Papers by Author: Keiichi N. Ishihara

Abstract: In this work, 10 wt.% stainless steel (AISI304, FeCrNi) was used as a binder in WC-based hardmetal. Graphite powder (2 wt.%) was added in the mixture to avoid the formation of η-phase ((MW)₆C) during sintering. NbC with 1, 1.5, 2 and 5 wt.% was used as WC grain growth inhibitor. The sintering process was done in a vacuum furnace at 1300°C for 1h. The results showed that there was no formation of η-phase or free graphite after sintering indicating the suitability of added graphite. Increasing the NbC contents resulted in decreasing of WC grains. 2 wt.% NbC was considered to be the optimal content for fine microstructure and uniform WC grain distribution. The highest hardness was achieved at 2 wt.% NbC with HV₃₀ of 1660 kg/mm². However, higher amount of added NbC (5 wt.%) caused the existence of coarse (Nb,W)C grains which decreasing the hardness.

Abstract: Catalytic ability on 12 kinds of carbide powders was investigated at room temperature using NOx gas degradation. They are largely classified into two groups, depending on whether the reaction involves a nitrogen gas in air or not. The carbon dangling bonds largely contribute to the reaction, while the accompanied metal atoms play an important role for adsorbing/dissociating nitrogen gas. Mechanical milling or annealing, as long as without agglomeration, is an effective method for activating powder catalysis, producing new surfaces with plenty catalytic sites. A new concept of catalysis is presented, based on the Schottky barrier-like model, where the charge imbalance is produced at the interface between the non-uniform thin oxide and the carbide.

Abstract: Lithium is one of the active metals and reacts with nitrogen even at room temperature. In this study, in order to grind and activate Li, the mechanical milling of Li with stable metal oxide, namely, Al2O3 and MgO, using a high energy vibrating ball mill was performed. In the case of Li- MgO system, it reacts with N2, but hardly reacts with O2. The reaction with N2 generally produces Li3N, while for some vigorous reactions the Mg3N2 and Li2O are produced as the major phases. In the case of Li-Al2O3 system, however, reactivities with both N2 and O2 are high. The difference will be explained in terms of the reaction mechanism and the Li state.