Snoek pendulum

Figure 5.1. Fraction, / of carbon atoms restored to the "atmosphere surrounding a dislocation, as determined by means of a Snoek pendulum.

Figure 5.2. (a) Arrangement of a Snoek pendulum, (b) Internal friction as a function of temperature, at different pendulum frequencies, for a solution of carbon in iron, (c) Diffusion of carbon in iron over 14 decades, using the Snoek effect (-30-200°C) and conventional radioisotope... 

It is worthwhile to present this episode in eonsiderable detail, beeause it eneapsulates very elearly what was new in physieal metallurgy in the middle of the eentury. The elements are an aecurate theory of the effects in question, preferably without disposable parameters and, to check the theory, the use of a technique of measurement (the Snoek pendulum) which is simple in the extreme in construction and use but subtle in its quantitative interpretation, so that theory ineluctably comes into the measurement itself. It is impossible that any handwaver could ever have conceived the use of a pendulum to measure dissolved carbon concentrations ... 

The Snoek pendulum, which in the most general sense is a device to measure relaxations, has also been used to measure relaxation caused by tangential displacements at grain boundaries. This application has been the central concern of a distinguished Chinese physicist, Tingsui Ke, for all of the past 55 years. He was stimulated to this study by Clarence Zener, in 1945, and pursued the approach, first in Chicago and then in China. This exceptional fidelity to a powerful quantitative technique was recognised by a medal and an invitation to deliver an overview lecture in America, recently published shortly before his death (Ke 1999). 

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