Open AccessFast chemical and isotopic exchange of nitrogen during reaction with hot molybdenum
Author(s) -
Yokochi Reika,
Marty Bernard
Publication year - 2006
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2006gc001253
Subject(s) - nitrogen , molybdenum , crucible (geodemography) , extraction (chemistry) , nitride , chemistry , chemical composition , chemical reaction , isotopes of nitrogen , inorganic chemistry , analytical chemistry (journal) , environmental chemistry , biochemistry , computational chemistry , organic chemistry , chromatography , layer (electronics)
Molybdenum crucibles are commonly used to extract nitrogen from geological samples by induction heating. Because nitrogen is known to be reactive with certain metals (e.g., Ti and Fe), we have tested the reactivity of gaseous nitrogen with a Mo crucible held at 1800°C. The consumption of nitrogen, determined by monitoring the N 2 / 40 Ar ratio of the gas phase, varied between 25 and 100%, depending on the reaction duration. Nitrogen of the reacted gas was found to be systematically enriched in 15 N relative to 14 N by 10‰ compared to the initial isotopic composition, without any correlation with nitrogen consumption. We propose that a rapid isotopic exchange occurs between nitrogen originally trapped in the crucible and nitrogen from the gas phase, which modifies the isotopic composition of the reacted gas. This process can significantly bias the isotopic determination of nitrogen in rocks and minerals when a Mo furnace is used for gas extraction. Meanwhile, the rate of N‐Mo chemical bonding may be controlled by the formation of nitride (rather than solid solution), a process slower than the isotopic exchange. The use of a Mo furnace for the extraction of trace nitrogen from rocks and minerals should therefore be avoided.