Scanning adiabatic

Measured by scanning adiabatic calorimetry with a heating rate of ... 

VSP experiments allow the comparison of various process versions, the direct determination of the wanted reaction adiabatic temperature rise, and the monitoring of the possible initiations of secondary reactions. If no secondary reaction is initiated at the wanted reaction adiabatic final temperature, a further temperature scan allows the... 

To perform such a measurement, four methods are available adiabatic calorimetry (or adiabatic scanning calorimetry), differential scanning calorimetry (DSC), the T-history method, and in-situ measurements. These methods are described here. 

Differential scanning calorimetry (DSC) can be performed in heat compensating calorimeters (as the adiabatic calorimetry), and heat-exchanging calorimeters (Hemminger, 1989 Speyer, 1994 Brown, 1998). 

Adiabatic calorimeters are complex home-made instruments, and the measurements are time-consuming. Less accurate but easy to use commercial differential scanning calorimeters (DSCs) [18, 19] are a frequently used alternative. The method involves measurement of the temperature of both a sample and a reference sample and the differential emphasizes the difference between the sample and the reference. The two main types of DSC are heat flux and power-compensated instruments. In a heat flux DSC, as in the older differential thermal analyzers (DTA), the... 

Isoperibolic instruments have been developed to estimate enthalpies of reaction and to obtain kinetic data for decomposition by using an isothermal, scanning, or quasi-adiabatic mode with compensation for thermal inertia of the sample vessel. The principles of these measuring techniques are discussed in other sections. 

Cruz-Orea, A., Pitsi, G., Jamee, P., and Theon, J. (2002). Phase transitions in the starch-water system studied by adiabatic scanning calorimetry. /. Agric. Food Chem. 50,1335-1344. 

TNT 220-260 300 (c) a) Differential Scanning Calorimeter 37.0 11.2 Adiabatic furnace Gross Amster (14)... 

Fig. 12 (a) Reduced temperature T — 7]SO/bp vs xcdSe phase diagram for CE8 + CdSe mixtures obtained from cooling runs by a.c. colorimetry. Ti-bpiii was found to be a weak function of x. (b) T — rIso/BP vs xcdse plot for CE6 + CdSe mixtures obtained from heating runs by adiabatic scanning calorimetry. For clarity the data in both diagrams are plotted vs the Ti-bpiii [428]. (Copyright 2010, The American Physical Society)... 

The methods used for the isothermal reactor can also be used here, but must be completed by a thermal study over the total temperature range in which the reactor will be operated. Therefore, DSC in the scanning mode, or adiabatic calorimeters such as the Accelerating Rate Calorimeter or simply the Dewar flask, can be used. 

The scanning or dynamic mode of operation ensures that the whole temperature range of interest is explored. This must be ensured also in adiabatic experiments, where it is essential to force the calorimeter to higher temperatures, in order to avoid missing an important exothermal reaction (see Exercise 2 in Chapter 4). 

This brief overview of offline measurements can be concluded by considering the measurements of the heat released by chemical reactions, which can be obtained via calorimetric measurements [7, 18]. The most diffused industrial calorimeters are the so-called reaction calorimeters, basically consisting in jacketed vessels in which the reaction takes place and the heat released is measured by monitoring the temperature of the fluid in the jacket. A class of alternative instruments are the scanning calorimeters (differential or adiabatic), in which the analysis is performed by linearly increasing the sample temperature with respect to time, in order to test the reactivity of potentially unstable chemical systems in a proper temperature range by measuring the released heat. 

Figure 5.6 Cyclic voltammograms obtained for a spontaneously adsorbed [Os(bpy)2 4-tet Cl]+ monolayer on a 5 pm radius gold microdisk electrode where the scan rate is 1333 V s 1. The theoretical fits to the data, using a non-adiabatic electron tunneling model at electrolyte pH values of 0.9 and 6.0, are denoted by O and , respectively. In both cases, k is 27 kj mol-1, while k° is 1.1 x 103 and 1.1 x 104 s 1 at pH values of 0.9 and 6.0, respectively. Reprinted with permission from D. A. Walsh, T. E. Keyes, C. F. Hogan and R. J. Forster, ]. Phys. Chem., 105, 2792 (2000). Copyright (2000) American Chemical Society...

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