An Experimental Determination of the Change in Temperature Accompanying Change in Magnetization of Iron

Abstract

Apparatus.---An apparatus is described which permits the measurement of the change in temperature of a ferromagnetic material consequent upon a change in its magnetization. The test specimen, of peculiar form and construction, is placed in a specially designed calorimeter. Around this is wound a solenoid which furnished the magnetizing field. Changes in temperature are measured by means of 102 thermocouples connected in series to a sensitive galvanometer. Methods are described for minimizing thermal and thermoelectric disturbances. The sensitivity of the system is such that a temperature change of 2.26\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$\ifmmode^\circ\else\textdegree\fi{}C can be detected. This corresponds to a thermal energy change of 87 ergs per ${\mathrm{cm}}^{3}$ for steel.Results.---Results are reported on for two specimens of carbon steel containing 1.08 percent and 1.35 percent carbon respectively. Detailed data are presented showing the relationship between temperature change and magnetizing field as the material is carried through various symmetric and asymmetric cycles of magnetization.The following is typical of a symmetric cycle which starts with the steel in a saturated condition. As the magnetizing field is diminished from +290 to +20 gauss the temperature of the steel rises gradually; this is followed by a very marked cooling between +20 and -8 gauss; if the magnetizing field is further diminished from -8 gauss through the coercive force (-9.6 gauss) to -90 gauss a sudden rise in temperature indicates the release in this region of the major portion of the hysteretic energy; between -90 and -290 gauss the steel cools gradually.Temperature changes for smaller cycles of magnetization are qualitatively the same as for the large cycle, except that the second cooling may be absent. Similar sharply defined regions of heating and cooling are characteristic of the different asymmetric cycles investigated.It appears that the total amount of hysteretic heat developed depends upon the rate of performance of the cycle, at least for those cycles which nearly saturate the steel. A rapid traversal yields a greater total heat than a slow traversal.