Adiabatic scanning calorimeter

A schematic of the operation of the Sinku Riku ULVAC SH-3000 adiabatic, scanning calorimeter is shown in Fig. 4.38. The calorimeter is detailed on the right It is a miniaturization of the classical calorimeter in Fig. 4.30. The sample is indicated by 1. It is heated by supplying constant power, outlined in the block diagram on the... 

Sinku Riku Adiabatic Scanning Calorimeter ULVAC SH - 3000... 

Figure 7.35 Adiabatic scanning calorimeter (according to Sykes, 1935 Moser, 1936).

From the above considerations, it should be clear that running an adiabatic scanning calorimeter in the constant heating (or cooling) modes makes it possible to determine latent heats when present and distinguish between first-order and second-order phase transitions. On the basis of Cp = P/t, it is also possible to obtain information on the pretransi-tional heat capacity behavior, provided one is able to collect sufficiently detailed and ac-... 

Figure 3. Schematic diagram of an adiabatic scanning calorimeter. Electric heaters and thermistors are denoted by H and R. PTR is a platinum resistance thermometer. The whole calorimeter is placed in a hot air temperature controlled oven. Details on a sample holder with stirring capabilities have been given elsewhere [21].

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... 

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

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. 

Calorimetric methods in which temperature-heat-content curves are obtained. An adiabatic calorimeter or a differential scanning calorimeter may be employed The latter instrument is much more convenient to use and is capable of almost the same accuracy and precision as the former technique. 

Accurate enthalpies of solid-solid transitions and solid-liquid transitions (fusion) are usually determined in an adiabatic heat capacity calorimeter. Measurements of lower precision can be made with a differential scanning calorimeter (see later). Enthalpies of vaporization are usually determined by the measurement of the amount of energy required to vaporize a known mass of sample. The various measurement methods have been critically reviewed by Majer and Svoboda [9]. The actual technique used depends on the vapour pressure of the material. Methods based on... 

Peroxide compounds are usually very reactive and flanunable. They have caused many catastrophic accidents around the world because of their reactive potential. Conventional methods to assess risk of such a reactive chemical have been done by experiments with precision machine such as DSC (differential scanning calorimeter), ARC (accelerating rate calorimeter), etc., but they need more finance, concentration and charge of danger. To overcome that, computer aided prediction method using group contribution method was used in this study. Some essential thermodynamic properties of chemicals were evaluated by this method, and then adiabatic temperature rise for each decomposition steps of peroxide compound were obtained, which can be a good index of the hazardousness of reaction. The result was approximate to other experimental and simulation data from references. 

Figure 5.3 Schematic design of a calorimeter with adiabatic scanning.

Scanning calorimeters, either adiabatic or isoperibol, single or twin design, allow the determination of the heat capacity of the sample as a function of temperature. Consequently, these instruments can be used to determine the temperature of a phase transition. The same holds for calorimeters, with which the temperature of the sample is not increased continuously but stepwise. 

The enthalpy as a function of time is readily available from, for example, drop calorimetry experiments or from adiabatic calorimeters with incremental temperature increases. Scanning calorimeters, however, furnish the heat capacity of the sample. In these cases, the phase transition shows as a peak and the enthalpy of transition is calculated by integration of the peak area. Traditionally, this is done after constructing a proper baseline under the peak between the start and the end of the peak. The definition of the start and the end of the peak and the shape of the baseline under the peak are somehow arbitrary, particularly when the phase transition is accompanied by a heat capacity change. The enthalpy change at the transition temperature trs can be calculated from the heat capacity curve by... 

Adiabatically operated single scanning calorimeters were used for determinations of the specific heat capacities of copper and brass (Sykes, 1935) and of silver, nickel, brass, quartz, and quartz glass (Moser, 1936). Sykes calorimeter is shown schematically in Figure 7.35. 

The requirements with regard to a calorimeter can be derived on the basis of the above analysis of the measuring problem. The necessary operating conditions have to be defined first an isothermal, isoperibol, adiabatic, or a scanning calorimeter What temperature range What heating rate Any other boundary conditions a constant pressure, constant volume, gas flow rate, and so on ... 

Basically, the methods consist of a variety of calorimetric methods and a few non-calorimetric methods. In calorimetry the following methods are nsed adiabatic, isoperibol, isothermal, heat condnction, drop and differential scanning calorimeters, and differential thermal analysis. Cryoscopic, vapor pressure, and enthalpy of solution methods are considered to be non-calorimetric methods. 

Another development in calorimetry, at least in retrospect, was the construction of adiabatic calorimeters operating at constant heating rate. In such an instrument the heating was carried out continuously (scanning calorimeter), i.e., the measurement was not interrupted every 20 K or so to check the isothermal condition, but was carried out in one, continuous run. In such operation, the heat losses were minimized since the experiment could be completed faster, but the accuracy of such scanning calorimeters was considerably less than that of the standard adiabatic calorimeters. The reason for the lesser accuracy is the fact that the heat could not be distributed nearly as uniformly in the sample as in the adiabatic calorimeter. In addition, the loss calibration was also less accurate. 

Figure 5. Mechanical/thermal design of a computer-controlled calorimeter capable of operating in the a.c. mode or in relaxation modes including non-adiabatic scanning [34, 35].

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). 

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). 

---