The fabrication of the corrosion-resistant film on the disk by the pretreatment process using benzotriazole (BTA) solution was for the purpose of corrosion resistant improvement of patterned media. The most suitable pretreatment condition that corrosion resistance was improved is 30-minute dipping to a borate solution containing 1.0% BTA added 3% hydrogen peroxide 3%. By using this pretreatment, the corrosion resistance of the Co alloy in the neutral environment was improved more than 20 times. When hydrogen peroxide was not coexist, the degree of corrosion-resistant improvement was small. The corrosion resistance of the record and the layers which constitute a hard disk conducted pretreatment is maintained in 65℃ and 90% RH condition. A nitrogen group derived from BTA giving corrosion resistance is introduced into the disk surface which prepared pretreatment process. The reason that the BTA layer formation promotes by hydrogen peroxide addition was explained by in the HSAB principle.

View full abstract

Novel lubricant with corrosion inhibiting benzotriazole groups was designed and synthesized to secure reliability of next generation bit patterned media (BPM). The novel lubricant exhibited excellent anti-corrosion ability compared to those of the conventional lubricants. Furthermore, the novel lubricant could be a good candidate for thermal assisted magnetic recording (TAR) because of its high thermal durability.

View full abstract

Effects of deposited salts on corrosion behavior for an 1100 aluminum alloy were investigated by a constant dew point test with NaCl, MgCl₂, and CaCl₂. In the constant dew point test, corrosion depth of the 1100 aluminum alloy depended on the deposited salts, increasing in the order of MgCl₂, CaCl₂, and NaCl. On the other hands, in an immersion test, corrosion depth was independent of the cation species in relatively dilute solutions but depended in concentrated solutions. Furthermore, in a polarization measurement, a cathodic reaction strongly depended on the cation species in the concentrated solutions. It is suggested that the deposited salts in the atmospheric corrosion affect not only the time of wetness but also the cathodic reaction around deliquescence relative humidity where concentrated solutions are formed.

View full abstract

The lifetime of metallic materials used for telecommunication facilities can be estimated using the corrosion rate when the materials are generally corroded. The corrosion rate differs not only due to local weather and/or atmospheric corrosive factors where the material is but also due to whether the material is directly exposed to rain even in the same location. To evaluate the differences in corrosion rates of steel and zinc due to rain exposure, we placed ACM sensors consisting of Fe/Ag-galvanic and Zn/Ag-galvanic couples in Nago city, Okinawa and measured corrosion currents as output of the sensors. The skyward-facing Fe/Ag sensor responded to rainfall quicker and more stably than the groundward-facing Fe/Ag sensor. This suggests that when a stable electrically conductive water layer was formed should affect the evaluation of the corrosion rate. The annual corrosion rate of steel was estimated to be about 0.09 mm/year, which was equivalent to the reported value in Nishihara, also in Okinawa. The corrosion current of the skyward-facing Zn/Ag sensor showed a tendency to decrease gradually. This made it difficult to estimate the corrosion rate of zinc by using the ACM sensor.

View full abstract

It has been recently pointed out that Alloy690 has the potential to become long-range ordering (LRO) of intermetallic compounds such as Ni₂M after long-term use in service conditions in nuclear power plants. However, it is quite difficult to experimentally evaluate the influence of the LRO of Ni₂M on SCC susceptibility. In the present study, authors developed the Ni₂M-stabilized alloy with excessively enhanced phase stability of Ni₂M based on the chemical composition of Alloy690. It was isothermally heat treated for up to 10000 h at 500℃ and 550℃. Microstructure observation, X-ray diffraction analysis and Vickers hardness test were subsequently conducted, and the results were compared with those of Alloy690. The Vickers hardness was significantly increased only in the Ni₂M-stabilized alloy after isothermal heat treatment over 1000 h at 500℃. The results of TEM analysis suggest that it may be caused by the LRO of Ni₂M. The influence of the LRO of Ni₂M on SCC susceptibility will be investigated by the samples obtained in the present study.

View full abstract

In the oxygen depleted underground neutral aqueous solution environment, carbon steel reacts with H₂O, producing H₂ gas and forming corrosion film on the steel surface. Corrosion rate is controlled by diffusion of reaction species through corrosion film. Diffusion constants of some species working in the corrosion process were obtained from literatures. However, no data were found on the diffusion constant of H₂O in iron oxides, which were estimated based on an appropriate assumption. Mass transfer model for the corrosion rate was used to simulate the corrosion rate of carbon steel. Liquid phase diffusion model of Fe²⁺or H₂O through pores in the corrosion film and solid phase diffusion model of H₂O through corrosion film itself were examined by simulation using the spread sheet of Excel. Change in corrosion current density and corrosion loss with time and pH and temperature dependence of corrosion current density were examined. By comparing simulated results with the experimental data, it was suggested that the solid phase diffusion of H₂O in the corrosion film controls the corrosion rate of carbon steel in oxygen depleted environment.

View full abstract