Typical Results from Different Calorimeters

A survey of the literature shows that although very different calorimeters or microcalorimeters have been used for measuring heats of adsorption, most of them were of the adiabatic type, only a few were isothermal, and until recently (14, 15), none were typical heat-flow calorimeters. This results probably from the fact that heat-flow calorimetry was developed more recently than isothermal or adiabatic calorimetry (16, 17). We believe, however, from our experience, that heat-flow calorimeters present, for the measurement of heats of adsorption, qualities and advantages which are not met by other calorimeters. Without entering, at this point, upon a discussion of the respective merits of different adsorption calorimeters, let us indicate briefly that heat-flow calorimeters are particularly adapted to the investigation (1) of slow adsorption or reaction processes, (2) at moderate or high temperatures, and (3) on solids which present a poor thermal diffusivity. Heat-flow calorimetry appears thus to allow the study of adsorption or reaction processes which cannot be studied conveniently with the usual adiabatic or pseudoadiabatic, adsorption calorimeters. In this respect, heat-flow calorimetry should be considered, actually, as a new tool in adsorption and heterogeneous catalysis research. 

In a typical experiment, the test sample and a suitable reference material are contained in two separate, identical ampoules kept at constant temperature in separate, identically constructed wells of the calorimeter. Ideally, the reference material is identical or very similar to the test sample in mass, heat capacity and thermal conductivity, but, unlike the test sample, it is thermally inert (i.e. the reference material will not undergo changes that result in heat production or absorption under the conditions of the experiment). One example is a small quantity of ordinary glass beads in air at room temperature used as reference for the same amoimt of a hydrated ceramic material which is expected to lose water under the same conditions. Consequently, most of the noise arising from temperature fluctuations is removed when the reference data are subtracted. A feedback temperature control system between the wells (a) serves to ensure that the temperature difference between the weUs is zero and (b) provides an output that measures any difference in electric power requirement of one well relative to the other, needed to keep the temperature of both weUs the same. This power difference, as a function of time, is the output from the calorimeter, which is recorded continuously or intermittently over the duration of the test. 

Studies using the base-catalysed hydrolysis of methyl paraben (BCHMP) test and reference reaction have been conducted with a variety of different solution-phase flow calorimeters. The results obtained from these studies have shown that the flow rate dependency of the thermal volume is different for each of the instruments used and indeed for each experimental arrangement e.g. sample and reference cell set-up). The determined value for can differ by as much as 15% (over a range of experimental flow rates) from the nominal engineered volume (typically approximately 1ml). This effect can be minimised by careful design of the flow cell and also by careful consideration of the sample and reference cell arrangements (more details can be found in ref. 22 and references therein). 

Zhang et al. [31] studied fire-retardant properties of PP/IFR/LDH nanocomposites, which were comprised by a typical intumescent flame retardant (IFR) system and LDHs with different bivalent metal cations. The results of pk-HRR, pk-MLR, pk-EHC, and ignition time (IT) obtained from the cone calorimeter tests of various samples were listed in Table 8.1 [31]. It could been seen from Table 8.1 that the IT values of PP/IFR/LDH samples with different divalent metal cations of Zn, Mg, Cu, and Ca were 55, 55, 54, and 52 s, respectively, which are longer than 48 s of the PP/IFR sample without LDH. These data showed that the PP/IFR samples with LDHs are obviously harder to ignite than the sample only with the IFR. 

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