Isoperibolic calorimeters

Figure Bl.27.4. Rotating bomb isoperibole calorimeter. A, stainless steel bomb, platinum lined B, heater C, thermostat can D, thennostat iimer wall E, themiostat water G, sleeve for temperature sensor H, motor for bomb rotation J, motor for calorimeter stirrer K, coimection to cooling or heating unit for thennostat L, circulation pump.

Albert H J and Archer D G 1994 Mass-flow isoperibole calorimeters Solution Calorimetry, Experimental Thermodynamics vol IV, ed K N Marsh and PAG O Hare (Oxford Blackwell)... 

In Figure 4 the results from the three different groups are in excellent agreement for butanol concentrations of 90 wt% and greater, although the data from the Russian group scatter somewhat more around our results than do the values interpolated from Westmeier s data.(14.16). At lower amphiphile concentrations the isoperibolic calorimeter measurements are in noticeably better agreement with the data of ref. 16 than with the Russian work (14-16). However, almost all results fall within the 95% confidence interval (dashed lines) for our results. 

It appears therefore that during the operation of all usual calorimeters, temperature gradients are developed between the inner vessel and its surroundings. The resulting thermal head must be associated, in all cases, to heat flows. In isoperibol calorimeters, heat flows (called thermal leaks in this case) are minimized. Conversely, they must be facilitated in isothermal calorimeters. All heat-measuring devices could therefore be named heat-flow calorimeters. However, it must be noted that in isoperibol or isothermal calorimeters, the consequences of the heat flow are more easily determined than the heat flow itself. The temperature decrease... 

It is, of course, not necessary to use a heat-flow microcalorimeter in order to determine the heat released by rapid adsorption phenomena. Dell and Stone (74), for instance, using an isoperibol calorimeter of the Garner-Veal type, found an initial heat of 54 4 kcal mole-1 for the adsorption of oxygen on nickel oxide at 20°C. The agreement with the value (60 2 kcal mole-1) in Fig. 19 is remarkably good, particularly if it is considered that very different methods were used for the preparation of the nickel-oxide samples (19, 74)-... 

The calorimetry lexicon also includes other frequently used designations of calorimeters. When the calorimeter proper contains a stirred liquid, the calorimeter is called stirred-liquid. When the calorimeter proper is a solid block (usually made of metal, such as copper), the calorimeter is said to be aneroid. For example, both instruments represented in figure 6.1 are stirred-liquid isoperibol calorimeters. The term scanning calorimeter is used to designate an instrument where the temperatures of the calorimeter proper and/or the jacket vary at a programmed rate. 

Figure 6.2 Schematic representation of (a) an adiabatic calorimeter, (b) an isoperibol calorimeter, and (c) a heat conduction (or heat flow) calorimeter. fc and 7] are the temperatures of the calorimeter proper and the external jacket, respectively, and is the heat flow rate between the calorimeter proper and the external jacket.

The basic output from a combustion experiment made with an isoperibol calorimeter is a temperature-time curve, such as the one represented in figure 7.2. In the initial or fore period (between ta and tf and in the final or after period (between tf and tf), the observed temperature change is governed by the heat of stirring, the heat dissipated by the temperature sensor, and the heat transfer between the calorimeter proper and the jacket. The reaction or main period begins at tu when, on ignition, a rapidtemperature rise results from the exothermic... 

In well-designed isoperibol calorimeters, the heat transfer between the calorimeter proper and the jacket takes place according to Newton s law, with conduction being the dominant mechanism [3,21,35-38]. In this case, the rate of temperature change during the initial and final periods, g, is given by... 

Because the instrument sketched in figure 10.1 is an isoperibol calorimeter, it only allows the study of fairly rapid processes (less than about 15 min). This... 

Instruction Manual ofTronac Model 550 Isothermal and Isoperibol Calorimeter System. Tronac Incorporated. 

L. D. Hansen, T. E. Jensen, S. Mayne, D. J. Eatough, R. M. Izatt, J. J. Christensen. Heat-Loss Corrections for Small Isoperibol Calorimeter Reaction Vessels. J. Chem. Thermodynamics 1975, 7, 919-926. 

The isothermal and isoperibol calorimeters are well suited to measuring heat contents from which heat capacities may be subsequently derived, while the adiabatic and heat-flow calorimeters are best suited to the direct measurement of heat capacities and enthalpies of transformation. 

Microcalorimetry has gained importance as one of the most reliable method for the study of gas-solid interactions due to the development of commercial instrumentation able to measure small heat quantities and also the adsorbed amounts. There are basically three types of calorimeters sensitive enough (i.e., microcalorimeters) to measure differential heats of adsorption of simple gas molecules on powdered solids isoperibol calorimeters [131,132], constant temperature calorimeters [133], and heat-flow calorimeters [134,135]. During the early days of adsorption calorimetry, the most widely used calorimeters were of the isoperibol type [136-138] and their use in heterogeneous catalysis has been discussed in [134]. Many of these calorimeters consist of an inner vessel that is imperfectly insulated from its surroundings, the latter usually maintained at a constant temperature. These calorimeters usually do not have high resolution or accuracy. 

