Isothermal Calorimetry Techniques

The calorimetry techniques have been used for many purposes in the cure of rubber, including to measure the heat of the overall cure reaction, but also for evaluating the kinetics of the heat evolved from the overall reaction. The only question at first was what way to use the calorimetry In the early eighties, it seemed to a majority of the authors that the isothermal condition would be preferable, but finally the operation in scanning mode was preferred. 

1 Measure of the Cure Enthalpy under Isothermal Conditions 

Another fact of high concern appears with the small sample used with some calorimeters it has been said that the question that always arises is how representative of the homogeneity of the batch is a 5 to 10 mg sample taken from a large batch (typically from 100-2000 g, as mixed on laboratory equipment). 

An improvement has been made for the calorimeter by making the sample cylindrical in shape and long enough so that the heat flux meter is placed at mid-height of 

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A gas flow techique was successfully used by Hacker et al. [66] in 1961, who studied the recombination of O atoms on quartz and platinum using ESR spectroscopy and isothermal calorimetry with mutually consistent results. However, only in the last few years has the technique been developed for the study of recombination under conditions far removed from those associated with static side arm systems. 

Thermal techniques such as isothermal calorimetry (ITC) and differential scanning calorimetry (DSC) have been used in formulation screens to predict the formulation with the greatest stability based on the assumption that excipients that increase the of the protein will stabilize the molecule at the recommended storage temperature. For example, a screen of preservatives performed during formulation development for interleukin-1 receptor found that the for the formulation... 

Mass spectroscopy (MS) and isothermal calorimetry (ITC) also have been utilized as screening tools. MS techniques, such as non-denaturing electrospray ionization MS (ESI-MS), use mass identification as the means for the detection of reversible binding events. MS analysis allows for simultaneous binding of multiple fragments, and hence direct stoichiometric detection of the binding events. Despite such advantages, application is at times limited because the protein of interest may... 

Various techniques have been developed in turn the Mooney viscometer, the Wallace-Shawbury curometer, the oscillating disc rheometer (ODR), and the moving disc rheometer (MDR), in addition to the calorimetry techniques. The isothermal calorimetry and its counterpart in scanning mode, the isothermal moving disc rheometer (MDR), and the improvement of this last technique with the rubber process analyzer run in scanning mode, are considered. 

In calorimetry techniques, enthalpy changes accompanying physical or chemical events, whether they are exothermic or endothermic, are measured and monitored either as a function of temperature or time. Thus, a calorimeter is able to collect a heat flux exchanged between the sample and the sensible part of the apparatus, generally made of thermocouples, and to register it. The result is a profile of the rate of enthalpy change, either as a function of temperature as the sample is heated at a known linear rate in differential scanning calorimetry (DSC), or as a function of time when the calorimeter is held at constant temperatnre in isothermal differential calorimetry (DC). 

Finally, the history has been similar both with the MDR or the calorimeter. After being utilized under isothermal conditions a few decades ago, the calorimetry technique is now widely used in the scanning mode, and the MDR, quite recently, could be used in scanning mode with the rubber process analyzer. 

Potential applications of thermal analysis and calorimetry to quality control is not limited in any way to those discussed in this chapter. Once some physical or chemical characteristic of a material or process is known and can be examined and/or characterized by these techniques, it is only the imagination that limits the possibilities for quality control applications. Both traditional techniques (DSC, TG, DMA, isothermal calorimetry, etc.) and non-traditional techniques (temperature modeling, etc.) have been shown to have potential uses for quality control. With the introduction of many new techniques (fast scanning DSC, sample controlled thermal analysis (SCTA), modulated and other temperature programmed techniques, etc.), many more new opportunities will arise for providing quality control tools. 

Fourier transform infrared (FTIR), and isothermal calorimetry (ITC) are techniques which have been utilized to examine macroscopic and molecular transitions of the skin. 

Isothermal Calorimetry The NMR and UV/vis techniques discussed above are used to determine a single binding constant K, from which AG° can be determined via Eq. 4.4. To determine the AH° and AS° ... 

