ABSTRACT

Excessive sample dimensions in either width or height, run the risk of appreciable temperature gradients within the material. A case could be envisioned, for example, where a sample powder is stacked in a tall DTA crucible which is located just below the hot zone of the furnace. The top portion of the powder will melt first, while at the same time the bottom of the crucible, where the thermocouple junction is, remains at a temperature below the melting point. The melting upper powder will act as a heat sink for heat propagating from the hot zone, motivating an endothermic deviation detected by the differential thermocouple. Thus, the onset of the melting endotherm would be indicated at the sample thermocouple junction at a temperature below the melting point of the sample. As a result, a falsely low melting point would be recorded.