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Melting, Solidification and Sintering/Coalescence of Nanoparticles

Wang, Ningyu

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2010, Doctor of Philosophy, Ohio State University, Industrial and Systems Engineering.

The research goal of this work is to develop an understanding of the mechanism of nanoparticle melting, solidification and sintering resulting from a laser-triggered nanoscale spark-plasma heat source. The study is motivated by the fact that physical properties of nanoparticles exhibit a strong size effect due to significant increase of surface area to volume ratio thus affects nanoparticle consolidation and related material processes. Molecular dynamics (MD) is a promising simulation method for understanding of material behaviors at nanometer scales and is selected as a major computational tool for this study.

A reversible nonhomogeneous surface premelting model of Au nanoparticles is demonstrated by our simulations. With temperature increase liquid-like atoms first appear at some vertices and edges of surface facets, then small liquid regions grow and at temperatures close to the particle melting temperature, most of the remaining solid-like surface atoms reside on {111} planes which are most stable against surface premelting. The appearance of a contiguous liquid layer (complete surface premelting) is size dependent and is not observed in very small nanoparticles.

An integrated molecular dynamics and two-temperature computational model has been developed to study ultrafast laser irradiation of Au nanoparticles at low intensity where surface premelting and solid-liquid phase transition are major interests. Conditions for temporary superheating and stable overcooling were examined carefully. Nonhomogeneous surface premelting mechanism like that in the equilibrium melting was also observed. The appearance of a contiguous liquid layer (complete surface premelting) is size dependent and is not related to surface premelting history. As shown by simulations when temperature of Au nanoparticles is stabilized they are in the thermodynamically equilibrated state and their lattice temperature and fraction of remaining solid atoms are function of only absorbed laser energy and independent on laser pulse duration.

Microcanonical critical droplet theory (MCD) was applied to interpret the stabilized state of our ultrafast melting simulations. Two forms of melting instability observed in our MD simulations, namely globally stable to metastable state and metastable to catastrophic solid inner core collapse, are also revealed by the MCD theory.

Systematic study of two Au nanoparticles sintering was conducted. Due to the high surface-to-volume ratio, nanoparticles can be significantly heated by surface energy release during sintering. During sintering in the liquid phase, the initial neck growth can be well described by the viscous flow model. For two particles with initial temperature just below the single particle melting temperature, the initial neck growth is initially controlled by viscous flow and then later by grain boundary diffusion. At initial temperatures well below melting, the sintering process occurs very rapidly and ends with a non-spherical oval particle shape. This is attributed to formation of liquid-like atoms in the neck region.

Stanislav Rokhlin, PhD (Advisor)
Dave Farson, PhD (Committee Member)
Jose Castro, PhD (Committee Member)
253 p.

Recommended Citations

Citations

  • Wang, N. (2010). Melting, Solidification and Sintering/Coalescence of Nanoparticles [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1284476300

    APA Style (7th edition)

  • Wang, Ningyu. Melting, Solidification and Sintering/Coalescence of Nanoparticles. 2010. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1284476300.

    MLA Style (8th edition)

  • Wang, Ningyu. "Melting, Solidification and Sintering/Coalescence of Nanoparticles." Doctoral dissertation, Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1284476300

    Chicago Manual of Style (17th edition)