Solid state amorphization

Phillpot, S.R., Yip, S., Okamoto, P.R. and Wolf, D. (1992) Role of interfaces in melting and solid-state amorphization, in Materials Interfaces Atomic-Level Structure and Properties, ed. Wolf, D. and Yip, S. (Chapman and Hall, London) p. 228. 

Either MA or MM processes drop under more general class of solid-state amorphization reactions, SSAR. Amorphization by irradiation of solids was observed yet in the era of study of materials for nuclear reactors. In 1962, Bloch [88] amorphized UgFe by exposing it to fluxes of nuclear fission fragments. Others obsawed amorphization... 

P.-Y. Lee, J.-L. Yang, Solid-State Amorphization in Ta-based alloy system by mechanical alloying technique, Mater. Sci. Eng.,... 

Stretchability denotes the suitability of a polymer in the solid state (amorphous or semicrystalline) to be stretched in one direction (occasionally in two directions). Of course, this processing step only serves a useful purpose in a specimen with a large aspect (i.e. length to diameter) ratio (fibres, films, sheets). The purpose of this operation generally is to achieve an improvement of mechanical properties, especially in the direction of stretching. 

Many aH NMR analyses have been carried out for molten- or solution-state of polyethylene to characterise the random-coil molecular chain.14,17,21 36-39 The relaxation evaluation for solid-state, amorphous polyethylene chains remain ambiguous because of the strong crystalline component that obscures the entanglement component in the amorphous phase. Perfect FID fitting in combination with TEM and SAXS was applied to evaluate the effects of prior concentration on amorphous chain characteristics. 

Because of their greater molecular mobility in the solid state, amorphous systems generally exhibit greater physical and chemical instability at any given temperature compared with their crystalline counterparts. 

A problem of solid state amorphism is an actual question of both fundamental and applied material science [1-3]. It is known that substances of the same chemical composition can form both crystalline and amorphous phases depending on the conditions of preparation and processing. Moreover, there are not only amorphous phases, which represent the class of non-crystalline solids. Glasses, semi-glasses, semiamorphous phases posses different properties which are still not clearly classified. The only reliable and strict criterion of crystallinity is occurrence of the translation symmetry (long order arrangement) in the structure of solids. 

First-order solid-state amorphization occurs due to an entropy catastrophe [39] causing melting of superheated graphite and decompressed diamond below Pg when the entropy of the ordered crystal would exceed the entropy of the disordered liquid. This condition is resolved with the occurrence of a kinetic transition to a (supercooled) glass whereby the exact kinetic conditions during carbon transformation will be critically Pg-depen-dent [39]. It is important to consider the crystal to liquid transition and the effect of a superheated crystal whereof the ultimate stability is determined by the equality of crystal and liquid entropies [40]. When this condition is met, a solid below its Pg will melt to an amorphous solid, particularly... 

Fecht, H.J. Defect-induced melting and solid-state amorphization. Nature 1992, 356, 133-135. 

Pikal, M. Chemistry in solid state amorphous matrices implication for biostbiliza-tion. Amorphous Food and Pharmaceutical Systems, H. Levine, ed.. Royal Soc. of Chemistry, London, pp. 252-272, 2002. 

It has been well known for a couple of decades that noncrystalline metallic alloys can be made by vapour- and melt-quenching. Recent results show that an amorphous phase can also be formed directly when a crystalline metallic alloy is subjected to various types of disordering processes. Solid-state amorphization can be induced through a variety of methods including absorption of atomic hydrogen, thermal interdiffusion reaction along the interface separating... 

The details of each timescale depend very much on the experimental situation. This will be discussed in Sect. 2.2 of this article. Here we give only some general remarks concerning the timescales r1 a and ra-.2 of the solid-state amorphization reaction. For the timescale TWa, we decide between an inhomogeneous reaction (e.g., multilayers of pure elements will form an amorphous interlayer) and the homogeneous transformation into the amorphous state, where the timescale t -, decreases to very low values due to the diffusionless transition. In the first case, the timescale for the amorphization of the entire sample is obviously determined by the diffusion process of one species... 

Table 2.5. Binary semiconductor/metal systems observed to exhibit solid-state amorphization by interdifiiision reactions. Type of experiment, typical reaction temperature (rR), maximum thickness of the amorphous layer (2f and references are listed. (S interdiffusion of polycrystalline metal with semiconductor single crystal, and A interdiffusion of amorphous semiconductor layers with polycrystalline metal)...

Relation Between Solid-State Amorphization and Melting... 

Solid-state amorphization can be induced through a variety of methods including irradiation, chemical reactions, mechanical-deformation techniques, pressure application, etc., as discussed above. As such, a crystalline phase can be driven into a disordered amorphous state as long as the kinetic constraints inhibiting stable phase formation can be maintained. 

B. Dorgin Kinetics of the Formation of an Amophous Layer during a Solid State Amorphization. Ph.D. Thesis, Dept, of Applied Physics Calif. Inst, of Tech., (1985) see also [8] for a description of interdiffusion reaction kinetics... 

---