Methods Combined with DTA

Abstract

Many crystalline substances show at distinct temperatures spontaneous, reversible structural transformations, the existence and temperatures of which can be observed very clearly in a DTA curve. However, the nature of the resulting products of reaction remains obscure, since these transformations receded during cooling. In these cases a combined DTA — X-ray apparatus like that described by Wefers will be very helpful, in which the continuous heating is interrupted from time to time so that the temperature remains constant as long as the recording of an X-ray diagram is needed. In practise the apparatus consists of an X-ray apparatus with a sample holder suitable for high-temperatures, which serves simultaneously as a DTA furnace combined with the remaining parts of a DTA apparatus. The method of Wefers makes it possible to identify reaction products with a short existence that are only stable over a small range of temperature.