Corrosion Behavior of Amorphous Nickel-Valve Metal Alloys in Boiling Concentrated Nitric and Hydrochloric Acids

The corrosion behavior of amorphous nickel-base alloys containing titanium, zirconium, niobium, tantalum and/or phosphorus in boiling 9 N HNO_3 solutions with and without Cr^ ion and in a boiling 6 N HCl solution was investigated. In boiling 9 N HNO_3 solutions alloys containing 20 at% or more tantalum were immune to corrosion, maintaining the metallic luster, and Ni-40～60Nb alloys showed low corrosion rates of the order of μm/year. In the boiling 6 N HCl solution only tantalum-containing alloys were immune to corrosion although a higher tantalum content was required in the 6 N HCl solution in comparison with 9 N HNO_3 solutions. Protective surface films on the Ni-Nb and Ni-Ta-(P) alloys were composed exclusively of NbO_2(OH) and TaO_2(OH). Consequently, the corrosion resistance is not provided unless alloys contain elements, the passive film of which is highly stable in these aggressive boiling acids, such as tantalum

The Corrosion Behavior of Sputter-Deposited Magnesium-Valve Metal Alloys

An attempt was made for preparation of magnesium alloys with valve metals, such as titanium, zirconium, niobium and tantalum whose melting points far exceed the boiling point of magnesium. These alloys became single phase solid solutions in wide composition ranges, but were crystalline in contrast to the fact that other alloys with valve metals such as nickel-, copper-and aluminum-base alloys were amorphous in wide composition ranges. The alloys containing sufficient amounts of valve metals showed high corrosion resistance due to spontaneous passivation in 1 M HCl at 30℃. The high corrosion resistance was attributed to the formation of passive oxyhydroxide films in which valve metal cations were remarkably concentrated. However, because of crystalline alloys and because of the presence of active magnesium, their corrosion resistance is lower than that of valve metals

CO_2 Methanation Catalysts Prepared from Amorphous Ni-Valve Metal Alloys Containing Platinum Group Elements

The amorphous Ni-valve metal (Ti, Zr, Nb and Ta) alloys containing a few at% of platinum group elements were activated by immersion into hydrofluoric acid and used for hydrogenation of carbon dioxide at 100-300℃. This surface activation led to formation of nanocrystalline surface alloys with high surface area, and to surface enrichment of platinum group elements on the titanium-, niobium- and tantalum-containing alloys, but not on the zirconium-containing alloys. The surface of the latter alloys was mainly composed of nickel. The activity and selectivity for methane formation on the titanium-, niobium- and tantalum-containing alloys were significantly affected by the difference in the platinum group elements; the ruthenium- and rhodium-containing alloys showed higher activity and selectivity for methane formation while the platinum-containing alloys exhibited the lowest activity for methane formation and produced mainly carbon monoxide. The zirconium-containing alloys showed the one order of magnitude higher activity for methanation of carbon dioxide in comparison with the titanium-, niobium- and tantalum-containing alloys and produced exclusively methane independent of platinum group elements contained. The alloying with zirconium seems very important to prepare the alloy catalysts having the extremely high activity

Effect of Molybdenum on the Corrosion Behavior of Amorphous Fe-Mo-C alloys in 1N HCl

The addition of molybdenum to amorphous Fe-18C alloy results in passivation by anodic polarization even in 1N HCl. However, its addition in a large amount increases the anodic current density in both the active and passive regions and lowers the corrosion potential. X-ray photo-electron spectroscopy was used to determine the correlation between the composition of surface film and the corrosion resistance of alloys. The alloying with a proper amount of molybdenum facilitates the formation of molybdenum-enriched surface film as a result of active dissolution and hence assists the passivation by the formation of passive hydrated iron oxy-hydroxide film. However, the excess addition of molybdenum leads to an excess increase in the anodic activity of alloys and accordingly is not greatly effective for increasing the corrosion resistance

XPS and Electrochemical Studies of Effects of Metalloid Additives on Corrosion Behaviors of Amorphous Iron-Chromium Alloys

XPS and electrochemical methods have been used to investigate the influences of metalloid additives, phosphorus, carbon, boron and silicon on corrosion behaviors of amorphous iron-chromium alloys. It was found that phosphorus accelerates active dissolution prior to passivation. This leads to the rapid enrichment of trivalent chromium in the surface film and to the rapid formation of the surface film with a good protective quality. On the contrary, silicon and boron do not facilitate active dissolution and interfere the chromium enrichment in the surface film owing to incorporation of silicate and borate in the surface film

The Electrocatalytic Oxidation of Ethylene and Methane, and Reduction of Oxygen on Gas-Diffusion Electrodes Made of Amorphous Nickel-Valve Metal-Platinum Group Metal Alloys

Exploratory work has been done on the performance of electrocatalytic reduction of oxygen and anodic oxidation of ethylene and methane on the gas-diffusion electrodes prepared from amorphous alloys containing one atomic percent platinum group elements. Gas-diffusion electrodes were made by coating the mixture of catalysts prepared by immersion in 46% HF from melt-spun ribbon shaped amorphous alloys, carbon black, polytetrafluoroethylene and sugar, and subsequent baking in nitrogen gas. The electrode made of catalyst prepared from amorphous nickel-niobium alloy containing platinum and ruthenium was the most active for electrocatalytic reduction of oxygen. For electro-oxidation of ethylene and methane, amorphous nickel-value metal alloy containing only platinum possesses higher activity in comparison to the electrode made of platinum black powder

Corrosion Behavior of Amorphous Nickel-Base Alloys in a Boiling Concentrated Sodium Hydroxide Solution

application/pdfPolarization curves were measured in a boiling 50% NaOH solution, and the specimen surface was analyzed by X-ray photoelectron spectroscopy. A combined addition of chromium and molybdenum to amorphous nickel-phosphorus alloys significantly enhances the corrosion resistance. Addition of copper and lead are also effective in improving the corrosion resistance. The surface film formed on amorphous nickel-base alloys consists mainly of hydrated nickel oxyhydroxide. Chromium is concentrated in the alloy surface immediately under the surface film when nickel-base alloys containing chromium are immersed or polarized anodically at potentials close to the corrosion potential.紀要類(bulletin)673229 bytesdepartmental bulletin pape