The corrosion rate of nickel, Ni-Cu alloy and Ni-Cr-Fe alloy in caustic potash is generally believed to be the same as that in caustic soda.
In order to ascertain this, the corrosion rate of the three kinds of materials in fused caustic has been examined.
Chlorates contained in diaphragm-cell caustic liquor considerably increase the corrosion rate of construction materials of the continuous concentrating system; hence, several reducing agents, such as sucrose, sulfite, formate and others, are added to remove chlorates from caustic before evaporation in the high temperature range starts.
The effectiveness of several reducing agents has been examined by adding them to diaphragm-cell and mercury-cell caustic liquor.
The corrosion rate of the three materials in fused caustic soda at 450°C is less than 50mdd, but that of Ni-Cr-Fe alloy in caustic potash ranges from 150 to 300mdd.
It is, therefore, concluded that caustic soda and caustic potash are not considered to have the same aggressiveness against Ni-Cr-Fe alloy.
The chlorate content in mercury-cell caustic potash liquor is less than 1ppm, but corrosion in concentrating stage is considerable.
As a reducing agent, glucose is most effective to reduce corrosion encountered in concentrating stage of both diaphragm-cell caustic soda and mercury-cell caustic potash.

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The contact corrosion of couples of aluminum and mild steel was studied by electrochemical means such as corrosion current and potential measurement, rapid polarization method and electromagnetic oscillograph as well as by weight loss measurement and chemical analysis of the corrosion products.
The inorganic corrosive media used were 0.42M NaCl, 0.001M CaCl₂, 0.06M MgCl₂, 0.03M Na₂⋅SO₄, 0.0008M SrCl₂, 0.42M NaCl+0.06M Mg⋅Cl₂, 0.42M NaCl+0.001M CaCl₂, 0.42M NaCl+0.0008M SrCl₂ and the artificial sea water.
Under the experimental conditions, aluminum was generally less noble than mild steel except in alkaline MgCl₂ solution.
In the artificial sea water, however, aluminum was generally less noble than mild steel and then became more noble than the mild steel in a few days, when the aluminum surface was covered with corrosion products containing iron and it was protected against further corrosion while corrosion of the mild steel proceeded spontaneously.
In most experimental conditions, aluminum sacrificially protected mild steel from corrosion, while in the alkaline MgCl₂ solution aluminum was at first anodic against mild steel and the corrosion current became negligible within 2hrs due to the formation of Mg⋅(OH)₂ on mild steel cathode.

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As corrosion inhibitors for metal, ethyl alcohol, diethyl ether, cetyl mercaptan, and methylcetyl sulfide were studied in aq. HCl solution.
Ethyl alcohol and cetyl mercaptan have two abilities, proton-donating and proton-accepting (electron-donating) (group I), while diethyl ether and methylcetyl sulfide have one, proton-accepting (group II).
Organic oxygen compounds are easily adsorbed on metal by donating electrons of their oxygen atoms at room temperature, while organic sulfur compounds are hardly adsorbed by electron donation of their sulfur atoms at this temperature.
Differences in adsorption behaviors were studied between I and II by means of corrosion test and corrosion potential measurement with Cu, Ni, and Fe coupons in acid media.
i Group I was always more effective for corrosion nhibition than group II in all conditions tested.
We considered that adsorption of organic corrosion inhibitors on metal might be brought about not only by electron donation of their functional atoms but also by their proton donation.
In our previous reports, we proposed the mechanism that inhibitors were adsorbed on metal by displacing the water molecules which were originally adsorbed by donating electron pairs of their oxygen atoms. In this paper another type of water adsorption was proposed. This water should be hydrogen-bridged to metal surface by accepting electrons from the surface. A metal can have two types of water molecules, which coexist on its surface.
Proton donation of inhibitors was closely concerned with the hydrogen-bridged water, and inhibitors might be adsorbed by combining it and/or displacing it, as following manners shown schematically,
M: H-O-H…H-SR or M: H-SR
At this time it is hard to say which, but we suppose that the distributional proportion of the two types of water might vary according to the characteristics of metal.

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