At room temperature, mercaptan can not be adsorbed on metal with electron pairs of its S-atom, but can with its active hydrogen attached to the S-atom. The adsorbed mercaptan on steel at room temperature changed to disulfide leaving hydrogen atom while the hydrogen was confirmed by means of its reaction with the unsaturated compound in the tube. To catch the hydrogen directly, another method was adopted in this report. Disulfide was found in the ether solution of mercaptan in which iron powder or a stainless steel tube was dipped at room temperature, while hydrogen was confirmed by gas chromatograph analysis of gaseous parts in the experimental apparatus. That is, hydrogen-bridged mercaptan on metal was decomposed to proton (·H) and mercaptan radical (R-S·). The proton penetrated into the steel and the radical coupled to become disulfide in the solution. In the hydrogen entrance into steel S-atom played an important role. We supposed that these phenomena could have some references with the occasion of hydrogen cracking of oil fields tubular goods.

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Inhibition of the corrosion of carbon steels by lithium molybdate in bellow 21.4mol/kg-H₂O alkaline lithium bromide aqueous solution was investigated in glass sealed tube at various temperatures. Lithium molybdate gives an excellent corrosion inhibition for carbon steel even at a concentration as low as 0.003mol/kg-H₂O in the presence of 0.36mol/kg-H₂O lithium hydroxide. In addition, this inhibitor is effective in the temperature range from 373 to 473K. It is concluded that the corrosion inhibition action by lithium molybdate results from the passivation of carbon steel by the compact film composed of molybdenum oxide such as MoO₂ and Fe₃O₄ formed on the surface of carbon steel, which inhibits anodic reaction.

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Localized corrosion behavior of welded part of type 304 stainless steel was investigated by using a scanning vibrating electrode technique in H₂SO₄ aqueous solutions containing various concentrations of KSCN at 298K. The distribution of corrosion current density on the specimen was measured during an electrochemical potentiokinetic reactivation test in 0.5mol/l H₂SO₄ solution containing 10^-2mol/l KSCN. Three parts, namely, weld metal, heat affected zone, and base metal, can be distinguished for difference in the current density at just the transition potential from passive to active region. Also, the distributions of current density were measured during an immersion test in 0.5mol/l H₂SO₄ solutions containing various concentrations of KSCN. The weld metal shows anodic peak current density at 10^-4mol/l KSCN, whereas shows the catholic peak current density at 10⁰mol/l KSCN.

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Combined effects of Si, P and Cu on stress corrosion cracking (SCC) of high purity 18Cr-14Ni steels in NaCl solutions were examined with 18Cr-14Ni-<0.1Si-yP-zCu steels (A) and 18Cr-14Ni-xSi-0.03P-1Cu steels (B). Repassivation potentials for crevice corrosion, E_R, were measured at 80°C. Decreasing P content for A-series steels and increasing Si content for B-series steels made E_R values less noble, while Cu content gave no significant effect on E_R for both series steels. To predict any sensitivity to SCC for a steel, each SCC test was conducted under applied potential just above E_R value determined for each steel. SCC tests in solutions up to 20% in NaCl concentration at 80°C showed that decreasing P content for A-series steels, increasing Si content for B-series steels and 1 or 2% Cu for both series steels were effective to avoid SCC in higher concentration of NaCl solutions. Critical temperature for SCC at and below which a steel would not suffer SCC was determined in 3% NaCl solution. The temperature became higher with decreasing P content and/or increasing Cu content for A-series steels. The critical temperature for the steel TS-8 with 0.006% P and 2% Cu was 130°C, which was markedly higher than that of 50°C for the steel TS-9 corresponding to type 304L steel. The critical temperature for B-series steels increased with increasing Si content, but did not exceed 120°C with Si content up to 2%.

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Uniform oxidation is the most common type of corrosion of copper tubes in heat-exchanging refrigerating and air-conditioning units. Recently an unusual type of corrosion, “ant nest corrosion”, has been reported in such copper tubes at the final leakage test before shipment or a short time after installation. The corrosion is characterized by complicated microscopic caverns containing porous copper oxide connected by tunnels. The microcaverns have voids and cracks, and the surfaces of the copper tubes are tarnished dark-brown or red-brown without bulky corrosion products and show no obvious defects indicating the leaks. Sixty four cases of such premature failures of copper tubes discovered during the 11 years from 1978 to 1988 are listed in Table 1, including date of detection, application of copper tube, time to failure, wall thickness, location of attack, surface color and possible corrosives. Nomenclature for the localized corrosion and classification of different types of the ant nest corrosion with its size are also described. Nine typical structures of the ant nest corrosion are presented in the copper tubes for both air-conditioning units and simulation tests.

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Magneto-optical (MO) disk is a new memory which has merits of optical memory and magnetic memory. The merits are “high density recording of 10⁸bit/cm²”, “disk-changeability and portability”, and “limitless rewritability”. The recording films of the disk, however, have the drawback of poor corrosion resistance and the achievement of sufficient disk-reliability is an important matter for the practical application. The corrosion of the recording films has been successfully prevented by coating protective layers and by improving corrosion resistance of the films themselves. Now the MO disk grows to have sufficient reliability and recording properties.

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