| Summary: | 碩士 === 國立臺灣大學 === 地質科學研究所 === 94 === Master Curve Model (MCM) is probably a universal kinetic model, and can be
used to predict the variations of various kinetic reactions as long as we can derive the
master curves and best apparent activation energy from experimental data. Unlike
general chemical kinetic model, which needs all three parameters, i.e. activation
energy Q, reaction order n, and collision frequency Ko, to construct the model, MCM
is a much simpler and more objective method.
Our previous work has shown that MCM can be used to describe and predict
complicated ceramic sintering reactions, not only for micron-or submicron powders,
but also for nanocrystalline ceramic powders. The purpose of this research is to test
the applicability of MCM on some simple chemical thermal decomposition reactions.
Four powders, including CaCO3, CuSO4·5H2O, CaSO4·2H2O, and Na2CO3, had
been thermally decomposed at various heating rate by thermo gravimetric analysis
(TGA). Without grinding and sieving process, no acceptable master curves can be
derived from the powders, but after grinding and sieving, three powders (except
Na2CO3) gave much better master curves. It indicates that the reaction rates on the
surface of the particles are different from that inside the bulk. Below 600oC,
Na2CO3 only showed physical desorption reaction, which is not a stable chemical
kinetic reaction, therefore no kinetic model is expected to be able to adequately
describe the reaction.
With some limitations, the preliminary results show that MCM indeed can
be used to interpret and predict the thermal decomposition reactions of simple
compounds. At least two factors will influence the accuracy of predictions of
MCM, i.e. the particle sizes as we have mentioned earlier and the heating rates.
In general, a faster heating rate gives a larger apparent activation energy.
Therefore, heating rate is a must considered factor when using MCM on the
analysis of thermal decomposition reactions.
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