Hello,

Look, what I think is you shouldn't just depend on previous research papers, the results obtained by them ane yours can be different as the condition where experiment had been conducted can be different. Also the material i.e. nitrate salt selected could be manufactured in a different process, under different conditions that will directly affect the quality of PCM you are using. I suggest you to thoroughly go through the research paper you have referred and try to find the conditions and perform the test once again.

I hope this may help you.

The crystallization temperature is not a material constant and depends on many factors. Appart from the experimental setup (heating rate, DSC type etc.) Tcr also strongly depends on sample purity.

In your DSC measurement, the crystallization takes place from undercooled liquid, which is a metastable state of matter with higher Gibbs energy than the corresponding solid.

In fact, the undercooling (that is, "distance" of Tcr from the equilibrium melting point) is the driving force of crystallization which is thermodynamically unfavorable process with negative entropy change.

From your DSC records it seems to me that 240°C is way too close to the melting point (low undercooling). It does not mean that crystallization cannot occur, however, it would need much longer time at such high temperature (so called "anti-Arrhenius" behavior).

Melting or solidificatio, crystalization piints are a materials parameter and directly related to the materials structur, with other related parameters are constant. There may be a change of structure during heating or cooling but the freezing and melting points remain the same. However there are restrictions for the process of heating and coolin, for example a fast cooling may create a costitutional supercooling process and show the freezing point looks like at a lower temperature. So to detect the actual freezing point you should be aware in cooling temperature rate and other related process parameters

for details I suggest to see the following book

The Art and Science of Growing Crystals. J. J. Gilman, Ed. Wiley, New York, 1963. x + 493 pp. Illus.

Perhaps of some interest to your query: https://www.researchgate.net/post/DSC_onset_temperature_salt-mixture

As mentioned by Tibor Dubaj, one probability is the purity of your sample. Obviously, the melting and solidification temperatures depend upon purity of the materials. Another very important factor is heating and cooling rate? If your instrument can be operated in different cooling rate after melting, try that. Otherwise, the solidification temperature mentioned in the literature may be recorded in a very low cooling rate as compared to your one.