Phase Transitions of Single Salt Particles Studied Using a Transmission Electron Microscope with an Environmental Cell

The hygroscopic behavior of 0.1 to 4 μ m NaBr, CsCl, NaCl, (NH₄)₂SO₄, and KBr particles were monitored using a transmission electron microscope (TEM) equipped with an environmental cell into which gases can be introduced. This instrument, commonly called an environmental transmission electron microscope or ETEM, allowed us to observe phase transitions and behavior of small particles at relative humidities between 0 and 100%. We used deliquescence relative humidity and efflorescence relative humidity values from the literature for each salt to calibrate the relative humidity in the environmental cell. Using our methodology, we reliably and accurately measured the phase transitions and hygroscopic behavior of inorganic particles with the ETEM.

Acknowledgments

This material is based on work supported by the National Science Foundation under Grant No. 0304213. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. We gratefully acknowledge the use of facilities within the center for Solid State Science at Arizona State University. In particular, we thank Karl Weiss, John Wheatley, Renu Sharma, and Peter Crozier for assistance.