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Date of Award
Spring 5-17-2019
Degree Name
Bachelor of Arts (A.B.)
Restricted/Unrestricted
Restricted
Abstract
Controlling and understanding crystal nucleation from a liquid is critically important for glass and nanocrystal formation. This senior thesis focuses on two projects that investigate this:(1) an experimental attempt to improve glass formation by changing the structure of the supercooled liquid and (2) an investigation of nucleation processes based on an analysis of molecular dynamics results for a metallic liquid. In the first project, we added Si, Al, and B, to liquid Ti 39.5 Zr 39.5 Ni 21 and Zr 80 Pt 20 . We demonstrate that the addition of the metalloid B can decrease the amount of icosahedral order in a Ti 39.5 Zr 39.5 Ni 21 , making it more difficult to form the icosahedral quasicrystal phase, which is the first phase to form at high temperature. An addition of 9 atomic percent of B in the Ti 39.5 Zr 39.5 Ni 21 liquid led to a partially amorphous sample during melt-spinning. Addition of B to Zr 80 Pt 20 did not, however, produce the same effect. Molecular dynamics investigations have shown that the Al 20 Ni 60 Zr 20 crystallizes to a body-centered-cubic (bcc) crystal phase. The second project is focused on identifying the critical cluster size for nucleation as a function of temperature in this system. We show that the nucleating clusters can be identified based on an order parameter constructed from spherical harmonics that characterizes the bcc order (Q8). We found that the optimal Q8 cutoff values for our intersectand-tag method (ITM) is between .305 and .375, with .33, and .34 being the more promising cutoffs. While further work is needed to definitively determine the critical cluster sizes, we outline here a method to do this from an examination of when dN/dt changes sign (with N being the number of atoms in a tagged cluster and t being time) in conjunction with ITM. Once the critical cluster size is established and the criteria for a cluster defined, the interfacial width and chemical compositions of clusters of Al 20 Ni 60 Zr 20 liquid are also properties of interests that can be further investigated.
Mentor
Ken Kelton
Additional Advisors
Anupriya Agrawal, Zohar Nussinov
Recommended Citation
Chang, Ryan, "Studies of Nucleation and Glass Formation in Metallic Liquids" (2019). Senior Honors Papers / Undergraduate Theses. 13.
https://openscholarship.wustl.edu/undergrad_etd/13