Reevaluation of the activity of arsenic in molten copper
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Reevaluation of the Activity of Arsenic in Molten Copper D.M. DABBS and D. C. LYNCH The activity of As in molten copper was recently reviewed by Lynch. ~ In that investigation the selected values for the sublimation of elemental arsenic to As4, As3, As2, and As were taken from Hultgren's compilation. 2 R. H. Lamoreaux has pointed out that the primary value in that reference for the heat of the reaction: ~As4(g) = ~As2(g) 1
[1]
is too large. 3 Lamoreaux further notes that the error appears to be related to the small condensation coefficient for Asa(g), which results in longer residence times for that species in the mass spectrometer ionization chamber. The small condensation coefficient leads to erroneously high As~ ion intensities, unless remedial measures are taken. The heats of sublimation for As4 and As2 vapor in Table I are those recommended by l.amoreaux. 3 These values are in agreement with the experimental work conducted by Rau; 4 Murray, Pupp, and Pottie; 5 and Drowart, Smoes, and Vanderauwera-Mahieu. 6 The heats of sublimation for As and As3 vapor in Table I have been calculated from data in the literature and the new heats of sublimation for ASh and As2 vapor. The data in the literature for these calculations are from a single source for each specie. Thus, the certainty of the resulting values for the enthalpy of sublimation for As and As3 vapor is unknown. Also listed in Table I are the standard Gibbs free energy equations used to calculate the equilibrium constants for reaction [1] and the equilibria between As(s) and As4(g), As4(g) and As:(g), ASh(g) and As3(g), and As2(g) and As(g). The equations in Table I were used to generate Figure 1, replacing Figure 3 in the original paper) Figure 1 represents the results of saturating the carrier gas with arsenic vapor at the source temperature (where As~ is the predominant species) and then allowing the gas mixture, alone, to equilibrate at 1373 K. The primary difference between the new plot and the original involves the dissociation of As4(g) to As2(g). This reaction occurs more readily than originally reported. In addition, the calculations were repeated assuming that only As,, As2, and As exist in the vapor phase. The thermodynamic data for A s 3 in Table I yield relatively high D . M . DABBS, Doctoral Candidate, and D.C. LYNCH, Associate Professor, are both with the Department of Mining, Metallurgical and Ceramic Engineering, University of Washington, Seattle, WA 98195. Manuscript submitted July 27, 1982. 502- VOLUME 14B. SEPTEMBER 1983
partial pressures for that specie. Those data, as noted earlier, come from a single source and its reliability is unknown. A high partial pressure for A s 3 , let alone its existence, has not been confirmed by mass spectrometric analysis of arsenic vapor. Accordingly, the calculations were repeated a second time neglecting A s 3. The results are also shown in Figure 1. The data in this figure show that when A s 3 is neglected, there are only slight increases in the partial pressures of As2 and As4 at the higher source te
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