Biomedical Engineering Reference
In-Depth Information
Heat flow sample Heat flow Black
(
)
(
)
CK
(13.12)
p
Cp
Heating Rate
where K
Cp
is the calibration constant.
In MDSC, the heating rate changes during the modulation cycle. h e
equation used for calculating heat capacity is
Q
d
modulation Perio
amp
CK
T
(13.13)
p
Cp
2
amp
where Cp is the heat capacity; K
Cp
is the heat capacity calibration constant;
Q
amp
is the heat l ow amplitude, and; T
amp
is the temperature amplitude.
13.6.3 Experimental
h ermal analysis measurements were carried out using modulated dif er-
ential scanning calorimetry (MDSC) on TA instruments model 2910 in the
temperature range from room temperature (RT) to 600 C in inert (N
2
) atmo-
sphere with a heating rate of 5 C/minute with ±0.75 C modulation per 60 sec.
13.6.4 Some of Important Results on Pure and Substituted
BiFeO
3
h e specii c heat and heat l ow data's for Bi
1-x
La
x
FeO
3
(x=0.0, 0.1, 0.2, 0.3,
0.4 and 0.5) compounds were obtained in temperature range from 200 C
to 500 C. h e specii c heat and heat l ow curves are plotted as a function
of temperature. Figure 13.31(a) shows the MDSC curves for pure bismuth
ferrite ceramic sample. It is clear from the i gure that the specii c heat, as
well as the heat l ow curves, for pure compound of bismuth ferrite shows
very clear anomalies—an exothermic peak at 363 C in specii c heat curve
and an endothermic peak at same temperature of 363 C in heat l ow curve
corresponding to antiferromagnetic phase transition with no other thermal
events (exo or endo) observed in the measured temperature region, which
is consistent with the reported value of Neel temperature that is 370 C
[120]; but due to limited temperature range of the used MDSC instrument
it was not possible to measure the ferroelectric to paraelectric phase transi-
tion temperature around 830 C [121]. Indication of single peak (endo and
exo) in both heat l ow and heat capacity curves indicate that the material is
thermally stable and almost phase pure.
