Immersion Enthalpy of Activated Carbon–Cyclohexane and Activated Carbon–Hexane. Difference in the Solid–Liquid Interaction Enthalpy Due to the Structure of the Solvent

The enthalpy of immersion for five activated carbons (with different surface chemistry) in cyclohexane and hexane was determined in order to observe the intensity of the solid–liquid interaction. The enthalpy of immersion was related to the properties of activated carbons, such as micropore volume, total basic groups content, and the EoWo product, that characterized each solid-liquid system. The values for the immersion enthalpy were between −21.2 and −91.7 J g−1 for cyclohexane and between −16.4 and −66.1 J g−1 for hexane. It showed greater interaction between the cyclohexane and the activated carbons and it was related to the properties of this adsorbate, such as molecular size and molecular arrangement. The difference in the enthalpy of immersion between the solvents per unit of micropore volume for the set of activated carbons was calculated obtaining a value of −487 J cm−3.

Medidas de adesão entre agregado e ligante asfáltico

<p>A adesão entre agregado e ligante asfáltico vem sendo apontada como uma propriedade de grande importância para a causa de defeitos encontrados em pavimentos asfálticos, tais como trincas por fadiga, e dano por umidade. Diferentes mecanismos existem na literatura para explicar a adesão entre os dois materiais, porém, estes mecanismos podem ser resumidos em três grandes grupos: inter- travamento mecânico, adesão física, e interação química. A ocorrência de mais de um mecanismo simultaneamente parece ser o fenô- meno mais provável, sendo a relevância de cada um dependente das características físicas e químicas do agregado e do ligante asfálti- co. No presente trabalho, dois procedimentos foram utilizados para acessar a adesão entre agregado e ligante. O primeiro constou do cálculo do trabalho de adesão através da energia livre de superfície dos materiais envolvidos e o segundo, da determinação da entalpia de imersão quando soluções de asfalto são postas em contato com o agregado. Todos os materiais usados foram provenientes da biblio- teca de referência do SHRP sendo um pedregulho como agregado, e três diferentes ligantes asfálticos. Os resultados mostraram a capa- cidade do microcalorímetro em detectar possíveis interações químicas na adesão entre agregado e ligante asfáltico, em conjunto com adesão física. A presença de grupos funcionais mais fortemente adsorvidos pela superfície dos agregados justificou os maiores valores de entalpia de imersão para as combinações onde esses grupos se encontravam presentes.</p><p><em><strong>Abstract</strong> Adhesion between the asphalt binder and the aggregate is critical to the performance and durability of asphalt mixtures. According to the literature, distresses mechanisms such as fatigue cracking and moisture induced damage are correlated to the nature and quality of adhesion between these two materials. Different mechanisms already exist to explain adhesion, but they can be summa- rized in three main groups: mechanical interlocking, physical adhesion and chemical interaction. Although discussions of isolated theo- ries and mechanisms help to clarify the understanding of adhesion, they can rarely be separated completely to each other. The physical and chemical characteristics of asphalt and aggregate will in fact determine the relevance of each of these mechanisms. This study presents the results of two procedures for adhesion measurement: (i) an indirect method based on the surface free energy components of asphalt binder and aggregate; and (ii) the determination of the enthalpy of immersion through the use of a microcalorimeter. The materials used, a gravel as aggregate and three different neat asphalts, were provided by the Strategic Highway Research Program's Material Reference Library. The results showed the capacity of the microcalorimeter in detecting possible chemical reactions together with physical adhesion. The presence of functional groups more strongly adsorbed by the aggregate surface justified the higher values of the heat of immersion. </em></p>

Time-dependent changes of adsorption and wetting properties of pillared montmorillonites

The changes of adsorption properties of uncalcined Al-pillared montmorillonite were studied. A soda-activated bentonite from Slovakia was reacted with polymeric hydroxoaluminium salt solutions. During storagein air at room temperature for three years, the basal spacing decreased by 0.15–0.2 nm; the specific surface area was reduced by 80% and the total pore volume by 40–60%. Adsorption experiments from ethanol-cyclohexane mixtures revealed the decreasing adsorption capacity and the increasing hydrophobicity. The changing surface character was also evident in the decrease in enthalpy of immersion in ethanol from 65.3 J/g to 8.3 J/g (sample B) and from 37.8 J/g to 5.2 J/g (sample C). The alteration probably arises from gradual formation of gibbsite-like interlayers and the redistribution of charges.

The Non-Ideality of the System Benzene + 1,2-Dichloroethane Adsorbed in Microporous Carbons at 293 K

In the case of simple vapour mixtures adsorbed by active carbons, the activity coefficients seem to depend essentially on the composition of the adsorbed phase, rather than on the degree of micropore filling. Consequently, the liquid–solid adsorption equilibrium of benzene + 1,2-dichloroethane mixtures has been investigated at 293 K, using a typical active carbon and following earlier work for adsorption from the vapour phase. This system has the advantage that the mixture is ideal in the liquid state, which provides a convenient reference for the study of the adsorbed phase. The activity coefficients, as well as the excess enthalpy of immersion of the carbon into the liquid mixtures, provide information on the modifications in the adsorbed state with respect to the ideal mixture. It is also shown that the introduction of the activity coefficients derived from the solid–liquid equilibrium increases considerably the accuracy of the Myers–Prausnitz–Dubinin model for the adsorption of the vapour mixtures.

Dubinin's Theory for the Volume Filling of Micropores: An Historical Approach

The origin and development of Dubinin's theory are presented within their historical context. The emphasis is put on the author's long-standing collaboration with M.M. Dubinin. It is shown how the main correlations between the structural properties of active carbons and the parameters of the DR and DA equations have been established and crosschecked. As shown recently, the adsorption of water by microporous carbons, corresponding to a type V isotherm, can also be described by the equation of Dubinin and Astakhov. This new approach includes the enthalpy of immersion into water, a thermodynamic consequence of Dubinin's theory.