Black, absorbing, and specialist pigments
المؤلف:
Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong
المصدر:
Shriver and Atkins Inorganic Chemistry ,5th E
الجزء والصفحة:
644
2025-10-13
309
Black, absorbing, and specialist pigments
Key points: Special colour, light absorbing, and interference effects can be induced in inorganic materials used as pigments. The most important black pigment is carbon black, which is a better defined, industrially manufactured form of soot. Carbon black is obtained by partial combustion or pyrolysis (heating in the absence of air) of hydrocarbons. The material has excellent absorption properties right across the visible region of the spectrum and applications include printing inks, paints, plastics, and rubber. Copper (II) chromite, CuCr2O4, with the spinel structure (Fig. 24.18), is used less frequently as a black pigment. These black pigments also absorb light outside the visible region, including the infrared, which means that they heat up readily on exposure to sunlight. Because this heating can have drawbacks in a number of applications, there is interest in the development of new materials that absorb in the visible region but reflect infrared wavelengths; Bi2Mn4O10 is one compound that exhibits these properties. Examples of more specialist inorganic pigments are magnetic pigments based on coloured ferromagnetic compounds such as Fe3O4 and CrO2, and anticorrosive pigments such as zinc phosphates. The deposition of inorganic pigments as thin layers on to surfaces can produce additional optical effects beyond light absorption. Thus, deposition of TiO2 or Fe3O4, as thin layers a few hundred nanometres thick, on flakes of mica produces lustrous or pearlescent pigments where interference effects between light scattered from the various surfaces and layers produces shimmering and iridescent colours.
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