The key difference between solidus and liquidus is that solidus temperature quantifies the temperature at which the substance becomes completely solidified, whereas liquidus temperature quantifies the temperature at which the substance becomes completely liquified.
The term solidus refers to the locus of temperatures below which a certain substance exists completely solid. Liquidus is the locus of temperatures above which a certain substance exists completely as a liquid.
CONTENTS
1. Overview and Key Difference
2. What is Solidus
3. What is Liquidus
4. Solidus and Liquidus in Tabular Form
5. Summary – Solidus vs Liquidus
What is Solidus?
The term solidus refers to the locus of temperatures below which a certain substance exists as complete solids. In other words, a solidus is the temperature range at which the substance occurs in a crystallized structure. A locus is a set of all the points whose locations satisfy or determine one or more specified conditions. A locus of temperature is a curve on a phase diagram. Typically, solidus temperature is abbreviated as Ts or Tsol. This temperature specifies the temperature below which the substance occurs in a completely solid state and also the minimum temperature at which a melt can co-exist with crystals in thermodynamic equilibrium. This term is very important in different fields such as chemistry, material science, and physics. Among other materials, metal alloys, ceramics, natural rocks, and minerals can be given as examples for solidus.
The solidus tends to quantify the temperature at which the melting of a substance initiates. However, at this point, the substance may or may not melt completely. This means the solidus is not always the melting point of that substance. This feature can be used as a distinction from liquidus.
The solidus is always either less than or equal to the liquidus. However, they might not coincide. We use the term “freezing range” to indicate the gap between solidus and liquidus. Within this gap, the substance tends to coincide in its solid and liquid phases and may look like a slurry.
Moreover, in eutectic mixtures, solidus and liquidus temperatures coincide at the eutectic point. At this point, the solid substance melts congruently.
What is Liquidus?
Liquidus is the locus of temperatures above which a certain substance exists completely as a liquid. The liquidus temperature is abbreviated as TL or Tliq. It is the maximum temperature at which crystals tend to co-exist with the melt in thermodynamic equilibrium. Mostly, the liquidus is useful for impure substances, including glasses, alloys, and rocks.
When considering temperatures above liquidus temperature, the material tends to be homogenous and liquid at equilibrium. Below this temperature locus, the substance tends to form more and more crystals in the melt, depending on the nature of the material. However, as an alternative method, we can get homogenous glasses from sufficiently fast cooling. This happens through the kinetic inhibition of the crystallization process.
In pure elements and compounds such as pure copper and pure water, the liquidus and solidus tend to be equal at the same temperature. In such cases, we can use the term “melting point”. However, for the impure substances such as honey, alloys, etc., we can see the broadening of melting point into a melting interval.
What is the Difference Between Solidus and Liquidus?
The term solidus refers to the locus of temperatures below which a certain substance exists as a complete solid. Liquidus is the locus of temperatures above which a certain substance exists completely as a liquid. The key difference between solidus and liquidus is that solidus temperature quantifies the temperature at which the substance becomes completely solidified, whereas liquidus temperature quantifies the temperature at which the substance becomes completely liquified.
The following table summarizes the difference between solidus and liquidus.
Summary – Solidus vs Liquidus
The terms solidus and liquidus are useful in many different fields, including chemistry, material science, and physics. The key difference between solidus and liquidus is that solidus temperature quantifies the temperature at which the substance becomes completely solidified, whereas liquidus temperature quantifies the temperature at which the substance becomes completely liquified.
Reference:
1. “Solidus.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “Cooling curve alloy” By Wizard191 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “SiO2 Li2O” (Public Domain) via Commons Wikimedia