Exothermic signal

Photo DSC experiments conducted in a ciear coating at L 400 nm - where only the substituted thioxanthone Z (Ri - Rg R3 H R4 = C00(CH2CH20)8 H) absorbs -demonstrates the increase of the poiymerization efficiency [25]. Under exposure, the mixture of Z + fi leads to a considerabie polymerization enthalpy whereas, in the presence of Z or S alone, the exothermic signal remains very small. The same is true when using a laser light at X, - 440 nm [26] for the excitation of a mixture S+fi- No polymerization occurs in the presence of or . The relative reactivity of fi at 363 nm and -t- at 440 nm shows a 35 1 ratio, thus defining a low quantum efficiency of excitation transfer. 

We can see that an increase in oxygen pressure yields an exothermic signal, and that the signal amphtude increases with pressure. 

Ray and Day (1990) used DTA investigations of the crystallization peak as a rapid method to determine the temperature for maximum nucleation of glasses to develop glass-ceramics. The height of the exothermic signal of the crystallization of lithium disilicate, Li2Si205, was measured at different temperatures for a constant time of 3 h. The results clearly showed a maximum of the crystallization peak with a sample heat treated at 453 3 C for nucleation of the base glass. Therefore, the temperature of 453 C was determined as the temperature for maximum nucleation. 

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]. 

Cudzilo investigated the B/PTFE reaction recorded both DTA and TG signal (Figure 5.24) [20]. At 557°C an exothermic reaction peaks followed by two endothermic reactions with local minima at 575 and 596 °C. These events are followed by two exothermic signals at 614 and 639 °C. These processes coincide with an overall mass loss of 45%. Thus perfectly matching the amount of BF3 formed at the given stoichiometry. 

A - the resins synthesized in two-step procedure, B - the resins obtained in one-step synthesis - Two exotherm signals were recorded... 

Thermal oxidation leads to some radicals bimolecular combinations which are rather exothermic. When heated above their melting point imder air, typically at temperatures ca 170-200°C, lifetime of polyolefins is extremely short. Hence, a exothermal signal is observed by Differential Scanning Calorimetry shortly for sample exposed at 200°C shortly (less than 1 min) after DSC cell is switched from nitrogen to oxygen (Figure 3.21). It is however significantly increased when stabilizers are added [42,114]. 

The presence of copper shifts the exothermal crystallization peak to 823 K for sample SI (10 at% Cu) and to 893 K for samples S3-S7 (30-70 at% Cu, Fig. 1). The exothermic peaks at 473 K and 550 K (Fig. Ic) arc associated with the presence of acetate in the precursor, as emerges from a comparison with the DSC curve of the pure nitrate precursor (Fig. If). Calcination at 623 K in air for 3 h results in an acetate free catalyst (Fig. Id). The exothermic signals appearing at 480 and 613 K after exposing this catalyst to methanol synthesis... 

Initial reaction period (cement hydration) Occurs upon contact of the cement with water and is observed as an early exothermal signal in the calorimetry plot of cement hydration. Cement powder surface wetting and initial rapid dissolution of the clinker phases, CaO and alkali sulfate are considered to be the main contributors to the heat release. 

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