Corrosion rates of mild steel and cast iron in concentrated sodium chloride solutions with and without addition of various inhibitors were determined from anodic and cathodic polarization curves.
In absence of inhibitor the corrosion rate of mild steel and cast iron increased within the concentration range of 10 to 50g/l. Within the range of about pH 5 to 11 the corrosion rate was almost independent of pH, but in the more acid range it increased rapidly as pH decreased and in the more alkaline range it decreased. In the neutral pH range corrosion was strongly accelerated by dissolved oxygen.
As an inhibitor for mild steel in sodium chloride solution, water glass was found to be most effective; the addition of 50g/l water glass plus 10g/l sodium hydroxide reduced the corrosion rate to about 1/140 of that in non-inhibited solution. The combination of 100g/l sodium nitrite and 1g/l sodium benzoate was second in effectiveness, reducing the corrosion rate to about 1/80. Among other inhibitors examined, sodium sulfite was effective and the corrosion rate decreased to about 1/30 by its addition.
For cast iron the best inhibition was obtained by sodium nitrite, and the addition of 100g/l reduced the corrosion rate to about 1/23. Sodium sulfite was second best; its addition of 1g/l reduced the rate to about 1/13. Among other inhibitors, water glass and Res-Cor W-711 were effective, which reduced the corrosion rate to about 1/7 and 1/4, respectively.
Generally the presence of passivating inhibitors deteriorates the electro-machinability. Since the passivating nature of inhibitors can be examined by determining polarization behaviors, a certain degree of estimation is possible as to the deteriorating effect of an inhibitor on the machinability.

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Serious corrosion was experienced on 18 Cr-Si-Al steel tubes used in the high temperature zone of an oil-firing furnace. In order to investigate the parameters for resulting corrosion, several corrosion tests were carried on thirteen types of steels including 18 Cr-Si-Al immersed in the fused salts of V₂O₅, K₂SO₄ and Na₂SO₄ at various temperatures. Chromium steels containing Al were found resistant to the vanadium-attack but badly corroded by a K₂SO₄ and Na₂SO₄ mixture with a small addition of V₂O₅. K₃Al⋅(SO₄)₃ was thought to be a possible factor for the corrosion because its molten phase resulting from the high temperature reaction provoked by K₂SO₄ and Al₂O₃ seemed to be able to exist in the temperature range of 700-900°C in which the corrosion of the tubes occurred.

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A pipeline carrying hot water buried in volcanic soils suffered severe corrosion in several months after installation. In order to study such a high corrosion rate, a field corrosion test was made with steel pieces. Also in a laboratory, corrosion tests using the soils were carried out at room temperature and 75°C for 30 days and some other tests were made with the soils. It was found that the high corrosion rate cannot be explained as the effect of pH values, specific resistivities and humic acid contents of soils.

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An investigation has been made into the influence of an a. c. component in output current of a potentiostat using silicon controlled rectifiers on the corrosion behavior of anodically polarized metals. The anodic behavior of Type 316 stainless steel and commercial pure titanium immersed in N₂-saturated 30% sulfuric acid solutions at 25°C was studied with d. c. alone and with superimposition of different proportions of 100c/s sinusoidal a. c. to d. c.
The passivation time measured galvanostatically at various current densities for the polished surface of stainless steel and the etched surface of titanium was not appreciably affected by a. c. superimposition in which the proportion of a. c. did not exceed 150% of each level of the d. c. applied, and the passivation time for these metals at a fixed level of d. c. increased sharply with increase in percentage of superimposed a. c. at percentages above 1, 000%. However, in similar experiments for the polished titanium the a. c. superimposition in percentages up to 2, 000% had little influence on the passivation time. The corrosion rate measured potentiostatically in passive state for the polished surface of stainless steel and titanium was not affected by superimposed a.c. in percentages not exceeding 150%.
On the basis of these observations, it is assumed that the potentiostat using the SCR may be tolerated to contain the 100c/s a. c. component above 150% of d. c. component in its output current owing to the presence of condenser current caused by the impedance at the metal-solution interface.

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The corrosion of “four-9” aluminium in pure water was investigated as a function of the intensity of γ-irradiation at ordinary temperature. A low exposure less than 10²R/hr produced no effect in practise, but the higher exposure remarkably retarded the corrosion. The minimum corrosion rate was observed at about 10⁴R/hr. An intensive exposure over this value stimulated the localized attack of the metal and the dispersion of the corrosion product. The formation of hydrogen peroxide was found to be insufficient in amount to cause the inhibition of corrosion at any rate of exposure, although the co-operative action of the oxidative free radicals and the hydrogen peroxide was postulated. The stimulation of corrosion at the highest exposure was attributed to the radiation chemical destruction of the protective film on aluminium.

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