Polarization of copper has been carried out in each of solutions of nitric acid added several p-substituted anilines. The addition of the p-substituted anilines makes the values of the corrosion potential Ecorr (V) noble in the following order: +0.01 (aminophenol)>-0.02 (aniline)>-0.06(nitroaniline)=-0.06(choroanilene)>-0.10(aminobenzoic acid)>-0.12 (benzamide)>-0.17(no addition). The Ecorr values are heightened by electron-donor substituents and lowered contrary by electron-acceptor substituents. The values of corrosion current density icorr (A/cm2) are reduced by the addition of the p-substituted anilines and the icorr values are in the following order: 1.3×10-5(nitroaniline)<2.5×10-5(benzamide)< 4.0×10-5(no addition)=4.0×10-5(aminobenzoic acid)<4.5×10-5(chloroaniline)<1.8×10-4 (aniline). The data show that the electronic-attractive substituent effect is large in the order NO2CONH2>COOH>Cl and the order agrees with that of the corrosion inhibition effects of the substituted anilines. The ab initio 3-21G molecular orbital calculations for the p-substituted anilines were carried out. The electronic charges on the atoms of the substituted anilines show that there are a possibility of two adsorption forms for the substituted anilines on the copper atoms. The one of adsorptions is caused by the benzene ring of the substituted anilines and another is by the substituents. The values of Ecorr are heightened by the increase of negative electronic charge of the benzene ring. The large negative charges on the substituents result in the smaller values of icorr.
Corrosion of ceramic coating films were investigated in various oxidizing aqueous solutions to apply the coatings to instruments of chemical plants. Factors to affect corrosion resistance were discussed from the viewpoint of dissolved oxygen content and film properties such as film material, crystallinity, chlorine content, element composition, splashed particles and pinhole ratio. The obtained results in this study are summarized as follows: (1) Corrosion of ceramic films were accelerated with increase of dissolved oxygen content. (2) Crystallinity and chlorine content of film strongly affected corrosion resistance of plasma CVD coatings. (3) Crystallinity of film and splashed particles in film strongly affected corrosion resistance of PVD coatings.
Cavitation erosion of ceramic coatings made by CVD and PVD was investigated to develop a ceramic coating having better erosion resistance. Evaluation method of cavitation erosion resistance of ceramic coatings was proposed using morphology, plastic flow of substrate under film and film adhesion strength. The obtained results in this study are summarized as follows: (1) Cavitation erosion of ceramic coatings can be evaluated by morphology, measured hardness and film adhesion strength. (2) PVD film began to be damaged earlier than plasma CVD film, because erosion damage initiated at splashed particles in the PVD film which would be easy to remove.
Corrosion behavior of several metals exposed in plutonium nitrate solution was studied. Plutonium nitrate solution with the plutonium concentration ranging from 0.01 to 300g/l was used as a corrosive medium. Specimens tested were type 304 ULC (304 ULC) stainless steel, type 310Nb (310Nb) stainless steel, titanium (Ti), titanium-5% tantalum alloy (Ti-5Ta), and zirconium (Zr). Corrosion behavior of these metals in plutonium nitrate solution was evaluated through examining electrochemical characteristics and corrosion rates obtained by weight loss measurement. From the results of the corrosion tests, it was found that the corrosion rate of stainless steels i.e. 304 ULC and 310Nb, increases by the presence of plutonium in nitric acid solution. The corrosion potential of the stainless steels shifted linearly towards the noble direction as the concentration of plutonium increases. It is thought that the shifts in corrosion potential of the stainless steels to the noble direction results an increase in anodic current and, hence, corrosion rate. Valve metals, i.e. Ti, Ti-5Ta and Zr, showed good corrosionresistance over the whole range of plutonium concentration examined here.
The Fe-(10-30)Cr alloys were oxidized for 60s at 1273K in 0.05 atm H2O-air with an infrared radiation furnace. Formed oxide films were characterized mainly by XPS:XRD and ellipsometric measurements were also done. As-rolled alloys were α single-phase except for a 10Cr alloy and the average grain size was 52±8μm(±1σ). They were polished with wet emery paper down to #1000, mirror finished with diamond slurry, and kept in a silica gel desiccator for one day bofore use. The pretreated specimens were covered with (Fe1-yCry)OOH film of about 2nm thick which contained very small amount of silicate, manganese and sulfer species: y increased proportionally with Cr content in alloy but less than that in alloys. The oxide scale formed on 10Cr alloy at 1273K for 60s was thick and showed spalling: structure and composition of the scale are similar to those formed on type 430 stainless steel by breakaway oxidation. Thin oxide film of (Cr1-xFex)2O3 was formed on (16-30)Cr alloys, x being less than 0.03 for 16Cr alloy and decreased with Cr content in alloy. The thickness was estimated to be more than 100nm and increased with Cr content in alloy. Bound water was detected only in the outermost part.
The high temperature corrosion characteristics in oxidation, hot corrosion and solid particle erosion of silicide ceramics were reviewed in comparison with the superalloys. The ceramics have much more superior resistance against such corrosion attacks than the superalloys, except for certain cases of hot corrosion environment. The excellent resistance of ceramics against high temperature corrosion are discussed based on the consideration of rate-controlling process.