https://www.youtube.com/watch?v=Nqxjfp4Gi0k
The most useful resource I found while investigating phase change materials was the following paper which explores several different types of low temp salt based PCMs: https://www.researchgate.net/publicat... The key to reducing the melting point of a PCM is to make what is called a eutectic mixture ( https://en.wikipedia.org/wiki/Eutecti... ). In this case that is a mixture of two different hydrated salts. When the two come together the freezing point of both is lowered to a temperature which depends on the particular salts used and the ratio between them. Sodium sulfate and table salt (sodium chloride)
Ths is very similar to the Study on solidification process of sodium acetate trihydrate for seasonal solar thermal energy storage
sodium acetate hot ice packs.
Sodium acetate trihydrate (SAT) has a phase change temperature of 58°C (136°F),
