57 research outputs found
Improved toughness of refractory compounds
The concept of grain-boundary-engineering through elimination of the grain-boundary silicate phase in silicon nitride was developed. The process involved removal of the silica from the nitride powder via a thermal treatment coupled with the use of nitride additives to compensate the remaining oxygen. Magnesium and aluminum nitrides are found to be the most effective additive for use as oxygen compensators. Strength decreases at elevated temperatures are not observed in the alumina containing material. The creep rate of a dual additive sialon composition was two orders of magnitude lower at 1400 C than commercial silicon nitride. A cursory analysis of the creep mechanism indicate that grain-boundary sliding is avoided through elimination of the grain-boundary silicate phase
Two-phase densification of cohesive granular aggregates
When poured into a container, cohesive granular materials form low-density,
open granular aggregates. If pressed upon with a ram, these aggregates densify
by particle rearrangement. Here we introduce experimental evidence to the
effect that particle rearrangement is a spatially heterogeneous phenomenon,
which occurs in the form of a phase transformation between two configurational
phases of the granular aggregate. We then show that the energy landscape
associated with particle rearrangement is consistent with our interpretation of
the experimental results. Besides affording insight into the physics of the
granular state, our conclusions are relevant to many engineering processes and
natural phenomena.Comment: 7 pages, 3 figure
Pulverization and Dispersion Technique for Agglomerated Particles of Alumina Powder in a Slurry
Densification of Alkoxide-Derived Fine Silica Powder Compact by Ultra-High-Pressure Cold Isostatic Pressing
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