Corrosion Resistant Oxide Research Articles

Cr segregation at the Fe-Cr surface: A first-principles GGA investigation

The segregation of Cr at the Fe-Cr alloy surface is essential in the formation of a thin, corrosion-resistant oxide film. Recent angle-resolved x-ray photoelectron spectroscopy measurements indicated Cr segregation at a high temperature in vacuum. However, two independent ab initio density functional theory calculations within the local density approximation (LDA) suggested no segregation. We have calculated the segregation energy for Cr at the Fe-Cr(001) surface using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation (GGA). Our GGA results support the previous LDA investigations. The disagreement between experiment and theory remains unresolved.

Studies on broad spectrum corrosion resistant oxide coatings

The corrosion resistant oxide coatings, developed and applied by the conventional vitreous enamelling techniques, showed superior resistance to a range of mineral acids at various strengths and temperatures, alkaline solutions, boiling water and chrome plating solutions. These coatings possess considerable abrasion and impact resistance as well as high thermal shock resistance. The properties of the coating system have been studied in detail and found to be strongly dependent on composition and processing parameters. These coatings have been characterized by X-ray diffraction analysis and SEM studies. Some of the coating materials have been found to be biocompatible.

Effects of EDM and its mitigation by surface modification on thermal fatigue properties

Electrodischarge machining (ED M) reduces the thermal fatigue resistance compared to conventional machining. The most common corrective treatments employed are electropolishing, shot peening, and the melonite nitrocarburising process, all of which can improve the thermal fatigue resistance. This improvement is attributed to a smoother surface and the elimination of the overtempered layer as well as the removal of the brittle recast layer. The corrosion resistant oxide layer on the melonite treated specimens also has beneficial effects on the thermal fatigue behaviour. The Charpy V notch impact energy of ED electropolished and shot peened samples is slightly higher than that of conventionally machined specimens. However, melonite treatment lowers the impact energy of the specimens compared to conventionally machined samples.

Fundamentals of The Shs Joining Process

AbstractThe process of self-propagating high-temperature synthesis offers potential for joining similar or dissimilar combinations of heat-resisting or refractory metals and refractory or corrosion resistant oxide or nonoxide ceramics or intermetallics by using the exothermy inherent in the synthesis reaction. The process offers unique capability for producing functionally gradient material joints between dissimilar materials to overcome mismatches in chemical, mechanical and physical properties, facility for incorporating reinforcing phases in the filler, and exceptional efficiency given that the energy for joining is largely internally generated. A systematic study of the fundamentals of the process critical for joining in either a primary or a secondary mode is being undertaken. Specialized fixtures are being employed to study the role of substrate temperature in bond formation and strength, and the role of precompaction density and applied pressure on joint density. A Gleeble thermomechanical simulator is being used to study the role of reactant composition, reactant particle size, heating rate and reaction mode, precompaction and applied pressure, and atmosphere. Ultimately, a model of the SHS process for joining will be developed to facilitate joint design, predict joint properties, and enable intelligent control.

ATI-O2系低圧CVDによるAl2O3薄膜の形成とその耐食性の評価

In order to obtain high corrosion-resistant oxide filmes, Al2O3 films were formed on the Pt substrate by low pressure CVD technique using aluminum-tri-isopropoxide (ATI, Al(OC3H7)3) and oxygen. The changes in the composition, structure, and corrosion resistance of the films were investigated as functions of deposition and heat-treatment temperatures. The structure of the films was amorphous at deposition temperatures in the range of 473-773K. The refractive index of the films increased with increasing deposition temperature, showing the increase in density of the films. The corrosion resistance of the films in 1.0 and 12.0 kmol·m−3 HCl and 0.01 kmol·m−3 NaOH solutions increased with increasing deposition temperature. Films deposited at 623 K were transformed into γ-Al2O3 and α-Al2O3 by annealing at 1073 K and 1173 K, respectively. The crystallized films hardly dissolved in a 12.0 kmol·m−3 HCl solution.

An Alkaline Prefilming Process for the Primary Piping in a New Japanese Boiling Water Reactor

A prefilming method called the alkaline process was successfully applied to a new Japanese boiling water reactor plant during the nuclear heatup phase during the plant preoperation phase. This method was developed to suppress deposition of radioactive corrosion products such as 60Co on ex-core components, which are primarily made of stainless steel. When stainless steel is exposed to actual reactor water that contains oxygen at pH of 8.0 to 8.5, at 288°C, for 410 h, corrosion-resistant oxide films can be formed. The results of the exposure tests indicate that an ∼30% reduction in the deposition of 60Co and 58Co was obtained by this process compared to ordinary operation procedures.