Melting
Phase transition from solid to liquid at melting point.
Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point. At the melting point, the ordering of ions or molecules in the solid breaks down to a less ordered state, and the solid melts to become a liquid. From a thermodynamics point of view, at the melting point the change in Gibbs free energy of the substances is zero, but there are non-zero changes in the enthalpy and the entropy, known respectively as the enthalpy of fusion and the entropy of fusion. Melting is therefore classified as a first-order phase transition.
- Type
- Physical process
- Also known as
- Fusion
- Classification
- First-order phase transition
- Key criteria
- Lindemann criterion, Born criterion, configuron percolation theory
Lore & Background
Melting occurs when the Gibbs free energy of the liquid becomes lower than that of the solid for a given material, with the temperature dependent on ambient pressure. Among theoretical criteria, the Lindemann criterion states that melting results from vibrational instability when the average amplitude of atomic vibrations exceeds a threshold relative to interatomic distances. The Born criterion is based on a rigidity catastrophe caused by the vanishing elastic shear modulus. Another criterion, based on configuron percolation theory, accounts for the mobility of broken chemical bonds in materials.
Reader's Guide
Melting is a fundamental phase transition central to materials science, thermodynamics, and condensed matter physics. Its study provides insight into the behavior of solids and liquids under varying temperature and pressure. The Lindemann and Born criteria offer theoretical frameworks for predicting melting conditions, while configuron percolation theory explains the role of bond breaking and mobility. Exceptions such as the negative enthalpy of fusion in low-temperature helium and the anomalous viscosity increase in sulfur highlight the complexity of melting behavior. Understanding melting is essential for applications ranging from metallurgy to cryogenics, and phenomena such as supercooling and glass formation illustrate the nuanced conditions under which melting and freezing occur.
Did You Know?
- Helium-3 has a negative enthalpy of fusion at temperatures below 0.3 K, meaning heat must be removed to melt it.
- Water on a very clean glass surface can supercool several degrees below freezing without nucleation.
- In ultrashort pulse physics, nonthermal melting can occur due to changes in interatomic potential from electron excitation, not from increased atomic kinetic energy.
Frequently Asked Questions
Who is Melting?
Melting, also called fusion, is the first-order phase transition in which a solid substance converts into a liquid. It occurs once enough thermal energy has been supplied to push the material past its melting point.
What are Melting's powers and role?
Melting dismantles the ordered lattice of ions or molecules in a solid and reorganizes them into a less-ordered liquid arrangement. Thermodynamically, it marks the point where the Gibbs free-energy difference between the two phases vanishes, even though entropy and enthalpy still change.
How does Melting's story end?
The process concludes the moment the last portion of solid has become liquid at the melting point. Past that temperature the substance simply warms as a liquid rather than undergoing any further phase change.
Why is Melting important to the canon?
As a textbook first-order phase transition, Melting is the go-to example for illustrating latent heat, Gibbs free-energy equality, and two-phase coexistence. It also anchors several key theoretical benchmarks, including the Lindemann criterion, the Born criterion, and configuron percolation theory.
What triggers Melting to act?
Melting is set in motion when heat or pressure raises the solid's internal energy until its temperature hits the melting point. At that threshold the crystal lattice can no longer sustain long-range order, and the material flows as a liquid.
More in Thermodynamics And Statistical Mechanics 1-22
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record