Calorimeter adiabatic vacuum

In 1968 Plesch and Westermann [131] published a report of 1,3-dioxo-lane polymerization in their adiabatic calorimeter under vacuum in CH2 CI2 with anhydrous perchloric acid as initiator. They confirmed that the polymerization can be an equilibrium involving only monomer and polymer without side reactions. For a one molar solution the ceiling temperature was found to be 1°C, - —18.6 1.2 cal deg" mole" ... 

To determine the entropy of n-butane at 298 K we must measure the heat capacity from within a few degrees of the absolute zero of temperature up to room temperature. This is done in an adiabatic vacuum calorimeter (Fig. 5,6) in which the sample under investigation is thermally insulated by locating it in an evacuated enclosure. A known quantity of electrical heat can be added and the rise in temperature measured with a platinum resistance thermometer. After a correction for the heat capacity of the vessel, the heat capacity of the compound it contains may be directly calculated from the equation... 

The construction principles of such chip calorimeters are similar to those of conventional calorimeters The heater corresponds to the furnace, and the center of the membrane corresponds to the calorimeter system, including the sample container. The thin membrane serves as the thermal path between the heater and the sample with very low thermal resistance and very low effective heat capacity. The thermopile measures the temperature difference between the sample site and the chip frame (surroundings). Because of the much larger lateral dimension of the membrane of at least two orders of magnitude, the heat exchange between the sample and the frame can be neglected. The chip calorimeter can therefore be considered a quasi-adiabatic calorimeter when vacuum is applied. 

The temperature dependences of heat capacity of the same full seq-IPNs in the 6-340 K range were studied [50] using adiabatic vacuum calorimetry. Using a calorimeter equipped with a static bomb and an isothermal shell, the energies of combustion of the CPU and of the... 

The true heat capacity has been measured at 13.4 to 296 K with an adiabatic vacuum calorimeter. The absolute entropy was calculated to be S598.i5 = 48.33 0.15 cal-mor -K" and the enthalpy difference H ge.-is- H°34= -6608.9 20cal/mol under standard conditions. A selection of smoothed values for Cp, Hj- H134, and Si34 is given in the following table ... 

Figure 3.6 Schematic representation of the bomb calorimeter for measuring the changes in internal energy that occur during combustion. The whole apparatus approximates to an adiabatic chamber, so we enclose it within a vacuum jacket (like a Dewar flask)...

Kinetic studies on the polymerisation of isobutene at low temperatures by titanium tetrachloride in various solvents form the subject of a series of papers by Plesch and his co-workers [9, 10, 13, 28, 32, 33, 71, 77, 80, 81]. The reactions were followed in an apparatus approximating to an adiabatic calorimeter by means of the temperature rise accompanying the polymerisation. In the early studies moisture was not rigorously excluded from the systems, but later [81] an elaborate vacuum technique was evolved and all reagents were carefully purified and dried. Titanium tetrachloride was also used as catalyst by Okamura and his collaborators [79] in a series of studies concerning the effects of solvent, catalyst, and co-catalyst on the DP of polyisobutene. 

Reactions were followed in an adiabatic calorimeter [4] according to the procedure described [5]. At the end of the polymerisations, the reaction mixture was quenched with ethanolic ammonium hydroxide and evaporated to constant weight in a vacuum oven at 40 °C. 

The kinetics were studied by adiabatic calorimetry [18] and high vacuum isothermal dilatometry [21, 22]. The calorimeter and the dilatometers were fitted with electrodes [21] for measuring the conductivity of the reaction mixtures. 

There are a number of different types of adiabatic calorimeters. Dewar calorimetry is one of the simplest calorimetric techniques. Although simple, it produces accurate data on the rate and quantity of heat evolved in an essentially adiabatic process. Dewar calorimeters use a vacuum-jacketed vessel. The apparatus is readily adaptable to simulate plant configurations. They are useful for investigating isothermal semi-batch and batch reactions, and they can be used to study ... 

Figure 1. Schematic diagrams of sections through adiabatic-type calorimeters. A Adiabatic shield calorimeter. B Semiadiabatic calorimeter, a, calorimetric vessel b, air or vacuum c, thermostatted bath d, thermometer e, stirrer f, calibration heater g, adiabatic shield.

Calorimetry. Polymer samples were ground in a Wiley mill, screened through a 100-mesh sieve, and vacuum dried at 35° C. for 15-20 hours. The samples were then pressed into cylindrical V2 X 3/8-inch pellets at 40,000 p.s.i.g. The pellets were then placed in a tared porcelain crucible and weighed. The crucible containing the sample was placed in the bomb of a Parr adiabatic calorimeter, and the sample was burned at an oxygen pressure of 450 p.s.i.g. at 25° C. The heats of combustion of the polymer samples were obtained by applying the following corrections to the experimental values ... 

The isobaric specific heat capacity () of zirconium trichloride was measured in a vacuum adiabatic calorimeter, with periodic heat input. The specific heat was measured between 7 and 312 K. These measurements formed part of a subsequent more detailed study by Efimov et al. [87EFI/PRO], and therefore, will not be discussed further. 

The thermal resistance R is supposed to increase from the isothermal to the isoperibol and then to the adiabatic type of calorimeter. It would probably be more correct and general to base the distinction between the adiabatic and the isoperibol calorimeters on the heat transfer (involving simultaneously the thermal conductance and the temperature difference) rather than on the value of the thermal resistance. For instance, a simple Dewar vessel calorimeter provides a very high thermal resistance between the central system and the surroundings, though it is simply an isoperibol calorimeter (called quasi-adiabatic in section 4.2.), whereas Swietoslawski s adiabatic calorimeters, which do not use any vacuum insulation, certainly provide a much lower thermal resistance [15]. 

Modem adiabatic calorimeters employ a technique whereby the enthalpy of vaporization is measured under conditions in which a measured amount of electrical energy is supplied to a heater immersed in the sample to compensate for the heat absorbed by the substance during the evaporation and hence the temperature is kept constant. The main differences among adiabatic calorimeters are that the vapour flows out of the calorimeter at atmospheric pressure (those of Mathews and Fehlandt [65]), into a vacuum, [67,69-71] into a gas stream [68], or into a closed recirculation system with continuous fluid flow [66]. 

SRM 705) and polyethylene (SRM 1475), are certified in the range 10 to 350 K. The measurements from 10 to 380 K were made with a vacuum adiabatic calorimeter operated automatically under the control of a minicomputer [% A Bunsen-type ice calorimeter was used in the range 273 to 1173 K, and a high-temperature drop calorimeter i] was used at the higher temperatures. SRM 720 is available in the form of small cylinders (about 5 mm x 2 mm) in 15-g lots. The polymers are available in 5- to 50-g lots. 

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