Thermal Analysis: Applications in the Geological Sciences
Creators:Norton, Kevin P.
Advisor:Tettenhorst, Rodney T.
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Geological Sciences Senior Theses; 1997
The success of thermal analytical techniques hinges upon temperature calibration. Among the methods used for calibration of temperature are magnetic transition standards,in which the loss of magnetism of a metal is measured with respect to temperature. The magnetic transition occurs abruptly at a given temperature, Tc. Previous work done by the National Institute of Standards and Technology (N.I.S.T.) displayed broad transition temperatures and large standard deviations, as was demonstrated by Gallagher et al. (1993). Through the use of simultaneous thermogravimetry/differential thermal analysis (TGLDTA) the magnetic transition of the metals may be defined more accurately. Simultaneous TGDTA achieves better calibration by removing dependency of Tc on the heating rate. A single set of alloys and pure metals based on the NiICo series were used,to accurately calibrate the instrument over a significant range of temperatures. These metals range in transition temperature from approximately 358 to 1130 degrees C. Samples used in this study were obtained from Ames Labs, Ames Iowa. The homogeneity of the metals was checked by consecutive measurements of the Tc without a temperature correction. The alloys studied had the compositions; 75%Ni/25%Co,50%Ni/50%Co, 25%Ni/75%Co, as well as pure Ni and Co. ICP spectrometry was used in order to verify the compositions of the alloys, but at the time of the preparation of this paper, the analysis was not yet completed. Initial measurements of Tc are nonlinear with respect to %Co. The magnetic transitions of the alloys were more closely spaced at higher temperatures than for lower temperatures. This would lead to accurate knowledge of the furnace conditions at higher temperatures, but leave gaps for lower temperatures. In order to separate the magnetic transition temperatures of the metals, new compositions of 80%Ni/20%Co, 65%Ni/35%Co, and 40%Ni/60%Co for the alloys are proposed. These metals display sufficiently sharp magnetic transitions over a wide range of temperatures which will be useful to calibrate thermogravimetric instruments.