ALUMINUM NITRIDE 153- What explanation can you give for the action of potassium
hydroxide in facilitating the change of the black to the red modi-
fication?
PREPARATION 13
ALUMINUM NITRIDE, A1N
The very active metals are capable of combining directly with
nitrogen to form nitrides. In the air the oxide is formed so much
more readily, that nitride formation is likely to escape notice;
but if the metal is presented in powdered form in a thick mass
the oxygen is all combined in the surface layer and only nitrogen
penetrates to the interior where pure nitride is formed.
Although aluminum is a very active metal, it enters into many
reactions with extreme difficulty on account of a thin, tenacious
coating of oxide, which keeps it physically separated from the
reacting material. Aluminum powder alone cannot be made to
burn in air, but when it is mixed with lampblack and any part is
brought to the kindling temperature, which is very high, the com-
bustion spreads throughout the mass. The function of the carbon
is to react with this oxide layer. Carbon alone reacts with alu-
minum oxide to yield the carbide
2A1 2 O 3 + 9C -» A1 4 C 3 + 6COIn the presence of nitrogen, however, the nitride instead of the
carbide is produced.
A1 2 O 3 + N 2 + 3C -> 2A1N + 3CO
Materials: finely powdered aluminum, 45 grams. The ma-
terial sold for use as a pigment and often labeled
" aluminum bronze " is nearly pure aluminum and
is suitable for the purpose. The small amount of
oil which it contains is no disadvantage,
carbon, lampblack, 5 grams,
magnesium ribbon, 4 inches.
Apparatus: 8-iiich square of asbestos paper to be laid on a
thick iron plate.
large porcelain mortar and pestle,
dark-colored glasses may be worn to protect the
eyes from the blinding light.
Bunsen burner.