Bulk and surface properties of liquid Ga–Tl and Zn–Cd alloys

Abstract

A simple thermodynamic model, based on the formation of self-associates, has been used to correlate the bulk and surface properties of mixing of liquid Ga–Tl and Zn–Cd alloys at temperatures of 973K and 900K, respectively. The model enables us to explain the positive deviation of the properties of mixing of the two liquid alloys from the ideal solution behavior. Our calculations indicate that the degree of phase separation in Zn–Cd, as measured using the Warren–Cowley short-range order parameter, is less than that in Ga–Tl. With regards to the surface, we show that the surface decomposition in Zn–Cd liquid alloys is greater than in Ga–Tl. We explain the contrast in the bulk and surface properties in terms of the possible roles of the entropic and enthalpic effects on the properties of mixing.

Temperature dependence of the bulk and surface properties of liquid Zn–Cd alloys

“…Although, in these figures, due to lack of experimental data, it is not possible to compare computed and experimental results, however, in Fig. 5, the results obtained at 800 and 900 K are in agreement with that reported in [4,9] (where at 800 K, the tendency for phase separation is maximum around equiatomic composition, and at 900 K, minimum diffusivity is 0.4 at C Zn ¼ 0:56). Thus, these agreements serve as evidence of the reliability of the following observations in Fig.…”

“…In the figure, we observed that at all temperatures, S cc ð0Þ [ S cc ð0; idÞ. This is an indication that Zn-Cd liquid alloys are homocoordinated (in agreement with the reports in [4,7,9]), and that the homocoordination which is weak is indicated by the relatively low peak at various temperatures, when compared with strongly homocoordinated alloys like Ga-Tl liquid alloys [9]. The figure also show that, when the temperature is increased, the position of maximum S cc ð0Þ shifts towards equiatomic composition, the values of S cc ð0Þ at all composition of Zn approach that of ideal solution (in agreement with the report in [7], from the study of experimental thermodynamic activity of Zn-Cd alloys at 800 and 900 K) and becomes nearly symmetrical about equiatomic composition (in agreement with the reports in [6,7]).…”

“…5. the change in temperature led to as much as 35.2% decrease in the magnitude of a 1 (i.e.when C Zn ¼ 0:81, a 1 ¼ 0.0671 at 743 K, while a 1 ¼ 0:0435 at 900 K). 6. that at all temperatures, the maximum magnitude of a 1 is though positive, but much less than unity is an indication that Zn-Cd liquid alloys are weak homocoordinated alloys, and this is in agreement with the reports in [4,9].…”

“…Also, it is worth noting that, as a result of lack of experimental data, which is the case with many metallic solutions (possibly due to reported experimental difficulties associated with measuring surface tension [4,15]), we can not compare computed and experimental results (the only experimental surface properties data of Zn-Cd liquid alloys we found in literature [47] is at 730 K, which is outside the temperatures of interest). However, we are of the opinion that since the model we employed has been used by many researchers successfully to compute surface properties [4,9,14,23,30], the results obtained in Figs. 7 and 8 are reliable.…”

“…To investigate the temperature dependence of the bulk properties of Zn-Cd liquid alloys, we opted for the self association model (SAM) [11] reputed for being an excellent theoretical recipe for calculating the thermodynamic properties of demixing binary liquid alloys, knowing that Zn-Cd system belongs to this group [9,[11][12][13][14][15], as it indicates its simple, eutectic type phase diagram [16,17]. A combination of the popular Darken's equation [18] and an empirical formalism for viscosity and diffusion coefficient of Singh and Sommer in [19] are employed in our study of the effects of temperature on the transport or dynamic properties.…”