In part due to increasingly stringent global restrictions, many companies have redesigned their products and processes to use safer alternatives. The significant reduction in use of Cd and Cd compounds by current TURA filers indicates that toxics use reduction options are available for many applications, and that Massachusetts companies are taking advantage of those opportunities.
Substantial information is available on Cd alternatives for soldering, plating, stabilizers, and pigments used in plastics. We also provide information on emerging alternatives to Cd-bearing batteries.
Alternatives for Plastics and Resins
Cadmium is used to create a range of yellow colors in plastics formulations. Cadmium sulfides and sulfo-selenides are used in pigments to create a family of yellow/orange/red pigments. Cadmium yellow is created using cadmium sulfide (CdS), cadmium red is cadmium selenide (CdSe) and cadmium orange is an intermediate cadmium sulfoselenide. Cadmium yellow is sometimes mixed with a hydrated chromium oxide pigment to create a bright, pale green mixture. Cadmium has also been used as a weathering, light and heat stabilizer in certain plastic formulations, especially in polyvinyl chloride (PVC).
Processes used in Massachusetts for Cd use as pigments and stabilizer additives include:
- Polymer compounding
- Plastic extrusion on copper wire
- Plastics blending and extruding
- Flexible plastics calendaring
A variety of alternatives are available for Cd in yellow pigments. Some alternatives pose significant health and environmental hazards, while others are superior from a health and environmental perspective.
As early as the beginning of the 1990s, many firms found that they were able to replace Cd in the majority of pigments in which it had been previously used. Alternatives include inorganic pigments based on acid solutions of synthetic oxo-nitrides, iron oxide pigments, bismuth vanadate pigments, organic/inorganic pigment blends using titanium dioxide, mixed metal oxide titanites, and/or iron oxide, rutile tin zinc compounds and others.
Cadmium has been used as a weathering, light and heat stabilizer primarily in PVC plastic formulations. In the United States, use of Cd-bearing stabilizers has decreased since 1990. Alternatives for Cd stabilizers include barium-zinc, calcium-zinc, antimony, organotin, and organic compound stabilizers. While these alternatives meet the necessary performance criteria for specific applications, antimony and organotin stabilizers are not considered to be safer substitutes because of their respective high toxicities.
Alternatives for Metal Products
Cadmium coatings are applied to various base metals to impart excellent corrosion resistance, especially in marine and alkaline environments. In addition to corrosion protection, Cd coatings provide a low coefficient of friction and therefore good lubricity, good electrical conductivity, easy solderability, and reduced risks of operating mechanisms being jammed by corrosion debris for many components in a wide range of engineering applications throughout industry.
Methods to reduce the use of Cd in metal plating applications include:
- Production process redesign to eliminate the need for the coating.
- Applying metallic-ceramic coatings to replace Cd in more expensive military applications, including landing gear axles of modern aircraft, gas-turbine-engine compressor sections and allied parts.
- Improved methods for the deposition of corrosion-resistant aluminum coatings for aerospace applications using ion- vapor-deposited (IVD) aluminum as an alternative to Cd.
- Using aluminum-molybdenum coatings in applications with specialized requirements, such as aerospace applications.
- Using metallic-ceramic coatings containing zinc, aluminum, or alloys of these metals to replace Cd for plating of fasteners in military and aerospace applications.
Alternatives for Batteries
Because it represents the biggest overall use of cadmium nationwide, it is appropriate to touch upon the availability of alternatives to Ni-Cd batteries.
Currently, the principal alternatives to NiCd batteries are lead-acid, Ni-metal hydride, and lithium-ion batteries as well as fuel cells. Nickel metal hydride batteries possess substantially greater energy-storage capacity and power per unit weight or volume than lead-acid batteries but are very expensive. Since 1991, rechargeable Ni-metal hydride batteries, with low discharge rates and long cycling stability, have been used for consumer applications such as portable computers, cordless appliances and communication equipment. A power-optimized version of Ni-metal hydride batteries are now fitted to commercialized hybrid vehicles. Lithium-ion and sodium–nickel chloride batteries have a lower environmental impact than lead–acid, Ni–Cd and Ni-metal hydride batteries.
Endnotes: Butterman, 2002; Llewellyn, 1994; Toxics Use Reduction Institute, Summary of Policy Analysis, Higher Hazard Substance Designation Recommendation: Cadmium (CAS # 7440-43-9) and Cadmium Compounds; Chromatics to Discontinue Production of Heavy Metal-based Colorants. The Wire Association International, 2006; Mulholland, B.M. Cadmium Free Colored Engineering Plastics for the Automotive Industry, in Annual Technical Conference, Society of Plastics Engineers, 1994; Wood, A., Cadmium-free Inorganic Pigments. Chemical Week, 2000; Jansen, M. et al., Inorganic Yellow-red Pigments without Toxic Metals. Nature, 2000; Endriss, H. et al., Bismuth Vanadate Pigments. Kunststoffe Plast Europe, 1996; Hatcher, H., et al., Providing Unique Solutions with a New Pigment Chemistry. Paint and Coatings Industry, 2004; Davis, The Product Side of Pollution Prevention: Evaluating the Potential for Safe Substitutes, 1994; Monaghan, D.P., et al., An Improved Method for the Deposition of Corrosion-resistant Aluminium Coatings for Aerospace Applications. Surface and Coatings Technology, 1993; Bielawski, M., Development of Unbalanced Magnetron Sputtered Al-Mo Coatings for Cadmium Replacement. Surface Coatings and Technology, 2004; Lambert, et al., Appropriate Battery Technology for a New, Rechargeable, Micro-solar Lantern. Journal of Power Sources, 2000; Otto, A. et al., Development of Fast Kinetics Metal Hydride Alloys and Battery Electrodes for High Power Applications. Journal of Alloys and Compounds, 1999; Bossche, P.V.d., et al., SUBAT: An Assessment of Sustainable Battery Technology. Journal of Power Sources, 2006.