Improvement of strength of carbon nanotube-dispersed Si3N4 ceramics by bead milling and adding lower-temperature sintering aids

Studies on the dispersion of carbon nanotubes (CNTs) in silicon nitride (Si3N4) ceramics to provide the latter with electrical conductivity have been carried out in recent years. The density and the strength of Si3N4 ceramics were degraded, however, because the CNTs prevented Si3N4 from densifying. The CNTs disappeared after firing at high temperatures owing to the reaction between CNTs and Si3N4 or SiO2, or both Si3N4 and SiO2. In order to improve the density and suppress the reaction, sintering aids for lower-temperature densification of Si3N4 are needed. In this study, we added HfO2 as a sintering aid to a Si3N4–Y2O3–Al2O3–AlN–TiO2 system to fabricate CNT-dispersed Si3N4 ceramics at lower temperatures. Furthermore, bead milling was applied to disperse the CNTs homogeneously. Agglomerates of CNTs were pulverized by bead milling without obvious changes in morphology to eliminate larger fracture origins in CNT-dispersed ceramics. As a result of both the addition of HfO2 and bead milling, we successfully fabricated dense CNT-dispersed Si3N4 ceramics with high strength and electrical conductivity

Top-Down Tuning of Nanosized ZSM-5 Zeolite Catalyst by Bead Milling and Recrystallization

Zeolites with high external surface area allow diffusing reactants greater access to catalytically active sites, which has led to interest in the preparation of nanosized zeolites. In this study, a top-down approach has been used for zeolite synthesis by first milling the zeolite to produce nanoparticles. This technique destroys the outer portion of the zeolite framework, causing a significant decrease in its catalytic activity. To remedy this, the damaged part was recrystallized using a dilute silicate solution after bead milling. The combined bead milling and postmilling recrystallization yielded nano ZSM-5 (MFI type zeolite), approximately 60 nm in size, with high crystallinity, and the zeolite powder showed a higher catalytic activity in cumene cracking in comparison with the raw ZSM-5 zeolite. Furthermore, the decrease in crystal size suppresses catalyst deactivation through coke deposition during cumene cracking