Measured isoperibol calorimeter

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... 

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. 

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. 

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 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. 

For the drop technique, the isoperibolic calorimeters are most frequently used. The calorimetric device consists of two main parts a furnace and a heated block. Between the calorimetric block and the furnace, there is a system of shields controlled by a mechanic, hydraulic or electromagnetic device, which prevents the heat transfer from the furnace to the calorimetric block. The calorimeter is made of copper with a cavity closed by a shield. A resistance thermometer wound on the block measures its temperature. Such a calorimeter can work up to 1700°C, especially when the furnace... 

Manin and Korolev reported having measured the enthalpy of solution of NiC Ccr) into water and into aqueous solutions of other electrolytes. The measurements were performed with an isoperibol calorimeter with a claimed accuracy of 0.6%. Their results for the enthalpy of solution into H2O are listed in Table A-25. The mean value of Aj i//° for the reaction ... 

This nomenclature is close to that proposed by Hemminger and Hohne in 1984. It makes use of the same three primary criteria the principle of measurement, the mode of operation and the construction principle. Each criterion leads to its own classification, as shown hereafter. The main difference from the 1984 classification is that, instead of only proposing two major methods of calorimetry (compensation of the thermal effects and measurement of the temperature differences, respectively) there are now three. This is obtained by splitting the second one into calorimeters that measure a heat-accumulation (including the adiabatic and the isoperibol calorimeters) and calorimeters that measure a heat-flow. 

In an isoperibol calorimeter the heat, q, released in the combustion reaction produces an increase of the temperature of the water inside it, which is measured by means of a suitable thermometer (usually a platinum resistance thermometer, a quartz thermometer or a thermistor). The stirrer ensures that the energy released in the combustion reaction is transferred to the calorimeter so that the combustion bomb, the water and the can are quickly brought to the same temperature. The heater is used to take the temperature of the calorimeter to the starting point of the experiment. It is desirable to have an experimental temperature increment of at least 1 K. Figure 2 shows a typical temperature-time curve obtained in an isoperibol combustion calorimeter. 

Figure 6.11 Measured temperature-time function of an isoperibol calorimeter after a sudden heat production (heat pulse) inside the calorimeter.

Figure 6.13 Measured curve of an isoperibol calorimeter for a constant heat flow of finite...

Figure 6.14 Measured temperature change of an isoperibol calorimeter for a heat pulse."...

An unusual large isoperibol calorimeter serves to measure the heat production of large car batteries under real loading and unloading conditions. The calorimeter chamber (40 x 60 x 40 cm ) is lar enough to contain not only test cells and... 

Solid + Liquid and Liquid + Liquid Reactions.—Macrocalorimeters for Rapid Reactions. In this section are described techniques which are available for measuring the energy or enthalpy of reactions which proceed sufficiently rapidly for isoperibol calorimeters to be used, i.e. the reaction is complete in about 15 min, and for which quantities of reactant between 100 mg and several grams are available for each determination. Such reactions constitute the most widely studied group. 

Thermochemical measurements on reactions between gases and solids, other than combustions, are uncommon. Gross and his co-workers measured the enthalpy of reaction between alkali-metal fluorides MF (M = Li or Na) and BFg to form MBF4 using an isoperibol calorimeter operated at 110 The stream of argon flowing over the heated fluoride was replaced by BF for a period of 10 min. Duus and Mykytiuk used a flow method to determine the enthalpy of the reaction... 

Fig. 1. Schematic diagram of experimental apparatus for measuring AS (H /H2) (A) computer, (B) electrochemical workstation, (C) solution-reaction isoperibol calorimeter,...

The isoperibol calorimeter is also termed an enviromnent constant-temperature calorimeter. The famous Nemst-type calorimeter is a typical low-temperature isoperibol calorimeter. Before the 1940s, the enthalpies of phase transition and heat capacity of hundreds of organic compounds were determined with an inaccuracy of between +0.5 to 0.2 percent by Nemst-type calorimeters. Low temperature adiabatic calorimeters were developed based on the Nemst-type calorimeter, and, at present, adiabatic calorimeters have replaced Nemst-type for most low temperature heat capacity and phase change measurements on organic compounds. Besides the Nemst-type calorimeters, the term isoperibol calorimeter also refers to other types of environment constant-temperature calorimeters such as the commercial LKB-microcalorimeter. 

In Fig. 5.2, three different types of isothermal and isoperibol calorimeters are shown a calorimeter that makes use of the phase change for heat measurement, a calorimeter that accepts the heat from a surrounding liquid, called a... 

The partial and integral enthalpies of formation for the B-Fe-Mn system at 1557°C were measured by [1995Wit] using a high-temperature isoperibolic calorimeter. 

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