Masaki Yasuda

On the oxidation of cyanide solutions with lead dioxide coated anode

Abstract The electrochemical oxidation of cyanide ion with and without coexistent metallic ions was studied. The PbO2-electrodeposited Ti anode was suitable for the purpose. The process required an excess amount of OH− since otherwise azulmin was formed by the side reaction. The interference effects of metallic ions (Cd, Cu, Fe and Zn) on the oxidation of cyanide were investigated. Of these, Fe ion was the most harmful.

On the RuO2TiO2 interlayer of PbO2 electrodeposited Ti anode

Abstract The degradation mechanism of electrodeposited β-PbO 2 on the RuO 2 TiO 2 loaded Ti substrate was studied. The electric resistance of the PbO 2 anode was increased the Ti/Ru ratio of the interlayer and the current density of electrodeposition, probably due to oxidation of the interlayer at the initial stage of electrodeposition, so that the electric contact between PbO 2 and the interlayer might fail. The β-PbO 2 deposited anodes prepared carefully to avoid destructive oxidation of the interlayer were examined as the oxygen evolution electrode in 1 M H 2 SO 4 . The Ti substrate became passive, caused by permeation of oxygen through PbO 2 and the interlayer, when electrolysis was conducted for many hours. The service life time depended on the Ti/Ru ratio of the interlayer and the operating current density.

Studies on the Mechanism of the Chlorine Electrode Process

The chlorine electrode process on the graphite anode under real conditions of chlor‐alkali cells has been studied. In relatively low potential range up to 1.25V vs. SCE, two consecutive charge‐transfer reactions occur, and the second is rate determining The potential deviates from the Tafel line at high current densities, where the carbon oxide forms on the electrode surface, and the active sites for the chlorine electrode process diminish.

On the Active Dissolution of Metals and Alloys in Hot Concentrated Caustic Soda

Abstract The corrosion behavior of carbon steel, austenitic stainless steels, Ni-base alloys, and nickel in hot, concentrated caustic soda solutions at the active potential range was investigated. ...

Studies on the Cathodic Reaction in the Diaphragm‐Type Chlorine Cell

Polarization of a rotating platinum cathode in mixed solutions of and containing dissolved chlorine was measured. At relatively low current densities, cathodic reduction of took place as the main reaction. The diffusion‐limiting current density was a function of the concentration of in solution and the reaction was first order with respect to . There fore, it was concluded that the mechanism was operative at low current densities. At high current densities, hydrogen formation is, of course, the main reaction.

Studies of the pH of the membrane surface in a laboratory chlor-alkali cell

The pH on the surface of an ion-exchange membrane was measured with a microprobe in a laboratory scale chlor-alkali cell to study the leakage of OH− through the membrane. The solution pH in the vicinity of the membrane facing the anode was found to be considerably higher than that in the bulk solution because of penetration and leakage of OH−. The pH varied with the membrane type. This explains why the carboxylate membrane is not protonated and can be used as a separator in chlor-alkali cells.

Cathodic behavior of zirconium in aqueous solutions

Abstract The electrochemical behavior of Zr has been studied by polarization measurements. The surface oxide and zirconium hydride formed by cathodic polarization of Zr have been examined by X-ray, SEM, and a hardness tester. Zirconium hydride would form on Zr cathode after the surface oxide is reduced at the potential, which is several hundred mV more noble than the predicted value shown by the Pourbaix diagram. The parameters for the hydrogen evolution reaction on the hydride formed Zr cathode differs from that on the oxide covered surface, which means that hydrogen evolution takes place on both surfaces under a different mechanism, while details are still veiled at present.

Mass transfer through the deposited asbestos diaphragm in chlor-alkali cells☆

Abstract Electrolysis of saturated NaCl solution was carried out in laboratory cells to investigate mass transfer through the deposited asbestos diaphragm under operating conditions similar to those of practical cells. It was found that hydrogen bubbles generated on the cathode screen penetrated into the asbestos mat, and significantly disturbed the brine flow.

Corrosion Behavior of Ni and Ni‐Based Alloys in Concentrated NaOH Solutions at High Temperatures

Corrosion behavior of SUS 310S austenitic stainless steel, Alloy 600, Monel 400, and Ni 200 and NaOH solutions in the concentration range 30-60% at high temperatures up to 166/sup 0/C was studied. In solutions containing dissolved oxygen or under oxidizing conditions, all the specimens examined were corroded seriously due to oxygen diffusion through the porous oxide layer consisting of ..beta..-Ni(OH)/sub 2/. In hydrogen-saturated solutions, on the other hand, these Ni alloys were corrosion resistant because nickel in the alloys was active to oxidation of hydrogen. The specimens were corroded by deaerated solution at high temperatures in which hydrogen evolution took place as the counterreaction. The corrosion rate controlled by the hydrogen formation reaction increased exponentially with the decrease of the Ni content in the alloy.

Corrosion Behavior of 18-8 Stainless Steels in Hot Concentrated Caustic Soda Solutions under Heat-Transfer Conditions

Abstract The corrosion behavior of AISI 304 and 316 stainless steels (SSs) in hot concentrated caustic soda solutions was investigated under heat-transfer conditions. The corrosion potential of the specimens was located in the active region; thus, the alloys were attacked in the form of general corrosion, depending on the heat-transfer conditions. AISI 316 was more susceptible than AISI 304. Such corrosion behavior is attributed to the failure of the passive film on the heated surface, caused by concentration of caustic solution next to the metal surface and erosion by gas bubbles. A molybdenum-free alloy, AISI 305J1, was tested under the same conditions as AISI 316 to clarify the detrimental effect of Mo on austenitic SS corrosion in hot concentrated NaOH. Intergranular corrosion was occasionally found when the potential was located in the passive region, depending on test conditions and heat treatment of the specimens.