The surface properties of activated carbons (AC) play a significant role when these materials are used for adsorption from liquid phases or as supports for catalysts. Different ways to describe the chemistry of carbon surfaces are considered: (1) according to the concept of chemical groups as developed in organic chemistry (XPS of AC is illustrated by nitrogen functions); (ii) by active surface area and polar surface area. No single method is able to give a quantitative description of the surface chemistry of a carbon material.

The reduction of NO by CO over silica was studied in the temperature range from 873 to 1273 K under an initial gas (NO, CO) pressure of 395 Pa. Reduction was carried out by a volumetric technique with a mass spectrometer for the analysis of the gaseous phase. The catalytic activity of silica is enhanced by its pretreatment in air or in vacuum in the temperature interval 873–1273 K and as a result the rate of reduction of NO is increased by a factor of > 3. In contrast, the rate of reduction of NO is not enhanced by pretreatment of the silica with water vapour at 973 K. The catalytic activity of silica seems to depend on the presence of a particular superficial structure occurring during heat treatment.

Two base-catalyzed silica aerogels were characterized by gas adsorption and thermoporometry, which led to a description of the microporous texture and pore size distribution between about 1 and 300 nm. The results are compared with those obtained on precipitated and pyrogenic silicas. The fractal dimension was determined at different length scales. It is shown that the surface of the secondary particles of both aerogels is fractal. A mass fractal dimension (D(m) = 1.8) was determined for the low density aerogel.

The intra-aggregate void size distribution of carbon blacks dispersed in water or in undecane was measured by thermoporometry. It appears that the interpenetration of the carbon black aggregates is deeper when dispersed in undecane than in water. This effect is attributed to the presence of an adsorbed film of alkane on the surface of carbon black which leads to a smaller sticking coefficient between the primary aggregates in the alkane than in water. The fractal dimension, measured from the void size distribution curves, is in good agreement with that obtained by STEM analysis on isolated aggregates. However, due to the interpenetration of the aggregates, the fractal character of the aggregates is limited to a very narrow range of lengths.

The pore size distribution curve and the cumulative pore volume of intra-aggregate voids of a pyrogenic silica dispersed in liquids were determined by thermoporometry. Two types of silica surfaces (hydroxylated and non-hydroxylated) and two types of liquids (water and undecane) were considered. It is shown that for the hydroxylated silica dispersed in undecane, the aggregates exhibit large voids giving rise to a high pore volume. Conversely, a more compact aggregate structure is observed when hydroxylated silica is dispersed in water or when hydrophobic silica is dispersed in undecane. These results indicate that for a pyrogenic silica of a given morphology the intra-aggregate void size and void volume are determined by the nature of the solid-solid interaction.

Capillary flow of liquid coal tar pitch into a coke bed was studied. Anomalies in the flow could not be attributed to a plugging effect for mesophase content lower than 20 wt%. The flow behaviour of small pitch droplets can be correlated with the change in physicochemical properties, as measured by the glass transition temperature, on penetration into the coke bed.

Les interfaces composites solide-liant sont fréquemment préparés à partir d'un précurseur liquide du liant.

Les proprietes de surface du carbone jouent un role important dans la dispersion et le comportement au frittage des catalyseurs supportes. L'etude de la phtalocyanine de fer est d'un interet particulier par l'etude des interactions du support carbone avec le catalyseur. La coalescence des particules PcFe sur le carbone graphite est considerablement abaissee par la presence de groupes oxygenes localise sur le bord des atomes de carbone qui agissent comme des ancres des particules supportes

Silica—water systems were frozen and their melting behaviour investigated by differential thermal analysis (DTA). The experimental curves exhibit two endothermic peaks located at a temperature T1 at the melting temperature T0 of bulk ice. Temperature T1 is lower than T0 and this endothermic peak appears irrespective of whether the system is a sol or gel. Peak T1 was attributed to the melting of ice filling the intra-aggregate void volume of silica particles. The amount of non-freezing water was determined by NMR measurements. Analysis of the experimental results led to a determination of the solid volume fraction øs and the specific void volume v1 of the aggregates.

La fusion de undécane gélifié par différentes silices est étudiée par analyse thermique différentielle. Les courbes obtenues permettent de mettre en évidence l'existence de deux pics. Un premier pic est situé à la température normale T 0 de fusion du undécane pur. Le second pic, situé à une température T 1 inférieure à T 0 est attribué à la fusion de undécane contenu dans des volumes intra-agrégats de la silice. L'analyse des résultats expérimentaux permet l'étude de la structure du gel.

The capillary flow of liquid pitch into a granular coke bed has been theoretically investigated. An equation relating the flow rate with temperature has been derived considering the pitch as a Newtonian liquid. For a given coke granulometry, the wetting angle and the viscosity of the pitch material are the most important factors governing its flow properties. A comparison with experimental flow measurements indicates that some pitches penetrate into the granular coke bed according to the developed equation of flow.

The aim of the paper is to describe the influence of the morphological parameters of silicas on gelification processes. The morphology of the silicas is characterized quantitatively by its BET surface area and its initial void volume and qualitatively by electron microscopy. It appears that the parameter which governs the value of the gelification threshold is the aggregate morphology, correlated with the initial void volume. The building of the solid framework leading to the gel state does not depend on the volume fraction of the dry powder but on the volume fraction of the silica aggregates filled with part of the liquid medium. It is suggested that the percolation theory may describe the gelification process of silica in non-polar liquids.

Co-carbonization of non-coking coals and pitch materials has been followed by optical microscopy and thermogravimetry. The results obtained at a heating rate ⪢ 5 K min−1, clearly indicate a strong correlation between the thermogravimetric behaviour of the blend and the development of anisotropic texture in the resultant coke. For non-interacting systems, i.e. no enhancement of the anisotropic texture, the instantaneous rates of weight losses during carbonization of each component in the blend are almost additive. In contrast, for interacting systems, the thermogravimetric behaviour of the blend differs widely from the one obtained by adding the rates of weight losses of each component taken separately. The improvement of anisotropy of a coke by adding pitch to the initial coal results from a chemical stabilization of the system by pitch in the temperature range where, in the absence of pitch cross-links are formed which hinder the subsequent formation of large organized aromatic units.

Une etude comparative de la sorption de phenol en solution sur le bois de hetre initial et le materiau pyrolyse a permis de differencier les phenomenes de transport de ceux relevant de l’adsorption physique proprement dite. La sorption de phenol est fortement limitee en milieu non gonflant du bois par des phenomenes de diffusion dans le reseau microporeux des derives ligneux deshydrates.

The authors studied the relation between oxygen-containing functions of cokes and contact angles of tars on cokes. Using two different cokes, a coal-tar pitch and polymer models, they showed that the coke-tar interactions depend on the hydrogen bonding between the two components and that above a critical value surface-chemical-function content has no influence on coke-tar interactions.

The limit of penetration of a given coal-tar pitch into two cokes during mixing of the coke and liquid tar has been studied. It was shown that tar penetration is limited by compression of gas occluded in pores. Mercury porosimetry of cokes and pyrolysed coke-tar mixtures as well as micrographs of cokes impregnated with tar allow one to estimate the limiting pore diameter of tar penetration into coke at ca. 6 μm for the system considered.

Les auteurs ont étudié l'effet de l'addition de faibles quantités d'hydrocarbures aromatiques sur la pyrolyse du méthane, dans un système à courant gazeux. Les résultats obtenus permettent de conclure que les réactions hétérogènes ont un rôle important dans le mécanisme de décomposition thermique du méthane.