Yoshihito Shigeno

In Situ measurement of effective gas diffusivity through hematite pellets during stepwise reductions

The Wicke-Kallenbach (W-K) method for effective gas diffusivity measurements could only be used in the vicinity of ambient temperatures. However, in the present study, this technique has been extended to temperatures of about 1273 K through use of a high-temperature cement. This newly developed high-temperature W-K method was applied toin situ measurements of the diffusive and viscous fluxes through hematite pellets during stepwise reductions. When the sam-ple (acid and basic pellets) is reduced, it swells significantly. However, a gas-tight seal between the holder and specimen was successfully maintained by use of a high-temperature cement. This cement, composed mainly of Na2O (20 mass pct) and SiO2, separates into a solid and liquid phase at elevated temperatures. Thus, it can move in the same direction as the expansion of sample and thereby maintain the gas-tight seal. With this new technique, the structural param-eters of gases based on the “dusty gas model” for D’Arcy’s flow, Knudsen diffusion, and mo-lecular diffusion were obtained. These parameters were compared with those estimated through pore structure models.

Structural changes of micropores in carbons by chemical vapor infiltration of carbon

Abstract Chemical vapor infiltration is now being used to produce advanced materials for aerospace applications. It is also applicable to carbons to enhance the resistance against oxidation. In the present study, methane pyrolysis was conducted for several kinds of carbons such as electrode-grade graphite, electrode-grade carbon, coke and activated charcoal. The structural change of micropores (radius

Infiltration of carbon in pores within coke and charcoal by methane cracking

In order to modify metallurgical coke to increase its resistance to oxidation by CO2, pores within the coke were infiltrated by methane cracking. Carbon produced by methane cracking can impregnate small pores (about 30 nm < pore radius < about 0.3μm) in which considerable oxidation takes place. This carbon can prevent CO2 from intruding into these pores, reducing the oxidation rate by one third.