Microcalorimeters Calorimetric techniques

In the various sections of this article, it has been attempted to show that heat-flow calorimetry does not present some of the theoretical or practical limitations which restrain the use of other calorimetric techniques in adsorption or heterogeneous catalysis studies. Provided that some relatively simple calibration tests and preliminary experiments, which have been described, are carefully made, the heat evolved during fast or slow adsorptions or surface interactions may be measured with precision in heat-flow calorimeters which are, moreover, particularly suitable for investigating surface phenomena on solids with a poor heat conductivity, as most industrial catalysts indeed are. The excellent stability of the zero reading, the high sensitivity level, and the remarkable fidelity which characterize many heat-flow microcalorimeters, and especially the Calvet microcalorimeters, permit, in most cases, the correct determination of the Q-0 curve—the energy spectrum of the adsorbent surface with respect to... 

The calorimetric technique used in the titration experiment illustrated in Figure 9 allows short time intervals between the injections due to a comparatively low time constant for the instrument in combination with the electrical compensation technique. Rather, slow heat conduction microcalorimeters can be used in fast titration experiments if a dynamic correction, based on the Tian equation (equation (17)), is employed (Bastos et al., 1991 Backman et al., 1994). 

Regular pulses of pure ethane on bulk V2O5 maintained at 823 K in a microcalorimeter linked to a gas chromatograph provided kinetic data of theoretical significance, as weU as an insight into the mechanism of the reduction process. The results of this work carried out using mainly calorimetric techniques led to the conclusion that diffusion of oxygen from the bulk is predominant in the selective oxidation of ethane and that the redox process plays a more important role than the acidic sites in the case of unsupported vanadium pentoxide. 

Various commercial calorimeters are now available for routine heat of immersion measurements. For research it is preferable to use a calorimetric technique which is consistent with thermodynamic requirements. We recommend the employment of a Tian-Calvet type of microcalorimeter, which by means of two thermopiles composed of a large number of thermocouple junctions allows the heat flux to be measured accurately at practically constant temperature (AT < 10 K). Whichever technique is used, the experiments must be devised in a manner which will allow the evaluation of a number of corrective terms due to partial evaporation of the liquid, bulb breaking, stirring and effect of atmospheric pressure. In practice, this does not present difficulties because the detailed procedures and calculations are described in the literature. ... 

A study of the relaxational transitions and related heat capacity anomalies for galactose and fructose has been described which employs calorimetric methods. The kinetics of solution oxidation of L-ascorbic acid have been studied using an isothermal microcalorimeter. Differential scanning calorimetry (DSC) has been used to measure solid state co-crystallization of sugar alcohols (xylitol, o-sorbitol and D-mannitol), and the thermal behaviour of anticoagulant heparins. Thermal measurements indicate a role for the structural transition from hydrated P-CD to dehydrated P-CD. Calorimetry was used to establish thermodynamic parameters for (1 1) complexation equilibrium of citric acid and P-CD in water. Several thermal techniques were used to study the decomposition of p-CD inclusion complexes of ferrocene and derivatives. DSC and derivative thermogravimetric measurements have been reported for crystalline cytidine and deoxycytidine. Heats of formation have been determined for a-D-glucose esters and compared with semiempirical quantum mechanical calculations. ... 

The volumetric-calorimetric data obtained by a Tian-Calvet heat-flow microcalorimeter connected to a gas-volumetric apparatus (as the one described in Chap. 1) being intrinsically molar quantities, their molecular interpretation often requires a multi-techniques approach. 

---