Hydration and Raman scattering studies of levitated microparticles: Ba(NO3)2, Sr(NO3)2, and Ca(NO3)2

Abstract

The phase transformation and hydration of inorganic salt particles composed of alkaline earth metal nitrates, Ba(NO3)2, Sr(NO3)2, and Ca(NO3)2, are investigated in a quadrupole cell, in which a levitated single microparticle is in dynamic equilibrium with water vapor under controlled humidity conditions. Laser Raman and Mie scattering techniques are used to probe the chemical and physical states of the microparticle before and after phase transformation. Because of the high degree of supersaturation that only a suspended solution droplet can attain before solidifying, metastable states not predicted from bulk solution thermodynamics often result. Thus it is found that, except for Ba(NO3)2 particles which form the stable anhydrous crystalline state upon efflorescence, Sr(NO3)2 and Ca(NO3)2 droplets solidify to a metastable amorphous state that contains residual water persisting even in high vacuum. Raman spectra of the amorphous particles reveal that the nitrate ions form contact-ion pairs with the bivalent cations and that the residual water molecules possess very little, if any, hydrogen bond characteristics. The deliquescence properties of the amorphous particles, which are found to be different from those expected of the bulk crystalline states, are also reported.

Cloud processing of mineral dust: direct comparison of cloud residual and clear sky particles during AMMA aircraft campaign in summer 2006

“…Although we cannot fully exclude the possibility that the particles had previously experienced clouds, it is interesting to find that almost all Ca-rich particles were in their characteristic spherical form even in clear-sky conditions. This is in accordance with the laboratory experiments and modeling studies which suggests that the active uptake of HNO 3 gas on the carbonate particles and the consecutive deliquescence readily takes place even under relatively dry conditions in the actual atmosphere (Tang and Fung, 1997;Krueger et al, 2003Krueger et al, , 2004Kelly and Wexler, 2005;Laskin et al, 2005;Gibson et al, 2006a, b).…”

“…The spherical shape of the processed Ca-rich particles most likely results from the expected amorphous metastable state of Ca(NO 3 ) 2 that contains residual water persisting even in high vacuum (Tang and Fung, 1997). From the bulk volume of the semi transparent particle, Ca, S and/or Cl are commonly found for elements Z>Na (Fig.…”

Sol-Gel SiO2-CaO-P2O5 biofilm with surface engineered for medical application

“…Figure 5 also illustrates the absence of peaks around 1046 cm -1 , assigned to the symmetric stretching of the nitrate groups. The absence of this absorption band confirms the total decomposition of the nitrate 31,39 . An additional peak, in Raman spectrum, appears near 720 cm -1 and is also assigned to carbonate groups 41 .…”

“…When calcium nitrate is decomposed by heat treatment at 400 °C for 15 minutes, calcium ions remain present in the silica network, as illustrated in Figure 5. Figure 5 is a Raman spectrum of the SiO 2 -CaO-P 2 O 5 film and shows a peak located at 1090 cm -1 (stretching vibration) assigned to calcium carbonate 39,40 . Figure 5 also illustrates the absence of peaks around 1046 cm -1 , assigned to the symmetric stretching of the nitrate groups.…”

Changes in background aerosol composition in Finland during polluted and clean periods studied by TEM/EDX individual particle analysis

“…These conversion products are highly hygroscopic (e.g. deliquescence RH for amorphous Ca(NO 3 ) 2 particles is only ∼13%, Tang and Fung, 1997). In PM 1−3.3 samples, several rounded Ca-rich particles seemed to be very thin (light contrast in TEM images), indicating that they have been in liquid form during the impaction on TEM grids.…”