Iridium, a platinum-group metal, is used in the form of a mixture of iridium and tantalum oxides in the catalytic layer of oxygen-generating electrodes owing to the unique catalytic properties and chemical stability of Ir.

The recovery of Ir from end-of-life products is important because of its low production, uneven geographical distribution of Ir sources, and high supply risks. However, recovery of Ir requires the dissolution of Ir in an aqueous solution, a procedure which involves the use of a strong acid and is, therefore, dangerous and environmentally hazardous.

Moreover, if metals other than Ir dissolve in the aqueous solution during the recovery of Ir, harmful effluents and gases would be generated and the separation of Ir from other metals would be difficult.

In this study, we developed a method that involves the extraction of only Ir from the catalyst layer of an oxygen-generating electrode and simultaneous recovery of Ir as a Ca-Ir composite oxide, where the composite oxide is soluble in hydrochloric acid. Only iridium oxide was volatilized from the catalyst layer of the oxygen-generating electrode and brought into contact with CaO via the gas phase. The composite oxide obtained was dissolved in hydrochloric acid and analyzed; the analysis revealed that Ir was highly soluble in hydrochloric acid and that the composite oxide did not contain Ta.

SUS301, SUS304 and SUS316L steels with different carbon content, austenite stability and grain size were prepared, and their mechanical properties were investigated by In-situ X-ray diffraction in tensile tests using Synchrotron radiation. In addition, the occurrence and growth of necking immediately after yielding was investigated using a CCD camera.

As is well known, the yield point increased with decreasing in grain size. Increasing rate of the yield point was dependent on carbon content, and the slope (Hall-Petch coefficient) increased with increasing carbon content. In SUS304 and SUS316L ultrafine grained structural steels, necking occurred immediately after yielding, the nominal stress decreased, and the necking progressed and fractured. On the other hand, in SUS301 ultrafine grained structure steel, after yielding at 1600 MPa (upper yield stress), a necking occurs and the stress decreases slightly (lower yield stress), but the progress of the necking stopped and propagated in the longitudinal direction of the specimen. The nominal elongation was Lüders deformation of 20％, followed by uniform deformation with a total elongation of 35％. This phenomenon is due to the large amount of strain induced martensitic transformation. In-situ X-ray diffraction results of tensile tests in SPring-8 showed that 65％ of austenite was transformed to martensite. On the other hand, its volume fraction for SUS304 and SUS316L ultrafine grained structural steels were 18％ at most. From the point of true stress-true strain curve, the plastic instability condition is satisfied because their work hardening rate is extremely small. Therefore, after the necking occurs, it breaks as it progresses. In SUS301 ultrafine structured steel, the work hardening rate is small just after yielding and the necking occurred immediately. However, its work hardening rate became large immediately after necking started. When the carbon content is high, the grain size is ultrafine, and the austenite stability is low, high yield point of 1600 MPa and large Lüders deformation can be obtained.

The microstructure changes in the precipitation hardening copper alloys during the thermal process after deformation are known to exhibit complex behavior due to the simultaneous progress of various phenomena such as precipitation, recovery, recrystallization, and grain growth. Understanding the mechanism is an important issue for designing the heat treatment processes.

In this study, the microstructure changes in the Cu-Co-P alloy during thermal process after a deformation was numerically simulated based on the N model coupled with the dislocation recovery model, where the interaction between dislocations and precipitation behavior was focused. As a result, the following peculiar phenomena were calculated:

The fcc-Co formation and the Co₂P precipitation on dislocations take place simultaneously in the Cu-0.32 at％Co-0.21 at％P-0.11 at％Sn alloy. The Co particles are left inside the bulk Cu matrix in the recovery process of dislocations, and then the Co particles are re-dissolved into matrix phase. The following mechanism was proposed to explain this peculiar behavior. Since the Co particles in the bulk matrix left by the dislocation recovery have high interfacial energy, they re-dissolve into the matrix phase to release this energy. Furthermore, the decrease in Co concentration in the matrix phase due to the Co₂P precipitation on the dislocation accelerates the Co particle re-dissolution.