No abstract

Covalently bonded ceramics exhibit preeminent properties—including hardness, strength, chemical inertness, and resistance against heat and corrosion—yet their wider application is challenging because of their room-temperature brittleness. In contrast to the atoms in metals that can slide along slip planes to accommodate strains, the atoms in covalently bonded ceramics require bond breaking because of the strong and directional characteristics of covalent bonds. This eventually leads to catastrophic failure on loading. We present an approach for designing deformable covalently bonded silicon nitride (Si 3 N 4 ) ceramics that feature a dual-phase structure with coherent interfaces. Successive bond switching is realized at the coherent interfaces, which facilitates a stress-induced phase transformation and, eventually, generates plastic deformability.

A simple method to prepare two-dimensional hexagonal boron nitride (h-BN) scalably is essential for practical applications. Despite intense research in this area, high-yield production of two-dimensional h-BN with large size and high crystallinity is still a key challenge. In the present work, we propose a simple exfoliation process for boron nitride nanosheets (BNNSs) with high crystallinity by sonication-assisted hydrothermal method, via the synergistic effect of the high pressure, and cavitation of the sonication. Compared with the method only by sonication, the sonication-assisted hydrothermal method can get the fewer-layer BNNSs with high crystallinity. Meanwhile, it can reach higher yield of nearly 1.68%, as the hydrothermal method with the yield of only 0.12%. The simple sonication-assisted hydrothermal method has potential applications in exfoliating other layered materials, thus opening new ways to produce other layered materials in high yield and high crystallinity.

No abstract

In this work, an efficient carbothermal reduction–nitridation strategy was rationally designed and delicately tailored to directly synthesize spherical granules of aluminum nitride. Effects of processing parameters, such as N2 pressure, additives and temperature on the nitridation ratio, especially on the morphologies of the AlN granules were elaborately investigated. The experimental results showed that the elevated N2 pressure of 0.9 MPa and additives of CaF2 and Y2O3 greatly favored for forming micrometer‐sized AlN granules with smooth spherical appearance. More significantly, the underlying formation mechanism of spherical morphology and large particle size was also attentively put forward.