Determination of standard thermodynamic properties of sulfides in the Ag-Au-S system by means of a solid-state galvanic cell

Abstract

Thermodynamic properties of the following phase reactions in the Ag-Au-S system have been investigated via electromotive force (EMF) measurements in solid-state galvanic cells with Ag 4 RbI 5 as a solid electrolyte: Ag(cr) + Ag 3 AuS 2 (cr) = 2Ag 2 S(cr) + Au(cr) Ag(cr) + 2AgAuS(cr) = Ag 3 AuS 2 (cr) + Au(cr) Ag(cr) + Au 2 S(cr) = AgAuS(cr) + Au(cr) AgAuS(cr) + Ag 2 S(cr) = Ag 3 AuS 2 (cr)The EMF temperature dependences observed for these reactions, together with auxiliary thermodynamic properties for Ag 2 S, acanthite, from Robie and Hemingway (1995), result in the following standard thermodynamic properties at 298.15 K and 1 bar (10 5 Pa): Δ f G o (Ag 3 AuS 2 , cr) = -69478(200) J/mol and S o (Ag 3 AuS 2 , cr) = 273.37(56) J/(mol⋅K) (uytenbogaardtite), Δ f G o (AgAuS, cr) = -27621(210) J/mol and S o (AgAuS, cr) = 128.11(60) J/(mol⋅K) (petrovskaite), and Δ f G o (Au 2 S, cr) = 1077(650) J/mol and S o (Au 2 S, cr) = 128.1(2.0) J/(mol⋅K). Au 2 S(cr) is a thermodynamically metastable phase, but the values of its thermodynamic functions are open to discussion.

Optical and biological sensing capabilities of Au2S/AuAgS coated gold nanorods

“…5 compares the XRD spectra obtained from the as-synthesized GNRs, and nanocomposite. The Au 2 S and AuAgS can be identified according to previous reports [23][24][25][26][27][28]. The unlabeled peaks may originate from the CTAB remaining on the nanocomposite, and the shell enshrouding the GNR consists of multiplex components including Au 2 S and AuAgS.…”

Experimental determination of the stabilities of Au2S(cr) at 25°C and at 25–250°C

“…Ag 2 S purchased from MERCK and recrystallized during one week in a Ti autoclave at 400°C in 1 m NaHS solution was used for II-T experimental series (Ag 2 S-Ag 3 AuS 2 assemblage). The method of AgAuS (petrovskaite) and Ag 3 AuS 2 (uytenbogaardtite) synthesis is given in Osadchii and Rappo (2004). Briefly, these solid phases were prepared in batches of 1-1.2 g by reacting Ag-Au alloys (electrum) and sulfur.…”

“…Thus, the values of D f G o ð298:15 KÞ ðAu 2 S ðcrÞ Þ determined in these two studies differ by 18.05 kJ/mol (3.16 log units for the stability constant). Recently, Osadchii and Rappo (2004) determined D f G o ð298:15 KÞ ðAu 2 S ðcrÞ Þ ¼ 1:077 kJ=mol with the aid of solid state galvanic cells. However, we believe that this value is in error because the heating of their galvanic cell which was used to determine DG o T for the reaction Ag (cr) + 2Au 2 S (cr) = AgAuS (cr) + Au (cr) provoked thermal decomposition of Au 2 S. The presence of elemental sulfur in this galvanic cell made impossible acquisition of thermodynamic data because, as noted by the authors, when an additional phase is present in the sample system, ''the EMF of the cell cannot be deciphered due to conflict with the Gibbs phase rule''.…”

“…In contrast, the Ag-Au sulphides Ag 3 AuS 2(cr) and AgAuS (cr) , which are stable to almost 200°C and whose thermodynamic properties have been recently determined (Baranova et al, 2002;Osadchii and Rappo, 2004;Gurevich et al, 2005) can be used to determine the formation constants of Au-hydrosulphide complexes. Therefore, the aim of the present study is to determine D f G o ð298:15 KÞ ðAu 2 S ðcrÞ Þ and the formation constants of Au-hydrosulphide complexes via solubility measurements of Ag-Au sulphides to 250°C and metallic gold at 25°C.…”

Contrasting Surficial Composition of Native Gold from Two Different Types of Gold Ore Deposits

“…The existence of gold and silver sulfides, which are thermodynamically stable at relatively low temperatures [12,27] at epithermal deposits of different genesis does not, therefore, seem surprising. Cocker et al [28] studied the origin of the minerals of the Ag-Au-S-Se system on the adularia-sericite epithermal Broken Hills deposit in New Zealand.…”