DSC Peak Maximum Temperature

By applying multiple heating rate DSC measurements and Ozawa s isoconver-sional model free method, an activation energy of 34.2 kcal mol1 and pre-exponential factor of 1.99 1012 s 1 were calculated from the DSC peak maximum temperature - heating rate relationship. 

Only one of the vacuum residues (sample 1) has a substantial evapoiizable fraction, as has already been shown using thermogravimetiy (n % = 181 °C, TS % = 237 °C, AG4(X) = 44 wt%). The boiling point, calculated from the DSC peak maximum temperatures and reduced to atmospheric conditions, is 410 °C. 

DSC peak maximum temperatures (at 10 K/min heating rate) in the distillation range agree quite well with the temp tures of the corresponding DTG maximum from thermo-... 

Thermogravimetry in air and the DSC oxidation experiments confirm the inferior oxidation, stability of blown bitumens. DSC peak maximum temperatures, the activation energy of the first oxidation peak, and the temperatures of corresponding DTG maxima for blown bitumens are inferior compared to distillation bimmens. 

Peak Maximum Temperatures (°C) from DSC and Derivative TGA (DTG) and Water Loss (moles water per mole drug) from TGA Data for Nedocromil Zinc Hydrates... 

Plots of DSC curves at various heating rates (Fig. 32) showed that the peak maximum temperature (Tp) increased with increasing heating rate (cp). Activation energy (Ea), was evaluated by using the empirically deduced equation [101 — 104] relating Tp and cp, regardless of the reaction order ... 

Collins and Wendlandt (155) used OL to determine the stabilizer concen-1 tration in polyethylene. The initial deviation of the curve from the baseline1 as well as the peak maximum temperature were both found to be a function of stabilizer concentration in the polymer. The method was compared to those using TG and DSC. 

The TVD curves of selected amino acids were determined by Contarini and Wendlandt (121). A comparison of the TVD and DSC peak temperature is shown in Table 11.8. The TVD peak temperatures are somewhat higher than those obtained by DSC. Obviously, the kinetics of the electrodedecomposition produces) reaction are different from those of the decomposition reaction. These electrode reactions probably involve one or more diffusion steps between the electrode surface and the amino acid or amino acid decomposition produces), which would be different from the decomposition kinetics themselves. The leading edge of the TVD curve peaks is reproducible to within +1-2%. However, after the peak maximum temperature is attained, the reproducibility falls to within +20% in some cases. This is related to the electrode-amino acid decomposition products interface, which, due to the nature of the reaction, would not be expected to be reproducible. The trailing edge portion of the curve also consists of several shoulder peaks that may be related to the consecutive and/or concurrent reactions previously described in the DSC curves. These reactions could produce decomposition products that would react with the aluminum metal electrode surface. 

A typical DSC curve peak integration is shown in Figure 12.17. In the fusion of dimethyl terephthalate, the peak maximum temperature found was 139.4 C with a AHf of 66.853 J/g. 

T and Values at Heating rate of S C/min and are Temperature and Degree of Conversion at the DSC peak Maximum, respectively. 

Most of the members of the series of w-alkanes evaporate in the DSC experiment at atmospheric as well as at 10 bar cell pressure due to the gas flow. Decrease of the gas flow rate from 5 to 1 or 2 cmVmin causes a true pyrolysis reaction for the higher n-alkanes, starting at about n-C Hg. This may recognized by the fact, that the peak maximum temperatures of the n- anes tested, from 1° " 60 122 longer differ at the... 

There is a considerable difference between the peak maximum temperatures of the reaction rate DTG in ermogravimetry, and the maximum temperatures of the peaks of the energy consumption in DSC. The mean of the DSC maximum in 1 bar argon (P = 10 K/min) exceeds the mean of from TGA by approximately 25 °C or 6 %. The suggestion that in DSC a energy flow takes place, and in TGA a mass transport, does not explain this difference. 

The corresponding peak maximum temperatures of the first and the last oxidation peaks were found in DSC at lower values than in the DTG curves, since the oxidation experiments in the DSC were carried out at 7 bar air pressure. However the peak maximum temperatures in DSC for the different ranges show good uniformity. The coefficients of variation of the corresponding means range only from 0.3 % to 2.75 %, and may therefore be used to calculate the Arrhenius coefficients. 

Table 4-137 DSC of the original samples (feed) in 10 bar methane. Peak maximum temperatures (°C)...

The DSC simulation was only carried out to determine the position of the peaks on the DSC curve (peak maximum temperatures), so the corresponding heats of reaction (Q ) were taken from literature. 

A rough estimation of reliability in predicting the actual weight loss rates (DTG) and heat consumption rates (DSC) was performed by comparing the peak maximum temperatures obtained experimentally with those obtained using equations 4-20 and 4-21, for the examples of oil shales E and KOR (Table 4-156). The difference of 4 % maximum between the experimental and the simulated data is acceptable. 

The oxidation reaction comprises three ranges of reaction, i.e. low temperature oxidation LTO, fuel deposition, and fuel combustion, which manifest discrete peaks at different temperatures. For example Fig. 4-165 presents the DSC plot of the oxidation of n-hexacontane in 1 bar air at a heating rate )3= 5 K/min. An increase of the heating rate shifts the peak maximum temperatures towards higher values, as expected. As a consequence additional peaks appear in the range of fuel deposition, as Fig. 4-166 shows for the example of oxidation of the dispersion medium in 1 bar air at a heating rate )8= 20 K/min. An increase of the pressure causes an increase of the area of the LTO peak, whereas peaks in the range of fuel deposition disappear and display only a shoulder on the flank of the LTO peak. The peak of the fuel combustion also becomes wider and flatter (Fig. 4-167, -hexacontane in 50 bar air, = 20 K/min). 

The software of the Simultaneous Thermal Analyzer, STA 780 (STA 1000) also allows the ASTM E 698-79 method to be used. Unfortunately there is no computer program to process data from simultaneous TGA/DTA (TGA/DSC) test runs. For computation according to ASTM E 698-79 only separately sampled DTA (DSC) data can be used, so the advantage of a simultaneous measuring instrumentation cannot be fully realized. The conversion levels at peak maximum temperatures are also unknown, and the total conversion can only be ascertained after termination of the test run. The installed software version C 4.20 offers plots similar to those of the DSCASTMKin vl.OO ... 

In principle Differential Scanning Calorimetiy and Thermogravimetry are suitable methods for investigation of the kinetics of pyrolysis and oxidation reactions of heavy crude oils and heavy petroleum products. The repeatability of selected values i.e. onset and offset point temperatures, and DSC (DTA) and DTG peak maximum temperatures, is excellent. For the pyrolysis reaction the coefficient of variation is 2 % maximum. In the oxidation reaction this is also true for the regions of low temperature oxidation and of fuel combustion. For the fuel deposition region of reaction the repeatability is worse. 

An isothermal DSC curve shows at a glance whether a reaction proceeds normally in other words, the rate of reaction and thus the heat flow reaches a maximum upon the reaction mixture s attainment of the reaction temperature. To locate a suitable isothermal reaction temperature, a dynamic experiment is carried out at 10 "C/min. The optimum isothermal temperature will lie between the start of reaction (at 20% of the peak height) and the peak maximum temperature. For example, an epoxy resin used for powder coating gives values of 180 °C to 220 °C. Conversely, an autocatalytic reaction shows an increasing reaction rate after an induction period. 

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