Replacement of Cadmium

Technically it is not easy to produce an exact drop-in replacement (especially at the same cost level). A key problem has been to produce a yellow that is as effective as cadmium. Economically there are also problems. Respondents to a survey by the Cadmium Association said that costs increased by 2-5 times over 50% found that productivity fell by 10-25% when moving to non-cadmium pigments, particularly with polyolefins. 

The need to replace heavy metals has also stimulated the introduction of new chemistry. An important development has been that by Rhone-Poulenc of inorganic pigments based on sulphur, with a crystalline structure that can be doped with various metal elements (rare earths). The colour strength is reported 

Clariant has added more than 50 colours to its cadmium-free Universal range, making a total of 180 colours. Special effects have been extended to include wood, pearlescence, and edge-glow effects. Colloids has also added 15 stock film grade colour masterbatches to its existing 3 5 colours to meet the restriction on heavy metals in the EC Directive on Waste Packaging, 94/62/EC, Article 11. 

Product Pigment concentration (%) High-lemperal u re suitability Contains cadmium pigment Heat stability rC) Light stability 

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The sealed nickel-metal hydride cell (more consistently metal hydride-nickel oxide cell) has a similar chemistry to the longer-established hydro-gen-nickel oxide cell considered in Chapter 9. In most respects (including OCV and performance characteristics), it is very similar to the sealed nickel-cadmium cell, but with hydrogen absorbed in a metal alloy as the active negative material in place of cadmium. The replacement of cadmium not only increases the energy density, but also produces a more environmentally friendly power source with less severe disposal problems. The nickel-metal hydride cell, however, has lower rate capability, poorer charge retention and is less tolerant of overcharge than the nickel-cadmium cell. 

Data in Table VIII show that replacement of cadmium by barium retards the rate of discoloration of the reaction mixtures. Finally, when... 

Concerns over worker safety, processing emissions and finished product acceptability continue to drive new product development in this area. Western Europe has led these initiatives however, there are now signs that the USA marketplace is changing in order to conform with these environmental trends. Technological aspects of the replacement of cadmium in liquid stabilisers and the reduction of volatile constituents and phenol in these materials is reviewed. 7 refs. 

As a final note on PVC, it is worth mentioning Vinyl 2010, which is an EU voluntary commitment study on the PVC industry initiated in 2001 for the following 10 years, including mid-term revisions of targets in 2005 and definition of new objectives in 2010. The plan includes for full replacement of lead stabilisers by 2015, in addition to the replacement of cadmium stabilisers by March 2001 [27, 30]. Also in Vinyl 2010, the following values are put forward for maximum permissible VCM concentrations in the final PVC products ... 

V.C.R. McLoughlin, The replacement of cadmium for the coating of fasteners in aerospace applications, Trans. Inst. Met. Finish. 57 (1979) 102-104. 

Replacement of cadmium pigments and diarylide pigments is due to toxicological limitations in certain applications. 

Liquid stabilizers may also contain low levels of diphenyl phosphite (Weston DPP) specifically to reduce plateout through chelation of reaction products containing barium. The use of an active aryl phosphite such as diphenyl or triphenyl phosphite (Weston TPP and Doverphos 10) adds to early color and brightness, but is of little value in extended color retention as compared with aryl-alkyl phosphites that undergo the Arbuzov reaction. A liquid stabilizer composed of about half phosphite, as is common, will usually have no more than a few percent of triaryl phosphite, most often DPP, the balance either aU a phenyl isodecyl phosphite, or a blend with a hydrolysis-resistant grade. The development of more sophisticated use of phosphites has been a major factor in the replacement of cadmium in mixed metal stabilizers. 

Replacement of Labile Chlorines. When PVC is manufactured, competing reactions to the normal head-to-tail free-radical polymerization can sometimes take place. These side reactions are few ia number yet their presence ia the finished resin can be devastating. These abnormal stmctures have weakened carbon—chlorine bonds and are more susceptible to certain displacement reactions than are the normal PVC carbon—chlorine bonds. Carboxylate and mercaptide salts of certain metals, particularly organotin, zinc, cadmium, and antimony, attack these labile chlorine sites and replace them with a more thermally stable C—O or C—S bound ligand. These electrophilic metal centers can readily coordinate with the electronegative polarized chlorine atoms found at sites similar to stmctures (3—6). 

Antimony tris(isooctylthioglycolate) has found use in pipe formulations at low levels. Its disadvantage is that it cross-stains with sulfide-based tin stabilizers (122). Barium—zinc stabilizers have found use in plasticized compounds, replacing barium—cadmium stabilizers. These are used in mol dings, profiles, and wire coatings. Cadmium use has decreased because of environmental concerns surrounding certain heavy metals. 

The future of cadmium plating is in question because of cadmium toxicity (83). Cyanide-free cadmium plating systems have experienced some growth. Acid cadmium, based on cadmium sulfate compositions, is replacing some cyanide baths in the United States. The fluoborate cadmium is reported in use in the UK, especially in barrel plating (84). Cadmium plating is covered by ASTM (85), U.S. government, and ISO specifications (86). 

Vacuum Deposited Coatings Aluminium coatings have been strongly considered as a replacement for cadmium in the protection of high-tensile steel... 

Health and Safety Cadmium metal and its compounds are toxic and are injurious to health, and for this reason, cadmium is being replaced by other forms of coating wherever possible. For a number of important applications, however, no suitable alternatives have yet been identified. Where cadmium plating continues to be used, it is essential to comply with the regulations covering the use of cadmium. 

The synthetic approach is very simple and does not require any special set up. In a typical room temperature reaction, 1.0 mL aqueous solution of cadmium chloride was added to 20 mL aqueous solution of soluble starch in a 50 mL one-necked round-bottom flask with constant stirring at room temperature. The pH of the solution was adjusted from 6 to 11 using 0.1 M ammonia solution. This was followed by a slow addition of 1.0 mL colourless selenide ion stock solution. The mixture was further stirred for 2 h and aged for 18 h. The resultant solution was filtered and extracted with acetone to obtain a red precipitate of CdSe nanoaprticles. The precipitate was washed several times and dried at room temperature to give a material which readily dispersed in water. The same procedure was repeated for the synthesis of PVA and PVP - capped CdSe nanoparticles by replacing the starch solution with the PVA and PVP polymers while the synthesis of elongated nanoparticles was achieved by changing the Cd Se precursor ratio from 1 1 to 1 2. The synthesis of polymer capped ZnSe nanoparticles also follows the same procedure except that ZnCb solution was used instead of CdCb solution. 

Nickel-cadmium rechargeable batteries are being researched. Alternatives such as cadmium-free nickel and nickel hydride systems are also being researched, but nickel-cadmium batteries are unlikely to be totally replaced. Nickel-cadmium batteries can be reprocessed to reclaim the nickel. However, currently, approximately 80% of all nickel-cadmium batteries are permanently sealed in appliances. Changing regulations may result in easier access to these nickel-cadmium batteries for recycling. 

The most important phosphors are sulphides and oxides of transition metals. The sulphides of zinc and of cadmium are the most important materials of the sulphide type. An important condition of achieving a highly efficient phosphor is to prepare a salt of the highest possible chemical purity. The emission of zinc sulphide can be shifted to longer wavelengths by increasingly replacing the zinc ions with cadmium. 

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