Investigation on the key factors in the hydrothermal synthesis of BN: The way of introducing sodium azide

Abstract

The way of introducing sodium azide (NaN3) into the reaction solution played an important role in the preparation of cBN by hydrothermal synthesis method. The results showed that both cBN content and crystalline perfection of the samples improved with increasing RN value, and pure cBN could be obtained at 300°C and 10 MPa when RN increased to 3:1. Here RN is defined as RN = NaN3(I)/NaN3(II), where NaN3(I) denotes the amount of NaN3 (in molar) that is added into the autoclave at the beginning of the reaction process, and NaN3(II) is the amount of NaN3 (also in molar) introduced into the autoclave at high temperature and high pressure (i.e. 300°C and 10 MPa). In order to explain the experimental results, a preliminary model was proposed in this paper.