The crystallization process is classified as an exothermic process, where heat is released and transported to the crystal and solution. Is it possible for this process to cause a slight increase in the solution temperature? Most of the temperature profiles during cooling crystallization didn't show a notch at a point where the crystallization happen. I also got the same trend. If some heat was released during the crystal formation, why an increment of temperature was not detected?
Study shows that- Crystal formation starts with first stage called as nuclei, the amount of energy required to under complete transformation until crystal get formed depends on cooling rate. Temperature variation is mostly get utilized in non uniform structure formation, generally leads to dendrites.
The main reason is the establishment of the steady state regime where the heat lost to the environment is compensating the heat injected to the system at the interface between the melt and the growing crystallites. At the very early stage of the crystallization process the transient regime dominates or appears which shows the local temperature variations more or less at the vicinity of the interface separating melt and solid phases. But this has very short duration depending upon the cooling rate, which is most control by the surrounding temperature (mold walls) and the heat conductivity of the growing crystal.
I some cases it does. There are many very violent exothermic reactions. It depends on the change in enthalpy, the rate of the process, the kinetic barriers, the thermal propertiez of the solution, etc.....
As Margules pointed, some systems have a strong exothermic process, but to observe it in cooling crystallization you must have a sow cooling rate: it is common practice that cooling rate is high enough to remove the heat of crystallization. But, in some processes, like zinc sulfate crystallization, the heat evolved is so high that changes the slope of the cooling curve
Thank you very much for the answers. I will try at different cooling rate and see the pattern.
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