| Fused boric acid reacted with urea to form a solid mass having
an indefinite composition, B20 3.xNH3• It was further heated in
an atmosphere of ammonia to 900°C, when the excess urea
was removed, leaving a refractory white residue. The product
was further heated in nitrogen atmosphere at temperatures
ranging from 1100° to 1400°C for 1-4 hours. The powders
obtained were boiled in water/HCI and filtered. The washed
samples were characterized by IR and X-ray studies and
chemical analysis.
At 900°C, two soluble phases were detected: one was
isostructural with ammonium borate pentahydrate and the other
with boric acid, wherein the OH g;·oups were partially replaced
by NH2• On further heating, reactions between NH2 and
NH:zfOH led to the formation of B-NH-8 and rmally B-N bonds.
With rising temperature, increasing amounts of the soluble
phase were converted to boron oxynitride and a nitride of 90%
purity was formed at 1400°C and of95% purity at 1600°C in
an inert atmosphere. |
