Cluster Formation in Solid-Liquid Interface Boundary Layers of KDP Studied by Raman Spectroscopy

Lu, Guang; Xia, Hengchuan; Sun, Deqing; Zheng, Weimin; Sun, Xun; Gao, Zeliang; Wang, J.Y.

doi:10.1002/1521-396x(200112)188:3<1071::aid-pssa1071>3.0.co;2-c

Cited by 16 publications

(12 citation statements)

References 7 publications

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“…As the supersaturation increases, the monomers aggregate, forming dimers, trimers, oligomer, and higher polymers. Such polymerization behaviors can be deduced from the shape of PO 2 peak at 1,077 cm −1 , which becomes progressively more asymmetric and broadens at higher supersaturation as reported previously (42)(43)(44). The P(OH) 2 Raman peak at 877 cm −1 shows a blue-shift behavior with respect to supersaturation as expected (33).…”

Section: Resultsmentioning

confidence: 99%

Multiple pathways of crystal nucleation in an extremely supersaturated aqueous potassium dihydrogen phosphate (KDP) solution droplet

Lee

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Solution studies have proposed that crystal nucleation can take more complex pathways than previously expected in classical nucleation theory, such as formation of prenucleation clusters or densified amorphous/liquid phases. These findings show that it is possible to separate fluctuations in the different order parameters governing crystal nucleation, that is, density and structure. However, a direct observation of the multipathways from aqueous solutions remains a great challenge because heterogeneous nucleation sites, such as container walls, can prevent these paths. Here, we demonstrate the existence of multiple pathways of nucleation in highly supersaturated aqueous KH 2 PO 4 (KDP) solution using the combination of a containerless device (electrostatic levitation), and in situ micro-Raman and synchrotron X-ray scattering. Specifically, we find that, at an unprecedentedly deep level of supersaturation, a highconcentration KDP solution first transforms into a metastable crystal before reaching stability at room temperature. However, a low-concentration solution, with different local structures, directly transforms into the stable crystal phase. These apparent multiple pathways of crystallization depend on the degree of supersaturation.multipath nucleation | liquid-droplet levitation | supersaturation | in situ X-ray diffraction | in situ micro-Raman spectroscopy N ucleation is the first step toward crystallization, in which atoms or particles aggregate to form clusters in a metastable liquid, called crystal nuclei. The crystal nuclei in metastable liquid grow continuously if their size exceeds a critical limit, and are subsequently stabilized. Based on the classical nucleation theory (CNT) (1, 2), nucleation is mainly governed by two factors, that is, interfacial free energy and volume Gibbs free energy (or chemical potential) between liquid and crystal phases. Although the volume Gibbs free energy acts to stabilize the crystal nuclei, the interfacial free energy works as an energy barrier preventing the formation of the nuclei. If the crystal-liquid interfacial free energy creates a sufficiently high energy barrier, the liquid can be supercooled, supersaturated, or even supercompressed. In case of liquid metals (3-6), the crystal-liquid interfacial free energy arises from configurational entropy differences between crystal and liquid. That is, the greater difference in local structural orderings between crystal and liquid phases results in higher interfacial free energy, which consequently leads to a higher nucleation barrier and thus deeper supercooling. This concept has been verified in various metallic systems for elements (7) and many alloys (8-12). However, many experimental and theoretical investigations have raised questions that CNT may not be adequate to describe the initial nucleation processes in biomaterials (13-17) and minerals (18)(19)(20)(21)(22)(23)(24)(25)(26).Recently, an alternate nucleation mechanism, called multipathway nucleation (or crystallization) (13-23, 25, 26), has been proposed fo...

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Section: Resultsmentioning

confidence: 99%

Multiple pathways of crystal nucleation in an extremely supersaturated aqueous potassium dihydrogen phosphate (KDP) solution droplet

Lee

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Their mixed crystals (KADP) with different compositions have also attracted much attention because of the existence of the interesting spin glass state in a certain intermediate mixing concentration range [20,21] crystals of KADP with perfect quality are still difficult to prepare, especially for the crystals with intermediate concentration [22]. Therefore, there are many puzzles in the growth process, such as the form of growth units [23,24], the molecular interactions between growth units, and crystal surfaces [25,26].…”

Section: Introductionmentioning

confidence: 99%

Crystal growth of KDP, ADP, and KADP

Ren

Xue

2008

Journal of Crystal Growth

148

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“…According to [15,16], there are no bands in Raman scattering spectra of KDP solutions that could be referred to KH 2 PO 4 ion pairs, which may indicate complete dissociation of KH 2 PO 4 salt. This prejudices the results of calculations of particle concentrations in KDP solutions fulfilled in the work [17], where partial dissociation of KH 2 PO 4 in concentrated solutions is reported.…”

Section: Resultsmentioning

confidence: 99%

“…This prejudices the results of calculations of particle concentrations in KDP solutions fulfilled in the work [17], where partial dissociation of KH 2 PO 4 in concentrated solutions is reported. According to [15] [12]. We can assume that oligomers in solution contain molecules of water, but closer to the surface of the face, H 2 O molecules escape to the solution.…”

Section: Resultsmentioning

confidence: 99%