pressurethat

Pressurethat, often written as pressurethat, is a theoretical term used to denote the threshold pressure at which a predefined transformation or response occurs in a material or system under specified thermodynamic conditions. The concept emphasizes that the onset of a change depends on the chosen observable and the experimental protocol, and is therefore context-specific rather than a universal constant. The term combines pressure with threshold to highlight the requisite pressure value that triggers a process.

In practice, pressurethat is determined by conducting controlled-pressure experiments at a fixed temperature and recording the pressure at which the observable criterion is met—for example the onset of amorphization, a sharp change in conductivity, or the appearance of a new phase. Because the measured value can depend on the rate of pressure application, sample geometry, confinement, and boundary conditions, the pressurethat definition must specify the observable and the detection criterion.

Pressurethat is related to, but distinct from, standard concepts such as critical pressure or yield strength. It serves as a practical descriptor for when a process begins, rather than a single material property, and is used to compare onset conditions across systems in fields like high-pressure physics, materials science, and geoscience.

Limitations include ambiguity in choosing observables and potential hysteresis between loading and unloading. See also threshold pressure, phase transition, critical pressure, and yield.