Does water expand on freezing more than any other known substance?

Several substances expand on freezing. Gallium expands [3.1%](https://www.newworldencyclopedia.org/entry/Gallium) and bismuth [3.3%](https://en.wikipedia.org/wiki/Bismuth). However, both of these are much less than water which expands [9%](http://www.iapws.org/faq1/freeze.html). Is there any substance that expands more than 9% on freezing?


We can generalize this question to any system at thermodynamic equilibrium and constant pressure. Density normally decreases with temperature, but sometimes increases. For example, heating [plutonium](https://en.wikipedia.org/wiki/Plutonium) increases it's density in three places: a solid-solid phase transition, a negative thermal expansion, and melting. These effects combine to make the density increase about 5% between ~320C to 640C, which is still less than cooling 4C water to -0.01C ice.


If we allow substances that dissolve/precipitate and reversible chemical reactions can we beat water? We do not allow super-cooling or super-saturation since that isn't thermodynamic equilibrium.




Silicon beats it.


Silicon has the familiar diamond-type semiconductor only when solid, and like the hydrogen-bonded structure of water ice the directional bonding adds volume to the solid phase. Melted silicon collapses to a structure more typical of a liquid metal, including its electrical conductivity.


[Wikipedia](https://en.wikipedia.org/wiki/Silicon) reports the density of solid silicon at room temperature and the liquid at the melting point:


Solid at room temperature: 2329 kg/m³


Liquid at melting point: 2570 kg/m³


Thus the solid at room temperature has 10.3% more volume than the liquid at the melting point ... with the thermal contraction from melting point to room temperature included.


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