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The combination of
thermogravimetry and mass spectrometry proves to be remarkably useful
for understanding and controlling the thermochemical reactivity of
functional materials. In this contribution the investigation of the
controlled modification of functional materials is demonstrated, i.e.
materials with specific chemical and physical properties have been or
need to be characterised and optimised for their integration in various
technologies or technical systems of the past the present and the
future. As a matter of fact the results of the thermoanalytical / mass
spectrometric measurements have to be considered as a fundamental tool
for the determination of compositional and energetic transformations but
a limited tool for a consistent interpretation of the occurring
structural and morphological changes, which might be the decisive
features for the processes or functions of interest. Therefore results
of studies by means of X-ray diffraction, analytical scanning and
transmission electron microscopy as well as various spectroscopies the
necessary and complementary data.
Ammonia absorption as
security system in cooling systems or heat pumps
Ammonia is a rather old
and conventional, but nevertheless thermodynamically efficient and
appropriate coolant. However, its odour and its toxicity prevent a more
widespread technical application. In the passed years we developed a
simple security system which binds effluent gaseous ammonia by a
heterogeneous solid state reaction. As ammonia absorbers transition
metal salts and molecular sieves are utilised. By TG-DTA-MS measurements
the reversible uptake and emission of ammonia and - as concurrent
reagent - of water vapour has been monitored. Based on the results the
construction of a feasible prototype is demonstrated.
Redox processes in
transition metal oxides
Physical properties
such as electrical and ionic conductivity, magnetism or colour are
drastically influenced by the oxygen stoichiometry of the functional
metal oxide. In turn and based on this observation the design of
tailor-made materials by means of controlled reduction or oxidation
processes is possible. Thermoanalytical techniques prove to be very
reliable tools for the quantitative determination of small mass changes
induced by such type of redox processes. In other words, standardized
procedures for the determination of oxygen stoichiometries can be
developed. There is, however, an important drawback, because for the
performance of reduction experiments reactive gases like hydrogen or
methane are required. This implies a careful and reliable handling of
the used thermoanalysers.
Ageing processes
Many functional
materials are developed and tested under laboratory conditions. Their
implementation in technical systems means an exposition to realistic and
often drastic thermal and chemical loads. The monitoring of such
circumstances by means of thermoanalytical studies is shown for
electrode materials used in solid oxide fuel cells. The results give
rise for a rather fundamental conclusion: the monitoring of realistic
technical conditions is vital for the implementation of novel functional
materials.
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