Thermal analysis (TA) is generally used for characterizing gas-solid reactions or the decompositions of solids in the range from zero to full conversion, i.e. the entire process is monitored. In conventional TA, the experiments are carried out isothermally or with a linear temperature change. Due to the experimental limitations, the initial part of the reaction cannot be described quantitatively at a desired temperature. At the beginning of the isothermal experiment, the system must reach the constant temperature selected. However, the reaction may occur before the temperature has settled. For the same reasons, it is impossible to quench the reaction at a desired time (or at a desired extent of the reaction). Also, the most frequently used non-isothermal mode of thermal analysis does not allow decomposition of the sample to a particular extent of conversion or quenching of the reaction at a certain time.
The novel pulse thermal analysis (PulseTA^®) method [1,2] has been developed to eliminate, or at least reduce, the difficulties mentioned above. The PulseTA^® method is based on the injection of a specific amount of the gaseous reactant into the inert carrier gas stream and monitoring changes in the mass, enthalpy and gas composition, resulting from the incremental reaction extent. Because a known amount of the selected gas, which can be used for calibration, is injected into the system, the method is also suitable for quantification of the evolved gas by MS or FTIR. In contrast to conventional TA and all its modifications, the reaction is controlled not only by the temperature, but also by transient change in the composition of the reactive atmosphere as well.
PulseTA^® offers three principle opportunities of thermoanalytical studies, depending on the kind of injected gas: (i) injection of a gas which reacts with the solid sample makes it possible to investigate all types of gas-solid reactions; (ii) injection of a gas which adsorbs onto the sample surface facilitates the study of adsorption phenomena under atmospheric pressure and at the particular temperature and, (iii) injection of an inert gas, enabling quantitative calibration of the mass spectrometric signals, allows to increase the sensitivity of TA measurements to such an extent that species in amounts lower than 0.01 wt% can be detected.
The most distinct feature of PulseTA^® is that changes of the gaseous atmosphere during experiments occur in a limited, short period of time after each injected pulse of the probe gas. The transient character of the pulse technique offers interesting opportunities for PulseTA^® applications which will be illustrated using examples from material science and catalysis.

[1] M. Maciejewski, C. A. Müller, R. Tschan, W.D. Emmerich and A. Baiker,
      Thermochim. Acta, 295 (1997) 167.

[2] M. Maciejewski, W.D. Emmerich and A. Baiker, J. Therm. Anal. Cal., 56 (1999) 627

- back to SKT 2000 abstracts -