Editing Hysteresis (section)

===Adsorption hysteresis===
Hysteresis can also occur during physical [[adsorption]] processes. In this type of hysteresis, the quantity adsorbed is different when gas is being added than it is when being removed. The specific causes of adsorption hysteresis are still an active area of research, but it is linked to differences in the nucleation and evaporation mechanisms inside mesopores. These mechanisms are further complicated by effects such as [[cavitation]] and pore blocking.

In physical adsorption, hysteresis is evidence of [[mesoporosity]]-indeed, the definition of mesopores (2–50&nbsp;nm) is associated with the appearance (50&nbsp;nm) and disappearance (2&nbsp;nm) of mesoporosity in nitrogen adsorption isotherms as a function of Kelvin radius.<ref>{{cite book|last1=Gregg |first1=S. J. |last2=Sing |first2=Kenneth S. W. |title=Adsorption, Surface Area, and Porosity|edition=Second|location=London|publisher=[[Academic Press]]|year=1982 |isbn=978-0-12-300956-2}}</ref> An adsorption isotherm showing hysteresis is said to be of Type IV (for a wetting adsorbate) or Type V (for a non-wetting adsorbate), and hysteresis loops themselves are classified according to how symmetric the loop is.<ref>{{cite journal|first1=K. S. W. |last1=Sing |first2=D. H.  |last2=Everett |first3=R. A. W. |last3=Haul |first4=L. |last4=Moscou |first5=R. A. |last5=Pierotti |first6=J. |last6=J. Roquérol |first7=T. |last7=Siemieniewska |journal=[[Pure and Applied Chemistry]] |volume=57|issue=4 |pages=603&ndash;619|year=1985|doi=10.1351/pac198557040603|title=Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)|s2cid=14894781 |doi-access=free }}</ref> Adsorption hysteresis loops also have the unusual property that it is possible to scan within a hysteresis loop by reversing the direction of adsorption while on a point on the loop. The resulting scans are called "crossing", "converging", or "returning", depending on the shape of the isotherm at this point.<ref>{{cite journal|first1=G. A. |last1=Tompsett  |first2=L. |last2=Krogh |first3=D. W. |last3=Griffin |first4=W. C. |last4=Conner |journal=[[Langmuir (journal)|Langmuir]] |volume=21|issue=8|pages=8214&ndash;8225|year=2005|pmid=16114924|doi=10.1021/la050068y|title=Hysteresis and Scanning Behavior of Mesoporous Molecular Sieves}}</ref>