Amorphous transformation

Lumpkin, G. R., Smith, K. L., Blackford, M. G., Giere, R. Williams, C. T. 19986. The crystal-line-amorphous transformation in natural zircono-lite evidence for long-term annealing. Materials Research Society Symposium Proceedings, 506, 215-222. 

Dennis JR, Hale EB (1978) Crystalline to amorphous transformation in ion-implanted silicon a composite model. JAppl Phys 49 1119-1127... 

Lumpkin GR, Smith KL, Blackford MG, Giere R, Williams CT (1998) The ciystalline-amorphous transformation in natural ziiconohte evidence for long-term annealing. Mater Res Soc Symp Proc 506 215-222... 

The potential of Eq. (1) with parameters determined in Refs. [10, 11] was thoroughly tested in computer simulations of silica polymorphs. In Ref. [10], the structural parameters and bulk modulus of cc-quartz, a-cristobalite, coesite, and stishovite obtained from molecular dynamics computer simulations were found to be in good agreement with the experimental data. The a to / structural phase transition of quartz at 850 K ha.s also been successfully reproduced [12]. The vibrational properties computed with the same potential for these four polymorphs of crystalline silica only approximately reproduce the experimental data [9]. Even better results were reported in Ref. [5] where parameters of the two-body potential Eq. (1) were taken from Ref. [11]. It was found that the calculated static structures of silica polymorphs are in excellent agreement with experiments. In particular, with the pressure - volume equation of state for a -quartz, cristobalite, and stishovite, the pressure-induced amorphization transformation in a -quartz and the thermally induced a — j3 transformation in cristobalite are well reproduced by the model. However, the calculated vibrational spectra were only in fair agreement with experiments. 

Table I. Temperature of Principal Amorphous Transformation for Various Crystalline Polymers...

Dynamic mechanical results for polypropylene crystal aggregates (40) grown at 60°C. from 0.1% xylene and for poly(1-butene) crystals (95) from a 2% Decalin solution have been obtained at temperatures from 210°K. For these specimens the peak caused by the principal amorphous transformation at 300°K. (103 c.p.s.) (64, 91) is greatly reduced while a loss maximum closer to the melting point is found at 390°K. (102 c.p.s.) for polypropylene and 340°-360°K. (102 c.p.s.) for poly(-l butene) these maxima are attributed to motion in the crystalline regions. 

Fig. 19 (a) Schematic representation of the reversible crystal-to-amorphous transformations in MOROF-1. Reprinted from ref 193, by permission fiom Macmillan Publishers Ltd Nature Materials. Copyright 2003. http //dx.doi.org/10.1038/nmat837. (b) Plot of Xu versus temperature for as-synthesized ( ) and evacuated (o) MOROF-1. The graph has been adapted from ref 63... 

We will consider three types of phase transformation (1) crystal —> crystal, (2) glass crystal, and (3) crystal -> amorphous. Transformations (1) and (2) are closely related to solidification from the melt and dissolution into a liquid. Solidification is a major theme in Chapter 29. There are two topics to address ... 

El-Eskandarany, M. S. Akoi, K Sumiyama, K. Suzuki, K. (1997). Cyclic Crystalline-Amorphous Transformations of Mechanically Alloyed Co7sTi25. Applied Physics Letters, Vol.70, No.l3, pp. 1679-1681. 

Lacks, D.J. (2000) First-order amorphous-amorphous transformation in silica. Phys. Rev. Lett. 84,4629-4632. 

C. Jaouen, J. Delafond, J.P. Riviere, Crystalline to amorphous transformation in NiAl ion irradiation studies in relation to cascade parameters, J. Phys. F Met. Phys. 17 (1987) 335-350. 

Except in the case of an amorphous transformation, the exponential term of the activation energy is usually small and can be considered constant if the temperature does not change much. It is estimated to be about 10 for TAGs [11]. 

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