Metastable amorphous state

A summary in the form of a diagram of metastable amorphous states is depicted in Fig. 13, in which the upstroke-downstroke hysteresis has been averaged out. The vertical arrow represents the pressure annealing from... 

The extensively studied (especially during the recent years) transitions of solids from the metastable amorphous state to the polycrystalline state (see ref. 58 and the references therein) are of autowave character and resemble very much the above regimes of solid-state cryochemical reactions. The action of autodispersion, which facilitates phase transition by allowing it to proceed on the surface of a fracture instead of in the glass volume, cannot be excluded in the case of those processes either. Actually, the two classes of processes are similar in their physical nature both are connected with rearrangement of the solid matrix and are of exothermic character, differing only in the extent of the thermal effect. It should be added that fracturing and autodispersion of the sample are very typical of the autowave destruction of amorphous states and can be seen even by the unaided eye. 

Many foods contain biopolymers and low molecular weight carbohydrates. These can be present in a metastable amorphous state that is sensitive to temperature and the state... 

In summary it was the aim of this lecture to discuss a new mechanism without rapid quenching which produces amorphous metals by solid state reactions. All parameter known so far summarize in the critical condition to be fast enough for the competing crystalline phases. The main subject was on the gas-crystal reaction were an interface limited process is expected for the reaction kinetic. This remains one on the vice versa case of the polymorphic crystallization of some metallic glasses. Pure metallic diffusion couples seem to exhibit a /t-law for the growth of the planar amorphous layers at least for longer times. This case comes close to the eutectic crystallization in the reverse subject. All amorphization processes lead into the same metastable amorphous state, which is far from being only a "frozen in" liquid. Solid state reactions are just a new way into the same minimum. 

Since polymer chains are largely immobilized below Tg, if they are cooled rapidly through T to below Tg, it is sometimes possible to obtain a metastable amorphous state in polymers which at equilibrium would be crystalline. As long as the material is held below Tg, this metastable amorphous state will persist indefinitely. When annealed above Tg and below T ,), the polymer will crystallize, as the chains gain the mobility necessary to pack into a lattice. 

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