DSC exotherm

The same may be observed with magnesium carbonate in cellulose [70] (Figure 26). The chemiluminescence intensity at a given temperature increases with pH of the sample almost linearly. As it is evidenced by DSC, the sample with pH 7.2 is the least stable. Figure 26 is also a demonstration of the much higher sensitivity of the chemiluminescence method when compared with DSC. DSC exotherms, which accompany the final stages of the cellulose decomposition... 

NOAA Chemical Reactivity Worksheet used confinement in drum for up to 3 months not expected to cause reaction, based on experience with actual mixture and lack of DSC exotherm below 500 °C... 

The DSC exothermic peaks can be used to obtain Xc(tmax) from /max. Figures 20.24 and 20.25 illustrate the linear regression analysis of the... 

It is disappointing that DSC exotherms, presumably caused by further crosslinking reactions, interfered with the detection of LC phase transitions in the cured enamels. These exotherms were broad, and recurred when the samples were cooled and reheated. This behavior may be attributable to slow consumption of -OH groups in the domains or to slow self-condensation of HMMM (21,22). If these reactions occur to any appreciable extent, their exotherms are likely to obscure the relatively weak endotherms produced by the low concentration of the LC phase. 

A third scalable method for one-carbon homologation, the conversion of an ester 5 to the terminal alkyne 7, was reported (Tetrahedron Lett. 2004,45,5597) by Kevin Hinkle of GlaxoSmithKline in Research Triangle Park, NC. The ester is reduced with Dibal, the intermediate is quenched with methanol, and the solution of liberated aldehyde is treated with K,CO, and the reagent 6 according to the Ohira procedure. Weinreb esters also work well with this protocol. The conversion was reported to work in 72% yield starting with 27 g of 5. Note that 6 has a DSC exotherm at about 70"C, so caution should be exercised in handling it. 

The reactivity value is obtained by using the peak temperature of the lowest differential thermal analysis (DTA) or differential scanning calorimeter (DSC) exotherm value as shown in column 2 of Table VI. Alternatively, it can be obtained from a qualitative description of the instability (or... 

Following preliminary DSC studies, isothermal decompositions of small quantities (1-3 mg) of compound are performed at temperatures generally below the observed DSC exothermic maximum. Samples are usually thermolyzed in sealed Pyrex tubes. Use of Pyrex usually precludes reaction with the container that often occurs with metal reaction vessels. Sealed vessels also prevent corrosive decomposition products, e.g. NO2 or HF, from damaging laboratory instrumentation. Sealed reaction vessels confine the decomposition products where they can easily be identified and quantified. It is obvious that highly reactive decomposition products such as formaldehyde are not observed by this technique, but they would not be expected to survive over the time of these decomposition experiments (seconds to hours, depending on the temperature). Seal vessel thermoylses mimic real storage scenarios where the sample is self-confined. However, autocatalysis may occur in sealed vessels that would not be observed in open ones. On the other hand, in unsealed tubes sublimation of the sample may become competitive with decomposition. 

Figure 3 Characteristic DSC exotherm (a) and endotherm (b). (From Provder et al., 1983. Reprinted with permission.)...

Figure 8. Relationship between DSC exotherm peak of wood flour oxidation by various nitrates and pH of the nitrates (145).

For each isothermal experiment, the evolution of the mass fraction of solid, / (f), could be obtained by numerical integration of the DSC exothermal peaks of solidification, after correction for the baseline and normalization with the value of AHyOf the phase(s) formed. As cocoa butter is composed of many TAGA, its maximum solid fraction at equilibrium, is not unity and depends on the crystallization temperature. Therefore, the crystallinity ratio,... 

Tjn, is constant, this is used as the isoconversion point for the Kissinger analysis (Kissinger, 1957) of the DSC exotherms at various scan rates, p. 

Compound C sublimes at > 270° without decomposition and shows endothermic, reversible solid phase transformations at — 24.lt and — 4.3° (DSC exothermic on cooling). The carborane C is very soluble in aliphatic and aromatic hydrocarbons or in many other solvents such as CHCla, and can be recrystallized from cold diethyl ether and pentane (slowly cooling to —78°) or also from hot ethanol. Figure 2 shows the X-ray structure of the C Bg skeleton of one molecule of C in the crystal state of the LT phase at 103 K." ... 

The relative degree of crystallinity, Xt, was determined from the partial area under the DSC exotherm defined as follows ... 

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