On Differential Thermal Analyzer Curves for the Melting and Freezing of Alloys
William J. Boettinger, Ursula R. Kattner
A model for the response of differential thermal analysis measurement techniques to melting and freezing is explored. The model, which uses a system of ordinary differential equations, predicts sample, sample cup and thermocouple temperature histories. Analytical solution of the equations for the melting of a pure material is used to determine the effect of sample size and heating rate on the melting onset temperature, peak temperature and peak height of the DTA curve. Using experimental DTA data for pure Ni, the thermal response constants of the model were determined. The response of the instrument is then calculated for specified enthalpy-temperature relations obtained from thermodynamic assessment of various alloys. The effect of melting and freezing kinetics is subsequently analyzed using diffusion micromodels that are coupled to the DTA heat flow equations. In particular, the DTA peak temperature is shown to be significantly higher than the alloy liquidus temperature for small freezing range alloys and for alloys where solid diffusion is slow. The change in DTA curves during freezing due to dendritic growth with large supercooling is determine.
Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science
and Kattner, U.
On Differential Thermal Analyzer Curves for the Melting and Freezing of Alloys, Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science
(Accessed December 2, 2023)