Modulation method and apparatus for thermally analyzing a material

#The present invention relates to a method for thermally analyzing a material, comprising the steps of establishing a heat flow path between a sample of said material and a heat source to thereby cause a flow of heat between said sample and said heat source, controlling the heating power of said heat source as a function of time, measuring a signal representative of said heat flow between said sample and said heat source and a signal representative of a temperature associated with said heat flow, and evaluating a functional relation between said measured heat flow and temperature signals; and to an apparatus adapted for carrying out said method.

#In the thermal analysis of materials, a sample of the material is heated by the heat source, and the flow of heat between the heat source and the sample is evaluated to thereby derive structural and compositional information about the material, in particular heat capacity, phase transitions, onset temperatures, etc. In particular, for the sake of accuracy and dynamic range, differential methods, e.g. differential scanning calorimetry (DSC), are being used. In these differential methods, a reference material is arranged in the heat flow symmetrically with respect to the sample to be analyzed, and the analysis is performed on the basis of the differential heat flow between the sample and reference materials.

#EP 0 559 362 A1 discloses a differential method wherein the temperature of the heat source is controlled in accordance with a predetermined temperature program so as to cause said heat source temperature to vary in correspondence with a linear rise of temperature superposed by a periodic temperature modulation having a predetermined modulation amplitude and frequency. A deconvolution technique is used to derive from the differential heat flow signal two separate signal components caused by the linearly changing component and the modulation component of the heat source temperature, respectively.

#FIG. 1 is a schematic diagram of an embodiment of an apparatus for thermally analyzing a material;

#FIG. 2 is a schematic diagram of an embodiment having a different type of controller;

#FIG. 3 is an embodiment similar to FIG. 1 but modified by incorporating first and second heaters;

#FIG. 1 schematically illustrates a heat source 1 having an essentially hollow cylindrical oven block 2 made of silver. The upper face of oven block 2 is formed as a removable lid 3 for opening and closing block 2 to permit access to the interior 4 thereof. A winding of heating wire 5 is wound onto the exterior cylindrical surface of oven block 2 to provide for resistive heating. Alternatively, a flat resistive heater could be applied to the lower face of oven block 2 opposite to lid 3 or any other suitable portion of oven block 2.

#A disc-shaped substrate 6 is arranged in the interior of oven block 2 in thermal contact therewith. Substrate 6 has two circular areas thereof formed as a sample holder and a reference holder, respectively, adapted to support a sample pan 7 and a reference pan 8, respectively. Each of the circular areas of the sample and reference holders are formed with a thermocouple arrangement for detecting the temperatures Ts and TR of the sample and reference pans 7, 8, respectively. The electrical signals representing the sample and reference temperatures TS and TR, respectively, are fed to the outside of heat source 1 by means of signal lines 9 and 10, respectively. A platinum thermometer 11 arranged at the bottom portion of oven block 2 detects a temperature TF of oven block 2, and a corresponding electrical signal is fed to the outside by signal line 12. Electrical heating power is supplied to heater winding 5 of heat source 1 by a power amplifier 13.

#The signal on signal line 12 representing the measured temperature TF of heat source 1 is applied to the input of a filter 14 which produces a signal representative of an average temperature TFav, at an output thereof. This average temperature signal is applied to one input of a subtractor 15 via signal line 16. The other input terminal of subtractor 15 is connected to the output of a temperature programmer 17. Temperature programmer 17 outputs a first control signal which represents a temperature-versus-time function for heat source 1. The output signal of subtractor 15 being representative of the difference between the first control signal from temperature programmer 17 and the average temperature signal TFav on signal line 16 is applied to a control input of a temperature controller 18 which generates a corresponding control signal for power amplifier 13. As a result, the control loop formed by signal line 12, filter 14, signal line 16, temperature programmer 17, subtractor 15, temperature controller 18 and power amplifier 13 drives the heater winding 5 so that the average temperature TFav of heat source 1 follows the temperature-versus-time function commanded by temperature programmer 17.