Curie temperature standards for thermogravimetry: The effect of magnetic field strength and comparison with melting point using Ni and Pb.

Thermogravimetric (TG) runs were made with a Ni sample over a wide range of heating and cooling rates using an electromagnet at three different field strengths. The extrapolated onsets and endpoints of the weight change induced by the magnetic field gradient were obtained from both TG and the differential curves (DTG). The onset upon heating and endpoint on cooling are very clearly dependent upon magnetic field strength and hence unsuitable for temperature calibration using this method. The endpoint upon heating and onset upon cooling, however, showed only a slight dependence upon the cube root of the magnetic field strength. Observed values of T(c) showed a linear dependence upon heating or cooling rates which extrapolated to a common point at zero rate, The value of T(c) derived from extrapolation to zero rate and then zero field is 339.15C for this uncalibrated system, which is 16C below the literature value.