Dealuminification in Cu-Al alloys is similar in mechanism to the dezincification that occurs in brass. Dealuminification was studied by means of accelerated immersion tests and anodic polarization measurements of various Cu-Al alloys, in which the content of Al was less than 12.4%. A mixed solution of 1/2mol CuSO₄+1/3mol CH₃COONa+1/3mol KCl+2/3mol CH₃COOH(pH=3.3) was used in both cases.
The results obtained were as follows:
(1) Dealuminification current that is obtained by deducting the anodic current of Cu at -0.05V from that of each alloys at -0.05V corresponds to the dealuminification rate of its alloy.
(2) Only α Cu-Al alloys have high resistivity to dealuminification.
(3) Dealuminification is increased by the appearence of phases other than α phase.

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Passivation and activation of titanium in deaerated non-oxidizing acid solutions were studied in order to investigate on the passivity of titanium. Critical potential for passivity and Flade potential shift towards noble direction with increasing chloride and hydrogen ion concentration, thus passivation becoming difficult. The critical potentials are expressed as E=E⁰+mlog[Cl^-]-n(RT/0.4343F)pH, where R, the gas constant, T, absolute temperature, F, Faraday constant, E⁰ and m are constants. The constant n varies from 0.9 to 3.0 with environmental conditions such as temperature and kind of anion. Such different pH dependence of the critical potentials is attributed to the presence of different equilibrium surface reactions corresponding to passivation or activation for the respective corrosion conditions. The equilibrium reactions are considered to be
Ti^a++2H₂O=TiO₂+4H⁺+(4-a)e,
2Ti^b++3H₂O=Ti₂O₃+6H⁺+(6-2b)e,
Ti+2H₂O=TiO₂+4H⁺+4e,
2Ti+3H₂O=Ti₂O₃+6H⁺+6e.
When the critical potentials expressed as equilibrium potentials of two former reactions, passivation or stability of passivity is affected directly by titanium ion. In such cases, as demonstrated for titanium-palladium alloy, corrosion resistance of titanium depends on the concentration of titanium ion in corrosive media.

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