104
C.R.S. Morais et al. / Journal of Alloys and Compounds 344 (2002) 101–104
Table 3
metry) and is defined by the function g(a) 5 2[1 2 (1 2
a)1 / 2], indicating a mean reaction order [16].
Kinetic parameters derived from application of the function g(a) in the
Coats–Redfern equation for f510 8C min21
Complex
Parameter
Value
Model
R2
Eu(btfa)3bipy
Ea (kJ mol21
)
)
)
)
)
64.69
4. Conclusion
A (s21
)
1.103103
0.999
r
The values of the kinetic parameters obtained by the
different integral and approach methods were in agreement
with the respective mathematical models. The apparent
activation energy values obtained by these different meth-
ods were similar, but the thermal stability order of the
various compounds were not.
Eu(btfa)3phen
Eu(hfc)3bipy
Eu(fod)3phen
Eu(fod)3bipy
Ea (kJ mol21
93.92
F1
R1
R1
R1
A (s21
)
4.473105
0.981
r
Ea (kJ mol21
80.05
A (s21
)
6.323104
0.999
r
Ea (kJ mol21
83.88
A (s21
)
1.993105
0.998
r
Ea (kJ mol21
92.56
Acknowledgements
A (s21
)
2.253106
0.999
r
The authors acknowledge CAPES and CNPq for scho-
larship and financial support of this work.
gravimetric profile and the heating rate, using decomposed
fraction (a) from 0.10 to 0.90.
References
The evaluation of the kinetic parameters regarding
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frequency factor (A) for the first and second steps were
more significant in each complex (Table 2). The apparent
activation energy for the methods of Horowitz–Metzger
and Van Krevelen are larger than those for the integral
methods of Coats–Redfern and Madhusudanan.
In this way, the matching of these values of activation
energy suggests the following decreasing order of thermal
stability for the first steps, which we consider most
significant, for the splitting of almost all of the b-di-
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Eu(fod)3phen.Eu(btfa)3bipy.
The kinetic models that better described the thermal
decomposition reaction for the Eu(b-dik)3L, were F1, R1
and R2 (Table 3). The model F1 indicating that the
mechanism is controlled by a reaction order and is defined
by the function g(a) 5 2 ln(1 2 a), indicating a first order
reaction. The model R1 indicating that the mechanism is
controlled by a one-dimensional phase-boundary (zero
order) and is defined by the function g(a) 5 1 2 (1 2 a).
The final model R2 indicating that the mechanism is
controlled by a phase-boundary reaction (cylindrical sym-