Heating-cooling hysteresis

The phenomenon of hysteresis is encountered in many areas of physics. It is associated with the delay of the dynamic response of cooperative systems to external perturbation. During a heating-cooling process in a system, thermal hysteresis (TH) commonly appears accompanying phase transitions. In particular, it is regarded as a signature of the first-order phase transition. But, the TH is less known than the magnetic hysteresis (MH), which is another type... 

Fig. 9.1. Various types of spin transitions (a) smooth or abrupt (b) incomplete at low or high temperature (c) with hysteresis on heating/cooling (d) two-step spin transition.

It was reported [8] that the first temperature cycle (a heating/cooling loop) may be irreproducible. A better reproducibility of the hysteresis curve is achieved after several temperature cycles. 

Figure 11 Hysteresis behavior observed on methane combustion activity on PdlAfOj during a heating cooling cycle (After ref 98)...

Hysteresis, the effect of the heating/cooling rate on the phase diagram [210] Chemically crossUnked hydrogel shrinks upon heating [207] Tip = 62°C [210] = 78.2°C [213]... 

From differential scanning calorimetric measurements a marked cooling-heating cycle hysteresis has been observed, showing that water encapsulated in AOT reversed micelles is only partially freezable and that the freezable fraction displays marked supercooling behavior as a consequence of the very small size of the micellar core. The nonfreezable fraction has been identified as the water hydrating the AOT ionic heads [56,57]. 

The transformation is beHeved to occur by a diffusionless shear process (83). It is often referred to as martensitic transformation, having a thermal hysteresis between the cooling and heating cycles. The transformation is dependent on particle size finer particles transforming at a lower temperature than... 

Expansion and contraction of siUca gel monoliths show hysteresis upon heating and cooling. As long as the sample was cycled below approximately 500°C, there was no hysteresis and the monolith was thermally stable (6,23). 

Differential scanning calorimetry measurements have shown a marked cooling/heat-ing cycle hysteresis and that water entrapped in AOT-reversed micelles is only partially freezable. Moreover, the freezable fraction displays strong supercooling behavior as an effect of the very small size of the aqueous micellar core. The nonfreezable water fraction has been recognized as the water located at the water/surfactant interface engaged in solvation of the surfactant head groups [97,98]. 

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