Calorimeter micro

A micro-bomb calorimeter exploded when the wrong proportions of sample and oxidants were used. Instead of 4 g of peroxide and 0.2 g of nitrate for 0.2 g of the sugar sample, 0.35 g of peroxide and 2.6 g of dextrose were used. The deficiency of peroxide to absorb the decomposition gases and excess of organic matter led to a rapid rise in temperature and pressure, which burst the bomb calorimeter. 

The Calvet microcalorimeter (16) is an improved version of the first heat-flow calorimeter described by Tian in 1924 (25). In this micro-... 

Calvet and Persoz (29) have discussed at length the question of the sensitivity of the Calvet calorimeter in terms of the number of thermocouples used, the cross section and the length of the wires, and the thermoelectric power of the couples. On the basis of this analysis, the micro-calorimetric elements are designed to operate near maximum sensitivity. The present-day version of a Tian-Calvet microcalorimetric element, which has been presented in Fig. 2, contains approximately 500 chromel-to-constantan thermocouples. The microcalorimeter, now commercially available, in which two of these elements are placed (Fig. 3) may be used from room temperature up to 200°C. 

Isothermal storage tests (1ST), scanning or isothermal heat-flux micro-calorimeters, thermal activity monitor (TAM)—see Section 2.3.2.1,... 

Conventional combustion calorimeters operate on a macro scale, that is, they require samples of 0.5-1.0 g per experiment. Unfortunately, many interesting compounds are available only in much smaller amounts. In the case of oxygen combustion calorimetry, however, several combustion microcalori-meters that only demand 2-50 mg samples have been developed in recent years. The achievements and trends in this area through 1999 have been reviewed [7-10], and interested readers are directed to these publications. Since then, a few new apparatus have been reported [11-17], Nevertheless, it should be pointed out that the general principles and techniques used to study compounds at the micro scale are not greatly different from those used in macro combustion calorimetry. 

Figure 7.8 Scheme of a micro rotating-bomb aneroid combustion calorimeter [75,76]. 

M. Sakiyama, T. Kiyobayashi. Micro-bomb Combustion Calorimeter Equiped with an Electric Heater for Aiding Complete Combustion. J. Chem. Thermodynamics 2000, 32, 269-279. 

A. Rojas, A. Valdes. An Isoperibol Micro-bomb Calorimeter for Measurement of the Enthalpy of Combustion of Organic Compounds. Application to the Study of Succinic Acid and Acetanilide. J. Chem. Thermodynamics 2003, 35, 1309-1319. 

A. Rojas-Aguilar, A. Valdes-Ordonez. Micro-combustion Calorimetry Employing a Calvet Heat Flux Calorimeter. J. Chem. Thermodynamics 2004, 36, 619-626. 

I. Wadso. Design and Testing of a Micro Reaction Calorimeter. Acta Chem. Scand. 1968, 22, 927-937. 

A. Rojas-Aguilar, M. Martmez-Herrera. Enthalpies ofCombustion and Formation of Fullerenes by Micro-combustion Calorimetry in a Calvet Calorimeter. Thermochim. Acta 2005, 437, 126-133. 

Stull, D.R. A semi-micro calorimeter for measuring heat capacities at low temperatures, / Am. Chem. Soc., 59(12) 2726-2733, 1937. 

FIGURE 13.3 Cal vet micro calorimeter. (From Solinas, V. and Ferino, L, Catal. Today, 41, 179-89, 1998.)... 

Since enthalpy changes can be obtained directly from measurement of heat absorption at constant pressure, even small values of AH for chemical and biochemical reactions can be measured using a micro-calorimeter.1112 Using the technique of pulsed acoustic calorimetry, changes during biochemical processes can be followed on a timescale of fractions of a millisecond. An example is the laser-induced dissociation of a carbon monoxide-myoglobin complex.13... 

