Definition
Most definitions of the term 'refractory metals' list the extraordinarly high melting point as a key requirement for inclusion. By one definition, a melting point above 4,000 °F (2,200 °C) is necessary to qualify. The five elements niobium, molybdenum, tantalum, tungsten and rhenium are included in all definitions, while the wider definition, including all elements with a melting point above 2,123 K (1,850 °C), includes a varying number of nine additional elements, titanium, vanadium, chromium, zirconium, hafnium, ruthenium, osmium and iridium. Transuranium elements (those above uranium, which are all unstable and not found naturally on earth) and technetium are never considered to be part of the refractory metals.
Read more about this topic: Refractory Metals
Famous quotes containing the word definition:
“Perhaps the best definition of progress would be the continuing efforts of men and women to narrow the gap between the convenience of the powers that be and the unwritten charter.”
—Nadine Gordimer (b. 1923)
“It is very hard to give a just definition of love. The most we can say of it is this: that in the soul, it is a desire to rule; in the spirit, it is a sympathy; and in the body, it is but a hidden and subtle desire to possessafter many mysterieswhat one loves.”
—François, Duc De La Rochefoucauld (16131680)
“The man who knows governments most completely is he who troubles himself least about a definition which shall give their essence. Enjoying an intimate acquaintance with all their particularities in turn, he would naturally regard an abstract conception in which these were unified as a thing more misleading than enlightening.”
—William James (18421910)