Question

Two other materials whose phase diagram has negative slope other than water ?

Answer 1

When evaluating the phase diagram, it is worth noting that the solid-liquid phase boundary in the phase diagram of most substances has a positive slope. This is due to the solid phase having a higher density than the liquid, so that increasing the pressure increases the melting temperature. However, the solid-liquid phase boundary for water is anomalous, in that it has a negative slope. This reflects the fact that ice is lower in density than liquid water (a well-known fact: ice floats), unlike most other substances which typically have denser solid phases.

But some materials have higher density in liquid form the solid form and some of the example of these are

1) CO₂

and

Element____Solid Density____Liquid Density____Melting Temp.
___________(g/cc) __________(g/cc)__________Celsius

Arsenic______4.70 ___________5.22___________817
Bismuth______9.80 __________10.07___________271
Gallium_______5.90 ___________6.09____________30
Germanium____5.32 ___________5.60___________940
Silicon________2.33___________2.51__________1410

So you can choose any of the two example for the answer thank you