The Liquidus Temperature, TL or Tliq, is mostly used for glasses and alloys. It specifies the maximum temperature at which crystals can co-exist with the melt in thermodynamic equilibrium. Above the Liquidus Temperature the material is homogeneous. Below the Liquidus Temperature more and more crystals begin to form in the melt if one waits a sufficiently long time, depending on the material. However, even below the Liquidus Temperature homogeneous glasses can be obtained through sufficiently fast cooling, i.e., through kinetic inhibition of the crystallization process. The crystal phase that crystallizes first on cooling a substance to its Liquidus Temperature is termed primary crystalline phase or primary phase. The composition range within which the primary phase remains constant is known as primary crystalline phase field. The Liquidus Temperature is important in the glass industry because crystallization can cause severe problems during the glass melting and forming processes, and it also may lead to product failure. The liquidus temperature can be contrasted to the solidus temperature. The solidus temperature quantifies the point at which a material completely solidifies (crystallizes). The liquidus and solidus temperatures do not necessarily align or overlap; if a gap exists between the liquidus and solidus temperatures, then within that gap, the material consists of solid and liquid phases simultaneously (like a "slurry").
