Heating rate influence

Subsequently, the release of ammonia (the only degradation product which could be measured quantitatively) was measured during a series of TGA experiments with variable heating rates. These experiments were performed to show how the heating rate influences the temperature and thus the possible occurance of thermal degradation, in a (small) curing TGA sample. 

A) The heating rate influences the temperature distribution inside the sample. Figure 3.1 shows an example of a temperature gradient in low-density polyethylene with a thickness of 10 mm. When the heating rate is 2.5 °C min the temperature difference inside and outside the sample is negligible. In contrast, the temperature difference is 10 °C at 40 °C min [1],... 

Fig. 9 - Examples of heating rate influence on observed phase separation temperature (composition far from w. ).

Marcilla, A., Hernandez, M.d.R., Garcia, A.N., 2007. Study of the polymer—catalyst contact effectivity and the heating rate influence on the HOPE pyrolysis. Journal of Analytical and Applied Pyrolysis 79 (1—2), 424—432. 

The stmcture of residual char particles after devolatilization depends on the nature of the coal and the pyrolysis conditions such as heating rate, peak temperature, soak time at the peak temperature, gaseous environment, and the pressure of the system (72). The oxidation rate of the chat is primarily influenced by the physical and chemical nature of the chat, the rate of diffusion and the nature of the reactant and product gases, and the temperature and pressure of the operating system. The physical and chemical characteristics that influence the rate of oxidation ate chemical stmctural variations, such as the... 

The thermal reactions of CaC204 H20 have been very fully investigated and this substance has been used as a thermal analysis reference material [1058], Dehydration, decomposition to the carbonate, and dissociation to CaO are all well separated, though kinetic characteristics are influenced by the presence of C02, 02 and H20 as well as by the reaction conditions, including heating rate, sample size, and sample container. Kinetic parameters for the oxalate decomposition reaction have been summarized by Gurrieri et al. [1059]. Values of E are close to 314 8 kJ mole-1. Decompositions [1057,1060,1061] of Sr (643—743 K) and Ba (663—743 K) oxalates involves some disproportion of CO, yielding residual carbon. 

Calorimetry shows that the rates of metabolism of plant tissues vary widely with species, with cell types, and with environmental conditions. This provides a means of exploring the mechanisms by which various agents influence the health of a plant community. Studies are being done on beneficial agents such as growth promoters and detrimental ones such as atmospheric pollutants. For example, a correlation has been found between the metabolic heat rates and the extent of damage to pine needles by ozone. 

Which polymorphic form of a compound is formed depends on the preparation and crystallization conditions method of synthesis, temperature, pressure, kind of solvent, cooling or heating rate, crystallization from solution, fusion or gas phase, and presence of seed crystals are some of the factors of influence. 

It must be also considered that the reaction rates of different thermal processes which can occur simultaneously are influenced by the treatment conditions (temperature, heating rate, pressure, static or dynamic atmosphere). This will affect the relative quantities of the products formed and in some cases also their nature, when recombination reactions give rise to secondary degradation products. On account of its sensitivity and resolution power Py-GC/MS will also provide useful information on minor components present in a material, including low molecular weight additives and pigments. 

In some MW-assisted reactions, in which a mixture of products is formed, the ratio of products may be influenced by the heating rate or by the polarity of the solvent. 

Also, Bose et al. [76] have shown that the steric course of /J-lactam formation can be influenced by the MW heating rate. For example, in the reaction of the benzoylox-yacetyl chloride 53 with the Schiff base 54 (Scheme 4.28) the cis adduct 55 is the main product at low irradiation power whereas high power favors the formation of the trans adduct 56. Lactams of this type can serve as intermediates for the side chain oftaxol and its analogs. 

Study the influence of the oven heating rate on the resolution of the two measured peaks. 

Ammonia TPD is very simple and versatile. The use of propylamine as a probe molecule is starting to gain some popularity since it decomposes at the acid site to form ammonia and propene directly. This eliminates issues with surface adsorption observed with ammonia. The conversion of the TPD data into acid strength distribution can be influenced by the heating rate and can be subjective based on the selection of desorption temperatures for categorizing acid strength. Since basic molecules can adsorb on both Bronsted and Lewis acid sites, the TPD data may not necessarily be relevant for the specific catalytic reaction of interest because of the inability to distinguish between Bronsted and Lewis acid sites. 

Rate equations predict the influence of the heating rate on amplitude as well as on the position of the peak when the heating rate increases, the initial polarization has to be released in a shorter time. As a result, the peak increases and shifts to a higher temperature. In fact, both peaks, Mj and M2, change with heating rate in a similar manner, but only the first has its temperature location (T ) dependent on the values of El and 7/Vv at the given heating rate. 

The glass transition temperature can be measured in a variety of ways (DSC, dynamic mechanical analysis, thermal mechanical analysis), not all of which yield the same value [3,8,9,24,29], This results from the kinetic, rather than thermodynamic, nature of the transition [40,41], Tg depends on the heating rate of the experiment and the thermal history of the specimen [3,8,9], Also, any molecular parameter affecting chain mobility effects the T% [3,8], Table 16.2 provides a summary of molecular parameters that influence the T. From the point of view of DSC measurements, an increase in heat capacity occurs at Tg due to the onset of these additional molecular motions, which shows up as an endothermic response with a shift in the baseline [9,24]. 

Influence of Residence Time. An approximate calculation of the residence time of the particles in the jet, assuming that they reach the gas velocity instantaneously (which is probably true for the small particles), shows that this time is about 1 msec. Estimating the rate of heating of particles of various sizes shows that particles less than 50m in diameter will reach a temperature of 1000°C. in approximately 1 msec., assuming a gas temperature of 4700°C. —an average heating rate of 10 °C. per sec. These estimates indicate that... 

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