Michael J. Pryor

The influence of corrosion product structure on the corrosion rate of Cu-Ni alloys

Abstract Cu, 90–10, and 70–30 Cu-Ni alloys corrode at widely dissimilar rates in boiling NaCl solution. The corrosion product films on the specimens were continuous and consisted entirely of Cu 2 O. The Cu 2 O films formed on the two Cu-Ni alloys were quite protective and exerted significant ohnmic polarization on both the anodic and cathodic local cell corrosion reactions. A defect structural model has been proposed which shows why the Cu 2 O formed on the Cu-Ni is more protective than that formed on Cu.

The kinetics of the oxidation of Al in oxygen at high temperature

Abstract The oxidation behavior of high purity Al has been studied at temperatures from 450 to 575 °C in dry oxygen at a pressure of 76 torr. The complex overall oxidation kinetics were found to be made up of two distinct and essentially independent portions. An amorphous γ-Al2O3 film, growing by outward diffusion of metal ions, forms with accurately parabolic kinetics throughout the temperature range. Roughly cylindrical crystals of γ-Al2O3 of constant terminal thickness, at any given temperature, grow into the metal from the amorphous oxide-metal interface by inward diffusion of oxygen through the overlying amorphous oxide film. Together the weight gains from these separate kinetic processes, when summed, can accurately account for the complex oxidation kinetics found between 450 and 575 °C. The mechanism of formation and growth of these two dissimilar oxidation products is considered in detail.

The potential dependence of reaction product composition on copper-nickel alloys

Abstract The potential dependence of reaction product composition has been studied on high purity binary Cu-Ni alloys (10–40%Ni) in 0·5M sodium chloride solution at 25°C. The results show that the reaction products contain Ni concentrations in excess of those in the alloys at 0·00 V and below. The composition of solid reaction product films is more potential dependent than that of the overall reaction products. Controlling mechanisms are discussed.

The protection of Cu by ferrous sulphate additions

It has been found that a film composed primarily of lepidocrocite (γ-FeO·OH) can be electrophoretically deposited on Cu cathodes from a NaClFeSO4 solution. The lepidocrocite film protects the Cu against corrosion by polarizing the local cathodes. The film has no detectable effect on the anodic dissolution of Cu.

The kinetics of the oxidation of aluminum—copper alloys in oxygen at high temperature

The oxidation behavior of high-purity aluminum-zinc alloys has been studied at temperatures from 475 to 575°C in dry oxygen at a pressure of 76 Torr. The oxidation product is duplex in nature consisting of both amorphous and crystalline γ-Al2O3. The crystalline γ-Al2O3 grows as roughly cylindrical crystals of constant thickness at any given temperature and alloy content; the crystals grow into the metal from the amorphous oxide-metal interface by inward diffusion of oxygen through the overlying amorphous film. The amorphous oxide film existing between the crystals of γ-Al2O3 grows with accurately parabolic kinetics throughout the temperature and alloy composition range. The amorphous oxide existing above the crystalline phase grows at a lower rate because of the additional resistance to cation diffusion conferred by the underlying crystalline phase. Increasing the zinc content of the alloy from 0.1 to 1.0% causes a reduction in the crystal nucleation density and an increase in the radial growth rate. The presence of Zn has no effect on the growth kinetics of the amorphous oxide between the crystals of γ-Al2O3.

The nature of protective films formed on a CuFe alloy

Abstract A Cu alloy (CDA 194) containing α-Fe particles in a Cu matrix develops protective corrosion product films in chloride solutions after an initial period of relatively rapid attack. The protective film is a mixture of Cu2O and lepidocrocite. The lepidocrocite produces significant polarization of the cathodic reduction of dissolved oxygen which accounts for its protective action. It is formed in the corrosion product film by galvanic corrosion of the Fe particles to ferrous ions, oxidation of the ferrous ions by dissolved oxygen and electrophoretic deposition of a positively charged Fe(OH)3 colloid on the cathodic Cu matrix.

The mechanism of stress corrosion cracking of Cu-base alloys

Abstract SCC of α-copper alloy solid solutions in neutral Mattsons solution is controlled by the rate of de-alloying at the crack tips. Only Mn and Zn alloying additions result in high rates of SCC because they can support large anodic current densities (> 0.1 A cm −1 ) at the crack tips, at the cracking potential. Solute is believed to be transported to the tips by pipe diffusion in the cores of dislocations generated at the crack tips. Certain ternary alloy additions having high total misfit parameters significantly reduce the rates of SCC.