Gold, thermodynamic data

No thermodynamic data have been found for gold selenates. 

Quantitative SNIFTIRS was introduced in 2002 and so far has been applied to the investigation of the orientation of adsorbed molecules in three systems pyridine at Au(llO) [40], citrate at Au(lll) [53], and 2-mercaptobenzimidazole at Au(lll) [54, 55]. Pyridine adsorption at gold single-crystal surfaces has long been used as a model system to study the coordination of organic molecules to metal electrode surfaces. The thermodynamics of pyridine adsorption has been thoroughly investigated with the help of the chronocoulometric technique [56-64]. The availability of the thermodynamic data made this an ideal system to test the performance of the quantitative SNIFTIRS. 

The explanations tentatively proposed in the literature [20, 25, 41, 61] for the variations of gold uptake with pH as shown in Figure 17.1, depend on the gold speciation that is considered. Some groups consider the presence of hydroxo-chloro anions as identified by Raman and XAFS [27-29], while others take into account the speciation deduced from thermodynamic data, that is the presence of neutral complexes, such as AuCfi at pH 2-5 [35] (see Section 17.1). 

If one reconsiders the case of pH lower than the PZC of Ti02 (conditions of anion adsorption), electrostatic adsorption of the gold anions is possible. However, the increasing gold uptake when pH increases is not consistent. The presence of neutral AuCl3(H20) between pH 2 and 5 deduced from thermodynamic data, which may interact with the support, could explain that the gold uptake increases as pH increases and becomes closer to the PZC. Literature data in geochemistry reports the same type of observation, that is... 

Resistance of ceramics to corrosion is due to one of three basic behaviors immunity, passivation, or kinetically limited corrosion. When a ceramic is thermodynamically incapable of spontaneous reaction with its environment it is referred to as having immunity. When the necessary thermodynamic data are available this type of corrosion resistance may be predicted by calculation. Metals, except for the precious metals such as gold, do not exhibit immunity. 

The potential dependence of ethyl xanthate coverage has also been determined for silver-gold alloys. In this system, xanthate chemisorbs onto silver sites in the alloy surface, and, as with silver itself, adsorption occurs at potentials below that at which silver xanthate is formed. Figure 11 presents the coverages determined for this system. The solid lines represent the Frumkin isotherm previously derived for silver. The isotherms for the alloys were obtained by introducing a silver activity term, taking values of activity derived from the thermodynamic data collated by... 

If the thiomalate ligand is not present in excess, it is completely displaced. When gold binds, the M ions are displaced in the gold metal ratio of 3 2, which suggests bidentate coordination. EXAFS data shows AuS2 coordination with Au—S bond lengths of 229 pm [20, 103]. In the presence of both cadmium and zinc, zinc is preferentially displaced which is possibly a consequence of thermodynamics as Zn7MT and CdyMT react at comparable rates. 

ICTFD A I DATA 0UTPUT 0P thermodynamic properties of gold... 

It is well known that small particles melt at a lower temperature than the corresponding bulk solid. Buffat and Borel measured a monotonic lowering of melting temperature with decreasing diameter for gold clusters supported on carbon substrates (7). They accounted for their data by means of a thermodynamic model due to Pawlow (16), which states that the melting temperature of small particles is inversely proportional to the particle radius. 

The energy of the adsorption process could be estimated on toe basis of toe literature data using bond energies for RS—H, H2, RS—SR and RS—Au at 87, 104, 74 and 40kcalmol , respectively . Values of —5 and —6 kcalmol per gold thiolate unit are obtained for adsorption of thiols and disulphides, respectively. Schlenoff and coworkers estimated values of —5 and —12 kcalmoP for adsorption of thiols and disulphides, from his own and earher published data on toe voltammetric curves corresponding to the thermodynamically controlled (equiUbrium) electrodeposition of alkanethiolates on gold . Recently, accurate thermodynamic parameters were obtained... 

The homogeneous model is also inconsistent with other data. Composition of a mixed monolayer could be modelled as a function of the composition of the deposition solution. This is based on the assumption that the binding sites on gold are independent (i.e. complete mixing of adsorbing species occurs) and that adsorption is governed by thermodynamic factors. The model shows systematic deviation from the experimental data, which suggests that the monolayers may phase-separate. ... 

Values of partial molar thermodynamic functions of silver and gold in the Ag Au alloy as a function of composition for 500 °C. The values for gold were obtained by integration of the Gibbs-Duhem equation (Section 3.2.4, data for 0.169 were omitted for the integration of the... 

Although one of the more complex electrochemical techniques [1], cyclic voltammetry is very frequently used because it offers a wealth of experimental information and insights into both the kinetic and thermodynamic details of many chemical systems [2], Excellent review articles [3] and textbooks partially [4] or entirely [2, 5] dedicated to the fundamental aspects and apphcations of cyclic voltammetry have appeared. Because of significant advances in the theoretical understanding of the technique today, even complex chemical systems such as electrodes modified with film or particulate deposits may be studied quantitatively by cyclic voltammetry. In early electrochemical work, measurements were usually undertaken under equilibrium conditions (potentiometry) [6] where extremely accurate measurements of thermodynamic properties are possible. However, it was soon realised that the time dependence of signals can provide useful kinetic data [7]. Many early voltammet-ric studies were conducted on solid electrodes made from metals such as gold or platinum. However, the complexity of the chemical processes at the interface between solid metals and aqueous electrolytes inhibited the rapid development of novel transient methods. 

G. T. Furukawa, W. G. Saba, and M. L. Reilly, Critical Analysis of the Heat-capacity Data of the Literature and Evaluation of Thermodynamic Properties of Copper, Silver and Gold from 0 to 300 K , National Bureau of Standards Reference Data Series NSRDS-NBS 181. 

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