Polarization curves were measured for a series of superalloys whose compositions laid at 760°C on the γ/γ'-phase tie-line passing through the composition of René 95 and its extension into the γ'-phase region. The specimens were prepared by a powder metallurgy. The measurement was performed by a potentio-dynamic method in a 5N sulfuric acid. Most of the parameters derived from the curves had a maximum at a γ'-phase content of 70%. The Ecorr and the logarithm of the peak current density varied in accordance with a simple low of mixture. Some difference was observed between the heat-treated and the as-HIPed specimens likely due to the difference of the size of the γ'phases of the alloys.
It is well known that reduced sulfur species lead to intergranular attack (IGA) of sensitized Alloy 600 at low temperature, however the effect of these species on Alloy 600 at high temperature is not clear. Static autoclave tests were performed to investigate the effect of reduced sulfur (CaS2O3) on the high temperature aqueous corrosion of Alloy 600. The results show that reduced sulfur can cause severe corrosion on Alloy 600 in high temperature water.
The corrosion test of aluminum alloys has been made in water-ethylene glycol mixture containing NaCl at temperature 40 and 80°C. In aqueous solution without ethylene glycol the pitting corrosion decreases with increase of temperature, while in water-ethylene glycol mixture the maximum depth of the pitting corrosion increases with temperature. In water-ethylene glycol mixture the hydrated oxide film on aluminum alloys becomes relatevely thin and porous. If comparing the pitting corrosion between in aqueous solution and water-ethylene glycol mixture, the ethylene glycol accelerates the glowth of pitting, probably because of its heterogeneous adsorption on the aluminum alloys.
To clarify the physical meaning of general corrosion resistance index (GI) obtained through the alloy contents on general corrosion rate of stainless steels in sulfuric acid solution, the study of the effect of alloy contents, immersion time and temperature on the general corrosion rate was carried out in 10.2mol·kg-1 sulfuric acid solution. It was assured that dependence of alloy contents on corrosion rate of stainless steels was ascribed to the apparent activation energy obtained by Arrhenius plot, and from the thermodynamical consideration of GI value, GI was expressed as a function of alloy contents through the change of apparent activation energy due to corrosion reaction.
The scanning tunneling microscope (STM) can be used not only in vacuum but also in air and in aqueous solution. There has been no device which can detect sub-micron range of the surface morphology change by electrochemical reaction. Therefore study on the possibility of in-situ quantitative evaluation of micro-corrosion around micron range was carried out by using the STM. The corrosion behavior of the low alloy steel in 1% NaCl and 0.1% HNO3 aqueous solution was studied by the STM. The local corrosion rate was obtained by the subtraction between STM images. The average corrosion rate was also obtained by averaging all data after subtraction between STM images. The obtained average corrosion rate was well coincident with the corrosion rate calculated from Faraday's conversion of the anode current density, while the local corrosion rate was more than 3 times larger than the average corrosion rate. From these results, it is concluded that the local corrosion behavior can be studied very accurately by the STM.
Anticorrosive films formed on copper from benzotriazole (BTA) were studied by a chemical shift of threshold energy of photoelectron emission from copper. The threshold for a polished copper surface was estimated as 4.20eV. After treatment with BTA solutions the threshold was increased by the formation of surface films. The chemical shift of thresholds was dependent on the concentration of BTA solution as well as on the treatment time. The threshold was drastically increased at BTA concentration of 8×10-5mol/l. When copper specimens treated with 1×10-4mol/l of BTA solution for only one minute, the threshold was increased to 4.98eV. When copper specimens were treated with BTA solution after oxidation of the copper specimen at the conditions of 50°C for 5min, a remarkable increase in threshold was observed. It is known that BTA is not effective for steel specimens. No chemical shift of the threshold was observed for iron specimens after BTA treatment with 5×10-4mol/l. It can be concluded that the photoelectron emission is very sensitive for surface film formed from BTA, and that our method is useful for the evaluation of anticorrosive films.
The cycles of three elements, nitrogen, sulphur and carbon in the biosphere of the earth have been described with special reference to the bacteria which utilizes the inorganic compounds of the elements. Ammonia is oxidized to nitrate by a coaction of the ammonia- and nitrite-oxidizing bacteria, the resulting nitrate is changed into nitrogen gas by the denitrifying bacteria. Nitrogen gas is reduced to ammonia by biological and industrial nitrogen fixations. Sulphate is reduced to hydrogen sulphide and this compound is oxidized to elemental sulphur or sulphate by the sulphur-oxidizing bacteria and photosynthetic sulphur-oxidizing bacteria. Finally, carbon dioxide is changed into organic compounds mainly by algae, while the gas is partially reduced to methane by methanogenic bacteria. Methane can be partially trapped by a coaction of the ammonia-oxidizing bacteria and C1 compound-utilizing bacteria.