|Ph.D Student||Gandman Maria|
|Subject||The Influence of Solid Surface Structure on Ordering|
at Solid-Liquid Interfaces
|Department||Department of Materials Science and Engineering||Supervisor||Professor Wayne D. Kaplan|
|Full Thesis text|
The investigation of solid-liquid interfaces is important for fundamental science, and for many technological processes. The concept of order in a liquid in the vicinity of a crystalline solid has been studied for the past 50 years. Only recently, by using in-situ TEM investigations combined with detailed image reconstruction, the existence of order in liquid aluminum (Al) adjacent to crystalline alumina (Al2O3) was proven to exist. However, due to the complexity of the TEM image analysis techniques only one interface between the liquid Al and solid Al2O3 was investigated.
In order to understand the influence of solid surfaces on the ordering phenomenon in liquids, a comparison between ordering in liquid Al at various interfaces with solid Al2O3 should be conducted. The effect of the ordering phenomenon on the solid-liquid interface energies should also be studied.
In the current study implementation of Cs-corrected high resolution TEM enabled direct quantification of the ordering phenomena. This enabled investigation of ordering in liquid Al as a function of the Al2O3 surface, and ordering at various Al2O3 surfaces was investigated. A higher degree of order in liquid Al was found at Al-Al2O3 interfaces with a higher interface energy. It was also found that ordering in the liquid is affected by the crystalline surfaces as long as the periodicity superimposed by the crystal is close to the nearest neighbor distance in bulk liquid Al. A technique which implemented in-situ EELS was developed and used for the investigation of the liquid Al density at various Al2O3 surfaces. The combination of HRTEM and EELS showed preferential oxygen segregation to specific Al-Al2O3 interfaces.
In-situ Cs-corrected HRTEM combined with EELS was also used for the investigation of the geometric confinement effect on order in liquid Al. It was found that liquid Al confined in a corner between two Al2O3 surfaces was more ordered than the liquid Al examined on the same Al2O3 surfaces separately. This confirmed the assumption that the growth of crystalline Al2O3 is enhanced by more ordered regions in the liquid.
Evaluation of the entropy decrease due to ordering showed that the expected gain in energy due to the ordering process is at least 40% of the Al-Al2O3 interface energy. The Gibbs adsorption isotherm was used to describe the ordering phenomenon and the Gibbsian excess parameter (Γ) was expanded to include order in addition to conventional chemical excess.