Deformation calorimeter

Figure 6.11 shows a famous example of the application of isothermal calorimetry. Gordon (1955) deformed high-purity copper and annealed samples in his precision calorimeter and measured heat output as a function of time. In this metal, the heat output is strictly proportional to the fraction of metal recrystallised. 

A 4.9 g sample of the liquid siloxane in a glass dish was put into a bomb calorimeter (on an open bench) containing 5 ml of sodium hydroxide solution to absorb combustion gases. The electric igniter system consisted of a metal wire in contact with a cotton-wool wick which dipped into the siloxane sample. The bomb was sealed, pressured up to 39-44 bar with oxygen, and the igniter was fired. A violent explosion blew the lid off the bomb (rated at 190 bar working, 250 bar test), and examination of the deformed bomb indicated that a maximum detonation pressure of around 900 bar had been attained. 

The above-mentioned method of deformation calorimetry has found a rather wide application. Modifications of the original design were constructed 72-75) and applied for investigating the thermomechanical behaviour of polymers and polymer composites. At the same time, the commercial Calvet-type calorimeters has been used in thermomechanical experiments on rubbers not only in the uniaxial mode 76-78 but also in torsion 79 80). Thus, deformation calorimetry has proved to be quite adequate in terms of sensitivity, specificity, rapidity and reliability and therefore seems to be the most promising experimental method of thermomechanical type. 

Equation (95) cannot be used to analyze the thermokinetics of processes that are accompanied by fast heat evolutions because the thermal response of a heat-flow calorimeter (the thermogram) is deformed by thermal lags. In this case a more complicated analysis 34, 32) is necessary but is rarely used, and we shall not discuss it here. In its place some authors use a semiquantitative... 

A body or substance placed in a calorimeter constitutes a thermodynamic system. Such a system can be characterized by indicating the boundary conditions relative to the surroundings and the values of all relevant physical quantities, namely, temperature, pressure, and volume (for solids, the stress and deformation tensors). 

Applications Involving Liquid—Caseous Transition Although this calorimeter type is only of historical interest nowadays, one interesting application should, however, be mentioned Williams (1963) described a deformation calorimeter suitable for use with different liquids. 

The deformation calorimeter serves to measure the heat released in the sample during a deformation. Calorimeters involving a liquid-gaseous transformation as well as other calorimetric procedures can be used for this purpose. The difference between the performed deformation work and the measured heat represents the energy stored in the deformed material. An obvious and common drawback of all measurements with deformation calorimeters stems from the fact that the sought quantity constitutes a minute difference between two measured values that are subject to uncertainties (i.e., deformation work and released heat) and are measured independent of one another and in different ways. If the stored energy accounts for about 10% of the deformation work, the heat and the deformation work must be measured with an uncertainty of 0.5% to determine the stored energy with an uncertainty of 10%. 

Wolfenden and Appleton (1967) described another deformation calorimeter in which metals are plastically deformed by the application of tensile forces in liquid nitrogen (Figure 7.5). 

Figure 7.5 Deformation calorimeter involving a liquid—gas transition (N2) (according to...

Figure 7.6 Flow rate of evaporated nitrogen in a deformation calorimeter involving a liquid—gas phase transition (see Figure 7.5)(according to Wolfenden and Appleton, 1967).

Wolfenden, A. and Appleton, A.S. (1967) Low-temperature liquid-vapor deformation calorimeter. Rev, Sci,... 

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