Dynamic pulse calorimetry

Thermophysical properties are defined, in Chapter 9 by Cagran and Pottlacher, as a selection of mechanical, electrical, optical, and thermal material properties of metals and alloys (and their temperature dependencies) that are relevant to industrial, scientific, and metallurgical applications, and this covers a wide range of different material properties obtained by numerous different measurement techniques. The focus in Chapter 9 is, however, on thermophysical properties that are accessible through dynamic pulse calorimetry Other non-calorimetric techniques have been developed but, with the exception of levitation (needed to measure technologically important properties like viscosity and surface tension) have been excluded from consideration. 

DYNAMIC PULSE CALORIMETRY - THERMOPHYSICAL PROPERTIES OF SOLID AND LIQUID METALS AND ALLOYS... 

As technology advances and specific needs for applications also change over time, the list of accessible thermophysical properties cannot be expected to remain static. Therefore, the following chapter can only be seen as a snapshot of the current state-of-the-art capabilities in the measurement of thermophysical properties by dynamic pulse calorimetry. 

Due to the increasing demand in the 1960s for data on the thermophysical properties of materieils xmder extreme conditions and at high temperatures on one hand, and the rapid advances in fast electronics, such as electrical pulse generation, data acquisition equipment, etc., on the other hand, dynamic pulse calorimetry became more popular and more commonly used, i.e., Cezairliyan 1969 [8], and Lebedev et al. 1971 [9]. 

The isobaric heat capacity is obtained mathematically by differentiation of the specific enthalpy. Graphically, Cp is given by the slope of the enthalpy versus temperature trace leading to an individually constant number for isobaric heat capacity in the liquid state and also for the solid state, if no phase transitions occur. This result for the solid state is in contradiction with measurement data obtained by techniques such as differential scanning calorimetry (DSC) but has been proved to be correct for the liquid state. Dynamic pulse-heating rates are usually too fast and small phase transitions, which are detectable by DSC or similar instruments, become undetectable. As a result, pulse-heating data for Cp... 

To extend pulse calorimetry to selected mechanical properties, NIST has developed a new apparatus called the pulse-heated Kolsky bar, or split-Hopkinson pressure bar apparatus [127, 128]. The combination of the two techniques produces high-rate dynamic loading, while simultaneously pulse heating the specimen with electrical current. 

Liquid-flow microcalorimefry is a reliable method to measure simultaneously the enthalpy changes and amounts of adsorption under dynamic conditions. Calorimetry experiments may be carried out in two different ways by following a pulse or saturation operating mode [64, 78-83]. In the pulse mode, small aliquots of a stock solution at a known concentration are injected into the carrier liquid (pure solvent) flowing through the adsorbent bed placed inside the calorimetric cell. In this case, the calorimetric system contains an additional loop injection facility (a manual injection valve with appropriate injection loops). The interpretation of the enthalpy data obtained is straightforward only when the whole amount of the solute injected is irreversibly adsorbed on the solid surface. 

J. E. Rudzki, J. L. Goodman, K. S. Peters. Simultaneous Determination of Photoreaction Dynamics and Energetics Using Pulsed, Time-Resolved Photoacoustic Calorimetry. J.Am. Chem. Soc. 1985, 107, 7849-7854. 

Unlike crystalline melting, the glass transition temperature is a relaxation transition. This means that it is dependent on the effective frequency of the measureirtent. This frequency is found by dynamic mechanical (DMA), dielectric relaxation, and pulsed nuclear magnetic methods. Quasi-static methods, such as dilatometry, differential scanning calorimetry (DSC), and thermomechanical analysis (TMA), show that the effective frequency depends on the rate of temperature scan. This is one of the reasons why the glass transition temperatures reported for various amorphous materials appear so diverse. 

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