Size and mechanics effects in surface-induced melting of nanoparticles

Abstract

Various melting-related phenomena (like surface melting, size dependence of melting temperature, melting of few nm-size particles and overheating at a very fast heating rate) are of great fundamental and applied interest, although the corresponding theory is still lacking. Here we develop an advanced phase-field theory of melting coupled to mechanics, which resolves numerous existing contradictions and allowed us to reveal exciting features of melting problems. The necessity of introducing an unexpected concept, namely, coherent solid-melt interface with uniaxial transformation strain, is demonstrated. A crossover in temperature dependence of interface energy for radii below 20 nm is found. surface-induced premelting and barrierless melt nucleation for nanoparticles down to 1 nm radius is studied, and the importance of advanced mechanics is demonstrated. our model describes well experimental data on the width of the molten layer versus temperature for the Al plane surface and on melting temperature versus particle radius.

Diffusion-driven and size-dependent phase changes of gallium oxide nanocrystals in a glassy host

“…Such a dependence resembles the relationship describing the depression of melting temperature, with respect to bulk, observed in several nanosystems. [46][47][48] In that case, the constant j is proportional to the difference (g sol À g liq ) between surface energy in the solid and liquid phase. 47,49 Similarly to that situation, the difference (g ord À g dis ) in surface energy between ordered and disordered LiGa 5 O 8 polymorphs is expected to be positive -with a resulting lowering of T ep at decreasing r -since a more ordered nanophase surface is likely associated with higher interface energy with the surrounding amorphous matrix.…”

Coherent solid/liquid interface with stress relaxation in a phase-field approach to the melting/solidification transition

“…1-4 below and Ref. 4). Thus, the melting temperature for an Al nanoparticle with a radius R > 20 nm is becoming larger than the bulk equilibrium melting temperature θ e (Fig.…”

“…We will further develop our model with a coherent solid-melt interface from Ref. 4. For simplicity, viscosity is neglected and shear strain is small.…”

“…That is why in Ref. 4 the radial transformation strain was assumed as the limit case. Here, we found that for relatively large particles with R > 10 μm, the maximum ε tφ = 0.018-i.e., almost the entire total tangential strain relaxes.…”

“…While the GL approach is widely used to model premelting 2 and melting, 3 mechanical issues have been addressed only recently for premelting 4 and melting. 4,5 Thus, models for a coherent solid-melt interface without 5 and with 4 surface tension were developed. However, the outstanding problem is related to the transformation strain tensor ε t that transforms the elemental volume of one phase into another in an unloaded state.…”