Low‐Temperature Synthesis of Highly Crystallized Hexagonal Boron Nitride Sheets with Li₃N as Additive Agent

Abstract

Highly crystallized hexagonal boron nitride (h‐BN) sheets were obtained by a versatile method modifying the original synthesis by using an additive agent and, as a consequence, decreasing the temperature for the ceramization step (1200–1400 °C). This synthesis is based on the polymer‐derived ceramics (PDCs) route using liquid‐state polyborazylene (PBN) mixed with lithium nitride (Li3N) micropowders as additive agent. We have demonstrated that incorporation of Li3N as a crystallization promoter allows the onset of crystallization of h‐BN at lower temperatures. Consequently, a high crystallization rate can be obtained from 1000 °C for bulk boron nitride, whereas the temperature has to be 1600–1800 °C under classical conditions. A series of samples incorporating Li3N (5 wt.‐%) and annealed at various temperatures from 600 to 1400 °C was prepared and structurally characterized by Raman spectroscopy, XRD analyis, and TEM. Well‐crystallized sheets with thicknesses of nanometers can be easily obtained by applying this method.

How to Increase the h-BN Crystallinity of Microfilms and Self-Standing Nanosheets: A Review of the Different Strategies Using the PDCs Route

“…and pressure [90][91][92][93][94]. Based on these relevant results, we decided to add lithium nitride (Li3N) in pure PBN in order to lower the onset crystallization temperature [95].…”

Catalyzed synthesis of rhombohedral boron nitride in sodium chloride molten salt

“…In addition, except some bend BN sheets broken down and fractured into flakes, the morphology was not changed before and after the transformation of t-BN. So the crystallization mechanism is not attributed to the dissolution and precipitation mechanism [31] which is widely used to explain the BN crystal phase change. Na may act as a catalyst in the transformation of t-BN into r-BN.…”

“…Reducible substances such as NaBH 4 or NaNH 2 were frequently used by researchers to synthesized r-BN in an autoclave [25][26][27][28][29][30]. Yuan [31] found t-BN was thermally transformed into a mixture of h-BN and r-BN in the present of Li 3 N after heating at 1000-1400°C. But few studies have been done on the formation mechanism of r-BN.…”

Novel chemical process for preparing h-BN solid lubricant coatings on titanium-based substrates for high temperature tribological applications

“…In previous work, we pointed out the effect of lithium nitride (Li 3 N) as a crystallization promoter to produce highly crystallized h-BN at a temperature of only 1000°C. The lowering of the onset crystallization temperature may expand the possible h-BN coating on metallic substrates [16].…”