| Five types of beryllia powders, one from sulphate, two
from hydroxide, and two of as received commercial
powders were studied for their densification behaviour
and microstructural development with and without a minor
addition of 1 % Fe20 3• Sinterings were carried out in
humid, dry and natural air and vacuUJl! at temperatures
between 1200°-l500°C. It is observed that beryllia_powders
with large surface areas are sensitive towards· moisture in
the sintering atmosphere resulting in low densification.
Densification for these powders is least in moist atmosphere
and maximum in vacuum. Fe20 3 addition improved
the densities in all the cases; more so in case of larger
surface area powders at lower sintering temperatures. The
influence of sintering atmosphere, surface area etc can be
virtually ignored in the presence of Fe20 3• Even inactive
powders resulted in a density of about 90% theoretical at
1500°C in presence of 1% Fe20 3• Further, the iron oxide
gets elimiitated from the system at higher temperatures
and especially in vacuum, thereby enabling utilization of
the beneficial influence ·on sintering, without its retention
in the sintered product. |
