Molybdenum anodic polarization

Anodic Polarization of Iron-Chromium-Molybdenum Alloys... 

Fie. 5.29 Anodic polarization curves for nickel-molybdenum alloys in 1 N H2S04. Redrawn from Ref 26... 

Examples of metals that are passive under Definition 1, on the other hand, include chromium, nickel, molybdenum, titanium, zirconium, the stainless steels, 70%Ni-30% Cu alloys (Monel), and several other metals and alloys. Also included are metals that become passive in passivator solutions, such as iron in dissolved chromates. Metals and alloys in this category show a marked tendency to polarize anodicaUy. Pronounced anodic polarization reduces observed reaction rates, so that metals passive under Definition 1 usually conform as well to Definition 2 based on low corrosion rates. The corrosion potentials of metals passive by Definition 1 approach the open-circuit cathode potentials (e.g., the oxygen electrode) hence, as components of galvanic cells, they exhibit potentials near those of the noble metals. 

Electro- chemical cleaning 80 wt.% cone. HjSO, 55 This method is generally performed for molybdenum alloy TZM. The recommended procedure is (i) solvent degreasing for 10 min, (ii) immersion in a commercial alkaline cleaner for 2 to 3 min, (iii) rinsing with cold water, (iv) buff and vapor blasting, (v) second immersion in a commercial alkaline cleaner, (vi) rinsing with cold water, (vii) electrochemical polishing with molybdenum workpiece polarized anodically at a current density of 50 A/m ... 

Figure 4.44. Anodic polarization curves of CH3OH on Wo,8Moo,2C catalyst as a function of temperature. Catalyst load 0.2 g cm , 4 M CH3OH and 1 M H2SO4 [213]. (Reproduced by permission of ECS—The Electrochemical Society, from Kawamura G, Okamoto H, Ishikawa A, Kudo T. Tungsten molybdenum carbide for electrocatalytic oxidation of methanol.)...

Figure 11 (A) Stripping voltammetry (20 m Vs at 55 °C) of CO layers on humidified PEM fuel-cell anodes (1) platinum catalyst (2) platinum/molybdenum catalyst. Voltammetry in the absence of adsorbed CO on the platinum/molybdenum catalyst is shown in (3). Molybdenum-mediated electro-oxidation of adsorbed CO takes place on the alloy catalyst in the peak at 0.45 V and at lower overpotentials [79]. (B) Steady-state polarization curves of PEM fuel-cell anode at 85 °C for platinum (squares) and platinum/molybdenum catalysts in the presence of 100 ppm CO (filled points) and pure H2 (unfilled points). (From Ref 79.)... 

At temperatures below about 125°C, CO adsorption on platinum is very strong. Even few ppms in the H2 stream cause substantial performance losses on the anode. Therefore, the use of platinum alone is not viable for HOR in the presence of CO in low temperature fuel cells. Thus, platinum-ruthenium, platinum-molybdenum and platinum-tin are being used as anode electrocatalysts for hydrogen oxidation in the presence of CO because they tolerate low ppms of CO without excessive polarization losses. Timgsten carbide (WC) also shows high CO-tolerance [38,44]. 

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