A Study Of Softening Deformation Process Of Pitch Materials By Thermomechanical Analysis

The thermomechanical analysis?TMA? was used to continuously monitor the softening deformation process of single-layer pitches?AR, P₁ and P₂? particles, and combined with optical microscopy to observe the change of morphological structure of pitch samples. The effects of experiment variables, including particle size, heating rate, pressing force, sample weight, gas flow and support disk on the softening behaviors and characteristic temperatures were further investigated. The melting point of other materials, including polypropylene, biphenyl, indium and magnesium was also determined by thermomechanical analysis. Experiment results showed that:Two declining stages were observed in TMA curves for AR pitch sample, correspondingly producing the two peaks of DTMA, which were the softening and flowing deformation processes of pitch, respectively. It is revealed that the tips of a few larger particles were first slightly flattened by softening deformation, and with the temperature increased, more particles were flattened in a series of microscopic photographs of pitch particles at the characteristic temperatures. In the process of the deformation, the inter-particle space decreased and the contact area increased, until the inter-particle space disappeared, and finally the sample was deformed to a cake. The softening deformation process of pitch particles corresponded to the first peak of DTMA curves. With the further increasing in temperature, pitch samples softened enough to flow which gave the second peak of DTMA curves. The characteristic temperatures T₂ and T₅, the first and the second maximum DTMA peak were found to be the useful indictors for the softening and flowing process.The TMA curves of mesophase pitch P₁ and isotropic pitch P₂ were similar to mesophase pitch AR in shape, only with the characteristic temperatures varied. Regarding the repeatability of measurement, the experiment results showed that the averaged T₂ and mid-temperature?Tm? from T1 and T3 were close, and Tm had the smaller deviation, therefore Tm was more appropriate to be used as an indictor of the softening stage. The difference?T*? between T3 and T1 may be a characteristic parameter for pitch materials, defining a temperature range that had two boundaries at half of the maximum deformation rate, and the value of T* may be associated with the molecular weight and its distribution.Two characteristic temperatures?Tm, T₅? of pitches were compared with their respective Mettler softening point Ts, with Tm = 88.0%±0.9%Ts, T₅ = 99.1%±0.3% Ts calculated on Kelvin scale. The Mettler point Ts was apparently a flowing temperature, which was the temperature T₅?as determined by TMA in the study?.The effects of several experiment variables on the softening behaviors and relative characteristic temperatures of the mesophase pitch P₁ were systematically investigated by TMA. It was found that the softening and flowing temperatures increased with the increase of heating rate and decrease of the applied pressure, while the flowing temperature T₅ increased almost linearly with the increase of heating rate. The particle size had some significant effects on the softening and flowing behaviors revealed by TMA, and a suitable range of particle sizes?40-80 mesh? was required to observe softening and flowing processes separately and simultaneously. With the increasing of sample weight, the characteristic temperatures shifted to higher regions. The effect of sample weight was more pronounced for the flowing temperature.The thesis also investigated the molten deformation of polymers and metals, including polypropylene, biphenyl, magnesium and indium by TMA, the effects of some experiment variables on the deformation of polypropylene were studied in detail. The molting temperature of polypropylene increased with the increasing of particle size and the decreasing of applied force. The sample weight and gas flow have only small effects.