Stability of amorphous alloy

As we will see in the next section, a relative low melting temperature is indeed favourable for glass formation. Since the Nagel and Tauc model has mainly been used to describe the stability of amorphous alloys we will treat this model in more detail in section 4. 

From these results it can be concluded that any favourable (2kp= Q ) or unfavourable (2kp Q ) influence on E, even if it were of the order of AH, would have little effect on the magnitude of AE. This means that the Nagel and Tauc criterion is less suited for describing thermal stability of amorphous alloys, i.e. their resistance against crystallization. As briefly indicated above, it is mainly the transformation kinetics that governs the thermal stability of amorphous alloys. A description of the kinetic approach to thermal stability will be presented in the following section. 

In the kinetic approach to thermal stability of amorphous alloys the rate of transformation is assumed to be diffusion-controlled (Uhlman, 1972 Davies, 1976 Takayama, 1976). Atomic motion is expected in all alloys to set in at a temperature where the viscosity ij reaches a critical value (about 10 P). In terms of entropy theory of viscous flow as proposed by Adam and Gibbs (1965) this latter quantity can be given by... 

The particular position taken by alloys for which 2kp = was already mentioned in connection with the Nagel and Tauc criterion discussed in sections 3.1 and 4.2. In the latter section we showed that the Nagel and Tauc criterion is less suited for describing the thermal stability of amorphous alloys. In the former section the possibility was discussed that amorphous alloys for which the criterion 2kp is satisfied may be amenable to easy glass formation owing to the presence of an enhancement of the deepness of the eutectic. 

Minic D.M. (2006). Synthesis, Characterization and Stability of Amorphous Alloys, Science of Sintering, Vol. 38, pp. 83-92 0350-820x... 

Thermodynamics of the stability of amorphous alloys of two transition metals. Journal of Less-Common Metetals, Vol. 140, No. 1/2, (June 1988), pp. 307-316, ISSN 0925-8388... 

The stability problem seems to be receding as more glassy metals are examined under reaction conditions and some are found to be remarkably stable. However, too little information about the factors determining the stability of glassy materials under reaction conditions is still available. There are methods, however, suitable for improving the thermal stability of amorphous materials. Alloying of properly selected components can result in glassy alloys with improved thermal stability or increased activity, which permit low-temperature application. 

Copper-based amorphous alloys also proved to be active in the oxidation of formaldehyde (108,109). As it was reported earlier in connection with the hydrogen evolution reaction (62) (see Section III,A,1), HF treatment leads to the formation of a copper-rich porous surface layer. As a result, electrodes with very high electrocatalytic activity for anodic formaldehyde oxidation could be prepared. It was found that the rate-determining step is a one-electron transfer and the oxidation proceeds via the hydroxymethanolate ion HOCH2O". However, it is not clear whether the catalytically active copper species is Cu° or Cu+. It would be interesting if either Cu° or Cu+ could be stabilized in amorphous alloys. 

Models exist that describe the thermal stability Tx in terms of transformation rates (kinetic approach), where Tx is proportional to AE. In these cases AE is estimated on the basis of a weighted mean sublimation energy of the constituent elements (Davies 1976) or the heat of compound formation (Kiibler et al. 1981) or the formation enthalpy AHh of a hole of size equivalent to the smaller type of atom (Buschow 1982). Of these possibilities the latter appears to be the most promising for predicting the thermal stability of a large variety of amorphous alloys. 

Takeuchi, A. Inoue, A. (2001). Calculations of Amorphous-Forming Composition Range for Ternary Alloy Systems and Analyses of Stabilization of Amorphous Phase and Amorphous-Forming Ability. Materials Transactions JIM, Vol, 42, No. 7 G ly 2001) 1435-1444, ISSN 0916-1821... 

It Is well established that the thermal stability of amorphous CuTl hydrides is much less than that of the corresponding non-hydrogenated amorphous alloys or crystalline hydrides example, a-CuTiH 43 ... 

Che] Chen, Jin-Chang., Shen, Bao-Gen., Zhan, Wen-Shan., Zhao, Jian-Gao., Effect of W Addition on Magnetic, Electric Properties and Thermal Stability of Amorphous Fe-B Alloys , Acta Phys.,Sin., 35(8) 979-88 (1986) (Experimental, Magn. Prop., Electr. Prop., 20)... 

The following mechanisms in corrosion behavior have been affected by implantation and have been reviewed (119) (/) expansion of the passive range of potential, (2) enhancement of resistance to localized breakdown of passive film, (J) formation of amorphous surface alloy to eliminate grain boundaries and stabilize an amorphous passive film, (4) shift open circuit (corrosion) potential into passive range of potential, (5) reduce/eliminate attack at second-phase particles, and (6) inhibit cathodic kinetics. 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

The glass stability of the Pd-Ni-P system is wider than that of the Pd-Cu-P system. For most bulk Pd-Ni-P glasses (10-mm diameter), AT> 90 K. The AT values of bulk amorphous Pd-Cu-P alloys are considerably smaller, ranging from 27 to 73 K. 

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