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Standard molar Gibbs free energy of formation of Pb5CrO8(s), Pb2CrO5(s), and PbCrO4(s)
| Content Provider | Semantic Scholar |
|---|---|
| Author | Sahu, Sulata K. Ganesan, Rajesh Gnanasekaran, T. |
| Copyright Year | 2010 |
| Abstract | J. Chem. Thermodynamics 42 (2010) 1–7 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct Standard molar Gibbs free energy of formation of Pb 5 CrO 8 (s), Pb 2 CrO 5 (s), and PbCrO 4 (s) Sulata Kumari Sahu, Rajesh Ganesan, T. Gnanasekaran * Liquid Metals and Structural Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India a r t i c l e i n f o Article history: Received 11 February 2009 Accepted 29 June 2009 Available online 3 July 2009 a b s t r a c t Standard molar Gibbs free energy of formation of ternary oxides Pb 5 CrO 8 (s), Pb 2 CrO 5 (s), and PbCrO 4 (s) were determined by measuring equilibrium oxygen partial pressures over relevant phase fields using manometry and solid oxide electrolyte based emf methods and are given by: D f G m Pb 5 CrO 8 ðsÞ 0:55=ðkJ mol Þ ¼ 1809:4 þ 0:6845ðT=KÞ ð837 T=K 1008Þ; Keywords: Gibbs energy Lead chromates EMF measurements D f G m Pb 2 CrO 5 ðsÞ 0:30=ðkJ mol Þ ¼ 1161:3 þ 0:4059ðT=KÞ ð859 T=K 1021Þ; D f G m PbCrO 4 ðsÞ 0:17=ðkJ mol Þ ¼ 909:8 þ 0:3111ðT=KÞ ð863 T=K 1093Þ; O 2009 Elsevier Ltd. All rights reserved. 1. Introduction 2. Literature survey Lead and Lead–Bismuth eutectic alloy are considered as suitable candidates for the Accelerator Driven Sub-critical Systems (ADS) as spallation target and coolant due to their favorable nuclear, ther- mal, and physical properties [1]. However, they are highly corro- sive towards the structural steels. One of the approaches to minimize this corrosion is to control the dissolved oxygen content in these liquid metals so as to form a protective oxide film on the steel surface [2–6]. Formation of a protective oxide film on the sur- face of the steel reduces direct dissolution of the steel components owing to the low diffusion coefficients of the alloying components through the oxide film [7]. To understand the composition of the protective oxide film and its stability, a detailed knowledge on the phase diagrams of (Pb + M + O) and (Bi + M + O) (M = alloying components of steels) systems as well as the thermochemical data on ternary oxygen compounds formed in these systems are essen- tial. Recently, a partial phase diagram of (Pb + Cr + O) system at 973 K has been established by the present authors [8]. In the pres- ent work, standard molar Gibbs free energies of formation of PbCrO 4 (s), Pb 2 CrO 5 (s), and Pb 5 CrO 8 (s) have been determined by measuring equilibrium oxygen pressures over appropriate ternary phase fields by manometry and solid oxide electrolyte based emf cells and the results obtained are reported. Preparation and thermal stability of the compounds existing in (Pb + Cr + O) system have been reported in the literature [8–13]. Three stable ternary compounds, viz., PbCrO 4 (s), Pb 2 CrO 5 (s), and Pb 5 CrO 8 (s) are known in this system and are reported to be stable in the temperature range of (478 to 1030) K, (873 to 1197) K, and (948 to 1108) K, respectively. A detail account of this is described elsewhere [8]. Through experiments involving thermal analysis in ambient of known oxygen partial pressures, Gadalla and Abadir [13] determined the standard Gibbs free energy of the two reac- tions: (a) 2 CrO 3 (l) + 2 PbO 2 (s) = 2 PbCrO 4 (s) + O 2 (g) (478 to 508) K and (b) (8/3) PbCrO 4 (s) = (4/3) Pb 2 CrO 5 (s) + (2/3) Cr 2 O 3 (s) + O 2 (g) (1030 to 1055) K. The data obtained were reported as D G rxn /(kJ mol 1 ) = 108.43 + 0.2134(T/K) and 304.60 + 0.2888(T/ K), respectively for the above reactions. It is to be pointed out that these measurements were made only in a limited temperature range (25 to 30) K under four controlled ambient oxygen pres- sures. The enthalpy of formation of PbCrO 4 (s) at 298 K ð D H f ;298 Þ had been determined by Dellien et al. [14] by solution calorimeter with NaOH and Na 4 EDTA as the calorimetric solvent. D H f ;298 of PbCrO 4 (s) was found to be 927.02 kJ mol 1 .The uncertainty in this data was calculated to be ±1.39 kJ mol 1 by taking into the account of the uncertainties reported by Dellien et al [14] for their measurements and the uncertainties reported for standard enthalpies of formation of PbO (s) and CrO 3 (s) in the literature * Corresponding author. Tel.: +91 44 27480302; fax: +91 44 27480065. E-mail address: gnani@igcar.gov.in (T. Gnanasekaran). 0021-9614/$ - see front matter O 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2009.06.026 |
| Starting Page | 1 |
| Ending Page | 7 |
| Page Count | 7 |
| File Format | PDF HTM / HTML |
| DOI | 10.1016/j.jct.2009.06.026 |
| Volume Number | 42 |
| Alternate Webpage(s) | https://cloudfront.escholarship.org/dist/prd/content/qt1c24230t/qt1c24230t.pdf?t=nh5t86 |
| Alternate Webpage(s) | https://doi.org/10.1016/j.jct.2009.06.026 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
