Chemical Processes - Isoconversional Kinetics of Thermally Stimulated Processes - page 220

decomposition of the mineral alunite, whose chemical formula is KAl 3 (SO 4 ) 2 (OH) 6 .
Alunite decomposes in two consecutive steps that respectively represent dehydra-
tion and desulfation [ 134 ]. Figure 4.45 compares the E ʱ dependencies estimated
for both processes in regular and mechanically activated alunite. It is seen that the
activation energy of either dehydration or desulfation is much lower in the mechani-
cally activated sample.
Solids can also be activated by exposure to different types of electromagnetic
radiation, including visible and ultraviolet light as well as X- and ʳ-rays. Interaction
of the radiation photons with ionic solids leads to bond breaking and the creation
of various defects in the crystalline lattice [ 135 ]. As a result, the solid almost uni-
versally becomes more reactive and the activation energy of decomposition drops
[ 92 - 94 ]. By way of example, Fig. 4.46 demonstrates the effect of pretreatment of
Fig. 4.45 The E ʱ depen-
dencies estimated by an
isoconversional method for
the thermal decomposition of
alunite [ 134 ]. Solid sym-
bols correspond to regular
(not activated) sample, and
open symbols to the sample
mechanically activated by
high energy ball milling.
Squares and circles, respec-
tively, represent dehydration
and desulfation steps
α
Fig. 4.46 Isoconversional
activation energies deter-
mined for the thermal
decomposition of strontium
nitrate [ 136 ]. Solid symbols
represent the untreated
sample. Open symbols
correspond to the samples
exposed to different doses
of 60 Co ʳ-radiation ( squares:
0.5 MGy; stars: 1.5 MGy;
hexagons: 2.5 MGy)
α