Molecular events in deliquescence and efflorescence phase transitions of sodium nitrate particles studied by Fourier transform infrared attenuated total reflection spectroscopy

Lu, Pei-Dong, Wang, Feng, Zhao, Li-Jun, Li, Wen-Xue, Li, Xiao-Hong, Dong, Jin-Ling, Zhang, Yun-Hong and Lu, Gao-Qing (2008) Molecular events in deliquescence and efflorescence phase transitions of sodium nitrate particles studied by Fourier transform infrared attenuated total reflection spectroscopy. Journal of Chemical Physics, 129 10: . doi:10.1063/1.2973623

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Author Lu, Pei-Dong
Wang, Feng
Zhao, Li-Jun
Li, Wen-Xue
Li, Xiao-Hong
Dong, Jin-Ling
Zhang, Yun-Hong
Lu, Gao-Qing
Title Molecular events in deliquescence and efflorescence phase transitions of sodium nitrate particles studied by Fourier transform infrared attenuated total reflection spectroscopy
Journal name Journal of Chemical Physics   Check publisher's open access policy
ISSN 0021-9606
1520-9032
Publication date 2008-09-01
Sub-type Article (original research)
DOI 10.1063/1.2973623
Open Access Status File (Publisher version)
Volume 129
Issue 10
Total pages 8
Place of publication College Park, MD, United States
Publisher American Institute of Physics
Language eng
Formatted abstract
The NaNO3 droplets with sizes of 1-5 μm generated from a nebulizer were deposited on a ZnSe substrate in a Fourier transform infrared attenuated total reflection (FTIR-ATR) chamber. After solidification of the droplets with dry N2 gas passing through the chamber, the solid NaNO3 particles were monitored by in situ FTIR-ATR spectra in cycles of deliquescence and efflorescence processes with varying relative humidities (RHs). With an increase in the RH, a dominant peak at ∼3539 cm-1, together with three relatively weak peaks at ∼3400, ∼3272, and ∼3167 cm-1, in the O-H stretching band of water was resolved by the high signal-to-noise ratio FTIR-ATR spectra. The dominant peak and the three relatively weak peaks were contributed by the water monomers and the aggregated water molecules adsorbed on the surfaces of solid NaNO3 particles, respectively. When the RH approached ∼72%, slightly lower than the deliquescence RH (74.5%), the band component at ∼3400 cm-1 became the main peak, indicating that the water monomers and the aggregated water molecules aggregated to form a thin water layer on the surfaces of solid NaNO3 particles. A splitting of the v3-NO3 - band at 1363 and 1390 cm-1 at the RH of ∼72%, instead of the single v3-NO3 - band at 1357 cm-1 for the initial solid NaNO3, was observed. We suggested that this reflected a phase transition from the initial solid to a metastable solid phase of NaNO3. The metastable solid phase deliquesced completely in the region from ∼87% to ∼96% RH according to the fact that the v3-NO3 - band showed two overlapping peaks at 1348 and 1405 cm-1 similar to those of bulk NaNO3 solutions. In the efflorescence process of the NaNO3 droplets, the v1-NO3 - band presented a continuous blueshift from 1049 cm-1 at ∼77% RH to 1055 cm-1 at ∼36% RH, indicating the formation of contact ion pairs between Na+ and NO3 -. Moreover, in the RH range from ∼53% down to ∼26%, two peaks at 836 and 829 cm-1 were observed in the v2-NO3 - band region, demonstrating the coexistence of NaNO3 solid particles and droplets.
Q-Index Code C1
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Institutional Status UQ
Additional Notes Article number 104509

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Engineering Publications
Australian Institute for Bioengineering and Nanotechnology Publications
 
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