Endothermic signal

The thermal variation of specific heat measured by adiabatic calorimetry is showninfig 1 At about 347 K a jump of occurs which corresponds to a first order transition. This is confirmed by 0. S. C. measurement which gives an enthalpy of transition AH = 1160+ 100 cal/mole. This transition which presents an endothermic signal is however irreversible, at least down to 4 K, To obtain the initial phase it is necsssary to crystallize again the trensformed product in eceto-nitrile. However the irreversibility is not due to solvent inclusion as evidenced by mass spectroscopy analysis,... 

On studying the Process 2 (catalyzed) residue in a similar fashion, no such exothermic ordering was observed. The Process 1 residue was observed to give a strong endothermic signal in the DSC thermal curve at temperatures above llO C due to the volatilization of the oil (hexane soluble) fraction. 

Bolis et al. [46] recendy summarized their data concerning calorimetry of CO adsorption on oxides. They concluded that, CO adsorption calorimetry is not a good technique for the characterization of the surface Lewis acidity at least for aluminas because the adsorption exothermic signal is in part combined by an endothermic signal due to surface reconstruction phenomena. Due to the nonspecific interaction of CO2 with basic sites, Rossi et al. [47,48] proposed the use of hexa-fluoro isopropanol as an alternative for the characterization of basic sites. The use of sulfur dioxide as a probe is also successful [49]. 

DSC analysis of Zinc/PTFE mixtures reveals a pre-ignition reaction commencing at 270°C that is followed by both fusion endotherm signal of PTFE and Zinc (Figure 5.21). At the fusion point of Zinc the actual combustion reaction starts vigorously. In nitrogen atmosphere the combustion reaction is delayed and does not start at the fusion of Zn [24]. 

The absence of any other exothermal or endothermal signal confirmed that the nanocomposite was also amorphous. This is in agreement with the results reported by Rattan et al. [17] that the PETg keeps its amorphous state in most practical experimental conditions. The decrease of Tg can be attributed to the plasticization effect of the organic modifier of the OMMT, characterized by a very low Tg. 

Thermogram (a) of Figure 11.7 shows the signals recorded upon cooling the same sample from the melt. The area under the exothermic peak corresponds to the heat of crystallization (at Tc) and is smaller than that of the endothermic signal... 

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