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Emerging Mirror Technologies
Published in Paul Yoder, Daniel Vukobratovich, Opto-Mechanical Systems Design, 2017
William A. Goodman, Paul R. Yoder
Silicon carbide, also known as carborundum, is a compound with equal portions of silicon and carbon atoms. It was first produced by Edward Acheson around 1893. Acheson developed an electric batch furnace to produce the material in bulk, and the Carborundum Corporation was born. Interestingly, natural crystals of silicon carbide, also known as the mineral moissanite (moys-uh-nite), were not discovered until 1904. Professor Moissan found the first samples of the mineral while exploring in California and Arizona. Some 85 years later, Kurt Nassau created moissanite gem stones. These gem stones are harder than sapphire, ruby, or emerald and register 9.25 on the Mohs hardness scale, a gemstone hardness that is second only to diamond. Moissanite gems have an index of refraction (n = 2.69) greater than diamond (n = 2.42) and 2.4 times the spectral dispersion. Mirrors made of silicon carbide are discussed in considerable detail in Section 6.5.4 of this volume.
Metals, Their Biological Functions and Harmful Impacts
Published in Karlheinz Spitz, John Trudinger, Mining and the Environment, 2019
Karlheinz Spitz, John Trudinger
Chromium was discovered at the end of the eighteenth century. The name chromium is derived from the Greek word chroma which means colour, since chromium reacts with certain other materials to determine their colours. For example, the green colour of emerald is caused by the presence of very small amounts of chromium in the crystal. Chromium, in the form of Cr (III), is an essential trace element for humans and animals. Its most common harmful effect on humans is chromium allergy caused by exposure to large amounts of chromium (especially Cr (VI) compounds) in the working environment. Chromium compounds are also assumed to be carcinogenic (RTI 2007). Environmentally, Cr (VI) compounds are generally considered to be toxic.
Atomic and Molecular Origins of Color
Published in Mary Anne White, Physical Properties of Materials, 2018
Interestingly, emeralds, which are green, also derive their color from Cr3+ ions, this time in a material with composition Be3Al2SiO6 (known as beryl when pure). The Cr3+ in this structure is in a very similar environment to that in ruby, but it experiences a different crystal field strength. The difference in color subtly illustrates the importance of the magnitude of the crystal field strength. Determination of whether the crystal field strength is less than or greater than in ruby is left as an exercise for the reader.
Chelate assisted phytoextraction for effective rehabilitation of heavy metal(loid)s contaminated lands
Published in International Journal of Phytoremediation, 2023
Akshaya Prakash Chengatt, Nair G. Sarath, Delse Parekkattil Sebastian, N. Shibin Mohanan, E. S. Sindhu, Satheesh George, Jos T. Puthur
Chromium is a hard, brittle, white, lustrous metal found commonly in nature. It is used in metal finishing formulations, pigments, synthetic emeralds, wood preservatives, catalysts, as a fungicide, chromium plating, etc. (Shrivastava et al.2002). The wide use of chromium has led to the contamination of the environment and has become a matter of concern in recent years (Zayed and Terry 2003).