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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 4-1) and 4 - 2 ) written for the sample (subscript s )
and the reference (subscript r) a r e : d h/dt = C S*dTS/dt-dqS/dt 0 = C r * dTr/dt-dqr/dt s ample
r eference sample
reference Combining equations 4-(3a) and 4-(3b) for the sample
and the reference: Combining equations 4-4a and 4-4b 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
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 e-writing equation 4-9 w ith the latter restriction: . P a g e - 38- ( CS-C )
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