Derivative TG curve

A slope change of a TG curve is the main feature used to analyze a sample. Sometimes, the slope change is uncertain in this case, a derivative TG curve can be used. The derivative TG (DTG) curve is a plot of versus temperature. Figure 10.28 shows comparison of TG and corresponding DTG curves. A peak in a DTG curve represents a maximum of mass change rate. DTG does not contain any new information other than the original TG curve however, it clearly identifies the temperature at which mass loss is at a maximum. 

Thermogravimetric analysis (TGA) was carried out to investigate the decomposition and thermal stability through the sample mass change during the heating process. The TGA and derivative TG curves are presented in Fig. 5.5b. A small weight loss of 5 % was seen below 150 °C, which is attributed to the evaporation of... 

Figure 27 (a) Thermogravimetry (TG) and derivative TG (DTG) curves of poly(bisphenol-A-carbonate) (PC) (b) total ion current (TIC) DPMS of PC. Reprinted with permission from Puglisi et al. [69]. Copyright 1999, American Chemical Society. 

TG-MS is ideally suited to reveal differences in pressure behaviour during thermal decomposition of materials. This has been illustrated by Mol [144] in TG-MS analysis of toluene diisocyanate (TDI) and methylene bis-4-phenol isocyanate (MDI)-based polyurethanes, where the observed greater increase in pressure for the TDI polyurethane than for the MDI derivative indicates a higher loss of low molecular weight fragments. This is not possible to deduct from the TG curves alone. Such indications are of great... 

Another successful example is the solid-state thermal synthesis of the wholly aromatic polyimide P-ODPM (Tg=410 °C) by the polycondensation of the aromatic salt monomer ODPMA derived from bis(4-aminophenyl) ether and py-romellitic acid (see Eq. 3, R =H). Figure 3 shows the DSC and TG curves of salt monomer ODPMA [27]. 

Foldvari, M., P. Kovacs-Palffy, N. M. Nagy, and J. Konya. 1998. Use of the second derivative of TG curves for investigation of the exchanged interlayer cation in montmoril-lonite. J. Therm. Anal. 53 547-558. 

The result can be expressed as either a TG curve, a plot of changing weight with respect to temperature or time, or a derivative of the curve, i.e. DTG, where the first derivative of the TG curve is plotted with respect to temperature or time. As well as providing information on the thermal decomposition of inorganic compounds, additional information can be deduced, e.g. sample purity and Mr. 

Applying the procedure of the calculations described earlier the appropriate pore/core size distribution (PSD) curves AV/Ar vs. r for adsorbents investigated may be calculated. From the heights of segments II of the TG curves the total pore volumes were estimated. In Figures 11 and 12 the pore/core size distributions derived from TG experiment are compared with those from nitrogen adsorption experiment. 

FIGURE 8.1 TG curves and derivative TG (DTG) curves of kraft lignin (KL), alcoholysis lignin (AL) and the wood powder of Japanese cedar and hardwood I KL, II AL, III wood powder of Japanese cedar, IV wood powder of fir. Decomposition temperature is indicated by arrows. 

Figure 6.2 A TG/DTG curve for calcium oxalate monohydrate (This material gives three distinct weight losses over a wide temperature range. The plot also shows the derivative of the TG curve (DTG curve), which can reveal extra detail such as the small event around 400°G that would not have been seen on the TG curve itself Courtesy of Anasys Thermal Methods Consultancy Ltd, UK.).

In either case, the resulting curve is the first derivative of the mass-change curve. A series of peaks are obtained, instead of the stepwise curve, in which the areas under the peaks are proportional to the total mass-change of the sample. A horizontal plateau in the TG curve gives a corresponding horizontal plateau in the DTG curve because dm/dt = 0. A maximum in the DTG curve is obtained when the TG curve has an inflection point where mass is being lost the most rapidly. 

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... 

The DTG curves are exactly proportional to the derivatives of the TG curves therefore, the area under the curves gives the change in mass precisely. Accordingly, DTG can give exact quantitative analyses. 

One such data center recording system, the Bascom-Turner instrument, has been described by Kaplan et al. (58) and Wendlandt (59). The latter reference discusses the use of this recorder in thermal analysis. An example of the application of the recorder to TG is shown in Figure 3.17. The TG data (of CaC202 H20) was recorded from a thermobalance and then replotted as . /f, mass-time, scaled and offset B, mass-temperature, scaled and offset C, mass-time D. mass-temperature E, first derivative ofTG curve or DTG and F, temperature-time curve. 

Two other important milestones in the development of the modern thermobalance occurred in 1958 and 1964. A multifunctional instrument, called the Derivatograph. was described by Paulik 35) et al. in 1958. The instrument could record not only the TG curve, but also its first derivative (DTG) and the differential thermal analysis jDTA) curve. In 1964. Weide-mann (3) described the Mettler system, which was perhaps the most sophisticated thermobalance ever commercially available. This system is described in detail by Wiedemann and Bayer (8). 

The EGD curves obtained on this apparatus resemble the derivative of TG curves. Results are not normally comparable to those obtained with DTA where products are contained. The qualitative effects of the operating vari-... 

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