Formation mechanisms of self-organized core/shell and core/shell/corona microstructures in liquid droplets of immiscible alloys

Effective control of phase growth under harsh conditions (such as high temperature, highly conductive liquids or high growth rate), where surfactants are unstable or ineffective, is still a long-standing challenge. Here we show a general approach for rapid control of diffusional growth through nanoparticle self-assembly on the fast-growing phase during cooling. After phase nucleation, the nanoparticles spontaneously assemble, within a few milliseconds, as a thin coating on the growing phase to block/limit diffusion, resulting in a uniformly dispersed phase orders of magnitude smaller than samples without nanoparticles. The effectiveness of this approach is demonstrated in both inorganic (immiscible alloy and eutectic alloy) and organic materials. Our approach overcomes the microstructure refinement limit set by the fast phase growth during cooling and breaks the inherent limitations of surfactants for growth control. Considering the growing availability of numerous types and sizes of nanoparticles, the nanoparticle-enabled growth control will find broad applications.

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“…However, immiscible alloys proved extremely difficult to process567, as illustrated with a typical immiscible alloy Al–Bi17 in Fig. 2.…”

Section: Resultsmentioning

confidence: 99%

Rapid control of phase growth by nanoparticles

et al. 2014

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“…As the liquid-phase separation process determines the final solidification structure, many studies have been carried out on it [1][2][3][4][5][6][7][8][9]. It turned out that the minor volume phase will generate in the form of droplets, and the structure evolution mainly involves nucleation and coagulation of the minor droplets due to Marangoni and Stokes motions.…”

Section: Introductionmentioning

confidence: 99%

Macrosegregation driven by movement of minor phase in (Al0.345Bi0.655)90Sn10 immiscible alloy

Zhang

2014

Appl. Phys. A

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Formation of macrosegregation structure in (Al 0.345 Bi 0.655 ) 90 Sn 10 (mass percent, the same below) immiscible alloy was investigated by spraying its melt into silicone oil. Two kinds of typical macrosegregation structures were obtained in the dispersed alloy spheres: core/ shell structure and crescent structure. Based on the estimated temperature field inside the alloy spheres, the velocities of thermal Marangoni, solutal Marangoni, and Stokes motions of the Bi-rich minor droplets were calculated. Analysis shows that surface segregation, Soret effect, thermal Marangoni motion, solutal Marangoni motion, and Stokes motion play a key role in the formation of Al/Bi-Sn core/shell structure. If the liquid alloy spheres solidify on the condition that the radius of the Bi-rich minor droplets is smaller than a critical value, it will form Al/Bi-Sn core/ shell structure, while the crescent structure will be formed when the liquid alloy spheres frozen on the condition that the radius of the Bi-rich minor droplets exceeds the critical value.

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“…During the processing of immiscible alloys under microgravity conditions a type of structure, known as core-shell structures, may be formed in which droplets of a minor phase (which coalesce to form the core) are enclosed in the liquid matrix of the majority phase (the shell) [1]. There has been heightened interest in these structures, especially in monotectic alloys, due to the possibility of fabricating heterogeneous functional particles with a combination of core and shell materials in which both the size and composition can be engineered [2].…”

Section: Introductionmentioning

confidence: 99%

“…The strong interplay of interfacial energy with temperature and/or composition gradients in immiscible alloys leads to Marangoni convection which, in the microgravity environment, has been used to explain the formation mechanism of core-shell structures [1,4,[6][7][8][9][10][11][12][13]. In such an environment, for instance during free fall, a temperature gradient between the surface and centre of the falling droplet may be developed.…”

Section: Introductionmentioning

confidence: 99%

Metastable monotectic phase separation in Co–Cu alloys

2018

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The liquid phase separation behaviour of metastable monotectic Co-Cu alloys was investigated as a function of cooling rate using a 6.5 m drop tube facility. A range of liquid phase separated morphologies were observed including stable two-layer core-shell, evolving core-shell and dendritic structures. It was found that in the core-shell structures the core was always the higher melting point (Co-rich) phase, irrespective of the core and shell volume fraction. In Cu-50 at. % Co alloy, high cooling rates were observed to yield two episodes of liquid phase separation, corresponding to binodal, followed by spinodal decomposition. The resulting structure comprised a core-shell structure in which the Co-rich core contained a very fine dispersion of Cu-rich particles with a Cu-rich shell which may, or may not, contain a similar dispersion of Co-rich particles.

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Formation mechanisms of self-organized core/shell and core/shell/corona microstructures in liquid droplets of immiscible alloys

Cited by 138 publications

References 39 publications

Rapid control of phase growth by nanoparticles

Rapid control of phase growth by nanoparticles

Macrosegregation driven by movement of minor phase in (Al0.345Bi0.655)90Sn10 immiscible alloy

Metastable monotectic phase separation in Co–Cu alloys

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