Fluidized-bed nitridation of fine silicon powder

Abstract Two-micrometer average sized fine silicon-powder, mixed with 300-μm average sized alumina particles as an inert fluidization conditioner, was nitrided with 90% N2/10% H2 mixture gas in a fluidized-bed reactor, operated at temperatures ranging from 1200 to 1300°C. Both batch and semi-continuous nitridation runs were made by feeding solid mixtures of different silicon powder fractions up to 30% by mass. When the content of silicon powder was lower than 5% in the batch operation, no β-phase was found in the product silicon nitride at any temperature investigated. When mixtures containing 30% or less silicon powder were used for the semi-continuous operation, α-silicon nitride was produced at any temperatures below 1250°C, while feeding mixtures containing 20% silicon powder at 1300°C resulted in the formation of 21% β-silicon nitride. Increasing silicon powder contents in the feed mixture facilitated the formation of β-silicon nitride due to the self-agglomeration of powder, which also led to the failure of fluidization.