Endothermic effect

In given work the possibilities enumerated above of varieties of thermal analysis used to reseai ch of solid solutions of hydrated diphosphates with diverse composition. So, for example, the results of differential-thermal analysis Zn Co j P O -SH O showed, that it steady in the time of heating on air to 333 K. A further rise of temperature in interval 333 - 725 K is accompanied with the masses loss, which takes place in two basic stages, registered on crooked TG by two clear degrees, attendant to removal 4,0 and 1,0 mole H O. On crooked DTA these stages dehydration registers by two endothermic effects. In interval 603 - 725 K on crooked DTA is observed an exothermal effect. 

Interaction between niobium oxide and fluorides, chlorides or carbonates of alkali metals in an ammonium hydrofluoride melt, yielded monooxyfluoroniobates with different compositions, MxNbOF3+x, where they were subsequently investigated [123-127]. According to DTA patterns of the Nb205 - 6NFL HF2 - 2MF system, (Fig. 18) a rich variety of endothermic effects result from the formation of ammonium monooxyfluoroniobate, its thermal decomposition and its interaction with alkali metal fluorides. The number of effects decreases and separation of ammonium ceases at lower temperatures and when going from lithium to cesium in the sequence of alkali metal fluorides. 

Balabanov et al. [499] found an endothermic effect in the thermographic pattern of the decomposition of niobium hydroxide at 435°C that corresponds to complete removal of water. At the above temperature, amorphous niobium hydroxide also converts into amorphous niobium oxide. Ciystallization of the amorphous oxide occurs at a higher temperature with the release of energy [28]. Researchers [499] reported on another exothermal effect at 549°C that was attributed to the crystallization temperature of amorphous niobium oxide. Decomposition of tantalum hydroxide and its conversion into crystalline tantalum oxide occurs at about 710°C [502] or at 670-700°C according to another source [132]. 

The authors of [99] proposed a calorimetric method for determining the degree of the polymer-filler interaction the exothermal effect manifests itself in the high energy of the polymer-filler adhesion, the endothermal effect is indicative of a poor, if any, adhesion. The method was used to assess the strength of the PVC-Aerosil interaction with Aerosil surface subjected to different pre-treatments... 

The performance of aluminium hydroxide/magnesium hydroxide-filled systems can be enhanced by incorporation of zinc hydroxystannate in halogen-free rubbers giving reduced smoke and toxic gas emission, coupled with higher flame retardancy. This action will be complimentary to the water release and endothermic effects of aluminium hydroxide/magnesium hydroxide filler systems. 

The interaction of the compounds, shown in table V, with vermiculite (90) are entirely different from their behaviour with montmorilIonite in that endothermic effects are observed in the initial adsorption process. The endothermicity is attributed to the removal of water which is tightly bound by vermiculite. This is also corroborated by the fact that none of the organocations takes a flat orientation upon adsorption in the interlayer exceeds 1.45 nm in all cases). 

It is observed in figure 9.6 that the calibration thermogram has two peaks associated with endothermic effects. The first (C) reflects the heating and some sublimation of I2. The second (D), recorded after connecting both the sample and reference cells to an auxiliary vacuum line, accounts for the sublimation of the remaining sample and its removal from the cell. The calibration constant, s, is simply the ratio between ArH°(9.11) and the total area (C + D). 

Figure 20.1 show as an example the thermogravimetric crave (TG) obtained for the natural ilhte. A continuous weight loss can be seen between 150°C and 980°C the differential thermogravimetric curve (DTG) showing two endothermic effects. The first one is centered at 150°C which corresponds to loss of ilhte water. The second one is centered about 580°C and is mainly associated to the loss of stractural water. 

Figure 3.14 shows a DSC trace obtained at the scan rate of 4°C/min from the mixtures milled for 5, 10, and 40 h. A very small thermal flow effect of either exothermic or endothermic nature is seen around 140°C at the DSC traces of mixtures milled for 5 and 10 h only. At temperatures >180°C, mixtures milled for 5 and 10 h exhibit three strong endothermic effects centered at around 271, 315 and 452°C but the one milled for 40 h shows only two endo effects at around 292 and 452°C. 

Differential thermoanalysis involves recording the temperature difference between an inert compound and the sample during heating. Such differences occur if reactions take place which either release (exothermic effect) or consume (endothermic effect) energy. These effects are recorded as peaks on a plot of the temperature difference versus the temperature. Such thermal effects are associated with the loss of adsorbed H2O and structural OH as in TGA and also with phase transformations. 

These results show that Ai lowers the deton val of TNT and of 60/40 RDX/TNT even more than does NaCl which acts as a heat absorbing or en do thermic material. Therefore, Al must have a strong endothermic effect at the C-J plane. This would be the result if Al2 (gas) was... 

For both ions, it is apparent that the equilibrium concentrations (which are inversely proportional to the selectivity coefficient) at low temperature are two to three times larger than the high-temperature values, which indicates the usual and rather important endothermic effect. It is furthermore apparent that there is a significant preference for zinc as compared with cobalt ions, corresponding to a free energy of about 0.2 kcal/equiva-lent. 

Potassium, sodium, and cesium forms of the L zeolite were studied by the thermogravimetric method. There is an endothermal effect on the initial potassium zeolite KL-DTA curve within 50°-300°C caused by the loss of adsorbed water. Most of the water (15.1%) is lost in this narrow... 

The thermal stability of hydrogenation products Ti(Al,Sn)H1 g is lower, than a stability of titanium dihydride. On samples thermograviagrams three endothermal effects are observed, and besides 20% of the hydrogen absorbed by an alloy is isolated already at 783 K and 823 K, and the most part of the stayed hydrogen is isolated at 900 K. 

For the smallest gas molecules dissolving in elastomers AHs is positive (endothermic effect) for the larger gas molecules the reverse is true (exothermic effect). The process is exothermic if the sorption energy evolved exceeds the energy needed to make a hole of molecular size in the polymer. 

In some works [3, 4] it is supposed, that PETP can have two morphological forms of crystals which define double endothermic effect in the field of fusion. Form I, to which more high-temperature corresponds originally endothermic peak of fusion, has been attributed folded structure, and for the form II responsible for more low-temperature peak of fusion, the crystal structure from more extended circuits has been offered. 

Displacement of peak of fusion on curves DTA in area of smaller temperatures specifies that in the modified fibres crystals have mainly morphological form II (the extended circuits of polymers incorporated into crystallites) while in initial PETP crystals mainly have morphological form I (folded structure). Therefore for initial PETP it is observed endothermic effect at temperature 269°C - speaking by fusion flat folded crystallites (morphological form I). At modified PETP - fibers this effect is observed at temperature 245 - 263°C, it speaks fusion of spherallite (the morphological form II). 

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