Thermogram profile

We have just seen that the recorded calorimetric signal is representative of the process rate. 

To express such behavior, the calorimetric signal must shift, starting from the initial instant, from a value representing a post-reaction equilibrium where V = 0 to the value corresponding to the initial rate V = a, which in this case equals 40. 

The time T of this transient state will depend on the response time of the equipment. 

Concretely speaking, the signal will increase from a zero value representing the equihbrium to a maximirm value Vm = 20 where it will meet the real curve, b. 

After the leaetion has taken off, it is possible to observe other situations due especially to the existence of a stationary process. In such a case, the calorimetric signal will be constant at a value lower than or equal to the initial value. 

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In this paper, the thermogram profiles of a number of papermaking pulps are examined. Different methods of presenting such curves are discussed, and the effects of changes in the rate of heating on the curves are examined. Where possible, the effects of such aspects as wood species, fiber preparation, crystallinity, or artificial aging on the thermograms are also discussed. 

Since the production of thermogram profiles is a relatively rapid operation now that suitable commercial equipment is available, it seems very likely that differences in papermaking pulps introduced by pulping and other chemical or physical treatments of pulps could be readily and rapidly followed with these techniques. It is even possible that further development and refinement, coupled with the use of well-defined standard pulp samples, may make such techniques applicable to process or quality control functions. 

H2 TPR measurements are used to probe the reducibility and may reveal more information on the nature of vanadium and molybdenum species. The assignment of the TPR peaks has been based on the literature study [9, 10] but also by using two reference samples V1-Z15 and Mol-Z15 prepared by solid-state ion exchange. TPR thermograms of V-Mo-Zeolite systems can be divided into two zones of H2 consumption (/) Mo-Zeolites exhibit two reduction peaks at 600 and 850°C corresponding to the reduction of Mo6+ into Mo4+ through the Mo5+ step and to the reduction of Mo4+ into Mo°, respectively while (ii) V-Zeolites led to a broad asymmetric feature around 710°C, which has been previously attributed to the reduction of V5+ into V3+. Finally, the TPR profiles of V-Mo-Zeolite catalysts seem more like a superposition of both Mo and V-catalysts TPR profiles. 

Figure 1. Thermogram of a Pittsburgh 8 coal sample. Crosshatched intervals a-f correspond to molecular weight profiles of FI ions in Figures 3a-f, respectively.

Similarly, differences in manufacturing substantially affect the DSC melting profile (7). In figure 8 we see thermal curves of nearly identical polyester yarns. Sample one and two are identical in composition--both contain a dyability additive--but were annealed at different temperatures as can readily be seen by the position of the annealing "scars" on the thermograms. The effect of the dyability additive apparently is that it lowers and broadens the melting peak destroying its characteristic first-run, double-peak behavior. 

Figure 4.39 [95] shows the NH3-TPD thermograms corresponding to H-MOR, H-HEU, H-LTL, H-FAU, H-MFI, and CoAPO-5 (calcined). The TPD profiles of the samples show two different regions that can be assigned to weak and strong acid sites. 

Much useful and interesting information can be obtained from a study of the features and profiles of integral and differential thermograms. Papermaking pulps have more or less unique thermograms show-... 

While a temperature-dependent IR spectrum allows one to examine specific elements of a transition, a DSC thermogram enables the visualization of transitions in their entirety and the calculation of associated thermodynamic parameters. The IR and DSC thermal profiles for identically treated samples of hydrated porcine SC are shown in Fig. 3. The results of a series of thermograms for intact, delipidized, fractionated, and reheated SC as well as extracted lipids suggest that these three major transitions near 60,70, and 95°C in intact SC are due to intercellular lipid, a lipid-protein complex associated with the comeocyte membrane, and intracellular keratin, respectively. Evidence supporting these deductions is elegantly presented by Golden et al. [33]. More recently, the presence of a subzero lipid transition at -9°C has also been reported [34]. 

The complexity of the SC membrane hinders such definitive interpretation, but, nevertheless, alterations in endotherms can be used to screen molecules suspected of altering membrane function. Conversely, one should note that the absence of additive-induced alterations in the phase transition profile does not rale out their perturbing effect, but rather indicates that the additive does not modify the gel phase. As described earlier, a DSC thermogram of hydrated but untreated human SC yields four endotherms, the first three of which can be identified as noncooperative lipid-associated phase transitions, while the high-temperature endotheim is attributed to keratin denaturation [33,37]. 

The simplest and most straightforward application of thermal analysis is concerned with studies of the relative stability of polymorphic forms. For example, DTA thermograms enabled the deduction that one commercially available form of chloroquine diphosphate was phase pure, while another consisted of a mixture of two polymorphs. DTA analysis was used to demonstrate that in spite of the fact that different crystal habits of sulfamethazine could be obtained, these in fact consisted of the same anhydrous poly-morph.f In a study aimed at profiling the dissolution behavior of the three polymorphs and five solvates of spironlactone, DTA analysis was used in conjunction with powder X-ray diffraction to establish the character of the various materials. ... 

Figure 9. Differential scanning calorimetry thermograms of polytetraoxanes obtained by y-ray-initiated polymerizations in the solid state. Dotted curves indicate the decomposed endothermic profiles caused by the extended chain crystals and folded chain crystals.

The thermograms of DTA and TG of the precursors showed different profiles, depending on the method used to prepare the solids. The precursors of the LFA and ALF samples showed an exothermic peak at 240 and 250 °C, assigned to the hematite production [7]. On the other hand, the LFAW sample displayed no exothermic peak, indicating that no crystalline hematite was produced. We can thus conclude that when lanthanum and iron nitrate are added to the ammonium solution (LFA), and vice-versa (ALF), lanthanum favors hematite production. However, when the reactants are added to water (LFAW), the formation of hematite is delayed, in accordance with the X-ray diffraction results. In all cases, there is a large endothermic peak bellow 100 C, due to the loss of physically adsorbed volatiles in the solids, in agreement with TG curves. 

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