Authors:M. González-Martín, B. Jańczuk, and J. Bruque
Calorimetric measurements were made of the heat of immersion in water of cassiterite that was either untreated or treated
with 60% HNO3. The heats of immersion of cassiterite and fluorite were also calculated theoretically from the surface Gibbs energy components,
and compared with the heat of immersion measured for cassiterite and that taken from the literature for fluorite. The results
of the measurements and calculation revealed that the heat of immersion depends on the degree of hydration of the surface
of cassiterite and fluorite. It was also found that it is possible to predict the heats of immersion in water of cassiterite
and fluorite from the Lifshitz-van der Waals and acid-base components of the surface Gibbs energy.
The heats of immersion (in water) of outgassed clinoptilolite and its ion-exchanged forms were measured with a Calve calorimeter
at 30°C, and the integral heats of sorption were calculated therefrom in order to use zeolites in heating and cooling applications.
The immersion and sorption heats were studied as functions of the water saturation degree and the cation contents. The changes
observed in the slopes of the sorption curves at low saturation for Ca2+ and Mg2+ ion-exchanged forms were related to the thermal destruction of the heulandite-type structure.
Chemical factors influencing bitumen-mineral adhesion have been examined by heat-of-immersion calorimetry. Two chosen minerals (quartz and calcite) and bitumen derived from Venezuelan and Middle East crude oils were characterised and the energy released by the bitumen-mineral interaction measured. Heat-of-immersion data are correlated with the concentration of heteroatomic species present in the bitumen and the structure of the mineral surfaces. Bitumen-quartz bonding is promoted by the presence of basic species in the bitumen and bitumen-calcite adhesion is favoured by the presence of acidic groups. A mechanism is proposed to account for the observed bond energies.
The strength of chemical bonds formed between eight rock-forming minerals and six bitumen samples were examined by heat-of-immersion
calorimetry. The materials were characterised by their physical and chemical properties. The amount of energy released by
the bitumen-mineral interaction was much larger than expected for an immersion reaction, exceeding usual values by a factor
of up to 102. An oxidation mechanism, catalysed at the mineral surface, is proposed to account for this observation, and trends in the
heat-of-immersion data are correlated with chemical properties of the bitumen and mineral samples.
A novel experimental cell for the determination of heats of immersion has been designed and constructed for use with a Setaram C-80 microcalorimeter. The cell contains a replaceable aluminium membrane which is used to separate the immersion liquid from the degassed solid. A membrane system considerably eases the problems associated with sample preparation. The construction and features of the cell which are essential for successful operation are discussed. Calibration experiments usingn-heptane have been carried out. The heat associated with events such as membrane breaking and liquid evaporation has been minimised and represents around 1% of the heat changes involved in a typical immersion experiment.
The interactions among five samples of activated carbons, obtained from different lignocellulosic materials with different
degrees of activation of approximately 20% and aqueous solutions of phenol and 4-nitro phenol are studied by means of the
determination of immersion enthalpies.
It is established that the obtained activated carbons are of a basic character and show values for the pH at the point of
zero charge, pHPZC, that range from 7.4 to 9.7 and, in all cases, higher total basicity contents than the values obtained for total acidity.
The immersion heat of the activated carbons in CCl4 and water is determined obtaining values which are higher for CCl4 immersion and vary from 31.4 to 48.6 J g−1. The hydrophobic factor, hf, it is calculated from the relation between of the immersion heat of the activated carbons in CCl4 and the immersion heat in water, the obtained values were 2.98 and 6.75, which are greater than 1 due to the greater values
obtained in CCl4 when compared to the values obtained in water.
Immersion enthalpies in phenol solution range from 7.6 to 13.9 J g−1 and for the case of 4-nitro phenol such enthalpies range from 12.7 to 20.5 J g−1; all the 5 samples studied showed a higher value for the heat of immersion in aqueous solutions of 4-nitro phenol.
Authors:I. Schulz, U. Illgen, J. Scheve, and K. Backhaus
For application in catalysis and adsorption processes, zeolites are synthesized on the surface of spray-dried kaolin microspheres. Various thermal effects are used for the rapid characterization of the zeolite type and content. From DTA measurements, the exothermic lattice break-down peak gives information on the zeolite type and the thermal stability of the sample. Measurements of the heats of immersion by a very simple and quick method allow conclusions about the type and the sorption properties of the zeolite part of the clay. The most precise method to estimate the zeolite content was a standardized technique of desorption and readsorption of water or organic compounds by means of a thermobalance.
The authors describe the determination of the SiO2, Al2O3, Na2O, SO3 and moisture contents of finely dispersed silicic acids and silicates by means of thermochemical methods. Special interest is paid to the determination of SiO2 and Al2O3 as well as to the advantages of the method and to disturbing factors. The possibility of using kinetic-catalytic analysis with thermometric end-point detection for Cu and Mn determination is discussed. In the second part of the paper the authors deal with the heat of wetting and heat of immersion of finely dispersed silicic acid, and give data for their determination under circumstances of industrial analysis too. Differences in the heats of wetting were found for the different types of silicic acid. These studies require further measurements to be made.