Microcalorimeters calibration

A modern adsorption microcalorimeter was built for the simultaneous measurement of isotherms and adsorption heats, establishing its correct functioning through adequate calibration of both the calorimeter part and the volumetric equipment of the adsorption part. For this purpose, the microcalorimeter calibration constant was found with values that go from 134.11 0.19 WV" to 156.67 0.23 WV. The adsorption isotherm was determined for a type NAZSM-5 zeolite as a reference solid to establish the correct functioning of the equipment. Micropore volume and superficial area were determined to be 0.20 cmVg and 296 m /g, respectively. These results agree very well with those obtained with commercial equipment. Finally, the differential heats of adsorption, for the same solid, were measured. The analysis of results gives valuable information about the studied C02/NaZSM-5 system, which is in concordance with other studies in the literature. 

Figure 15 gives a diagrammatic representation of a volumetric line which is used in connection with a high-temperature Calvet microcalorimeter 67). Other volumetric lines which have been described present the same general features (15, 68). In the case of corrosive gases or vapors, metallic systems may be used 69). In all cases, a sampling system (A in Fig. 15) permits the introduction of a small quantity of gas (or vapor) in a calibrated part of the volumetric line (between stopcocks Ri and Ro in Fig. 15) where its pressure Pi is measured (by means of the McLeod gage B in Fig. 15). The gas is then allowed to contact the adsorbent placed in the calorimeter cell C (by opening stopcock Ro in Fig. 15). The heat evolution is recorded and when it has come to completion, the final equi-...

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... 

Briggner LE, Wadso I. Test and calibration processes for microcalorimeters, with special reference to heat conduction instruments used with aqueous systems. J Biochem Biophys Methods 1991 22(2) 101-118. 

Willson RJ, Beezer AE, Hills AK, Mitchell JC. The imidazole catalysed hydrolysis of triacetin a medium term chemical calibrant for isothermal microcalorimeters. Thermochimica Acta 1999 325 125-132. 

As has been shown in this chapter, the differential scanning calorimeter and microcalorimeters have been shown to have wide applications in all aspects of pharmaceutical sciences, such as in preformulation and formulation development. However, the utility of these instruments is only possible with careful attention to following established calibration procedures. The DSC and other calorimeters are a critical part of a pharmaceutical scientists armamentarium. 

Calorimetric measurements at a salt concentration of 0.8 M (NaCl) were carried out with a differential scanning microcalorimeter microDSC III (Setaram, Caluire, France). The melting of naphthalene was used to calibrate the apparatus. The sample cell was filled with 850 mg carrageenan solution (0.2% w/w in 0.8M NaCl) and the reference cell with exactly the same amount of NaCl solution. Heating and cooling curves were recorded in the temperature range from 10 to 120°C at a rate of 1.0°C min-1. 

DTA Instrumentation. The differential thermograph used in this study has been described in detail (1, 2, 3). The microcalorimeter cell which used 0.005 gram of sample was used. The thermograms were recorded on an x-y recorder with the differential temperature, A T, on the y-axis and the sample temperature, T, on the x-axis. The sample temperature was measured with the same thermocouple as the AT. This produces thermograms with peak locations independent of heating rate. The heating rate was 4°C./minute. The calorimeter was calibrated with zone-purified dotriacontane, AHr + AHf = 51.7 cal./gram. 

A new batch microcalorimeter has been developed for measuring the dissolution of small amoimts of easily or slightly soluble solids. The calorimeter has been calibrated by dissolution of potassium chloride and successfully tested by measurements of the enthalpies of dissolution of acetanilide and adenine [16]. 

During the calibration of the Calvet microcalorimeter [10] and the KRM calorimeter [282], it was found that the calculated value treated as heat capacity changes in time. 

For a lot of compounds, it is possible to induce crystallization of amorphous fractions by subjecting the sample to humidity or solvent vapors, since adsorption of water or solvent in amorphous sections will reduce the glass transition temperature. By exposing samples to a controlled atmosphere in an isothermal microcalorimeter, the heat of crystallization can be measured and the amorphous content may be calculated after having performed a calibration of the system (Figure 8.8). In addition to finding conditions that are suitable to induce crystallization of the... 

At the times when the classical calorimeters were built, no computers existed and all evaluation was done by hand. Therefore, there was a need for simple formulas to calculate the quantities of interest from the measured curves. The construction of the calorimeters was such to give a signal strictly proportional to the heat flow rate into the sample itself with a calibration factor almost not influenced by the heat transfer to the sample and its heat capacity. The price to be paid for this comfort was a rather low sensitivity of the calorimeter with a need for large samples and large time constants in the range from some seconds up to many minutes in the case of very sensitive microcalorimeters (see Section 7.9.2). 

Wadso has described a batch microcalorimeter basically similar to Benzinger s but principally intended for measurement of enthalpies of reaction involving small sample volumes Oess than 5 cm of each component). Electrical calibration experiments indicated that the precision attainable was better than 1 per cent for rapid processes involving 4 mJ or slow (1 h) processes of 60 mJ, but better than O.OS per cent for the rapid production of ca, 0.5 J. ... 

An adsorption micro calorimeter for the simultaneous determination of the differential heat of adsorption and the adsorption isotherm for gas-solid systems are designed, built, and tested. For this purpose, a Calvet heat-conducting microcalorimeter is developed and is connected to a gas volumetric unit built in stainless steel to record adsorption isotherms. The micro calorimeter is electrically calibrated to establish its sensitivity and reproducibility, obtaining K=154.34 0.23 WV h The adsorption microcalorimeter is used to obtain adsorption isotherms and the corresponding differential heats for the adsorption ofCO on a reference solid, such as a NaZSM-5 type zeolite. Results for the behavior of this system are compared with those obtained with commercial equipment and with other studies in the literature. 

In order to establish the correct functioning of the microcalorimeter, which is then connected to the volumetric adsorption unit, the sensitivity is evaluated determining the calorimeter constant. The calibration constant reports the voltage generated by the calorimeter when a heat flow is emitted from inside the micro-calorimetric cell. There are two methods to determine the calibration constant K by application of electric power and by the stationary method [9, 10]. 

The calibration constants were obtained for the operation conditions of the microcalorimeter. Constants between range 134.11 0.19 WV to 156.67 0.23 WV are determined. These values show the sensitivity of the microcalorimeter built here, which is higher than that of equipments reported in literature and even of those built in our laboratory previously. This constitutes a significant contribution to the construction of this type of instruments. Values by the method of state stationary condition were obtained and were of the order same and magnitude. 

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