Sample calorimetric cell

One of the conclusions deduced from the thermochemical cycle 2 in Table V, for instance, is that in the course of the catalytic combustion of carbon monoxide at 30°C, the most reactive surface sites of gallium-doped nickel oxide are inhibited by the reaction product, carbon dioxide. This conclusion ought to be verified directly by the calorimetric study of the reaction. Small doses of the stoichiometric reaction mixture (CO + IO2) were therefore introduced successively in the calorimetric cell of a Calvet microcalorimeter containing a freshly prepared sample of gallium-doped... 

The initiation system consists of a nitrogen laser and the necessary optics to lead the beam to the sample cell. The laser emits pulses at 337.1 nm with 800 ps duration, with a typical repetition rate of less than 5 Hz. The optical components, aligned between the laser and the calorimetric cell, consist of an iris (I), a support for neutral density filters (F), and a collimating lens (L). The iris is used to cut out most of the laser output and allow only a thin cylinder of light to pass through its aperture, set to 2 mm. The laser energy that reaches the cell is further... 

The duration of each dosing experiment is about 15-50 minutes (depending on the sample and of the time constant of the calorimeter), which was long enough to yield well-resolved heat-flow peaks and a stable horizontal baseline of the microcalorimeter. For all catalysts presented here, adsorption always reached thermodynamic equilibrium. Prior to adsorption measurements, the samples were pretreated in the calorimetric cell by heating overnight under vacuum. 

Adiabatic The temperature of the sample results from its thermal activity. This technique gives direct access to the thermal runaway curve. The results must be corrected by the adiabacity coefficient, since a part of the heat released in the sample is used to increase the temperature of the calorimetric cell. This rends the kinetic evaluation complex. 

Introduction of sample bulb (2) into stainless steel calorimetric cell already filled with immersion liquid (7). 

Micro-calorimetric adsorption measurements require a proper in situ vacuum activation at a higher temperature than the adsorption process. A first pre-treatment under oxygen is performed in the calorimetric cell in order to eliminate the impurities present on the sample (essentially carbonates, nitrates, carbonaceous residues and water present from the preparation, calcination and exposure to atmosphere) and to avoid the partial reduction of the surface of an oxide that is easily reduced under vacuum. 

An adiabatic low-temperature c orimeter designed specifrcally for a vapor-deposited sample is depicted in Fig. 1. This calorimeter equips with a built-in cryorefrigerator which enables to keep the calorimetric cell at cryogenic temperatures for a long time. 

The enthalpies of fusion of K2TiFe and K3TiFy were determined by AdamkoviCova et al. (1995a,b) using the high-temperature calorimeter Setaram HTC 1800K. The calorimeter was in the DSC mode at scanning rate of 1 K min The sample was sealed in a platinum crucible and placed in the upper alumina cmcible of the calorimetric cell. 

The carbon sample is weighed in the calorimetric cell (out of the microcalorimeter) and then connected to vacuum for outgassing. 

Heats of hydrogen, acetonitrile and MEA adsorption were determined with a modified SETARAM microcalorimeter DSC-111. After reduction and outgassing under flowing He at 723 K, the sample was cooled to room temperature. The temperature was then fixed to 313 0.01 K where micropulses of the probe molecule were fed to the catalyst using a 6-way sampling valve flushed with He. The thermal event in the calorimetric cell was then recorded as a function of the adsorbate uptake, which was monitored by a thermal conductivity detector. 

The measurement of very small absorption coefficients (down to lO-5 cm-1) of optical materials has been carried out by laser calorimetry. In this method, the temperature difference between a sample illuminated with a laser beam and a reference sample is measured and converted into an absorption coefficient at the laser energy by calibration [13]. Photoacoustic spectroscopy, where the thermal elastic waves generated in a gas-filled cell by the radiation absorbed by the sample are detected by a microphone, has also been performed at LHeT [34]. Photoacoustic detection using a laser source allows the detection of very small absorption coefficients [14]. Photoacoustic spectroscopy is also used at smaller absorption sensitivity with commercial FTSs for the study of powdered or opaque samples. Calorimetric absorption spectroscopy (CAS) has also been used at LHeT and at mK temperatures in measurement using a tunable monochromatic source. In this method, the temperature rise of the sample due to the non-radiative relaxation of the excited state after photon absorption by a specific transition is measured by a thermometer in good thermal contact with the sample [34,36]. 

Assuming that the heat of adsorption is directly depending on the acidic or basic strength one obtains information about the amount, strength and distribution in strength of such sites but not about their nature. In such a technique a vacuum line with gas manifolds is attached to a cell placed into a Tian-Calvet type calorimeter maintained at the desired temperature. Successive increments of the probe molecules are introduced over the sample placed in the calorimetric cell and the heat of adsorption is then measured. One may then plot the differential heats of adsorption versus coverage or even its derivative, i.e. the number of... 

