Advances in the Understanding of Gelation in the Framework of the Test ASTM D5133

Abstract

This work presents a theoretical survey that sheds light on the physical meaning of the gelation index, that is, the main parameter involved in ASTM D5133. More specifically, it is proved that the pulse-shaped region of the gelation curve can be explained as the relief of the supersaturation of the solution, which is a nucleation process that finishes when the saturation ratio takes a value equal to 1. Comparison between experiments and the theoretical approach put forward in this work reveals qualitative agreement. This work also confirms the poor reproducibility of ASTM D4684, which is an alternative test for the evaluation of gelation in engine oils. Particularly, it is shown that the poor reproducibility of this test can be attributed to a systematic error made during the measurements. The lack of accuracy of the temperature, in particular the final test temperature, could be the main cause for discrepancies between laboratories. Finally, it is shown that in order to predict gelation within ASTM D5133, not only must the gelation index be considered, but the gelation index temperature also plays an important role.

Old instruments in the physics and chemistry cabinet at Goya Secondary School. Analysis of their didactic use in teaching physics today (Los antiguos instrumentos del gabinete de física y química del IES Goya. Análisis de su uso didáctico en la actual enseñanza de la física)

“…The process of using them once again is a powerful opportunity to restore their purpose in constructing knowledge. Authors like Maroto Centeno et al (2008) have used copies of these instruments to teach physics and found that students’ motivation increased when using these instruments, while also providing contextualized learning.…”

“…El proceso de volver a ponerlos en funcionamiento es una potente oportunidad para recuperar su función en la construcción del conocimiento. Autores como Maroto Centeno et al (2008) han utilizado copias de dichos instrumentos para la enseñanza de la física y han comprobado el aumento de la motivación de los alumnos al usar estos instrumentos además de promover un aprendizaje contextualizado de la misma.…”