Colloids as model systems for metals and alloys: a case study of crystallization

Abstract

Metallic systems are widely used as materials in daily human life. Their properties depend very much on the production route. In order to improve the production process and even develop novel materials a detailed knowledge of all physical processes involved in crystallization is mandatory. Atomic systems like metals are characterized by very high relaxation rates, which make direct investigations of crystallization very difficult and in some cases impossible. In contrast, phase transitions in colloidal systems are very sluggish and colloidal suspensions are optically transparent. Therefore, colloidal systems are often discussed as model systems for metals. In the present work, we study the process of crystallization of charged colloidal systems from the very beginning. Charged colloids offer the advantage that the interaction potential can be systematically tuned by a variation of the particle number density and the salt concentration. We use light scattering and ultra-small angle x-ray scattering to investigate the formation of short-range order in the liquid state even far from equilibrium, crystal nucleation and crystal growth. The results are compared with those of equivalent studies on metallic systems. They are critically assessed as regards similarities and differences.

Bcc crystal-fluid interfacial free energy in Yukawa systems

“…One of the implications is that the barrier of crystal nucleation is strongly reduced such that it would be easier to nucleate a bcc-crystal from the melt than a fcc-crystal. 55 Our results can in principle be verified by adjusting experimental data on crystal nucleation in charged suspensions [59][60][61] to classical nucleation theory, where the interfacial free energy enters as one of the crucial parameters.…”

Solid phase properties and crystallization in simple model systems

“…Thus, our tentative conclusion would be that attractions in metals (i) stabilize the bcc phase and (ii) also change γρ −2/3 cr and ∆H f disproportionately to give a lower Turnbull coefficient. Note, however, that experimental studies on metastable metal droplets seem to give Turnbull coefficients which are systematically larger than the simulated values (α fcc ≈ 0.6...0.8, α bcc ≈ 0.6) [35].…”

Nucleation and growth of micellar polycrystals under time-dependent volume fraction conditions

“…in protein crystallization [1]), and as a means to understand crystallization in atomic and molecular systems, for which colloids are often regarded as a model system [2] whose characteristic time and length scales are more readily accessible. Thanks to advanced light scattering techniques and scanning confocal microscopy, experiments have provided unprecedented information on the nucleation and growth of crystals, including the volume fraction dependent nucleation rate or the structure of the nuclei [3][4][5][6][7][8][9][10][11]. Most experiments have focussed on hard-sphere or charged colloids, although more recently more complex systems, such as thermosensitive colloidal microgels or mixtures of colloids and polymers have emerged [12][13][14][15][16].…”