Phase-change material
A phase-change material stores and releases heat as it changes phase, allowing thermal energy to be absorbed or delivered near a chosen temperature.
What a phase-change material is
A phase-change material, often shortened to PCM, is a material chosen because it absorbs or releases a useful amount of heat while changing phase. Most practical examples use a solid-to-liquid and liquid-to-solid transition, but some systems use solid-solid transitions or higher-temperature phase changes.
Latent heat
When a PCM melts, it can absorb heat without a large rise in temperature. When it freezes, it releases that stored heat. This latent heat effect lets a PCM store more thermal energy in a narrow temperature band than many ordinary materials can store through temperature change alone.
Choosing the transition temperature
The phase-change temperature must match the job. A PCM for keeping a room comfortable may need to melt near indoor comfort temperatures. A PCM for electronics, refrigerated transport, solar thermal storage, or industrial heat recovery needs a different transition point.
Material families
Common PCM families include paraffin waxes, fatty acids, salt hydrates, molten salts, eutectic mixtures, and engineered composites. Organic PCMs can be stable and noncorrosive but may be flammable. Salt hydrates can offer high storage density but may suffer from supercooling, corrosion, or phase separation.
Encapsulation and heat transfer
Because many PCMs become liquid during use, they often need containers, capsules, porous supports, or composite structures. Designers also add fins, graphite, metal foams, heat exchangers, or conductive fillers when heat must move into and out of the material quickly.
Where PCMs are used
Phase-change materials appear in thermal energy storage, building wallboards, heat-pump systems, cold packs, vaccine and food transport, electronics cooling, textiles, solar thermal systems, and industrial process heat. The same principle can serve either heating or cooling depending on the temperature range.
Limits and safety
PCMs are not magic thermal batteries. A poor match between material, temperature, power rate, container, and duty cycle can make storage ineffective. Designers must also consider flammability, corrosion, leakage, volume change, cycling life, toxicity, cost, fire codes, and end-of-life handling.
Why it matters
Phase-change materials can shift heating and cooling loads in time, reduce peak demand, smooth temperature swings, and help use renewable electricity or waste heat more effectively. They are one way to make thermal energy storage denser and more useful in buildings, industry, transport, and devices.