Snoek effect

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... 

Using Eq. (26.1) it is possible to obtain the temperature dependence of the hydrogen jump rate from the experimental data on ultrasonic loss. The Snoek relaxation measurements are especially informative if they are performed at a number of excitation frequencies. It should be noted that the Snoek effect can be observed only for sufficient elastic anisotropy, X -X2, of hydrogen sites. For hydrogen in pure b.c.c. metals, the Snoek effect has not been found [16], in spite of the uniaxial symmetry of tetrahedral sites occupied by hydrogen in these materials. It is believed that the absence of the observable Snoek effect is due to the small value of X1-X2 for hydrogen in the tetrahedral sites of b.c.c. metals. 

Han] Haneezok, G., Ilczuk, J., Kuska, R., Moron, J.W., Migrational Relaxations in a-C-Fe-V in the Region ofthe Snoek Effect , PAyj. Status Solidi A, 33(1), 313-324 (1976) (Morphology, Experimental, 22)... 

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 ... 

DeVries JH, Eskes SA, Snoek FJ, Pouwer F, Van Ballegooie E, Spijker AJ, Kostense PJ, Seubert M, Heine RJ. Continuous intraperitoneal insulin infusion in patients with brittle diabetes favourable effects on gly-caemic control and hospital stay. Diabet Med 2002 19(6) 496-501. 

As may be seen from Eq. (7), one of the characteristics of the Snoek relaxation in crystalline metals is a direct proportionality between the relaxation strength and the (dilute) interstitial concentration, C. This simple relationship is a consequence of the fact that every interstitial atom produces an identical elastic dipole. In attempting to adapt Eq. (7) to the case of an amorphous host, we must again consider the effects of structural disorder. As discussed in more detail in Section 5, it appears the major modification to Eq. (7) may result from the fact that the elementary act of reorientation now occurs between sites whose energies are not precisely equal, but are split by an... 

The conclusion that the reorientation relaxation is of the Snoek type is strongly supported by observations of a second relaxation process known as the Gorsky effect. This relaxation provides an entirely different perspective on the interstitial population, since it focuses on the H-interstitial as a dilatation center rather than as an elastic... 

The effect of Co on the Snoek peak height was investigated by [2004Sai]. They found that Co decreased the height of flie peak owing to strain fields generated by the difference in the atomic size of the Fe and Co atoms on flie ferrite lattice. 

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