New measurements on time decrease of permeability

Abstract

2014 The disaccommodation of Fe-Si alloys has been measured. In the region where the magnetostriction constant h1 changes sign the disaccommodation is little affected. It seems that the disaccommodation due to carbon is larger than the effect due to a corresponding atomic percentage of nitrogen, although the contrary is true for internal friction. The ratio of the diffusion coefficients of 12C and 13C in pure iron has been determined, again by measuring the disaccommodation. We find a value of (1,04 ± 0,01) in agreement with a (m)-1/2 relationship for the diffusion coefficient. LE JOURNAL DE PHYSIQUE ET LE RADIUM TOME 20, FEVRIER 1959, Introduction. The time decrease of permeability (disaccommodation) due to interstitials in iron according to Neel [1, 2] originates from a direct non-mechanical interaction between the interstitials and the magnetization vector. It is argued that a magnetostrictive interaction alone is too small to account for Snoek’s [3] observations. Brissonneau [4] has brought additional evidence in showing that besides 900 walls, 1800 walls also contribute to the disaccommodation in iron. It seems worth-while to present more data which strengthen the theory. We have measured the disaccommodation of alloys in the silicon-iron system for which Carr and Smoluchowski [5] have shown the magnetostriction constant h1 (3/2 03BB100 ) to change sign in a (3/2 100 range of composition in which h2 is small. We also want to stress the difference in disaccommodation produced by the same amount of interstitial carbon and nitrogen and compare this with the difference in opposite direction in internal friction. Finally it is shown that the disaccommodation is a tool adapted to measure small changes in relaxation time. It can give information about the diffusion process upon which it is based. Measurements in the silicon-iron system. Four alloys of Si and pure iron produced by vacuum melting and casting [6] have been kindly put at our disposal by Professor J. D. Fast of Eindhoven. Rings made from all of these alloys have been heated together in an atmosphere of purified dry hydrogen and methane for 30 hours at 1000 C. After this water was suddenly poured upon the quartz container to gas quench the specimens. After 20 hours annealing the 4.5 wt % Si rings scemcd already saturated with carbon with respect to the gas atmosphere. We assume that all alloys were saturated after 30 hours. The carbon contents relative to the 4.5 % Si alloy can then be calculated for all specimens (Smith [7]). The values of the disaccommodation reproduced in figure 1 have been reduced to the same amount of carbon in all alloys assuming proportionality between time decrease and carbon concentration. We think that this amount is about 5/1000 wt % of carbon, on the basis of separate experiments on the 4.5 % Si alloy. In figure 1 two kinds of measurements are reproduced : a) gives the change in reluctivity a(l iti) = Ar at 262 °K during 1 hour after demagnetization. For all alloys investigated the relaxation is then completed for about 50 % ; b) shows the change in reluctivity at a higher temperature (290 OK) during very long times of waiting. The reluctivity for t = 0 is arrived at by extrapolating measurements performed at lower temperatures. yo (2,6.10-4 Oe, 290 °K) has a maximum value of about 870 for the 6 % Si alloy while for the other alloys it is between 600 and 700. The points in a) and b) indicate that the influence of magnetostriction on time decrease and consequently interaction energy [1, 2, 4] is small. We have also measured the field of stabilization for iron and the 4 . 5 % and the 6 % alloy. For a carbon content of 0.005 wt % this field is about 10 times larger in iron than in the alloys. We suppose this to be due to the (preferential) occupation of sites near the Si atoms. We also suspect that the magnetic strain energy due to interstitials is lowered by this. The fact that the disaccomArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphysrad:01959002002-3024100