Tian-Calvet heat-flow microcalorimeters

A Tian—Calvet heat-flow microcalorimeter which, due to the 480 thermocouples of its thermopile, ensures all at once a good isothermicity of the experiment and a high sensitivity allowing to use a small sample (for an activated carbon, typically 50-100 mg) relatively easy to wet. 

The measurement of the heat of adsorption by a suitable calorimeter is the most reliable method for evaluating the strength of adsorption (either physical or chemical). Tian-Calvet heat-flow microcalorimeters are an example of high sensitivity apparatus which are suitably adapted to the study of gas-solid interactions when connected to sensitive volumetric systems [10-14, 50-55]. Volumetric-calorimetric data reported in the following were measured by means of either a C-80 or MS standard heat-flow microcalorimeter (both by Setaram, F), connected to ahigh vacuum (residual pressure... 

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. 

An apparatus with high sensitivity is the heat-flow microcalorimeter originally developed by Calvet and Prat [139] based on the design of Tian [140]. Several Tian-Calvet type microcalorimeters have been designed [141-144]. In the Calvet microcalorimeter, heat flow is measured between the system and the heat block itself. The principles and theory of heat-flow microcalorimetry, the analysis of calorimetric data, as well as the merits and limitations of the various applications of adsorption calorimetry to the study of heterogeneous catalysis have been discussed in several reviews [61,118,134,135,141,145]. The Tian-Calvet type calorimeters are preferred because they have been shown to be reliable, can be used with a wide variety of solids, can follow both slow and fast processes, and can be operated over a reasonably broad temperature range [118,135]. The apparatus is composed by an experimental vessel, where the system is located, which is contained into a calorimetric block (Figure 13.3 [146]). 

The heats of adsorption of the probe molecules were measured in a heat-flow microcalorimeter of the Tian-Calvet type from Setaram, linked to a glass volumetric line to permit the introduction of successive small doses of gases [6]. The equilibrium pressure relative to each adsorbed amount was measured by means of a differential pressure gauge (Datametrics). Successive doses were sent onto the sample until a final equilibrium pressure of 133 Pa was obtained. The adsorption temperature was maintained at 353 K in order to limit physisorption interactions between the probe molecules and the zeolites. All the samples were pretreated at 773 K under vacuum overnight prior to any calorimetric measurement. 

The Calvet microcalorimeter (16) is an improved version of the first heat-flow calorimeter described by Tian in 1924 (25). In this micro-... 

Heat-flow microcalorimetry was developed originally by Calvet (39). He modified a calorimeter previously conceived by Tian (40). In the Calvet microcalorimeter, heat flow is measured between the system and the heat block... 

Microcalorimetric studies of the adsorption of ammonia (Critical diameter 0.3 nm) have been carried out using a Tian-Calvet type heat-flow microcalorimetric (C-80 model, Setaram, France). The microcalorimeter has been connected to a volumetric vacuum adsorption unit for catalyst treatment and probe molecule delivery. A validyne low pressure transducer (USA) attached with vacuum system has been used for precision pressure mecisurement. 

The best-known calorimeter of this type was developed by Tian and Calvet (Fig. 17). Here the defined heat-conduction path to the thermostated surroundings (a large aluminum block) consists of a large number of differential thermocouples coupled in series (thermopile). This arrangement permits optimum determination of the heat flow rate to the surroundings, and such an instrument can be very sensitive (microcalorimeter). 

Flow microcalorimeters using heat-flux Tian-Calvet detection... 

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