Thermogravimetry crucibles

The number of experimental factors which influence the results increases considerably when thermogravimetry is combined with other techniques such as DTA, gas chromatography46, mass spectrometry, X-ray etc. A systematic discussion of all these additional factors would lead too far, therefore only a representative example will be discussed here. One of the often-applied multiple techniques is the combination TG-DTA. Besides the actual thermal reactions of the sample, the important factors in DTA are the heat capacity and the thermal conductivity of the sample. Optimum heat transfer is required for such thermoanalytical measurements therefore the shape of the sample and its contact with the crucible is of special importance. 

Thermogravimetry. Thermogravimetric analysis (TGA/DTG) was performed on a Seiko instrument. The samples were heated in platinum crucibles up to 1000°C with a heating rate of 3 C/mn in 60 mL/min under flowing dry air. 

The large number of sample holders used in thermogravimetry are described in Chapter 3. Sample holders range from flat plates to deep crucibles of various capacities. Materials used in their construction may vary from glass, alumina, and ceramic compositions to various metals and metallic alloys. 

Concurrent with the DSC and the TMA measurements, the water content of the polymer under study was determined thermogravimetri-cally (TG) with a Mettler TA-1 thermoanalyzer. The sample was contained in a quartz cylindrical crucible and was heated to decomposition at 10 C/min under a nitrogen flow of about 8 J2-/hr. 

A final set of definitions leads to the classification of the types of systems. One can distinguish three types. The first is the open system. In such a system mass and energy flux may occur across the boundaries, as indicated by the open sample crucible in Fig. 2.1. The experimental set up of thermogravimetry is a typical example of an open system. The open sample crucible in Fig. 2.1 is placed on a temperature controlled balance. The sample to be analyzed, contained in the crucible, is the system. Across its boundaries flows heat from the furnace, and mass can be lost by evaporation or gained by interaction with the atmosphere. All changes in mass are recorded by the balance. 

Thermogravimetry (TG) is defined by ICTAC (International Confederation for Thermal Analysis and Calorimetry) as a technique in which the mass change of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature programme. In TG experiment, the sample is placed in a crucible which is positioned in a furnace balance detects the mass loss, while the results are presented as a plot of mass against temperature (T) or time (t). The alternative presentation is the derivative of the original experimental curve dm/dt (or dm/dT) plotted against temperature T or time t. 

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