Sulauspiste

Sulauspiste, in chemistry and materials science, is the temperature at which a solid substance changes into a liquid under a specified pressure, typically at standard ambient pressure (about 1 atm or 101.3 kPa). For a pure crystalline substance, the melting point is a well-defined temperature; for mixtures or impure samples, melting occurs over a range due to varying composition and crystal structure.

The melting point is influenced by pressure, impurities, and crystal form. While most solids have a relatively constant melting point near ambient pressure, impurities depress or broaden the transition, and different crystal forms (polymorphs) can have distinct melting points. In some substances, the melting behavior is accompanied by phase transitions or polymorphic changes before or during melting. In polymers and some inorganic compounds, the term fusion temperature is used to describe the melting transition, particularly for crystalline regions.

Common methods to determine sulauspiste include melting point apparatus, differential scanning calorimetry (DSC), differential thermal analysis (DTA), and hot-stage microscopy. These techniques measure the onset and completion of melting and can provide information about purity and crystallinity.

Examples of typical melting points at standard pressure include water ice near 0 °C, iron around 1538 °C, sodium chloride about 801 °C, and sulfur around 115 °C. Understanding sulauspiste is important in quality control, materials development, metallurgy, geology, and food science, where precise temperature control during heating or processing is required.