page_title: Georges Urbain
section_title: Elements
hierarchical_section_title: Georges Urbain / Elements
caption_attribution_description: English: Hafnium and zirconium are two of the elements that are most similar to each other. Therefore they are hard to separate. The silvery, heavy hafnium so far is used only for a few special technical applications. Hafnium carbide (HfC) and tantalum hafnium carbide (Ta4HfC5) are very hard and mechanically enduring, the latter has with more than 4000°C the highest melting point of all materials. After being exposed to air for more than a year, the surface is slightly oxidized and therefore darker and less glossy.
context_page_description: Georges Urbain was a French chemist, a professor of the Sorbonne, a member of the Institut de France, and director of the Institute of Chemistry in Paris. Much of his work focused on the rare earths, isolating and separating elements such as europium and gadolinium, and studying their spectra, their magnetic properties and their atomic masses. He discovered the element lutetium. He also studied the efflorescence of saline hydrates.
context_section_description: Urbain developed new and more efficient techniques for the separation of rare earths. By taking advantage of the weights of rare earths, he was able to design procedures to separate light from heavy   fractions, using magnesium and bismuth nitrates. This enabled him to test and refute a number of inaccurate rare earth "discoveries" claimed by other scientists.
  Urbain discovered the element lutetium (atomic number 71) independently in 1907 when he demonstrated that Jean Charles Galissard de Marignac's ytterbia contained two substances. Through spectral analysis of both, he was able to characterize them and prove that they were distinct elements.
  Urbain called his two components "neoytterbia" and "lutecia". 
  These components of ytterbia were independently isolated around the same time by Austrian chemist Carl Auer von Welsbach and the American chemist Charles James. Urbain and Welsbach accused each other of publishing results based on the other party. The dispute was officially settled in 1909 by the Commission on Atomic Mass, which granted priority to Urbain as the first to describe the separation of lutetium from ytterbium. Urbain's "lutecia" was adapted to "lutetium". Urbain's name "neoytterbium" was temporarily adopted, but later  Marignac's name was restored to the element ytterbium. 
  In 1911 Urbain isolated another new element which he called "celtium", but his studies were interrupted by World War I. In 1922, he announced his new element, fully characterizing its emission spectrum, but mistakenly identifying it as a rare earth. George de Hevesy and Dirk Coster also characterized it, placing it more accurately, and  called it "hafnium". A decades-long controversy over credit and naming was eventually decided in favor of hafnium. Although Urbain was right in detecting the presence of a new element,  the spectra and the chemical behavior he described were not a good match to the element later isolated. In part, the controversy resulted from the different techniques used by chemists like Urbain, who favored  chemical reduction techniques, and  physicists who increasingly relied on new X-ray spectroscopy methods.
  As of 1919, Urbain had completed an extensive study of phosphorescence spectra, and demonstrated that trace impurities could dramatically alter results. By introducing impurities into artificially prepared mixtures, he was able to duplicate the results reported by other researchers, again testing claims about possible new elements.
  Urbain was also a composer and sculptor.
caption: The element  hafnium, detected by Urbain as "celtium"
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