The jacket that contains the bucket with its bomh provides a thermal shield to control the heat transfer between the calorimeter bucket and its surroundings. In an isoperibol calorimeter, it is not necessary to prevent this transfer, as long as a means of precisely determining the amount of heat transferred during Ihe determination can be established. 

For the adiabatic calorimeter, the jacket temperature must be adjusted to match that of the calorimeter vessel temperature during the period of the rise. The two temperatures must be maintained as close to equal as possible during the period of rapid rise. For the isoperibol calorimeter, the temperature rise may require a radiation correction. In either case, an individual test should be rejected if there is evidence of incomplete combustion. Furthermore, although it is required to check the heat capacity only once a month, this may be inadequate. A more frequent check of heat capacity values is recommended for laboratories making a large number of tests on a daily basis. The frequency of the heat capacity check should be determined to minimize the number of tests that would be affected by an undetected shift in the heat capacity values. 

Solution calorimetry of BaU03+x was performed in an 880 cm3 isoperibol calorimeter described by Nocera et al. (21). 

The first experiments of gas adsorption calorimetry by Favre (1854) were made with an isoperibol calorimeter. More recently, refinements were introduced by Beebe and his co-workers (1936) and by Kington and Smith (1964). Because of the uncontrolled difference between the temperature of the sample and that of the surroundings, Newton s law of cooling must be applied to correct the observed temperature rise of the sample. In consequence, any slow release of heat (over more than, say, 30 minutes), which would produce a large uncertainty in the corrective term, cannot be registered. For this reason, isoperibol calorimetry cannot be used to follow slow adsorption equilibria. However, its main drawback is that the experiment is never isothermal during each adsorption step, a temperature rise of a few kelvins is common. The corresponding desorption (or lack of adsorption) must then be taken into account and, after each step, the sample must be thermally earthed so as to start each step at the same temperature. In view of these drawbacks,... 

Calorimetry. Heats of solution were measured at 30°C using an LKB model 8725-2 isoperibol calorimeter. Details of the procedure have been given (5). The heats of mixing known weights of water or ether with 25 ml of 0.1-0.5M acid solutions in sulfolane were determined. Some of the acid solutions contained some known concentrations of water as well. In addition, the heats of solution of NEt4CF3S03 in sulfolane and in a 0.211M HSbCl6 solution in sulfolane were determined at three concentrations between 0.02 and 0.04M. 

The thermokinetic parameter as defined above provides semiquantitative information on the kinetics of the processes occurring in a calorimeter. The rigorous mathematical modeling of the thermokinetics for heat-flow calorimeters (2,34,42,130-132) and isoperibol calorimeters (133) has been recently discussed. Using these methods it is possible to obtain quantitatively the energetic as well as the kinetic parameters describing a number of important processes such as adsorption, desorption, consecutive processes involving the formation of adsorption intermediates, and chemical reactions. 

Heats determined using isoperibol calorimeters. Heats of immersion. 

There was a maximum in the curve of differential heat versus surface coverage. Heats determined using isoperibol calorimeters. 

Fig. 5 Schematic diagram of an isoperibol calorimeter (top) and a thermal activity monitor (TAM) (bottom).

Solution calorimetry allows us to investigate processes that involve enthalpy changes. Adiabatic microcalorimeters and isoperibol calorimeters used in batch modes or flow modes allow for the precise determination of the heat of solution. Mixing the reactants is accomplished by breaking a bulk allowing reactants to mix or by special chambers where the reactants are mixed together. 

RC measurements can be classified either as devices using jacketed vessels with control of the jacket temperature (heat balance calorimeters, heat flow calorimeters and temperature oscillation calorimeters) or as devices using a constant surrounding temperature, e.g., jacketed vessels with a constant jacket temperature, (isoperibolic calorimeters and power compensation calorimeters) such instruments may also feature single or double cells. 

Isoperibolic calorimeter. One of the characteristics for the isoperibolic calorimeter is to maintain the temperature of the cover at a constant value. The heat effect of the process taking place in the calorimeter is evaluated from the time course of the temperature curve. The typical course of this curve at an exothermic process is shown in Figure 4.2. 

Isoperibolic calorimeters also comprise calorimeters based on the measurement of heat flow, since they fulfill the condition Tg = constant, changes. With these calorimeters, the temperature difference (Tc - Tg) is not measured but directly the heat flow between the calorimetric vessel and the cover. 

One important factor, which influences the selection of the measurement method, is the duration of the chemical reaction investigated. For fast reactions, i.e. when the reaction is over at least within 30 min, the most suitable calorimeter is the isoperibolic calorimeter, since the heat effect can be determined quite precisely. The reaction proceeds in the calorimetric vessel, provided with a thermocouple, the drop-device of one component into the other, and the stirrer. The calorimetric cover is heated to a constant temperature. At the measurement of heats of mixing, respectively of heats of dissolution, both liquid components must be thoroughly heated before mixing to the same temperature before mixing. This can be made in such a way that the one component is placed just above the other one in a second crucible, which is then overturned or immersed and both components are mixed. 

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