Mass loss curves

TGA. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are other means to confirm the above structural models. Figure 4.4.8 shows the thermal analysis data for sample I. Curve (a) shows a TG datum of a mass loss about 22% after heating over 350°C. The derivative curve (b) of mass loss curve (a) clearly shows that there are at least four steps during the decomposition of the sample. This finding was further confirmed by the DTA data curve (c) shown in the same figure. It is clearly seen that there are four endothermic peaks. The DTA and TGA curves were similar for all samples. Note that the relative ratios of mass... 

Fig. 4.4.8 TGA and DTA result of sample 1. (a) Mass loss curve (b) Derivative curve of (a) (c) Differential thermal analysis curve. (From Ref. 10.)...

The mass loss curve is expected to have a linear asymptote of slope... 

A typical mass loss curve for the three heating rates is shown in Figure 2. The fractional residual (char) mass at 600°C is given for each species in Table I. Considerable data are available from the 1iterature particularly from thermogravimetry studies, on the influence of specimen and heating parameters on mass loss characteristics. 

Moon et al. (61) showed from the mass loss curves for the degradation of PLLA and PLLA-MWCNT nanocomposites that PLLA degraded without forming any residue, but the nanocomposites left a residue of about 3-10% (Figure 9.14). Additionally, the decomposition temperature (Td), at 10% weight loss, was found to increase with the MWCNT loading by 10-20%. Rapid weight loss also took place at around 300 °C in both PLA and PLA nanocomposites. Similar results were also obtained by (64,73,75,76). 

Fig. 2 shows Che mass loss curve for one of the experiments. The initial and final weights for the gasification reaction are also indicated. Fig. 3 shows the reactivity as a fimction of the degree of conversion, i.e. the reactivity profile, for the same experiment according to equations 8 and 9. In addition, the figure shows the average reactivity (from eq. 8) between 20 and 80% conversion. 

For drying of wet material, experimental and calculated mass loss curves of the water for different gas temperatures are shown In Fig.7. To avoid intaraction with the pyrolysis process, a gas temperature of 150 C has been chosen for the drying of wood. At this tempo-ature the drying velocity is low, thus wood in the expo-iments contained only a small amount of water. Because pyrolysis of wood starts at temp atures of about 200 C, wet slate particles have b n used for drying experiments at higher temperatures. 

In order to test the applicability of the model over a wider range of conditions the kinetics derived at 10 C/tnin from Table 1) was used to predict the pyrolysis of wheat straw heated to 300 C at 10°C/min, then kept isothermal for 60 min, before heating to bOO C at 10°C/min, see Fig. 3. The experimental data show that the addition of a 60 min hold time at 300°C results in somewhat different mass loss curve. The initial mass loss follows that of the data heated directly to 600 C, but when 300 C is reached, the mass loss rate becomes much lower, and after 60 min at 300 C, the conversion is only about 0.8. Full conversion is reached when the temperature is raised to 600 C. The char yield for the two experiments was approximately the same. The model, which fit the direct heating to 600°C reasonably well, does not work for the case with a 60 min isothermal segment at 300°C is inserted. The model predicted that the pyrolysis was far too fast, and a full conversion is predicted under the isothermal segment. This shows that first order kinetics only works well on the data on which it was fitted. A single first order model cannot predict the pyrolysis behavior under different conditions. 

The results confirm that TGA experiments are not significantly affected by heat transport phenomena if low initial sample masses as well as the described TGA configuration and experimental procedures are applied. The temperature gradients inside the samples are sufficiently small to allow the fitting of formal kinetic models to the experimental mass loss curves assuming a homogeneous sample temperature. Cellulose samples with initial sample masses of around 5 mg and higher can only be submitted to kinetic analyses under consideration of the enthalpy balance. 

The comparison of the results of a round-robin study published by GrCnli et al. to our results for p = 40 K/min (the only heating rate investigated in both studies) shows that the correspondence between the experimental mass loss curves is very good. Nevertheless, the activation energy of 198.4 kJ/mol for the irreversible 1" order reaction from this work is considerably lower than the 211 - 232 kJ/mol found for the results from the different laboratories participating in the round-robin study. Instead,... 

The characteristics of a single-stage mass-loss curve are illustrated in Figure 2.2. Two temperatures may be selected as characteristic of any... 

The recording of more prono qced horizontal mass plateaus in the TG curve is possible by use of a quasistatic heating rate mode, as previously mentioned. This method was first used by Honda (9) and also by Lufcaszewski and Redfern (6) and Paulik and Paulik (21). With th s technique, provision is made for the interruption of the linear temperature rise cycle and continuation of the heating at a constant fi ed temperature. This method gives mass-loss curves that are, in general, steeper than those obtained under dynamic conditions and provides more accurate data on the final decomposition temperatures. Io... 

Figure 2.6. Effect of chart speed on the shapes of mass-loss curves. (I) Low chart speed (11) high chart speed (6).

Figure 2.7. Effect of atmosphere on the mass-loss curve of CaC204 -HjO (500-mg sample heated at 300°C/h) (1).-, dry 02 -, dry N2-...

Table 2.2. Comparison of Self-generated and Dynamic N2 Mass-loss Curves for Mn(CH3C02)2 4HzO (57)...

A comparison between a conventional (c) and a derivative (b) mass-loss curve is given in Figure 2.36. The derivative curve may be obtained either from the TG curve by manual differentiation methods or by electronic differentiation of the TG signal. Accessory equipment is available for most... 

Figure 2.36. Comparison between Jo) integral (TG) and (6) derivative iDTG) mass-loss curves.

One of the most important components of a thermobalance is the sample holder. The geometry, size, and material of construction have a rather important effect on the mass-loss curve obtained. A large variety of sample holders have been described, a representative number of which are shown... 

The use of materials with magnetic transitions which could be displayed on a mass-loss curve and referred to the temperature. 

Figure 3.12. Magnetic transition effective mass-loss curves al heating rates of 20 and 100°C/ min 1 (II).

Figure 3.16. Effect of temperature perturbation on mass-loss curve, (rr) Time base recorder heating rate slowed down at A, (h)X — Y recorder.

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