The absolute entropy of Ni_0.667Zr_0.333and Ni_0.333Zr_0.667amorphous alloys

Abstract

The heat capacities of amorphous and crystalline Ni 0.667 Zr 0.333 and Ni 0.333 Zr 0.667 alloys were measured in the temperature range from ∼12 K to the crystallization points for the former or to ∼900 K for the latter. The results together with the data on the thermodynamic properties of the Ni-Zr melt were used for the calculation of the absolute entropy of the amorphous alloys on the assumption that the entropies of a substance in undercooled liquid and glassy states coincide at the glass-transition point. The entropy and heat capacity of the amorphous alloys was found to exceed those of the crystalline ones. The residual entropy of Ni 0.333 Zr 0.667 and Ni 0.667 Zr 0.333 amorphous alloys at 0 K is, respectively, 2.7 ± 2.1 and 0.2 ± 1.7 J mol −1 K −1 , which is significantly below the residual entropy values typical for traditional oxide glasses (4-17 J mol −1 K −1 ). This points to a much higher degree of order in amorphous metallic alloys as compared to glassy oxides.

Structure-property relations characterizing the devitrification of Ni-Zr glassy alloy thin films

“…43 It follows that the differences observed between these local units of crystalline and amorphous phases would thereby distinguish them from each other. 44,45 The amorphous (disorder) to crystalline (order) transition consists of a reduction in residual entropy of the system, 46 with an increase in the extent of CSRO. MD simulations applied to the transformation of the as-deposited amorphous Ni-Zr alloy to the annealed crystalline Ni 7 Zr 2 alloy also showed an overall increase in the average coordination number as a result of annealing the system.…”

Thermodynamic Modeling of the Undercooled Liquid in the Ni–Zr System

“…29) There are numerous measurements of both latent heats of crystallization from the undercooled liquid. 27,[30][31][32][33][34][35] In the case of the Ni-Zr alloys, it is difficult to measure the glass transition temperature, which it was not detected on the DSC heating curve. 29,36) Altounian et al 34) have pointed out that higher heating rates are required to observe the glass transition because the enthalpy change of the transition is much smaller than that of the crystallization.…”

Application of CALPHAD Method for Predicting of Concentration Range of Amorphization of Transition Metals Melts

“…The prognosed concentration regions are shown in the figure as dark filled areas at 800 K. This temperature is selected in this work as a typical value of Tg, by considering the experimental data for transition metals based amorphous alloys. The known compositions of amorphous alloys [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] are also denoted in Fig. 1 as symbols.…”