Relation between self-diffusion and viscosity in dense liquids: new experimental results from electrostatic
J Brillo1, A I Pommrich, A Meyer
1Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Köln, Germany. juergen.brillo@dlr.de
Physical Review Letters
|November 24, 2011
Summary
High-precision measurements reveal that nickel self-diffusion (D) and viscosity (η) in liquid Zr64Ni36 follow the same temperature dependence. This finding contradicts the Stokes-Einstein relation, showing Dη=const across a wide temperature range.
Area of Science:
- Materials Science
- Physical Chemistry
- Condensed Matter Physics
Background:
- Understanding the thermophysical properties of liquid alloys is crucial for materials processing and fundamental physics.
- The Stokes-Einstein relation is a cornerstone in describing diffusion and viscosity in liquids, but its applicability to metallic melts is debated.
Purpose of the Study:
- To precisely measure the self-diffusion coefficient (D) and viscosity (η) of liquid Zr64Ni36.
- To investigate the temperature dependence of D and η over an extended range.
- To test the validity of the Stokes-Einstein relation for this metallic system.
Main Methods:
- Electrostatic levitation technique for in situ measurements of density, viscosity, and self-diffusion.
- Oscillating drop method to determine viscosity (η).
- Quasielastic neutron scattering experiments to determine the self-diffusion coefficient (D).
Main Results:
- High-precision in situ measurements of Ni self-diffusion, density, and viscosity were achieved for liquid Zr64Ni36.
- Both the self-diffusion coefficient (D) and the inverse of viscosity (1/η) exhibited identical temperature dependencies.
- A constant product of Dη was observed over a broad temperature range (>800 K) and across 1.5 orders of magnitude.
Conclusions:
- The experimental results demonstrate that Dη=constant for liquid Zr64Ni36, directly contradicting the predictions of the Stokes-Einstein relation.
- This finding suggests unique atomic transport mechanisms in this specific liquid alloy system.
- Further theoretical and experimental investigations are warranted to elucidate the underlying physics governing diffusion and viscosity in such metallic melts.
Related Concept Videos
01:17Viscosity
When water is poured into a glass, it falls freely and quickly, whereas if honey or maple syrup is poured over a pancake, it flows slowly and sticks to the surface of the container. This difference in the flow of different kinds of liquids arises due to the fluid friction between the liquid layers and the liquid and the surrounding material. This property of fluids is called fluid viscosity. In this example, water has a lower viscosity than honey and maple syrup.
The SI unit of viscosity is...
The SI unit of viscosity is...
01:27Viscosity
Viscosity is a property of fluids that measures their resistance to flow. It is influenced by factors such as the surface area of contact, the gradient of flow speed, and the fluid's viscosity constant, called the coefficient of viscosity. The coefficient of viscosity, also known as dynamic viscosity, is denoted by the symbol η. It determines the proportionality between the viscous force and the gradient of flow speed.Newton's law of viscosity states that the viscous force on a faster-moving...
01:24Van der Waals Interactions
Atoms and molecules interact with each other through intermolecular forces. These electrostatic forces arise from attractive or repulsive interactions between particles with permanent, partial, or temporary charges. The intermolecular forces between neutral atoms and molecules are ion–dipole, dipole–dipole, and dispersion forces, collectively known as van der Waals forces.
01:20Stokes' Law
Viscous forces, like friction, are intermolecular forces that resist the relative motion of molecules over each other. When a solid body moves through a liquid, viscous forces drag it in the opposite direction. The force's magnitude depends on the solid's shape and size, as well as its speed and the liquid's coefficient of viscosity, density and temperature.
The expression for the force on a solid spherical object in a fluid is called Stokes' law. Stokes' law is valid only for low Reynolds...
The expression for the force on a solid spherical object in a fluid is called Stokes' law. Stokes' law is valid only for low Reynolds...
01:18Newtonian Fluid: Problem Solving
Newtonian fluids exhibit a constant viscosity, meaning their shear stress and shear strain rate are directly proportional. This property ensures a predictable and stable response to applied forces, maintaining a linear relationship between force and flow. Examples include water, air, and light oils, consistently demonstrating this proportional behavior regardless of external conditions.
A velocity gradient forms within the fluid when a Newtonian fluid is placed between two parallel plates, with...
A velocity gradient forms within the fluid when a Newtonian fluid is placed between two parallel plates, with...
02:57Surface Tension, Capillary Action, and Viscosity
Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...