In the CSM laboratory, Rueff et al. (1988) used a Perkin-Elmer differential scanning calorimeter (DSC-2), with sample containers modified for high pressure, to obtain methane hydrate heat capacity (245-259 K) and heat of dissociation (285 K), which were accurate to within 20%. Rueff (1985) was able to analyze his data to account for the portion of the sample that was ice, in an extension of work done earlier (Rueff and Sloan, 1985) to measure the thermal properties of hydrates in sediments. At Rice University, Lievois (1987) developed a twin-cell heat flux calorimeter and made AH measurements at 278.15 and 283.15 K to within 2.6%. More recently, at CSM a method was developed using the Setaram high pressure (heat-flux) micro-DSC VII (Gupta, 2007) to determine the heat capacity and heats of dissociation of methane hydrate at 277-283 K and at pressures of 5-20 MPa to within 2%. See Section 6.3.2 for gas hydrate heat capacity and heats of dissociation data. Figure 6.6 shows a schematic of the heat flux DSC system. In heat flux DSC, the heat flow necessary to achieve a zero temperature difference between the reference and sample cells is measured through the thermocouples linked to each of the cells. For more details on the principles of calorimetry the reader is referred to Hohne et al. (2003) and Brown (1998). 

For the determination of reaction parameters, as well as for the assessment of thermal safety, several thermokinetic methods have been developed such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), accelerating rate calorimetry (ARC) and reaction calorimetry. Here, the discussion will be restricted to reaction calorimeters which resemble the later production-scale reactors of the corresponding industrial processes (batch or semi-batch reactors). We shall not discuss thermal analysis devices such as DSC or other micro-calorimetric devices which differ significantly from the production-scale reactor. 

Another interesting application of micro reactors is to use them as calorimeters. They may show excellent performance in terms of sensitivity [9-12]. Moreover, their performance in terms of heat exchange allows study of the kinetics of fast exothermal reactions under isothermal conditions. Such a development was realized by Schneider [13, 14], who studied such a reaction with a power of up to 160 kW kg-1. This type of calorimeter is simple to use and determines the reaction kinetics in a short time, with very small amounts of reaction mass, and without any hazard for the operator. 

The energy involved in the folding and association of copolymer chains in solutions can be measured by a micro-calorimeter (MicroCal Inc). We used US-DSC at an external pressure of 180 kPa. The cell volume is only 0.157 mL. The heating rate can be varied and the instrument response time is normally a few seconds. All the DSC data should be corrected for instrument response time and can be analyzed using the software in the calorimeter. Note that the concentration used in DSC is normally not lower than 10-3 g/mL, much higher than that used in LLS (10 6-10 3 g/mL). 

It is not surprising to see that the chains with a higher hydrophilic comonomer VP content have a higher transition temperature. However, it is rather interesting to see that for each pair of the copolymers with a similar VP content, the copolymer prepared at 60 °C has a lower transition temperature than its counterpart prepared at 30 °C. In order to check this shift in the transition temperature, we also measured the partial heat capacity (Cp) of these copolymers in solution using a micro-calorimeter. Figure 7 shows that for the two copolymers prepared at 60 °C, the temperatures at which the maximum... 

Most calorimeters used in biochemical work and in studies of living cells and tissue pieces are usually microcalorimeters. This term is not well defined but the micro- prefix is primarily used for calorimeters with a thermal power sensitivity of 1 iW or better. The volume of a microcalorimetric (batch) vessel is usually 1-25 ml. It is common, and frequently suitable, to use typical microcalorimeters at a reduced sensitivity, for example, in work on fast growing microbial suspensions or... 

Figure 6. Schematic diagrams of sections through two types of twin calorimeters. A Twin heat conduction (micro)calorimeter (vessels not shown). B Semiadiabatic twin calorimeter, a, vessel holder b, thermopile c, heat sink d, vessel (stirrer, thermometer, heater not shown) e, air or vacuum.

Three different approaches are chiefly applied micro-, flow and heat flux calorimetry. Heat flux calorimetry is certainly the best choice for bioprocess monitoring (Fig. 17) [264]. In a dynamic calorimeter, the timely change of temperature is measured and various heat fluxes (e.g. heat dissipated by stirrer, or lost due to vaporization of water) need to be known in order to calculate the heat flux from the bioreaction ... 

Chemists always need to know bond energies, often for unusual combinations of elements, for which bomb combustion calorimetry experiments have never been done, partly because the appetite of conventional bomb combustion calorimeters for large samples is not easily met for rare compounds. Thus there is a need for future micro rotating-bomb calorimeters. 

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