1:45 PM - 2:00 PM
[AAS11-18] In-situ observation of the deliquescence process of ammonium sulfate nanoparticles under atmospheric pressure using a transmission electron microscope
Keywords:Aerosol, TEM, Deliquescence
Major aerosols consist of a mixture of inorganic salts and organic matter in the size range of 0.01-10 μm, and their surface morphology and phase separation exhibit heterogeneous structures that depend on particle size. Aerosols play an important role in the Earth's heat budget and in chemical reactions in the atmosphere. Nevertheless, the origin of their diverse heterogeneous structures, their size dependence, and their effects on surface chemical reactions are not well understood. This is because it is not easy to extract size dependence and local phenomena near the surface from conventional experiments on systems with many dispersed fine particles. In this study, we address this issue by visualizing the deliquescence process of individual particles in “in-situ” observation experiments using a fluid-reaction transmission electron microscope.
We used two Si chips with amorphous SiN membranes to fabricate an experimental cell that creates an atmospheric pressure environment. Ammonium sulfate particles were placed on one of the chips as a sample of a simulated aerosol, and then sandwiched between the two chips. The silicon chip has an amorphous silicon nitride window with an area of 20-50 μm × 500 μm and 50 nm thickness that allows electron beams to pass through. The experimental cell is placed in the Poseidon holder (Protochips Inc.) and loaded into the TEM (JEM-2100F, JEOL) with an acceleration voltage of 200 kV. First, characteristics of the initial sample were observed. Then, nitrogen gas and water vapor were mixed in a desired ratio using mass flow controllers and flowed into the cell. The humidity before or after the cell was monitored using a hygrometer. Because the holder used to observe the cell in the TEM was designed to observe liquid samples, there was a problem that the humidity before and after the holder changed greatly. Therefore, we improved the holder so that we could control the humidity.
As a result, we succeeded in conducting in-situ TEM observation of the deliquescence process of ammonium sulfate microparticles. In the presentation, we will discuss the size dependence of water absorption, the size dependence of deliquescence, the relationship between deliquescence and crystal facets, and the dehydration process.
This work was supported by JSPS KAKENHI Grant Number 23H00515.
We used two Si chips with amorphous SiN membranes to fabricate an experimental cell that creates an atmospheric pressure environment. Ammonium sulfate particles were placed on one of the chips as a sample of a simulated aerosol, and then sandwiched between the two chips. The silicon chip has an amorphous silicon nitride window with an area of 20-50 μm × 500 μm and 50 nm thickness that allows electron beams to pass through. The experimental cell is placed in the Poseidon holder (Protochips Inc.) and loaded into the TEM (JEM-2100F, JEOL) with an acceleration voltage of 200 kV. First, characteristics of the initial sample were observed. Then, nitrogen gas and water vapor were mixed in a desired ratio using mass flow controllers and flowed into the cell. The humidity before or after the cell was monitored using a hygrometer. Because the holder used to observe the cell in the TEM was designed to observe liquid samples, there was a problem that the humidity before and after the holder changed greatly. Therefore, we improved the holder so that we could control the humidity.
As a result, we succeeded in conducting in-situ TEM observation of the deliquescence process of ammonium sulfate microparticles. In the presentation, we will discuss the size dependence of water absorption, the size dependence of deliquescence, the relationship between deliquescence and crystal facets, and the dehydration process.
This work was supported by JSPS KAKENHI Grant Number 23H00515.