[Seepy]

I'm doing an experiment to create microfractures in rock like structures using temperature. I am looking at possibly using gypsum (similar to plaster of Paris) as a synthetic rock.

Gypsum has a chemical structure of CaSO₄.1/2H₂O. I am worried that this attached water molecule is capable of expanding when I freeze the sample hence creating the wrong type of fracture. Is this what will actually happen or will the expansion of water not happen as it is now bonded to the Calcium Sulfate?

Thanks

[Hunter2]

This water is not liquid or ice, its built in the molecules of Gypsum. So nothing will happen.

[Seepy]

Brilliant! Thank You

[marty63]

I don't know much about the chemistry of it but from practical experience plaster of paris is one of the few casting materials that actually expands as it sets. Which is why it makes such a great thing to cast with because it reproduces the surface detail due to this expansion into the mould as it sets. I think that it is due to part of the water added becoming bound into the plaster as the waters of crystallisation.