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First Direct Study of the Ammonolysis Reaction in the Most Common Alkaline and Alkaline Earth Metal Hydrides by in Situ SR-PXD

Pistidda, C.; Santoru, A.; Garroni, S.; Bergemann, N.; Rzeszutek, A.; Horstmann, C.; Thomas, Diana LU ; Klassen, T. and Dornheim, M. (2015) In Journal of Physical Chemistry C 119(2). p.934-943
Abstract
We report on the first in situ synchrotron radiation powder X-ray diffraction study (SR-PXD) of the ammonolysis reaction of selected alkaline and alkaline earth metal hydrides (i.e., LiH, NaH, KH, MgH2, and CaH2). The investigation was performed using an in situ SR-PXD pressure cell at an initial NH3 pressure of 6.5 bar in a range of temperature between room temperature (RT) and 350 degrees C. The results of this work give new important insights into the formation of metal amides and imides starting from the corresponding metal hydrides. LiH was observed to react with NH3 to form LiNH2 already at RT, and then it decomposes into Li2NH at 310 degrees C through the formation of nonstoichiometric intermediates of the Li1+-xNH2-x form. The... (More)
We report on the first in situ synchrotron radiation powder X-ray diffraction study (SR-PXD) of the ammonolysis reaction of selected alkaline and alkaline earth metal hydrides (i.e., LiH, NaH, KH, MgH2, and CaH2). The investigation was performed using an in situ SR-PXD pressure cell at an initial NH3 pressure of 6.5 bar in a range of temperature between room temperature (RT) and 350 degrees C. The results of this work give new important insights into the formation of metal amides and imides starting from the corresponding metal hydrides. LiH was observed to react with NH3 to form LiNH2 already at RT, and then it decomposes into Li2NH at 310 degrees C through the formation of nonstoichiometric intermediates of the Li1+-xNH2-x form. The formation of NaNH2 takes place nearly at RT (28 degrees C), and it melts at 180 degrees C. As for LiH, KH reacts with NH3 at RT to surprisingly form, what it seems to be, cubic KNH2. However, we believe this phase to be a solid solution of KH in KNH2. At high temperature, the possible formation of several solid solutions of K(NH2)(1-y)H-y with defined composition is also observed. The formation of Mg(NH2)(2) was observed to starts at around 220 degrees C, from the interaction beta-MgH2 and NH3. At 350 degrees C, when all beta-MgH2 is consumed, the formation of Mg(NH2)(2) stops and MgNH is formed by the reaction between beta-MgH2 and NH3. Our results indicate that the formation of the beta-MgH2 is a key step in the synthesis of Mg(NH2)(2) at low temperature (e.g., via ball milling technique). CaH2 was observed to react with NH3 at around 140 degrees C to form CaNH. At higher temperature the appearance of new reflections of possible Ca1+xNH phases, with the same crystalline structure of CaNH but with a smaller cell parameter was observed. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry C
volume
119
issue
2
pages
934 - 943
publisher
The American Chemical Society
external identifiers
  • wos:000348094000008
  • scopus:84921320541
ISSN
1932-7447
DOI
10.1021/jp510720x
language
English
LU publication?
yes
id
81239e6c-5340-42ef-a69a-a4201c008537 (old id 5193552)
date added to LUP
2015-03-30 13:02:26
date last changed
2017-07-23 03:19:37
@article{81239e6c-5340-42ef-a69a-a4201c008537,
  abstract     = {We report on the first in situ synchrotron radiation powder X-ray diffraction study (SR-PXD) of the ammonolysis reaction of selected alkaline and alkaline earth metal hydrides (i.e., LiH, NaH, KH, MgH2, and CaH2). The investigation was performed using an in situ SR-PXD pressure cell at an initial NH3 pressure of 6.5 bar in a range of temperature between room temperature (RT) and 350 degrees C. The results of this work give new important insights into the formation of metal amides and imides starting from the corresponding metal hydrides. LiH was observed to react with NH3 to form LiNH2 already at RT, and then it decomposes into Li2NH at 310 degrees C through the formation of nonstoichiometric intermediates of the Li1+-xNH2-x form. The formation of NaNH2 takes place nearly at RT (28 degrees C), and it melts at 180 degrees C. As for LiH, KH reacts with NH3 at RT to surprisingly form, what it seems to be, cubic KNH2. However, we believe this phase to be a solid solution of KH in KNH2. At high temperature, the possible formation of several solid solutions of K(NH2)(1-y)H-y with defined composition is also observed. The formation of Mg(NH2)(2) was observed to starts at around 220 degrees C, from the interaction beta-MgH2 and NH3. At 350 degrees C, when all beta-MgH2 is consumed, the formation of Mg(NH2)(2) stops and MgNH is formed by the reaction between beta-MgH2 and NH3. Our results indicate that the formation of the beta-MgH2 is a key step in the synthesis of Mg(NH2)(2) at low temperature (e.g., via ball milling technique). CaH2 was observed to react with NH3 at around 140 degrees C to form CaNH. At higher temperature the appearance of new reflections of possible Ca1+xNH phases, with the same crystalline structure of CaNH but with a smaller cell parameter was observed.},
  author       = {Pistidda, C. and Santoru, A. and Garroni, S. and Bergemann, N. and Rzeszutek, A. and Horstmann, C. and Thomas, Diana and Klassen, T. and Dornheim, M.},
  issn         = {1932-7447},
  language     = {eng},
  number       = {2},
  pages        = {934--943},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry C},
  title        = {First Direct Study of the Ammonolysis Reaction in the Most Common Alkaline and Alkaline Earth Metal Hydrides by in Situ SR-PXD},
  url          = {http://dx.doi.org/10.1021/jp510720x},
  volume       = {119},
  year         = {2015},
}