient temperature, cadmium forms a fume of brown-colored cadmium oxide [1306-19-0] CdO, when heated in air. Other elements which react readily with cadmium metal upon heating include the halogens, phosphoms, selenium, sulfur, and tellurium. The standard reduction potential for the reaction... 

Plastics and Synthetic Products. To prevent degradation of plastics at elevated processing temperatures, it is necessary to use suitable heat stabilizers. Eor example, flexible poly(vinyl chloride) (PVC) manifests uncontroUed color development in the absence of stabilizers. Accordingly, cadmium salts of organic acids are typically used in a synergistic combination with corresponding barium salts, in about a 1 3 cadmium barium ratio, to provide a cost-competitive heat stabilizer for flexible PVC. 

Cadmium hydroxide is the anode material of Ag—Cd and Ni—Cd rechargeable storage batteries (see Batteries, secondary cells). Cadmium sulfide, selenide, and especially teUuride find utiUty in solar cells (see Solarenergy). Cadmium sulfide, Hthopone, and sulfoselenide are used as colorants (orange, yellow, red) for plastics, glass, glazes, mbber, and fireworks (see Colorants for ceramics Colorants forplastics Pigments). 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

Cadmium nitrate is the preferred starting material for Cd(OH)2 for use as the anode ia alkaline batteries. The siatered anode matrix of such batteries is saturated with cadmium nitrate (480—500 g/L Cd) and cadmium hydroxide is formed thereia by standardized electrolysis and dryiag (37). The tetrahydrate sells for 29.10/kg ia 20 kg lots. Other uses iaclude photographic emulsions and as a colorant ia glass and ceramics. 

CdSe forms sohd solutions with CdS which are used as pigments ranging ia color from orange to deep maroon and are called cadmium sulfoselenides. Other uses are ia photocells, rectifiers, lumiaous paiats, and as a mby colorant for glass manufacture. CdSe currentiy sells for 1.50/g as phosphor-grade (99.999% purity) material. 

Cadmium acetate is a colorant for glass and textiles, a glaze for ceramics where it produces iridescent effects, a starting material for preparation of the cadmium haUdes, and is an alternative to the cyanide bath for cadmium electroplating. In 1991, cadmium acetate dihydrate sold for 59.50/kg in 2 kg lots of reagent-grade material. 

The only components in a coating powder which might cause the waste to be classified as hazardous are certain heavy-metal pigments sometimes used as colorants. Lead- (qv) and cadmium-based pigments (qv) are seldom used, however, and other potentially hazardous elements such as barium, nickel, and chromium are usually in the form of highly insoluble materials that seldom cause of the spent powder to be characterized as a hazardous waste (86). 

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