The anodic and cathodic polarization of molybdenum in 1N H2SO4 was investigated. In deaerated solutions, two stable rest potentials, 0.368 and --0.020v vs. NHE, were observed, depending on the activation procedure. In aerated solutions, only the rest potential of 0.368v was observed. From the more noble rest potential, an anodic Tafel slope of 44 _ 4 mv and a corrosion current of 1.5 _ 0.8 ~a/cm 2 were obtained. For the h.e.r., a Tafel slope of 70 _+ 3 mv and an exchange current of 0.10 _+ 0.04 ~a/cm 2 were obtained. Two distinct active-passive transitions were observed between the two rest potentials. The short-time galvanostatic transients exhibited two linear regions in the potentialtime responses and could be represented by an electrical model of two R-C networks in series. Capacitance values were determined from the slopes of the two linear regions. The first capacitance was attributed to MoO2 at the Mo-MoO2 interface and was a constant value of 3.75 ~f/cm 2 throughout the potential region investigated. The second capacitance was surmised to be a pseudocapacitance, and ranged from 200 to 600 ~f/cm 2. However, for sufficiently large polarization from the more noble rest potential, the second capacitance was too large to be measured.Few investigations have been made of the electrochemical behavior of pure molybdenum. Some early work (1-3) indicated that molybdenum passivated easily and that the end product of its electrochemical oxidation was hexavalent molybdenum. In acidic solutions, experimental rest potentials of 0.390v vs. NHE (4), 0.368v vs. NHE (5), and 0.000-0.058 pH v vs. NHE (8) have been reported. Anodic Tafel slopes of 70 mv (7) and 45 mv (4, 5, 8) have been determined for the dissolution reaction and cathodic Tafel slopes of 76-104 mv (6, 9, 10) have been reported for the h.e.r, on molybdenum. More recently, the anodic passivation (11) and the mechanism of the dissolution reaction (8) have been studied.As indicated above, two different stable rest potentials of molybdenum in acidic solutions have been reported. The anodic region above the more noble rest potential and the cathodic region below the more active rest potential have been investigated previously. It seems appropriate that one laboratory group investigate the electrochemical behavior of molybdenum in the region between these two stable rest potentials and in the potential regions previously investigated. ExperimentalThe test cell was a conventional one and made from Pyrex glass with a nominal capacity of 1 liter. The test solution was 1N H2804. Prior to introduction of a molybdenum electrode, the test solution was either aerated or deaerated (Air Reduction Prepurified N.,, 99.997%) for 24 hr.Planar (0.005 cm thick sheet, 99.9% Mo) and cylindrical (0.825 cm diameter rod, 99.9% Mo) molybdenum electrodes (Fansteel Metallurgical Corporation) were used. Both types of electrodes had an exposed area of 1 cm 2.Subsequent to fabrication, the general electrode surface preparation procedure was as follows:1. Mechanical polishing to 4/0 emery paper...

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The kinetics of the electrode processes of antimony in normalKCl‐normalHCl solutions have been investigated. The rest potential of antimony in acidic chloride solutions can be expressed empirically by the equationEnormale=0.182−0.060 pH+0.020log][normalSb)(IIIand is attributed to the redox reactionnormalSb+2H2O=HSbO2+3H++3eThe empirical rate equations for the electrodissolution and electroreduction reactions near the rest potential areInormala=k̅normala][OH−SbIII−1e2FE/RTandInormalc=k̅normalcH+2e−FE/RTThe rate of electrodeposition of Sb(III) can be expressed asInormalc,normaldep=k̅normalc,normaldep][H+][normalSb)(IIIe−FE/2RTA mechanism which is consistent with the experimental results is proposed.

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