A Tian-Calvet microcalorimeter (model BT 2.15, Setaram, France) was used to measure the enthalpies of adsorption of propane and propylene at room temperature. The samples (0.1 g) were treated under different conditions (i) vacuum at 523 K, (ii) vacuum at 773 K, (iii) He at 1073 K and (iv) H2 at 1073 K, all for 4h. Then, thqr were s ed into a Pyrex RMN tube in pure He and placed into the microcalorimetric celL A conventional manometric system coupled to the microcalorimet was used to m isare the amount adsorbed employing a (type 660) manometer witii a pr xsion of 0.001 Torr. The maximum apparent leak rate of the manometric system (including tire calorimetric cells) was 10 Torrmiri in a volume of about 60 cm. ... 

The thermoreversibility of the monoesterification reaction between nonandiol or HTPB and EPR g-SA has been studied by using a calorimetric cell attached to a FTIR spectrophotometer. The stoichiometric reaction conditions chosen are ratio SA/OH, 1/1.5. The procedure was as follows the sample, after casting from solution onto KBr disks at room temperature under vacuum, was rapidly brought to 220°C and left at this temperature for 30 min such a procedure was chosen because at T > 200°C the esterification reaction does not occur at all [66] we can consider this situation as the zero reaction time (actually, as shown by the first spectrum of Fig. 12, a certain amount of ester is already present at T = 220°C, probably due to the time necessary to cast the film and to bring it to 220°C). 

A well-established stepwise procedure was followed [16, 23, 25, 56]. Small successive doses of the adsorptive were admitted and left in contact with the adsorbent until the thermal equilibrium was attained. The 1st run of adsorption performed on the activated sample (pretreated in high vacuum conditions and/or in controlled atmosphere) will be hereafter referred to as ads. I. At any individual dose of gas introduced in the system, the evolved heat AQ " was measured within the calorimetric cells, while the adsorbed amount Anads was measured by volumetry. Ads. I was followed by a desorption run (des. I), performed by simple evacuation of the cell. In such a way the reversibly adsorbed phase was desorbed and either the pristine surface was restored, in case of an entirely reversible adsorption, or the pristine surface was not recovered, in case of a (partially) irreversible adsorption. Ads. II was subsequently performed in order to assess which fraction (if any) of the pristine surface sites was irreversibly occupied by the adsorbed phase (in the adopted conditions). By subtracting the ads. II curve from the ads. I one, the adsorbed fraction not removed by evacuation is evaluated. The ads. n component will be hereafter referred to as the reversible adsorbed phase, whereas the (ads. I - ads. n) component will be referred to as the irreversible phase (in the adopted conditions). Subsequent runs of adsorption (ads. IE, IV etc.) are performed in some cases, if the irreversible modification of the surface is expected/suspected not to be extinguished during the ads. I [21, 23, 26]. Adsorption measurements are usually performed at least twice on a virgin portion of the same batch of the material, activated in the same conditions, to check the experiments reproducibility. The routinely run protocol of adsorption-desorption-adsorption cycles is schematically illustrated in Fig. 1.8. 

The last term in Eq. 1.20 represents either the compression work during adsorption or the expansion work during desorption, and is null when two calorimetric cells (one with the sample, the other as reference element) are connected differentially, as in the case of the equipment here described. Equation 1.20 so simplifies in Eq. 1.21 ... 

The standard operating procedure for heat measurement is as follows [49,54]. The glass bulb containing the solid sample after the sample evacuation (and pre-coverage) stage is introduced into the calorimetric cell, which has been previously filled with... 

A detailed general view of the equipment calorimeter is shown in Figure 1. The diagram shows microcalorimeter with the calorimetric cells made of stainless steel (sample and reference), which are embedded inside a large block (also divided in two parts) in stainless steel, which acts as deposit of the thermostatic liquid. Due to its thermal difhision coefficient, this set allows the rapid heat conduction towards the surrounding of the calorimeter. The whole set is placed inside... 

The measurement of an enthalpy change is based either on the law of conservation of energy or on the Newton and Stefan-Boltzmann laws for the rate of heat transfer. In the latter case, the heat flow between a sample and a heat sink maintained at isothermal conditions is measured. Most of these isoperibol heat flux calorimeters are of the twin type with two sample chambers, each surrounded by a thermopile linking it to a constant temperature metal block or another type of heat reservoir. A reaction is initiated in one sample chamber after obtaining a stable stationary state defining the baseline from the thermopiles. The other sample chamber acts as a reference. As the reaction proceeds, the thermopile measures the temperature difference between the sample chamber and the reference cell. The rate of heat flow between the calorimeter and its surroundings is proportional to the temperature difference between the sample and the heat sink and the total heat effect is proportional to the integrated area under the calorimetric peak. A calibration is thus... 

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