Simultaneous TGA-DTA

Data for the uncatalyzed polycondensation from STA (simultaneous TGA/DTA) experiments under high-flow inert gas at atmospheric pressure [8] are shown in Figure 2.28. These data also demonstrate the dependency of the overall polycondensation rate on the polymer film thickness. 

Figure 16.25 A schematic simultaneous TGA-DTA instrument. A weight change on the sample side displaces the beam and a drive coil current returns the beam to zero. The current is proportional to the weight change and serves as the TGA signal. The temperature change between the sample and reference pans is measured by thermocouples attached to the pans. The temperature differential is the DTA signal. (Courtesy of ThermoHaake, Inc., Paramus, NJ, www.thermo.com, and Seiko Instruments, Japan.)...

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 ... 

No. 3 to No. 12 externally computed using peak maximum tempmituies of simultaneous TGA/DTA measurements... 

Kinetics according to ASTM E 698-79 from simultaneous TGA/DTA experiments... 

Software only for the Simultaneous Thermal Analyzer STA 780 was available for kinetics according to Borchardt and Daniels. Similarly to the kinetics program according to ASTM E 698-79, only separately sampled DTA data can be processed using the Borchardt and Daniels program. The DTA data from simultaneous TGA/DTA experiments cannot be... 

No. 2 Externally calculated using DTA data from simultaneous TGA/DTA measurements No. 3 Externally calculated using DTG data from simultaneous TGA/DTA measurements No. 4 Values at the conversion in the DTG peak maximum... 

While TGA provides useful data when a mass change is involved in a reaction, we have seen that many reactions do not have a change in mass associated with them. The use of both TGA and DTA or TGA and DSC provides much more information about a sample than either technique alone provides. There are several commercial thermal analysis instrument manufacturers who offer simultaneous combination systems, often called simultaneous thermal analysis (STA) systems. Simultaneous TGA-DTA and simultaneous TGA-DSC instruments are available. Instrument combinations cover a wide temperature range and come in both analytical sample size (1-20 mg)... 

Figure 3.7 shows the use of both magnetic and melting point standards in a simultaneous TGA/DTA instrument. The melting points were used initially to establish the magnetic transition temperatures for subsequent independent use to calibrate standalone TGA units. Table 3.3 lists some of the recommended materials used to calibrate the temperature axis of TGA instruments. 

Setaram offers thermogravimetric analyzers with ambient-1600 °C capability (Labsys TGA), ambient-2400°C capability (SETSYS Evolution TGA), and ambient-2100°C with large-volume capability (96-line TGA). The SETSYS Evolution TGA is a modular TGA with two weighing capacities of 35 or 100 g. Simultaneous TGA-DTA measurements up to 2400 °C and TGA-DSC up to 1600 °C can be made. Coupling to a gas analyzer is also possible. The 96-line TGA can weigh samples up to 100 g, and simultaneous TGA-DTA/DSC measurement is available. A gas humidity generator accessory is available. An advanced thermokinetics software package is available. For more information, see vww.setaram.com. 

Thermal and Oxidative Stability. The thermal and oxidative stability of various mixtures of 1 and 3a was determined to 1500 C by simultaneous TGA/DTA analysis. The scans were run at 10 °C/min at a gas flow of 50 cc/min in either nitrogen or air. When heated to 1000°C and 1500 °C under inert conditions, the various mixtures containing 1 and 3a afforded char yields of 79-80 and 77-78%, respectively. During the heat treatment, similar exothermic transitions (DTA) as found during the DSC scans were observed. Moreover, above 1000 °C, an exothermic transition is observed which is attributed to the formation of crystalline ceramic components such as SiC and B4C. Upon cooling, the carbon/ceramic masses were reheated to 1500 C in air. The oxidative stability of the charred mass was found to be a function of the amount of 1 present and the initial heat treatment. Charred samples obtained from heat treatment to 1000 C and 1500 °C of 10/90,25/75, and 50/50 molar weight percent of 1 to 3a showed chars of 98, 98, 99% and 90, 97, 98% respectively, when reheated in air (see Figures 3 and 4). 

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