Catalytic effects were investigated on the direct nitridation of silicon granules, impregnated with 0.125-2.0% by mass or calcium, yttrium, iron, copper, silver, chromium, or tungsten, in a stream of nitrogen with 10% hydrogen, using a tubular flow reactor operated at temperatures ranging from 1200 degrees to 1390 degreesC. Calcium and yttrium suppressed the formation of beta -silicon nitride while iron enhanced the formation of beta -silicon nitride over the temperature range investigated. An addition of 0.125% calcium resulted in about 99% overall conversion with 100% alpha -phase and a 2.0% yttrium addition yielded an overall conversion over 98% with an alpha -phase content above 97%. Copper promoted not only the nitridation but the formation of alpha -silicon nitride at 1200 degreesC, but enhanced the beta -phase formation at higher temperatures. The role of liquid phases on the formation of alpha-/beta -silicon nitride was also discussed based on the nitridation of silicon impregnated with copper, calcium, silver, chromium, and tungsten.