I have the DSC output file of a salt (that undergoes melting and solidification) which contains the time,and heat flow data.It can be converted to Enthalpy Vs time curve. How to do the same?
Dear Hakeem,
I normally use the following equation for DSC measurements of aqueous suspension of substances with the conc. of 1 mg/mL:
{K+[(Cp-BL)/V]}*M*0.004187
where K is the intrument constant, Cp - heat flow value for your sample, BL - heat flow value of pure solvent (if it is a solution), V - volume of sample cell, M - molar mass of substance, and 0.004187 is the factor for the conversion of cal to kJ.
Which DSC did you use?
Kind regards, Simon.
Since enthalpy represents the heat change during the phase transition, you cannot really generate an enthalpy vs time curve.
You can however generate a Cp vs time curve but it's interpretation needs to be thought through as Cp cannot be truly measured around a phase transition.
Convert the heat flow curve to a heat capacity (Cp) curve, which is in heat capacity units, though more correctly an apparent heat capacity, since it is not measured under equilibrium thermodynamic conditions. Cp is represented by the baseline region of the curve since during transitions an excess heat capacity or latent heat is superimposed.
The integral of the Cp curve is the enthalpy change (∆H) curve, since Cp=(dH/dT)p or incrementally: Cp=(∆H/∆T)p. Some DSC instruments offer a menu choice to convert data to ∆H. For measurement of glass transition temperature (Tg) the ∆H data can be linearly fitted and the lines above and below Tg intersect at Tg. The Cp (or heat flow) data, being a derivative of ∆H versus T, thus shows an inflection at Tg that is normally observed.
Dear All - Thanks for your inputs - Yes it is Cp Vs Time curve - I am attaching my DSC output file for your reference
Based on all three responses, it has to be remembered that before DSC measurement the instrument needs calibration for enthalpy and some instrument (specially old). If the instrument is calibrated then you have option and the software can change easily whatever you want either heat flow vs time ot enthalpy vs time.
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