Calorimeters thin-wall

The adsorbent—a powder generally, but it could be a metal or oxide film— is placed in a glass tube (the adsorption cell C in Fig. 15) which is connected to the volumetric and vacuum lines. The bottom part of the tube, which contains the adsorbent and is located in the calorimeter cell, is made of thin-walled (0.2-0.3 mm) blown tubing (A in Fig. 18). In order to avoid the slow diffusion of gases through a thick layer of adsorbent (see Section VII.A), the sample is often placed in the annular space between the inner wall of the adsorption cell and the outer wall of a cylinder made of glass,... 

The VSP (Figure 8-8) is essentially an adiabatic calorimeter. A small amount of the material to be tested (30-80 mg) is loaded into a thin-walled reactor vessel. A series of controlled... 

In a series of publications, Stevenson et al. have demonstrated that the enthalpies of generation of polyacene dianions can be obtained by calorimetric measurements. Compared to their calculated instability in the gas-phase 70), THF solutions of polycyclic dianions are thermodynamically and kinetically stable as evidenced by their spontaneous formation and persistence. The solvation energy of the dianions plus that of two cations must overcome the repulsive interaction of the charges. This aspect has been demonstrated by Stevenson in his studies on the cyclooctatetraene dianion 70). The dianion sodium salts were prepared in THF in thin-walled glass bulbs and the bulbs were crushed under water in a calorimeter system. The heat of aquation of the solvent is taken into account and thus, the net change in the heat content of the calorimeter vs. the millimoles of dianion salt is obtained. The plots are linear and the slopes represent the enthalpies of the following reaction (Eq. 20) ... 

Kullberg measured the heat evolved when small amounts of red HgO(cr) were dissolved in solutions of 0.3 and 1 M KSeCN in a reaction solution calorimeter. The HgO(cr) was contained in a thin-walled glass ampoule, which could be broken inside the calorimeter... 

The substances under examination were contained in thin-walled silver vessels, weighing only a few grammes, and consequently possessing only a moderate capacity. The silver vessels were a good fit in the bore of the calorimeter. 

To enable the temperature to be accurately determined before they were introduced into the calorimeter, a thermocouple was pushed into a little silver tube soldered into the middle of the vessel. When necessary (for example, in the case of calcium oxide) the vessels were hermetically sealed by soldering the cover on. In some few cases (e.g. mercury and bromine) the substance was first enclosed in a small thin-walled glass tube which was sealed. 

FIGURE 16.36 Calorimeter (a) slug (plug) calorimeter, and (f>) thin-wall (thin-skin) calorimeter. 

Calorimeter.—The calorimeter consists of a thin-walled glass U-tube inside an outer vessel. The space between the U-tube and the vessel is evacuated and the walls are silvered. In the inlet arm of the U-tube there is a small sensitive platinum resistance thermometer (Tl), a heater (H2), and a mixing device to promote thermal equilibrium in the vapour. In the outlet arm there are two platinum resistance thermometers (T2, T3). The electrical leads of the heater and thermometers are taken out through the tops of the U-tube. 

The thickness of the samples used for the cone calorimeter test is an important parameter that affects the relative reduction of HRR in nanocomposites compared to pure polymer. We observed, for example, that the relative reduction in the PHRR is 45 and 19% for sample thicknesses of 3 and 8 nun, respectively (5 wt% of 3-aminobenzenesulfonate/LDH in DGEBA cured with triethylene tetraamine). Therefore, the flame retardant effectiveness of LDH is increased signiflcantly for thin samples compared to thick samples. Gilman et al. reported that the trend in the function of the thickness of polyamide-6/montmorillonite (5 wt%) is opposite. The reduction in PHRR compared with neat polymer is about 60% for 8-mm-thick samples and 20% for 1.6-mm-thick samples. This is the usual result seen in charring systems. The superior performance of thin samples of LDH nanocomposites indicates that they may have excellent potential for thin-walled FR products. 

The samples were loaded in thin Lindeman glass capillaries (GLAS, Muller Berlin, Germany) with 0.01 mm of wall thickness and diameter (0 = 1.4 0.10 mm) using a syringe and a small capillary tubing. The capillaries were heated at 50°C for 10 min in order to melt all existing crystals and nuclei. The samples were quenched by rapid introduction of the capillaries into the calorimeter coupled with XRD precooled to -8°C. 

The glass wall which surrounds the calorimeter block is naturally made as thin as possible, and it is desirable that there should be good thermal contact between them. Otherwise irregularities in the rate of change of temperature may easily be observed. The block was therefore cemented with Woods metal into the vacuum vessel. For this purpose some of the alloy was put into the vessel the block, electrically heated from the inside, was then introduced and pushed down a suitable depth into the Woods metal. 

A new DSC cell, based on the DTA principle (as is the Du Pont DSC cell previously discussed) has been described by David (HO). The calorimeter cell, as shown in Figure 6.36, contains a differential thermocouple of a new thin-form design that is isolated from the cell wall and bottom to provide greater sensitivity. This thermocouple consists of a sheet of negative Platinel II type thermocouple alloy coupled to a positive Platinel II alloy. Flat shallow containers are employed for the sample and reference materials. Two addi-... 

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