lämpötilahysteresi

Lämpötilahysteresis, or temperature hysteresis, refers to the phenomenon where the property of a material or system depends not only on the current temperature but also on its thermal history. This means that the value of a property at a given temperature can be different depending on whether the temperature was reached by heating or cooling.

This effect is commonly observed in phase transitions, such as melting and solidification, or in magnetic materials. For instance, a substance might melt at a slightly higher temperature than the temperature at which it solidifies. This difference between the melting point and the freezing point is the hysteresis. Similarly, in ferromagnets, the magnetization may not retrace the exact same path when the temperature is increased and then decreased, exhibiting a magnetic hysteresis loop which is related to temperature changes.

The underlying cause of temperature hysteresis is often the presence of metastable states. These are states that are not the most energetically favorable but can persist for a period. The energy barriers preventing a system from reaching its equilibrium state need to be overcome, and the required energy might differ depending on the direction of temperature change. This can be due to factors like the formation of nucleation sites or internal stresses within the material. Understanding temperature hysteresis is crucial in applications where materials undergo thermal cycling, as it can affect their performance and reliability.