Green tinge

here's some good news for those seeking non-toxic industrial colouring agents. Researchers at the Indian Institute of Technology (iit) in Chennai have developed an inorganic compound -- calcium-doped praseodymium phosphate -- that has the potential to impart green colour to paints, plastics and glasses much the same way as the commonly available but toxic chromium oxide. Used widely in industrial applications, chromium oxide is a known carcinogen that can damage the kidneys and the lungs.

V Sivakumar and U V Varadaraju of iit's chemistry department say their pigment is based on praseodymium compounds, which are commonly found in beach mineral, monazite. It can impart green to yellow hues to materials, as per their findings that appeared in the June issue of the Bulletin of Materials Science (Vol 28, No 3).

While scientists elsewhere have successfully developed eco-friendly pigments for other colours from rare earth metals, a benign green colourant was proving evasive till recently. The first one to emerge on the scene was calcium-doped cerium phosphate that was reported by Japanese scientists in 2003.

The iit scientists claim their pigment is comparable to calcium-doped cerium phosphate. To produce it, they dissolved praseodymium oxide and calcium carbonate in diluted nitric acid to which monoammonium phosphate was then added. The pigment was obtained from the precipitate after it was dried, ground and heated to 1,100 degrees Celsius to remove ammonia, nitrogen oxide and residual water.

The scientists say the new compound has to be evaluated for its economic and industrial feasibility before it finds use in everyday products. "The demands of the pigment industry are generally very stringent (for instance, colour should be fast and uniform)," Varadaraju said.

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