What phase is formed when both liquid and solid coexist in a thermal equilibrium diagram?

In a thermal equilibrium diagram, when both liquid and solid exist together, they form what is referred to as the liquid + solid phase, commonly known as a pasty phase. This phase is characterized by the presence of both phases in equilibrium under specific temperature and pressure conditions.

In the context of phase diagrams, the region where solid and liquid coexist is usually identified as a two-phase region. When temperature and/or pressure conditions allow both states to exist, it indicates that a balance has been achieved between the solid and liquid states, with the possibility of phase transitions occurring if conditions change.

This allows for interactions between the solid and liquid, enabling properties such as flow and viscosity to be influenced by the proportions of each phase present. The pasty phase is particularly important in materials science and metallurgy, as it pertains to processes like casting, where the material can behave like a solid while exhibiting some fluid-like characteristics due to the liquid phase present.