Cadmium pigments are stable inorganic colouring agents which can be produced in a range of brilliant shades of yellow, orange, red and maroon. Their greatest use is in plastics but they also have significant application in ceramics, glasses and specialist paints.
Modern day Cadmium pigments are carefully engineered products manufactured in regulated chemical plants with full Health and Safety and Environmental permits under responsible care management. They are calcined to a high temperature to convert to the stable hexagonal form before then undergoing a series of further processes resulting in highly stable pigment grade products with controlled particle size, surface area and surface treatment to ensure they are not only correct for colour but also meet extremely low solubility limits.
Cadmium pigments are specific Cd compounds, with different CAS numbers and REACH registration files.
Cadmium zinc sulphide = CI Pigment Yellow 35, CAS Reg. No. 8048-07-5, Reach No. 01-2119981639-18-0001
Cadmium sulphoselenide orange = CI Pigment Orange 20, CAS Reg. No. 12656-57-4, Reach No. 01-2119981636-24-0001
Cadmium sulphoselenide red = CI Pigment Red 108, CAS Reg. No. 58339-34-7, Reach No. 01-2119981636-24-0001
These substances are specifically excluded from the classification and labelling entries in the DSD and GHS tables covering cadmium compounds. A risk assessment of these products conducted by the EU concluded that these products offer no significant hazard to either human health or to the environment. REACH registration has confirmed that no hazard classifications apply – either for human health or to the environment.
Chemical grade cadmium sulphide (CAS Reg. No. 1306-23-6) is a manufacturing intermediate and is not put on the market by ICdA member companies as a pigment.
Most cadmium pigments are used in plastics. These pigments disperse well in most polymers to give good colouring and high opacity and tinting strength. The pigments are insoluble in organic solvents, have good resistance to alkalis and in most cases will remain colour fast for the life of the plastic. As a result, cadmium pigments have been used in a wide range of plastic products. Nowadays, their greatest application is in complex polymers which are processed at higher temperatures and require the unique durability and technical performance of a cadmium pigment. Their use is almost mandatory in many nylon, acrylonitrile butadiene styrene (ABS), polycarbonates, high density polyethylene, silicone resins and other modern thermoplastic polymers processed at high temperatures which preclude the use of organic pigments and also most alternative inorganic pigments in the range of hues provided by cadmium. Cadmium pigmented engineering polymers such as ABS are widely used in products which include telephones, gas pipes and fittings, electricity cables, beverage crates and motor vehicle radiator fans. Pigments are usually incorporated in plastics in proportions of 0.01 to 0.75 per cent by weight.
(b) Specialist and industrial paints
Bright cadmium yellows, oranges and reds are major pigments for artists' colours where their permanence and opacity are the accepted standards against which other pigments are judged.
Cadmium yellows and reds can have service temperatures well above 300 C and are used in coatings for process chemical and steam pipes. They can also be incorporated in latex and acrylic coatings.
Cadmium pigments are usually incorporated in these paints in proportions of 10 to 15 per cent by weight.
(c) Ceramics and glasses
The unique abilities of highly stable cadmium pigments to withstand high processing and service temperatures make them the only choice in much of their colour range for glasses, ceramic glazes and vitreous and porcelain enamels. In transparent glasses the cadmium pigment particles are colloidally dispersed to produce the colours by selective absorption and scattering. The addition of 0.5 percent by weight of cadmium pigment produces bright transparent glasses with colour ranging from intense yellow through to ruby red depending upon the composition.
The bright colours of cadmium pigments are ideally suited to ceramics, vitreous enamels for glass and porcelain enamels for iron and steel domestic products.
(d) Miscellaneous uses
Cadmium pigments have a number of other minor uses in rubber, paper and inks although these are small in terms of cadmium consumption.
Fig.1 Manufacture of cadmium pigments.
Fig.1 Manufacture of cadmium pigments
(Size : 0.02 MB)