An electrochemical recycling process of the noble metal such as Pt and Ru from the membrane electrode assemblies (MEAs) in fuel cells was investigated for the environment-friendly process without aqua regia. The dissolution rate of Pt in HCl solution was about 50 times as fast as those in H 2 SO 4 and HClO 4 solutions. The Pt dissolution rate increased linearly with HCl concentration. Pt dissolution under fluctuating potential using saw-tooth wave is 15 times faster than that under constant potentials. The electrochemical dissolution method can also be applied to the dissolution of Pt and Ru in the PtRu catalysts. The chemical methods using aqua regia, HCl-H 2 O 2 mixed solution, and HCl only were also investigated for the comparison as the electrochemical methods. The Pt dissolution rate decreased according to the order of aqua regia > 11.3 M HCl-0.36 M H 2 O 2 > 1 M HCl-10.3 M H 2 O 2 > 1 M HCl. The vaporization rate of oxidants (NOCl and Cl 2 ) from aqua regia at 333 K was 40 times as fast as that at 298 K by a spectrochemical method.

Soil-reinforcement interaction parameters used in the design of reinforced soil systems are typically evaluated by measuring pullout resistance. A combined two-dimensional and three-dimensional interaction mechanism is proposed to evaluate the pullout resistance of geogrid strip reinforcement embedded in dense granular soil. Pullout tests were conducted using uniaxial geogrid reinforcement of various specimen widths. Results from the pullout tests confirmed that a three-dimensional interaction mechanism had developed at both edges of the strip reinforcement. This interaction mechanism is caused by a confinement of the dilating zone of soil around the reinforcement as described by Schlosser and Elias (1978). For the type of geogrid reinforcement and backfill material used in this investigation, the combined interaction mechanism is applicable for a strip reinforcement width, B, greater than 20 cm. For strip reinforcement with B less than 20 cm, the influence of restrained soil dilatancy results in the development of a purely three-dimensional interaction mechanism across the strip reinforcement width.

For a strip geogrid reinforcement, pullout resistance per unit width is known to increase with decreasing specimen width at low applied normal stresses. This phenomenon can be explained by a conceptualized model for a pullout interaction mechanism consisting of combined 2-D and 3-D interaction mechanisms, and the results obtained from laboratory pullout tests can be extended to the field. In this paper, a series of pullout tests on stiff extruded geogrid specimens embedded in dense sandy gravel was carried out and the normal stresses at the soil-reinforcement interface were measured by small-diameter earth pressure cells. On the basis of these tests, the fundamental behavior of soil-geogrid reinforcement interaction is explained and the conceptualized pullout interaction model is corroborated. It is shown that restrained positive dilatancy, observed at low applied normal stresses, results in an increase in actual normal stresses at the soil-reinforcement interface at the edges of the geogrid, thereby increasing the pullout resistance of the reinforcement.

No abstract

No abstract