Furnace for differential thermal analysis
The invention relates to a furnace for differential thermal analysis of long duration, in which relatively large quantities of samples are examined. Large sample containers are required when carrying out differential thermal analysis with large quantities of samples, for example at very slow heating rates. The large containers naturally require correspondingly large furnaces in which the temperature frequently varies from one location to another. 
     Relatively large temperature gradients are obtained within the furnace when heating the furnace, particularly in the area of the upper cover of the furnace or the lower seal. These lead to variations in temperature not only in the furnace but also, when using large quantities of samples, within the sample itself. Measurements can be falsified in this way. 
     The object of the invention is accordingly to provide a furnace in which the temperature is as spatially uniform as possible, for carrying out differential thermal analysis of long duration, in other words for examining large volumes of samples. 
     According to the invention there is provided a furnace for differential thermal analysis of long duration, which comprises two symmetrical halves having equal heat capacities, in which equal sized bores are provided for receiving a sample container, and additional bores are provided in the lower half for a differential thermoelement. The two halves of the furnace are advantageously provided with filament windings which have the same electrical resistance. 
     In a furnace of this type, a highly uniform distribution of the temperature may be obtained. This enables very precise differential thermal analyses to be carried out at extremely low heating rates down to 10 -2  ° C. min -1 . 
    
    
     An embodiment of the invention is described in more detail below with reference to the accompanying drawing, which is a cross-section through a differential thermal analysis furnace having two symmetrical halves, an upper half 1 and a lower half 2. The halves are formed with symmetrical cylindrical parts. Two large bores 3 are provided symmetrically with respect to each other in the two halves for receiving a sample container 4 and a container 4a for a comparison material, and smaller bores 5 having the same diameter are provided in the lower section 2 for receiving differential thermoelements 6 and optionally control elements. The sample container 4 may have a volume of, for example, about 20 cm 3 . 
     Both halves of the furnace 1 and 2 are provided with filament windings 7 in their external jackets so that the same heating power is generated when a given voltage is applied in each half of the furnace. The heating rate is adjusted in such a way that the temperature in the comparison material rises linearly with time. The comparison material must not undergo a thermal reaction in the temperature range being used for the test. If the difference between the temperature of the sample and the temperature of the comparison material is plotted as a function of temperature, the desired differential thermal analysis diagram is obtained.