Molybdenum, salts structure

The specific role and the fate of Mo in the alloy has been investigated [141]. It has been found that Mo is not at all stable but tends to be leached out, which would be the origin of the deactivation observed on cathodic load. The deactivation results in a progressive increase in the Tafel slope, which cannot be reactivated in situ by addition of molybdenum salts. On the other hand, that Mo is leachable can be inferred also from the observation that in situ deposited Co-Mo alloys are quickly dissolved as the current is interrupted [528, 529]. This seems to indicate a provisory activation of the cathode by Mo, which cannot be recovered in a simpley way once decayed [141]. However, this contrasts somewhat with the claim of long term stability and resistance to cell shut-downs for the thermally prepared Ni-Mo coating [5]. The structure of the layer may differ depending on the details of the preparation procedure. 

The aim of this work was to deposit molybdenum on a steel substrate at temperatures sufficiently low (< 650°C) in order to avoid structural modifications of the substrate. This is why the LiCl-KCl eutectic was selected as the solvent. A literature survey shows that molybdenum deposits have already been obtained from molten chlorides, fluorides, oxides, and mixed fluoride-oxide media, and that many questions concerning the chemistry of the molybdenum solutions and the reduction mechanism remain unanswered. In this paper, we will talk about the preparation of the molybdenum salt used as a solute, then describe the electrochemical kinetic investigation performed, and finally briefly outline a practical application of the knowledge gained during this work. 

Salts of about a dozen isopolymolybdate anions have been isolated from aqueous or nonaqueous solutions. The formulas of these anions are listed in Table 3 and their structures (see below) are based predominantly on six-coordinate molybdenum in contrast to those of vanadates and chromates. 

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