In this way, we produce a binding titration just like we did from an NMR or a UV/ vis study. This allows us to determine K., and AH°. From we get AG°, and then we can solve for AS°. As promised, a single titration has produced all the quantities of interest. Isothermal calorimetry is thus a very powerful technique for evaluating binding. It does require fairly sophisticated instrumentation that is dedicated to such measurements. Also, fairly large quantities of material are sometimes needed, especially for hydrophobic binding interactions which can have fairly small AH° values, and thus release or absorb relatively little heat. 

Thermal methods play a key role in both the identification and the characterization of solid forms. A thermal method can be defined as a method where the heat flow is measured as a function of an externally varied parameter. If this parameter is, for example, time and all other parameters are held constant, the method is called isothermal calorimetry. In solution calorimetry, a solid is dissolved in a particular solvent and the associated heat of dissolution is measured. Probably the most frequently used thermal technique is differential scanning calorimetry (DSC) [8], where temperature is varied and the associated heat flow is measured. 

J.W. Beckmann, J.S. Wilkes, R.R. McGuire, "2,4,6—Trinitrotoluene Thermal Decomposition Kinetic Parameters Determined by the Isothermal Differential Scanning Calorimetry Technique", Thermochim. Acta. 19. 111—118 (1977). 

Lipid oxidation is an exothermic phenomenon that can be followed, at least at elevated temperatures, by DSC or (preferably) by isothermal calorimetry [41-44], Measurements can be performed under a static air atmosphere or, better, under oxygen flow or oxygen pressure. In the isothermal mode, induction times can be defined according to published procedures using other techniques (see Fig. 4). Figure 5 compares the oxidative stability at 130°C of three very different oils (safflower, blackcurrant seed, and Nujol). Induction time values can be used... 

In situ thermal transitions were also described by Taylor et al., who examined the isothermal dehydration behavior of trehalose dihydrate [29]. For small particle size fractions (<45 fjLm), heating at 80°C caused loss of peak definition until, at 210 min, amorphous material was present. In contrast, a larger particle size fraction (>425 fim) converted to the crystalline anhydrous form of the material. The kinetics of this conversion was probed from the Raman data using peak height ratios with time a two-stage rearrangement was indicated. A broader consideration of pharmaceutical hydrates, including their characterization by several techniques (NMR, Raman spectroscopy, and isothermal calorimetry) can be found in the literature [30] as can a review of the use of spectroscopic techniques for the characterization of polymorphs and hydrates [31]. 

Several authors have addressed crystallization measurements and kinetics of SPS [23-26,78-82]. The experiments were carried out in both isothermal and non-isothermal mode by means of differential calorimetry techniques (DSC) [24-26,78-82]. 

If the van t Hoff and isosteric methods are simple ways for estimating the adsorption enthalpy of single component from isothermal adsorption data, they have the disadvantage to not take into account the temperature dependence on the enthalpy and entropy and to be not enough accurate. Moreover they are not adapted to the adsorption of gas mixtures. The best mean to determine the adsorption and coadsorption enthalpy is to measure them by using a differential calorimetry technique coupled with others techniques allowing the measure of adsorbed amount and composition as for example the manometry and the chromatography. 

The precision of isothermal calorimetry has mainly been assessed in round-robin studies of heat of hydration. As an example, a German study with international participation (Lipus and Baetzner 2008) in 2006/2007 gave a standard deviation for repeatability of 5-7 J g" (within one lab) and a standard deviation for reproducibility (between the labs) of 13.6 J g the latter when regarding only the device used by most of the participants. This value is slightly better than those for the other calorimetric techniques. 

Determination of the heat of hydration after 1, 3 or 7 days is made to classify cements into different types, based on their reactivity, and this type of measurement is most important for low-heat cements used in mass concreting. Solution calorimetry according to ASTM C186 (2013) or EN 196-8 (2010) and semiadiabatic calorimetry according to EN 196-9 (2010) have been the preferred techniques for this, but isothermal calorimetry is becoming more and more used. As discussed previously, the different types of... 

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