I want to determine the latent heat enthalpy and melting point of natural Beeswax in order to develop an iso-thermal heat block system (620C - 640C). The TGA-DSC measurement for the off-shelf beeswax showed a linear increasing relationship on Q Vs T.
What could be the potential source for this linear increment deviating from the flat/baseline? Can the deviation be attributed from the instrument calibration fault or sample? such as long calibration of DSC - thermal drift - or sample's property such as thermal conductivity linearly increase with temperature or impurities?
#DSC #Phase_Change_Material, #TGA, #Theramal Conductivity #Enthalpy #Materials_sceince
Dear Dan,
Thank you so much.
Accordingly, I attempted to determine slopes for different regimes of the curve using Origin. As attached here, the values varied up to 65%. Hopefully, the dispersion in the values may narrow by further refining /purifying the natural beeswax into its constituent .
One question: Can I calculate the latent heat of fusion from this curve or associated ASCII data? The data contains columns of Time (min), Temperature (°C), Weight (mg), Heat Flow (mW), Temperature Difference (°C), Temperature Difference (µV) and Sample Purge Flow (mL/min)
Thanks indeed,
Brook
The slope using these curves does not reflect the Cp, you should follow the protocol given by the DSC! for the latent heat determination you can do this directly on the DSC plot, but pay attention: the melting and crystallization for this material is too broad, the choice of the onset and the end may be critical...
Sorry for not being clear. I was intending to explain the (linear) relationship between Q and T. Zakariaa is correct that the slope is not Cp. Cp can be calculated by dividing the heat flow by the heating rate. As the heat capacity typically change with temperature, that is why you see the change in Q with T. But I am not sure why your curves seem quite steep, it may be just because the way you plot the data or other factors could play a role as well. To estimate the melting enthalpy, you need to properly determine the baseline and then integrate under the curve. It seems like the crystallization and melting peaks are not very well-defined. This could be due to the nature of the materials or it could be due to the instrument calibration. Make sure the setup is well calibrated. Also maybe you can try to increase the amount of materials used to reduce the signal to noise. Or run modulated DSC to check if there is any kinetic factor playing important roles here. Hope this helps.
Dear Dan,
Before you evaluate the curve, make sure you run for the blank sample as well so that it can be subtracted with your sample curve. Sometimes it helps a lot. If you are focusing for the DSC curve, you may use stand alone DSC instrument. Sometimes you might not be seeing any slope or peak if you are using TGA/DSC instrument like STA6000 (Perkin Elmer), TGA/DSC 1 (Mettler Toledo), etc. Good luck!
Dears Dan, Zakariaa and Fareezex
Thank very much you for the valuable highlights. It helped me a lot. Today, I took the second measurement and obtained the baseline: run similar protocol as before except here the two alumina pans were empty. As Dan pointed it out, in this case too, the measurement exhibited steep slope. I suppose the instrument has some kind of linear drift with increasing temperature. Can this data somehow be used to correct the drift in the sample data?
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