Fluorine is the most reactive chemical element. That is why it is not found in nature in its elemental form, but only in compounds, such as fluorite – that was the accepted scientific doctrine so far. A special fluorite, the "fetid fluorite" or "antozonite", has been the subject of many discussions for nearly 200 years. This mineral emits an intensive odor when crushed. Now, for the first time, scientists from the Technische Universitaet Muenchen (TUM) and the Ludwig-Maximilians-University Munich (LMU) have successfully identified natural elemental fluorine in this fluorspar. They report their results in the international edition of the scientific journal Angewandte Chemie.
Being the most reactive of all chemical elements fluorine calls for extremely careful handling. It is so aggressive that glass laboratory instruments cannot resist it and even bricks burn when exposed to fluorine gas. Yet elemental fluorine has numerous industrial applications including corrosion prevention or fuel tank diffusion barriers and it is used for the production of sulphur hexafluoride, which serves as insulating material in high voltage switches.
Because of its extreme properties, until now chemists were convinced that fluorine cannot occur in nature in its elemental form, but only as a fluoride ion, for instance in minerals such as fluorite (CaF2), also known as fluorspar. A certain variety of it, the so-called "fetid fluorite" or "antozonite" from the "Maria" mine in Woelsendorf in the Upper Palatinate (Germany), has been an object of contention in science for some 200 years. When crushed, it emits an unpleasant, pungent smell.
A number of eminent chemists, among them Friedrich Woehler (1800-1882) and Justus von Liebig (1803-1873), proposed various substances to explain the odor. Over the years, scientists resorted to olfactory tests, chemical analyses and complex mass spectrometer studies – coming to very different conclusions. Next to elemental fluorine, substances like iodine, ozone, phosphorus compounds, arsenic, sulphur, selenium, chlorine, hypochlorous acid and hydrofluorocarbons were made responsible for the smell. Direct evidence that this fluorspar has inclusions of fluorine and that the gas does not form during crushing was lacking hitherto.
Now, finally, a scientific team led by Florian Kraus, head of the Fluorine Chemistry Work Group at the Department of Chemistry of the Technische Universitaet Muenchen, and by Joern Schmedt auf der Guenne, head of the Emmy-Noether Work Group for Solid State NMR at the Department of Chemistry of the Ludwig-Maximilians-University Munich, have succeeded in directly proving the presence of fluorine in "antozonite" beyond any doubt. Using 19F-NMR spectroscopy, they were able to identify the fluorine "in-situ", i.e. non-destructively in its natural environment, and thereby put an end to the long discussions about the cause for the odor of "stinking fluorspar".
"It is not surprising that chemists doubted the existence of elemental fluorine in fetid fluorite," explain the researchers. "The fact that elemental fluorine and calcium, which would normally react with each other at once, are found here side by side is indeed hard to believe." However, in the case of "antozonite" there are very special conditions: The elemental fluorine is generated through minute uranium inclusions in the mineral, which constantly emit ionizing radiation and thus split the fluorite into calcium and elemental fluorine. The fluorine remains in minute inclusions, separated from the calcium by the non-reactive fluorite and thus retains its elemental form. The ionizing radiation also leads to the formation of calcium clusters, which give "antozonite" its dark color.
Technische Universitaet Muenchen: http://www.tum.de
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
Researchers say the right mix of erosion and stress creates Earth’s natural sandstone arches and columns
Michael Slezak goes deep under the outback to find a home for the southern hemisphere's first WIMP detector, which could confirm our best direct signal yet
Pick the right plastic off a refuse tip, then shred, melt and convert it into feedstock for 3D printers – it's a living for some of India's poorest people
Sky surveys suggest that dark matter or some other mysterious dark material may be lighting up the universe with too much ultraviolet radiation
Rare particle scattering detected at CERN may help test how the Higgs boson imparts mass to other particles – and perhaps lead to new physics
The 260-foot-wide crater is in remote Siberian area called Yamal, which translates as "end of the world"
It's not a plot from a Bond film: Zapping diamonds could tell researchers more about the insides of giant planets.
The traditional Japanese art of folding paper is now adding grace and ease to the deployment of fragile solar panels, seismometers and other vital instruments in outer space.
Some areas of country are at higher risk for powerful quakes than once thought
Cage-shaped molecules made of 40 boron atoms may lead to new "wonder" materials with unique properties