Masakatsu Ueda

Theoretical evaluation for thermodynamic stability of constituents of hydrogen storage alloy in concentrated alkaline solution at higher temperature

Abstract In order to evaluate thermodynamic stability of constituents of LaNi 5 in 6 M KOH solution at various temperatures less than 70°C, potential–pOH diagrams in La– and Ni–H 2 O systems were drawn at various temperatures based on the thermodynamic data of La and Ni species and the reaction equations. Solubilities of La and Ni species were calculated using the evaluated pOH values at various temperatures. As a result, it was found that La(OH) 3 was extremely stable at any temperature and Ni was easily oxidized to Ni(OH) 2 and HNiO 2 − at higher temperature. The deterioration in the charge–discharge performance of LaNi 5 at high temperature was considered to be attributed to the oxidation of not only La but also Ni.

Theoretical evaluation for thermodynamic stability of constituents of Mm-based hydrogen storage alloy in 6 M KOH solution at relatively high temperatures

Abstract Potential-pOH diagrams of some components constituting AB 5 -type Mm-based (Mm: misch metal) hydrogen storage alloy were drawn at various temperatures to predict the deterioration behaviors of the alloy in an alkaline solution at relatively high temperatures. Based on these diagrams, the thermodynamic stability of each constituent of the alloy in 6 M KOH solution at various temperatures was evaluated. As A components, in the charge–discharge potential range, Nd(OH) 3 was extremely stable at temperatures lower than 70°C, while Ce(OH) 3 was oxidized to CeO 2 at the end of discharge above −0.496 V versus NHE at 70°C. On the other hand, as B components, Mn, Al and Co dissolved easily as HMnO 2 − , AlO 2 − and HCoO 2 − ions in 6 M KOH solution and their solubility increased with increasing temperature. However, HCoO 2 − ion was reduced to metallic Co at the charge process. All oxidation reactions, particularly the dissolution of Mn and Al, proceeded at relatively high temperatures.

On the Evaluation Methods of Ni-Base Corrosion Resistant Alloy for Sour-Gas Exploration and Production

Abstract The effect of Cr, Ni, and Mo contents of Ni-base alloy on the corrosion behavior in H2S—CO2—Cl− environment with elemental sulfur at elevated temperature was investigated. The environmental with elemental sulfur was more corrosive than that without elemental sulfur. The stress corrosion cracking (SSC) resistance of Ni-base alloys increases with increasing Ni and especially Mo contents. The main effect of the elemental sulfur is considered that the generation of H2S due to the cathodic reaction of elemental sulfur at a location underneath sulfur deposition, which is related to the viscosity of elemental sulfur. Recommendable chemical composition of Ni-base alloys in H2S—CO2—Cl−-S environment was proposed from the view points of phase stability, stress corrosion cracking, and hydrogen embrittlement (HE). Suitable high-Ni alloys had more than 12%Mo and 15%Cr and the phase stability parameter (Md) value below 0.911.

Effects of tungsten on precipitation behaviour of intermetallic compounds in the HAZ of duplex stainless steel: Study of weldability of high-tungsten duplex stainless steel (2nd Report)

Summary This paper describes an investigation of the effects of tungsten on the precipitation behaviour of intermetallic compounds in the HAZ of duplex stainless steel and the mechanism of these effects to clarify the advantage of having some Mo replaced by W. Fine precipitates of sigma phase are observed in electron micrographs of the simulated HAZ of a 25% Cr-7% Ni-0.3% N sample steel containing 4% Mo, whereas fine precipitates of the chi phase are observed in that containing 3% Mo and 2% W. The addition of tungsten delays sigma phase precipitation in steel aged at 850–950 °C × 600 sec. The sigma phase and austenite phase are identified in steel containing less than 8% W aged at 800–900°C, whereas the sigma, chi, and austenite phases are detected in steel containing more than 12% W. Based on these results and the chemistry data of the respective phases determined with an electron probe microanalyser (EPMA), the phase diagram at 900°C is experimentally derived. The chi phase is precipitated with a smalle...

Effects of tungsten on pitting corrosion resistance and impact toughness in the HAZ of duplex stainless steel ‐ study of weldability of high‐tungsten duplex stainless steel (1st Report)

Summary This paper describes an investigation of the effect of tungsten on the HAZ properties of duplex stainless steel in a programme to develop highly pitting corrosion resistant duplex stainless steel. The steels tested were modified SUS329J4L duplex stainless steel containing added tungsten. The welded joints produced by gas tungsten arc (GTA or TIG) welding and the simulated HAZ were evaluated in terms of the pitting corrosion resistance, impact toughness, and microstructure, including an analysis of precipitates. The results suggest that tungsten added up to 2 mass% is effective for improvement of the pitting corrosion resistance without heavy loss of impact toughness in the HAZ. Tungsten addition exceeding 3 mass%, however, decreases both the HAZ impact toughness and pitting corrosion resistance by accelerating the precipitation of intermetallic compounds during the welding thermal cycles. It is thus demonstrated that the pitting corrosion resistance in the HAZ of duplex stainless steel is improved...

Effect of Testing Temperature on Sulfide Stress Cracking of Low Alloy Steel

In this study, effects of environmental temperature on susceptibility to sulfide stress cracking (SSC)—a type of hydrogen embrittlement (HE) occurring in sour environments—of low alloy steels were ...