The analysis is thermodynamic in nature, and ignores reaction kinetics. The diagrams are useful in predicting the conditions under which an ore will be reduced to its metal. In metallurgy, the Ellingham diagram is used to predict the equilibrium temperature between a metal, its oxide and oxygen and-by extension-reactions of a metal with sulfur, nitrogen, and other non-metals. The diagrams were first constructed by the British physical chemist Harold Johann Thomas Ellingham (1897–1975) in 1944. This analysis is usually used to evaluate the ease of reduction of metal oxides and sulfides. An Ellingham diagram is a graph showing the temperature dependence of compounds’ stability. The ability of metals to participate in thermic reactions can also be predicted from Ellingham diagrams. This effect was used by Theodore Harold ‘Ted’ Maiman (1927–2007) in 1960 to make the first successful laser, based on ruby. When the optical arrangement is such that the emission is stimulated by 694-nm photons reflecting back and forth between two mirrors, the emission grows strongly in intensity. The picture of a beautiful ruby is presented in Fig. When yellow-green light is absorbed, it is transmitted as red. This crystallographic arrangement results in light absorption in the yellow-green region of the spectrum. The red color is caused mainly by the presence of Cr III. Each Al III ion (and thus each Cr III ion) in the corundum crystal is surrounded by six oxide ions in a distorted octahedral coordination (Fig. Ruby is considered one of the four precious stones, together with sapphire, emerald and diamond. Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Ruby’s name comes from ruber, Latin for red. A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum (α-alumina), Al 2O 3, in which a small fraction of Al III is replaced by Cr III.
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