In situ investigation of decomposing ammonia and ammonobasic solutions under supercritical conditions via UV/vis and Raman Spectroscopy

Ammonothermal Synthesis of Nitrides: Recent Developments and Future Perspectives

“…Ar ecent study showed that ammonia decomposition is restrained in common Inconel 718 autoclaves, which was attributed to passivation layers on the autoclave walls partially shielding the catalytically active metal surface. Besides, in situ formation of NaNH 2 from NaN 3 was monitored by Raman and UV/Vis spectroscopy.T he investigationsi ndicate that degradation of dissolved NaN 3 to Na, and subsequentf ormation of NaNH 2 ,p roceeds between 600 and 650 K. [163] Future studies could furtherg ive information about dissolvedi ntermediates, as well as their formation and degradation conditions.…”

“…Besides, in situ formation of NaNH 2 from NaN 3 was monitored by Raman and UV/Vis spectroscopy. The investigations indicate that degradation of dissolved NaN 3 to Na, and subsequent formation of NaNH 2 , proceeds between 600 and 650 K . Future studies could further give information about dissolved intermediates, as well as their formation and degradation conditions.…”

“…Recent in situ Raman spectroscopy studies showedt hat ammonia decomposition is kinetically inhibited to some extent within common Inconel 718 autoclaves (Section 3.2.2). [163] Reduced decomposition of ammonia wasa lso observedw ith silver capsules as the growth environmentsinces ilver is ap oor catalystf or that process. [52] Pressure loss due to hydrogen diffusion through the autoclave walls is frequentlyo bserved at elevated temperatures, which was also restrained in experiments with silver capsules.…”

“…Noteworthy, decomposition of ammonia is favored in the presence of catalysts, and the chemical equilibrium is not necessarily reached within the reaction time. Recent in situ Raman spectroscopy studies showed that ammonia decomposition is kinetically inhibited to some extent within common Inconel 718 autoclaves (Section 3.2.2) . Reduced decomposition of ammonia was also observed with silver capsules as the growth environment since silver is a poor catalyst for that process .…”

Crystalline Nitridophosphates by Ammonothermal Synthesis

“…Supporting fundamentalr esearch on the reaction mechanisms, intermediate species and dissolution/crystallization processes, however,m ight be necessary.T herefore, in situ measurements such as X-ray,N MR, or Ramant echniques may providei mportant insights into these processes. [41,42] Experimental Section General Loading of the autoclaves with solid starting materials (see below) were conducted under exclusion of oxygen and moisture in an argon-filled glovebox (Unilab, MBraun, Garching, O 2 < 1ppm, H 2 O < 1ppm). The condensation of ammonia into the autoclaves was performed using avacuum line ( 0.1 Pa) with argon and ammonia (both:A ir Liquide, 99.999 %) supply.T he gases were further purified by gas cartridges (Micro torr FT400-902 (for Ar) and MC400-702FV (for NH 3 ), SAES Pure Gas Inc.,S an Luis Obispo, CA, USA), providing ap urity level of < 1p pbV H 2 O, O 2 and CO 2 .T he amount of condensed ammonia was detected using am ass flow meter (d-6320-DR, Bronkhorst, Ruurlo, Netherlands).…”