Can someone please guide me on how to measure the specific heat of a liquid and powder samples by using SETARAM ABSYS evo or SETARAM micro-DSC? The tests are to be conducted in the temperature range of 20oC to 80oC.
Thanks in advance
Hi,
The easiest way is the sapphire method, if you have a sapphire standard available. I've attached an application note as well as literature Cp values for sapphire.
good luck
I agree that the sapphire standard method is the best approach. It is also literature standard. Be sure to run a pan blank. Make sure the pans are good and flat on the bottom.
For the general procedure of cp measurement, please read the conference paper attached.
For liquids, it is important to ensure that the vessel has little head space and a vapor-tight seal if it is likely they will have an appreciable vapor pressure at the high end of the temperature. Setaram offers single-use high pressure crucibles for use with very high pressure - and for lower pressures, their standard gas-tight crucibles should work.
Regarding Cp determination in general with your instruments: The other respondants have excellent answers for planar DSC systems (such as the LABSYS evo without the Cp rod - the Cp rod is similar to the Tian-Calvet principle with a few modifications and if you have it I will connect you with some of my friends from SETARAM who can provide a more detailed response on the theory and operation of the Cp rod).
However, the responses misunderstand the unique nature of your Setaram instrument. The SETARAM MicroSC is not based on the traditional planar DSC method, but rather on a 3-dimensional calorimetry method known as the Tian-Calvet (sometimes just called Calvet) method. The Tian-Calvet method is very different, both in principle and in practice, from typical DSC methods - in general, it offers higher sensitivity to small heat effects (such as Cp) and is able to be directly calibrated by the Joule effect rather than calibrating relative to characterized standards, which substantially reduces the error associated with calibration that traditional planar DSCs experience.
The Tian-Calvet method does require a blank to be run to eliminate the baseline, but it is possible to calibrate directly using the Joule effect (the product literature should describe the Joule effect calibration). Furthermore, the Joule effect calibration is independent of gas atmosphere, pressure, and flow rate, as it does not need to compensate for changes in heat loss owing to radiation and convection the way a planar DSC does - this is because the 3D sensors completely surround the sample and reference, resulting in up to 95% of the heat transfer in the system being observable by the sensor (as opposed to ~20%-30% in a planar DSC, as 70%-80%, depending on gas flow rate and temperature, is transmitted via convection and radiation, as opposed to conduction to the temperature sensor). The added sensitivity of the Tian-Calvet method to heat transfer in the system results in a highly accurate method of Cp determination, without the need to measure relative to an external standard such as sapphire (although sapphire may be used as a reference to validate the method).
Therefore, in your special case, I would instead recommend that you calibrate your microSC with the Joule effect device, run your blank, and then run the Cp run at a relatively high rate of ramp for the instrument (the highest it can do is 2°C/min, so that is what I would suggest).
If you would like some more information on the Tian-Calvet method, Calvet produced a book on his method, called "Recent Advances in Microcalorimetry" - there have been significant technical improvements in equipment since then, but it describes the principles of the method quite well. It is available both in the original French and it was translated to English in the early 80s. It is a remarkably straightforward, clear, and enjoyable read in either language, in addition to being extremely informative.
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