Thermogravimetric analysis intermediates

In most of the studies discussed above, except for the meta-linked diamines, when the aromatic content (dianhydride and diamine chain extender), of the copolymers were increased above a certain level, the materials became insoluble and infusible 153, i79, lsi) solution to this problem with minimum sacrifice in the thermal properties of the products has been the synthesis of siloxane-amide-imides183). In this approach pyromellitic acid chloride has been utilized instead of PMDA or BTDA and the copolymers were synthesized in two steps. The first step, which involved the formation of (siloxane-amide-amic acid) intermediate was conducted at low temperatures (0-25 °C) in THF/DMAC solution. After purification of this intermediate thin films were cast on stainless steel or glass plates and imidization was obtained in high temperature ovens between 100 and 300 °C following a similar procedure that was discussed for siloxane-imide copolymers. Copolymers obtained showed good solubility in various polar solvents. DSC studies indicated the formation of two-phase morphologies. Thermogravimetric analysis showed that the thermal stability of these siloxane-amide-imide systems were comparable to those of siloxane-imide copolymers 183>. 

When solids react, we would like to know at what temperature the solid state reaction takes place. If the solid decomposes to a different composition, or phase, we would like to have this knowledge so that we can predict and use that knowledge In preparation of desired materials. Sometimes, intermediate compounds form before the final phase. In this chapter, we will detail some of the measurements used to characterize the solid state and methods used to foUow solid state reactions. This will consist of various types of thermal analysis (TA), including differentlEd thermal analysis (DTA), thermogravimetric analysis (TGA) and measurements of optical properties. 

The thermal decomposition of hydrated rare earth oxalates, M2(Ox)3 nSLsO, has attracted considerable attention [397—400]. Wendlandt and his coworkers [397, 39S] have used both thermogravimetric (TGA) and differential thermal analysis (DTA) for studying the thermal decomposition of the rare earth, Th4+ and U4+ oxalates. The DTA curve for Eu2(Ox)3 IOH2O consists of three endothermic peaks centered at about 160°, 200° and 285° C respectively. The thermogravimetric analysis [397] shows the presence of unstable intermediate hydrates on going from the decahydrated to the anhydrous oxalate. The thermal decomposition of Eu2(Ox)3 IOH2O can be summarized as... 

Programmable fnmaces may be interfaced to a gas chromatograph, generally with some sort of intermediate trapping, bnt are rarely interfaced directly to spectroscopic techniqnes. Thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TGA-FT-IR) is an important exception, since many thermal units are capable of heating samples to pyrolysis temperatnres, with the resnlting pyrolysate swept directly into the cell of the FT-IR."... 

Remark.- We see that vaeancies are intermediate components from the point of view of the global reaction. If the speeds of both processes are very different, as long as the contributions of both processes are notable, vacancy concentration varies with time and thus the pseudo-steady state test is not satisfied. It is only when one contribution becomes negligible that the system could possibly be in pseudo-steady state. The test will then give two zones of a pseudo-steady state mode but with two different ratios between calorimetric and Differential Thermogravimetric Analysis (DTAG) measurements, one for each zone. 

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