Question

a. Draw a process diagram to produce AlN powders by carbothermic reduction process. Include all possible steps, and briefly explain each step if needed.

b. In this process, what would be the keys to obtain high quality sinterable AlN powders?

Answer 1

a)

Alumininum Nitride powder synthesis by Carbothermic reduction process.

Carbothermal reduction of Al₂O₃ to AIN involve intimate mixing of vapors of Aluminium oxide with a source of carbon at high temperature in a flowing nitrogen atmosphere or at high temperature.Rreaction temperature lies in the range of 1400 to 1500 ^oC.

Overall reaction is

Al₂O₃(s) + 3C(s) +N₂(g) = 2AIN(s) + 3CO(g)

The reaction may proceed via two steps

1. Al₂O₃ + C = Al₂O₂ + CO

2. Al₂O₂ + 2CO +N₂ = 2AIN + 2CO₂

b)

The reaction rate depends on

i) Reactivity of Al₂O₃, Particle size, and mixing :- By reducing particle size surface area increased and mixing ratio can also be improved.

ii) The degree of reaction depends on combined effect of reaction temperature, residance time in reactor, carbon source.