Thermodynamics of Nanomaterials

Contact: Jörg Weissmüller

Alloy phase diagrams document equilibrium states of multicomponent systems, for instance in the temperature-composition domain. They form an indispensable engineering data base for materials selection and optimization in technological applications. For nanoscale materials, the energetics of the many interfaces has a significant impact on the driving forces for phase transformations and on the resulting equilibrium states. Phase diagrams of nanoscale alloys therefore depend on the grain- or particle size as an additional dimension in configuration space. Many of the relevant issues still await a systematic study. Our experiments on matrix-isolated nanoparticles and on nanocrystalline metal hydrides provide insights that can be generalized to nanoscale phase equilibria in a wider context.


Selected Publications:


J. Weissmüller

Alloy Effects in Nanostructures
NanoStruct. Mater. 3 (1993), 261

J. Weissmüller and C. Lemier
On the Size-Dependence of the Critical Point of Nanoscale Interstitial Solid Solutions
Phil. Mag. Lett. 80 (2000), 411

J. Weissmüller, P. Bunzel and G. Wilde
Two-Phase Equilibrium in Small Alloy Particles
Scripta Mater. 51 (2004), 813

C. Lemier and J. Weissmüller
Grain Boundary Segregation, Stress and Stretch: Effects on Hydrogen Absorption in Nanocrystalline Palladium
Acta Mater. 55 (2007) 1241

 

The free energy, G, of nanocrystalline alloys with a pronounced tendency for grain boundary segregation exhibits a minimum when plotted as the function of the grain size, D. The minimum corresponds to a metastable state of the alloy in which grain growth is suppressed and the nanoscale grain structure remains stable to elevated temperature.

The free energy, G, of nanocrystalline alloys with a pronounced tendency for grain boundary segregation exhibits a minimum when plotted as the function of the grain size, D. The minimum corres- ponds to a metastable state of the alloy in which grain growth is suppressed and the nanoscale grain structure remains stable to elevated temperature.

 

The Gibbs phase rule imposes restrictions on the topology of alloy phase diagrams. For instance, three phases can only coexist in a single point in the temperature-composition domain. These rules are apparently violated in certain nanoscale systems, such as the Bi-Cd alloy nanoparticle in the figure.

The Gibbs phase rule imposes restric- tions on the topology of alloy phase diagrams. For instance, three phases can only coexist in a single point in the temperature-composition domain. These rules are apparently violated in certain nanoscale systems, such as the Bi-Cd alloy nanoparticle in the figure.