Differential enthalpic analysis

CVR computerized virtual reality DEA differential enthalpic analysis... 

Quantitative characterisation of Au-Co/PTFE composite coatings by differential enthalpic analysis, Z. Serhal, P. Ber ot, J. Morvan, M. Rezrazi, and J. Pagetti, Sun Coat. TechnoL, 2002, 150, 290. 

All the displacive inversions of silica exhibit well discernible enthalpic effects on DTA (differential thermal analysis) curves. Pure quartz produces a minor but... 

Differential thermal analysis (DTA) is a thermal technique in which the temperature of a sample, compared with the temperature of a thermally inert material, is recorded as a function of the sample, inert material, or furnace temperature as the sample is heated or cooled at a uniform rate. Temperature changes in- the sample are due to endothermic or exothermic enthalpic transitions or reactions such as those caused by phase changes, fusion, crystalline structure inversions, boiling, sublimation, and vaporization, dehydration reactions, dissociation or decomposition reactions, oxidation and reduction reactions, destruction of crystalline lattice structure, and other chemical reactions. Generally speaking, phase transitions, dehydration, reduction, and some decomposition reactions produce endothermic effects, whereas crystallization, oxidation, and some decomposition reactions produce exothermic effects. 

Two closely related methods dominate the field—the older method, differential thermal analysis (DTA), and the newer method, differential scanning calorimetry (DSC). Both methods yield peaks relating to endothermic and exothermic transitions and show changes in heat capacity. The DSC method also yields quantitative information relating to the enthalpic changes in the polymer (26-28) (see Thble 8.5). 

Referring to the analysis of kinetic barriers that contribute to the differential rates, outlined above, it would appear that enantioselectivity may not reside in any single part of the kinetic scheme. In fact, analysis of the distribution of entropic and enthalpic contributions to the enantioselectivity of CaLB in mixtures of organic solvents showed that the gradual replacement of one organic solvent with the other may lead to a switch from one state to another [145]. More information on the response of individual steps in the kinetic scheme to a change of solvent is needed to arrive at a conclusive answer. 

Differential scanning calorimetry (DSC) scans also point out a clearly different behavior the e y transition produces poor enthalpic effects (only a very broad endothermic peak centered at 105 °C) while the 8 mesomorphic Y transition presents a well-defined endothermic peak (at 102 °C, associated with formation of the mesomorphic form) followed by an exothermic peak (at llO C, associated with yphase crystallization) [44], Moreover,several features of the dynamic mechanical analysis (DMA) scans can be rationalized on the basis of the different routes of thermal transitions of e and 8 phases toward the Y phase, being direct and through a mesomorphic phase, respectively [44],... 

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