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	Pulse Thermal Analysis (PulseTA®)

Pulse Thermal Analysis (PulseTA®) was developed in 1996 [1,2] in order to increase the potential of conventional thermal analysis, and arrived on the market in 1997.   The basis of the PulseTA® technique is the injection of a specific amount of the desired gas into the inert carrier gas stream and monitoring of the changes in the mass and enthalpy which result from the incremental reaction progress. In addition, with coupled TA-MS systems such as the NETZSCH STA 409 C - MS or TG 209 C - FTIR, PulseTA® makes it possible to analyze gas phase composition changes resulting from the reactions caused by the injected pulses (Figure 1). The PulseTA® box can be used with both the Skimmer and capillary as well as the FTIR coupling systems.   Bild 1: PulseTA® Box   Depending on the type of gas injected, PulseTA® offers three primary options for the investigation of gas-solid reactions [3]:   Bild 2 Injection of gas which reacts chemically with solids enables investigations of the changes of the solid phase and gas composition resulting from the injected pulse. Any chemical reactions such as reduction, oxidation or, for example, catalytic processes between solid catalyst and gaseous reactant(s) can be investigated at desired temperatures. When investigated by PulseTA®, gas-solid reactions occur only during the duration of the pulse, making it possible to monitor very slight progresses of the reaction and permitting investigations of the reaction product(s) with reference to a well-known reaction extent. Figure 2 shows the results of the measurements of redox sequence [4] in the zirconia-supported PdO catalyst: reduction of PdO by methane and subsequent reoxidation of Pd by oxygen at 500°C. Bild 3 Injection of gas which adsorbs on the solid Due to the capability to simultaneously monitor mass changes and thermal effects, PulseTA® can be applied for the investigation of adsorption phenomena occurring under atmospheric pressure at required temperatures. Figure 3 depicts the adsorption of ammonia at 200°C on ZSM-5 zeolite. The observed exothermal effect (Figure 3, section A) is related to the weight gain resulting from the NH3 chemisorption, which enables the determination of the heat of the reaction per mole of adsorbed ammonia. Section B of Figure 3 presents the reversible physisorption process.   Injection of inert gas Calibration of the mass spectrometer signals: An interesting feature of PulseTA® is that it allows direct calibration of the mass spectrometer signals obtained in the coupled TA-MS systems. The calibration is carried out by introducing a known amount of the gas into the carrier gas and determining the relationship between the amount of the injected gas and the intensity of the MS signal. Bild 4   The results presented in Figure 4 confirm the accuracy of the MS signal quantification carried out by PulseTA®. During the calcination of CaCO3, two pulses of the reaction product CO2 were injected before and after the MS signal (m/z = 44) resulting from the decomposition. The stoichiometric weight loss for a given amount of CaCO3 (4.62 mg) is 2.03 mg, the amount of evolved CO2 measured by the TG curve was 2.02 mg. The amount of CO2 calculated from the MS data by comparing the mean value of the integral intensities of two pulses with the integral intensity of the CO2 evolved during decomposition corresponds to 2.01 mg.   The capability for exact calibration of the MS signal by means of PulseTA® significantly increases the potential of the coupled TA-MS method. There is a considerable advantage in using this method to determine the content of certain species in the investigated system as compared to conventional elemental analysis. With conventional micro-analysis, only the total amount of analyzed species can be measured and it is impossible to resolve the species evolved in multistage reactions or to determine very small amounts of the products.   Calibration of FT-IR Signals:   Figure 5 shows the linear dependence between the amount of decomposed NaHCO3 and intensity of the trace signals of evolved CO2. Figure 6 demonstrates the traces of CO2 evolved during decomposition of different amounts of the reactant and 1ml pulses of CO2 injected before (50°C) and after decomposition (250°C).   Bild 5 Bild 6 Bild 7 Linear dependence between amount of evolved gas and integral intensity of FT-IR signal (peak area) enables the quantification of FT-IR data. The influence of the temperature on the shape and intensity of the FT-IR signals is given in Figure 7. At each temperature two pulses of CO2 have been injected into the carrier gas stream.   References:   Proceedings 11th ICTAC, Philadelphia, PA (USA), 1996, p. 202. Proceedings 13th Int. Symp. Reactivity of Solids, Hamburg (Deutschland), 1996, P-OC-095. Thermochimica Acta, 295, 167 (1997). Journal of Physical Chemistry, 100, 20007 (1996). Proceedings 25th NATAS Conf., McLean, VA (USA), 1997, p. 508.   Also read: "Auf der Suche nach Diamanten oder Erdöl: Anwendungen für die Puls Thermische Analyse", published in GIT-Laborzeitschrift 06/2001, p. 616. You can download this article in PDF format (655 KB in German).     back