Bernard Tremillon

Proprietes chimiques et electrochimiques en solution dans le thiocyante de potassium fondu: Formation de complexes cyanure

Abstract Molten potassium thiocyanate can be used as a solvent between its melting point, 173°, and its decomposition temperature, about 275°. An electrochemical study (polarography and anodic voltammetry) has been carried out in that medium, at 195°. The elements of column Ib, dissolved in molten KSCN, can exist only at the +1 oxidation state. Those of column IIb exist only at the +2 oxidation state; the disproportionation of mercurous ions has been reported. Fe2+, Co2+, and Mn2+ ions have been observed and are the only stable oxidation states. The higher oxidation states, Cu2+, Fe3+ oxidize thiocyanate ions into sulfur and cyanogen; therefore they cannot exist. Reciprocally, the metals are corroded by SCN- ions with the formation of cyanide and metallic sulfide. Furthermore, concentrated stable metallic cations provoke the thermal decomposition of SCN-, with the formation of metallic sulfide and cyanogen. Only complexes more stable than thiocyanate complexes can be formed in that medium: these are mainly sulfides (insoluble) and cyanides. The following cyanide complexes have been reported. Ib column. Complexes of the M(CN)2− type: Cu(CN)2−, Ag(CN)2−, Au(CN)2−, (pK2-values are 5.70, 3.20, and 11.2, respectively). IIb column. Only one complex, Hg(CN)2 (pK2=6.5), in the case of mercury, and several complexes in the case of zinc or cadmium: Zn(CN)2, Zn(CN)3−, Zn(CN)42− (the pK-values are 5.1, 6.1, and 8.6 respectively), CdCN+, Cd(CN)2, Cd(CN)3−, (1.8, 3.9, and 5.1, respectively). Cobalt(II) enters into a more complicated reaction: Co3+ ions reduce the solvent in the presence of cyanide ions and lead to the formation of Co(CN)63− complex. At the same time, there is a precipitation of cobalt sulfide and iron(II) is precipitated from the solution as ferrous ferrocyanide. A comparison is made with the stabilities of the same complexes in aqueous solutions and it is shown that the order of stability for complexes of the same type is preserved. The stabilities are, nevertheless, much lowered because of the strong complexing power of thiocyanate ions towards metallic ions.

Realisation D'Une Electrode Indicatrice D'Ions Oxyde Dans Les Sels Fondus Au Moyen D'Electrolytes Solides

Abstract Solid solutions of CaO in ZrO2, are ionic conductors. Conduction involves oxide ion (O−-) vacancies in the crystal lattice. Membranes of such materials are selectively permeable to the ion O−-. Taking advantage of this remarkable feature, a novel “oxide indicator electrode” has been developed for measurements in a fused sodium-potassium chloride solvent in a range of temperatures between 720 and 800°C. The potential response was in concordance with the applicable Nernst Equation when the melt was basic, i. e., “rich” in O−- In “acidic” melts, deviations from the Nernst Equation were apparent due to contributions of anionic (chloride) conductance. Using our indicator electrode, sodium oxide was successfully titrated to a potentiometric end point by precipitation with coulometrically generated Cu+ and Ni++: the relevant solubility products of cuprous and nickelous oxide have been evaluated as 10−12.4 and 10−9.6, respectively, at 1000°K.

Reactions of Formation and Stability of Iron (II) and (III) Oxides in LiCl ‐ KCl Eutectic Melt at 470°C

The study of the different oxides of iron (II) and iron (III) was carried out potentiometrically in LiCl-KCl eutectic at 470/sup 0/C by means of an yttria-stabilized zirconia electrode indicator of the oxide ion activity and an iron electrode indicator of the ferrous ion activity. These measurements were complemented by the determination of cyclic voltammograms and by x-ray diffraction and infrared spectrophotometrY analysis of certain compounds formed. The main results obtained are the following: strong oxidizing power (oxidation of Cl-/sup 1/ ions into Cl/sub 2/) and high oxoacidity (great stability of ferric oxide) of Fe/sup 3/ ions; possible redissolution of Fe/sub 2/O/sup 3/ in the oxide ion rich media by the formation of ferrate (III) ion; FeO/sub 2/-*Fe/sup 2 +/ ions react with O/sup 2/- ions to to form ferrous oxide, which is probably stabilized in the form of a solid solution FeO-LiFeO/sub 2/ of composition Fe/sub 1-y/Li/sub y/O. Magnetic oxide, Fe/sub 3/O/sub 4/, is stable and can be obtained by the action of oxide ions on a mixture of iron (II) and iron (III). This work is pertinent to the construction of rechargeable and high performance batteries. 34 refs.

Chemical And Electrochemical Properties In Solution In Molten Alkali Hydroxides VI. Solubility Product Of Mercuric Oxide

Abstract The solubility product of mercuric oxide in molten alkali hydroxides at 227[ddot] C is determined experimentally: Ks = 10−13.3 mol.2l−2 This value agrees with that calculated using thermodynamic data (Ks = 10−12.8mol.2l−2).

Chemical Solubilization of Metal Oxides and Sulfides in Chloride Melts by Means of Chlorination Agents

Molten salts, especially molten chlorides, are useful as dissolving phases for solid-liquid extraction of metals from various materials (ores, slags, etc.). The extraction proceeds in the case of chloride melts, by the transformation of insoluble compounds (primarily oxides or sulfides) into soluble chlorides. It requires the action of “chlorinating agents”, whose differences in chlorinating power allow for selective dissolutions. Such a “wet” procedure offers several advantages over the more classical “dry” chlorination. The transformation of insoluble oxides into species soluble in chloride melts requires that a sufficiently high pO2- be imposed upon the melt under consideration. Two sorts of chemical reagents may be used in order to achieve this goal: either oxoacids (i.e., acceptors of O2- ion), or oxidizing reagents that transform O2- into oxygen. HCl gas, of the former category, and Cl2, of the latter category, are the simplest chlorination reagents and appear to be approximately equal in chlorinating power. A more powerful action may be produced by coupling Cl2 with a reducing reagent with is oxidized by the Cl2 to produce an oxoacid much stronger than HCl. For instance, in the carbochlorination process, the reducing agent is carbon or carbon monoxide in the sulfochlorination process, the reducing agent is sulfur or sulfur chloride. Very high levels of pO2- are attainable as a result of the use of these reagents (e.g. pO2- = 27 with the gaseous CO + Cl2 mixture in LiCl-KCl eutectic at 470°C, versus PO2- = 11 with Cl2alone), allowing for dissolution of practically all of the most insoluble metal oxides. In order to predict the conditions of selective operations, the chlorination of several metal oxides (Al2O3, Fe2O3 and Fe3O4, TiO2 and ilmenite, SiO2) is considered to exemplify the application of rationale which relies on the use of potential-pO2- diagrams. The generation of these diagrams is briefly discussed. The case of some sulfides, treated through the consideration of potential-pS2- diagrams, is also examined.