# 16 t he principles of d sc a re derived from the

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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 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 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.

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