Kirkendall Effect

The Kirkendall effect consists in the fact that if the temperature is sufficiently high, two solid phases adjacent to one another reduce the volume of one phase while the volume of the other phase increases. The effect is particularly clearly visible if the phase boundary was marked beforehand, since a shift in the marking relative to the external sample geometry is then observed. The phase boundary does not move itself, but matter moves between the phases and thus the position of the phase boundary relative to the external sample geometry.

history

Schematic representation of the Kirkendall effect

The Kirkendall effect was named after Ernest Kirkendall (1914-2005), who observed the changes in volume during his doctoral thesis in the late 1930s, although he did not yet give the correct interpretation. In 1942 and 1947 Kirkendall published two papers that also describe the scope of the discovery. It was not until 1950, when one of the opponents of Kirkendall's interpretation (RF Mehl) was convinced at a conference, that it began to prevail.

description

Kirkendall observed the effect on metals and alloys, especially copper / brass , which was heated to 780 ° C, for example. With his colleague Alice Smigelskas he was able to visualize the shift of the phase boundary with the help of molybdenum wires that had been introduced at the phase boundary; these marker wires then move accordingly.

In the phase that reduces its volume, characteristic holes near the phase boundary, the Kirkendall holes, often arise . Together with the volume changes, these influence the stability of metal connection points, which is why the Kirkendall effect is also of practical importance, for example in reactor technology or in semiconductor technology , if connection points between aluminum and gold are used there.

The importance of the Kirkendall effect lies in the fact that it has been proven that diffusion in the solid takes place via voids . (The alternatives of direct exchange of place or ring exchange of particles have not been observed so far.) The Kirkendall effect arises from a flow of vacancies between the phases. This in turn occurs inevitably when the mobility of the atoms in the various phases is different, i.e. when the diffusion constants differ.

literature

• Hideo Nakajima: The Discovery and Acceptance of the Kirkendall Effect: The Result of a Short Research Career. In: JOM. 49, No. 6, 1997, pp. 15-19 (History of the Kirkendall Effect and the Enforcement of Interpretation; HTML version ; English).

Web links

• Friedhelm Frerichs: Introduction: Introduction to the Kirkendall effect . In: Investigations on the Kirkendall effect in the entire concentration range of binary diffusion systems. Dissertation, University of Oldenburg, 2001.

Individual evidence

1. ↑ E. Kirkendall, L. Thomassen, C. Upthegrove: Rates of Diffusion of Copper and Zinc in Alpha Brass. In: Transactions of the AIME. 133, 1939, pp. 186-203.
2. ^ EO Kirkendall: Diffusion of zinc in alpha brass . In: Transactions of the AIME . tape 147 , 1942, pp. 104-109 .
3. ↑ A. D Smigelskas, E. O Kirkendall: Zinc diffusion in alpha brass . In: Transactions of the AIME . tape 171 , 1947, pp. 130-142 .