The Formation Mechanisms and Some Properties of Boron Nitride from Ammonium Thiocyanate and Orthoboric Acid

Abstract

In previous paper (Yogyo-Kyokai-Shi 77, 1 (1969)), the synthetic conditions of the hexagonal boron nitride from ammonium thiocyanate (NH4SCN) and orthoboric acid (H3BO3) were reported. In present paper, the formation mechanisms and some properties of the hexagonal boron nitride were reported.The heat-treated samples were examined by a chemical analysis, heating-loss measurement, X-ray diffraction, infrared spectroscopy, and polarizing and electron microscopy.In an ammonium atmosphere, the formation mechanism of hexagonal boron nitride could be shown as follows.nH3BO3+n/2NH4SCN160°-200°C→[-HN⋅BO(OH)]n→[HN=BH]n[I] [III]250°C→[BNH]n300°-440°C→[BNH0.8]n450°-500°C[BNH0.3]n→800°C→[BN]n[IV] [V] [IV]Borazin ring was observed to grow gradually from 250°C. A structure [IV], structure [V] and structure [VI] had eight, about eighteen, about one hundred and fifty borazin rings, respectively.In a flowing atmosphere of nitrogen, on the other hand, gas almost not played an important role on synthesis of hexagonal boron nitride, therefore while it was partially followed the same process as above mentioned, but boron oxide was simultaneously formed.The average distance of layer-plane (La) and the average distance of layer interval (Lc) values were gradually increased from 800°C and rapidly increased from about 1450°C. When samples synthesized (previous paper) were heat treated at 1450°C and 20kbar, La and Lc values became about 290 and 275 (A), respectively, and a lattice parameter C0 value was nearly equal to that of a complate hexagonal boron nitride. It was clear that pressure was much effective to grow boron nitride crystal.