Hygroscopic Particle Behavior Studied by Interdigitated Array Microelectrode Impedance Sensors

详细信息    查看全文

• 作者：Eric Schindelholz ; Lok-kun Tsui ; Robert G. Kelly
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：January 9, 2014
• 年：2014
• 卷：118
• 期：1
• 页码：167-177
• 全文大小：601K
• ISSN：1520-5215

文摘

The hygroscopic behavior of soluble salts bears importance in many research fields including atmospheric sciences, corrosion, porous building materials, and pharmaceuticals. Several methods have been used to study deliquescence (solid to liquid) and efflorescence (liquid to solid) phase transitions of these salts. In this study, we measured the deliquescence and efflorescence RH values of single salt microparticles deposited on an interdigitated microelectrode sensor via electrical impedance. The salts examined were NaCl, LiCl, NaBr, KCl, and MgCl₂. Measured values were in agreement with in situ optical microscopic observations and, with the exception of MgCl_2, literature values. In the case of MgCl₂, deliquescence occurred at 33% RH and 12鈥?5% RH, with the latter range being previously unreported. The depressed deliquescence RH was hypothesized to be a result of the formation of a metastable MgCl₂ hydrate. Incomplete efflorescence of MgCl₂ was also observed after exposure to <1.5% RH for up to 22 h due to formation of solid shells which trapped fluid. The phenomena elucidated by these results provide an explanation for the anomalous water retention and uptake behavior of MgCl₂ below 33% RH reported elsewhere in the literature. The results presented in this study validate the use of this method as an alternative or complementary method for study of bulk-phase transitions of substrate-deposited particles across a broad RH range. These findings also demonstrate the utility of this method for detection of fluid trapping which cannot be directly ascertained by gravimetric and line-of-sight techniques commonly used in the study of hygroscopic particles.