The
crystal growth velocity of spherulitic As2Se3 in a supercooled melt of the same composition was studied
by optical microscopy and thermoanalytical methods in isothermal and
nonisothermal conditions. The time dependence of crystal size is linear,
which suggests the crystal growth is controlled by interface kinetics.
Crystal growth velocity was determined as the slope of these linear
dependences. The experimental results presented in this paper considerably
extend the previously reported range of crystal growth velocity. All
isothermal crystal growth velocity data can be well described by the
standard two-dimensional surface nucleated growth model (2Dsg) including
crystal growth viscosity decoupling (ξ = 0.647). The activation
energy of crystal growth for microscopic experiments is in a good
agreement with values obtained from thermoanalytical experiments,
and the ratio of the activation energy of crystal growth and the activation
energy of viscous flow well corresponds to an independently determined
decoupling parameter. The same model successfully describes also crystalline
layer thickness and growth pattern at the amorphous As2Se3 surface in nonisothermal conditions.
The dehydration of calcium oxalate trihydrate was studied using DSC method and open sample crucibles. The dehydration proceeds in two steps where first two molecules of water are released around 80 °C and consequently the last molecule of water is released at a temperature around 130 °C. The kinetic analysis of overlapping peaks was done and the apparent activation energy, pre-exponential factor and kinetic exponents of kinetic model (reaction order model) were evaluated for both effects.
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