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Unformatted text preview: s the temperature of the sample.
 i s the thermal resistance between the Page  35a F igure 17
S implified model of t he DSC sample chamber. R  t hermal resistance
Ts  s ample t e m ~ e r a t u r e
Tp  t hermal en;rgy s ource/sink
C s  specific heat of sample
d h/dt  e nergy g enerated/absorbed
b y t he sample
d q/dt  r ate of energy flow t o/from
t he sample P age 36s ample/source a nd the heat s ource/sink,
a nd between the r eference/source a nd the
heat s ourcelsink. ( A l l e nergy exchanges occur through the thermal resistance R ) . E quations 41) and 4  2 ) written for the sample (subscript s )
and the reference (subscript r) a r e : d h/dt = C S*dTS/dtdqS/dt 0 = C r * dTr/dtdqr/dt s ample
r eference sample
reference Combining equations 4(3a) and 4(3b) for the sample
and the reference: Combining equations 44a and 44b for the sample
and reference: P age  37 a nd differentiating equation 4  6 y ields Substitution of equation 4  7 A i nto equation 4  5 g ives r earrangement of equation 4  8 y ields It is assumed that the reference material generates no
energy (undergoes no phase transistions) and thus dh /dt
r = 0. T hus for a constant heating rate ( d T / dt) t he rate of energy
P
flow to or from the reference is constant ( dqr/dt =
2 c onstant) and therefore d q / dt
r 2 = 0 a nd d T / dt
P = d Tr/dt. R ewriting equation 49 w ith the latter restriction: . P a g e  38 ( CSC )
r s pecific heat difference between the  sample and reference material.
d T / dt
P r ate of change of the temperature of  the heat s ource/sink.
i s a thermal time constant which is  a m easure of the thermal response of the s a m p l e .
d qg/dt  r ate of change of heat flow between
the sample and the surroundings
through the thermal resistance R . d h/dt  r ate that energy is generated by the
sample while t h e s a m p l e is
undergoing a transition. 4 4 T ypical D S C C urves
A t ypical D S C curve is shown in Fig. 1 8 . P ositive excursions from the bas...
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This note was uploaded on 10/08/2009 for the course CME MAT E 630 taught by Professor Dr. during the Fall '09 term at University of Alberta.
 Fall '09
 Dr.

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