Temperature Calibration of TMAs Using Modulated Temperature and Curie Temperature Reference Standards

This article presents the concept of calibrating temperature in thermomechanical analyzers (TMA) using reference standard magnetic materials whose Curie temperatures are well-known. This concept has not been tested experimentally to the best of the author's knowledge. Electrical current applied to a unifilarly wound furnace results in the furnace acting as an electrical inductor. A magnetic material sample located within such a furnace practically constitutes a solenoid core. A modulated temperature program directly results in a corresponding varying force exerted by the sample against the TMA probe, if the probe's axis and the central induced magnetic field line of force are coaxial, and, furthermore, if the direction of the central magnetic field line of force and the expansion direction of the probe are identical. If a sample undergoes a Curie transition, then the force which the sample exerts against the probe will diminish to zero as the transition goes to completion. Using a modulated temperature program throughout this phase transition allows determination of transition completion, by observation of the point at which the force required to maintain the sample's physical position reaches a steady state from it's previously non-steady state. This revised version was published online in August 2006 with corrections to the Cover Date.