Using In-situ FTIR Spectrometer To Investigate The Reaction Mechanisms Of BN In Solvothermal Condition

Using Fourier transformation infrared (FTIR) spectrometer as the main tool and BBr₃ and N(CH₃)₃ as starting materials, the reaction process of Br₃BN(CH₃)₃ forming boron nitride (BN) was systematically investigated, and the formation mechanisms of both cubic boron nitride (cBN) and turbostractic boron nitride (tBN) were understood. Then according to the obtained mechanism, through improving both equipments and methods, controllable synthesis of pure phase of BN was realized. The main results are as follows:In order to well know the formation mechanism of BN from complex compound Br₃B·N(CH₃)₃, first the thermal stability of Br₃B·N(CH₃)₃ was studied and primary reaction model was proposed. Then, FTIR spectrometer was used to in-situ monitor and collect the spectra of Br₃B·N(CH₃)₃ forming BN, verifying the intermediate BrB=NCH₃ existence, and its transmutation rules with temperature and reaction time was understood. According to the monitor results, formation mechanism model of BN was presented. Furthermore, based on the verification experiments results, the proposed mechanism was modified and the reaction mechanisms of cBN and tBN in benzene-thermal condition were understood.Through the above investigation, it is known that the final product structure is directly related to the intermediate compound. Therefore, how to control the intermediate compound is the key to realize BN selective synthesis. According to the reaction mechanism model (see the Scheme 3), on one hand, the equipments in possession and synthetic methods were improved and perfected, realizing the controllable synthesis of tBN with high yield and cBN with rather high quality. On the other hand, a new selective-phase synthetic method was proposed, using which a pure and new phase of cubic boron nitride (named c₁BN) nano-crystal with rather high quality in benzene-thermal route was successfully prepared for the first time.Understanding the reaction mechanism is the base to realize the controllable synthesis of materials. However, because of the complexity and mutability of the solvothermal system, for a long time, people had to do many experiments to conclude and summarize the rules. And the solvothermal reaction mechanism in extreme conditions is a completely new subject. No one has ever studied it before. Considering these, it is the first time for us to explore the formation mechanism of BN in benzene-thermal condition. Although the results are still imperfect, it is confirmed that they are not only of strong innovation but also of great value for both basic and application studies. In addition, through systematically literature study, it is found that the raw materials for BN synthesis can be presented as BX₃ (X: H, 0, F, Br and etc) and NR₃ (R: H, Li, CH3 and so on). Thus, the mechanism proposed in this paper is rather universal. Moreover, the developed new equipments and methods are not only fit for BN preparation, but also suit to form other metastable materials.