Phase transitions in the urea/n-nonadecane system by calorimetric techniques
Por:
López-Echarri A., Ruiz-Larrea I., Fraile-Rodríguez A., Díaz-Hernández J., Breczewski T., Bocanegra E.H.
Publicada:
1 ene 2007
Resumen:
A calorimetric study of urea/n-nonadecane, CO(NH2) 2/C19H40, and the deuterated derivatives, CO(ND2)2/C19D40 and CO(NH 2)2/C19D40, around the structural phase transition temperature is presented. For this purpose differential scanning (DSC), temperature-modulated (AC) and adiabatic calorimetry have been used and the obtained results are compared. Leaving apart the noticeable peak associated with the main phase transition at 158.5, 149.4 and 154 K respectively, small anomalies of the specific heat are found at lower temperatures and their corresponding entropic and enthalpic changes are reported. Heating and cooling experiments show the influence of the temperature rate and the thermal history on the detailed profile of the specific heat traces. The presence of thermal hysteresis and latent heat as a way to characterize the order of the phase transitions is discussed. Finally, a tentative approach to the urea and the alkyl chain contributions to the specific heat and their influence on the phase transition mechanisms is presented. © 2007 IOP Publishing Ltd.
Filiaciones:
López-Echarri A.:
Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain
Ruiz-Larrea I.:
Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain
Fraile-Rodríguez A.:
Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Díaz-Hernández J.:
Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Puebla, Mexico
Breczewski T.:
Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain
Bocanegra E.H.:
Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain
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