Low-Temperature Preparation of α-Si3N4 Powder via Combined High-Energy Ball Milling and Molten Salt Nitridation Method

Abstract

In this work, α-Si3N4 powder was synthesized by a combined high-energy ball milling and molten salt nitridation method using silicon powder as raw materials, and NaCl-NaF binary molten salt as reaction medium and diluents. The effects of nitridation temperature, soaking time, and NaF content in the molten salt on the formation of α-Si3N4 were investigated. The results show that the nitridation of silicon powder was completed at NaF content of 10wt% in the molten salt after nitridation at 1200°C and held for 4 h. The α-Si3N4 content in the as synthesized powder is 96wt%. The α-Si3N4 whiskers with 40-280 nm in diameter and several microns to tens of microns in length appear in the final products. The crystal growth process of α-Si3N4 whiskers follows vapor-crystal (VC) mechanism.