Shear-Driven Chemical Decomposition of Boron Carbide

Abstract

We report, for the first time, the observation of a shear-induced decomposition of boron carbide into B 50 C 2 and nanocrystalline graphite at pressures from 1.0 to −3.5 GPa. It is proved that shear under modest compression provides finer controllability and more effective initiation capability than either compression alone or compression under high temperature. Most importantly, shear, as a driving force, is proved capable of overriding materials' energy surfaces and thus realizing new chemical reactions as well as structural transformations that have not been discovered. Consequently, shear is of great significance shedding light on new technologies for both material synthesis and advances in material sciences.

Superhard Boron-Rich Boron Carbide with Controlled Degree of Crystallinity

“…These bands are commonly associated with disordered carbon and are often referred to as the "D" and "G" bands, respectively. These two bands indicate disordered sp 2 -and sp 3 -bonded carbon in the BC-2 sample and they have been reported in the literature for the deposition of boron carbide material [7,16,21,46,47]. The Raman spectrum of the BC-2 sample matches well with that found by Gao et al in 2019 for B 50 C 2 [7].…”

“…Boron atoms in B 4 C belong to an icosahedron with a carbon chain in B 4 C or one boron atom in the icosahedron can be substituted by a carbon atom and form a C-B-C chain. In contrast, some of the boron atoms in B 50 C 2 are in single atom form and take positions in interstitial sites, with carbon being isolated [ 7 ].…”

“…Boron carbide is the third hardest material after diamond and cubic boron nitride. Elemental boron can form base structures consisting of B 12 icosahedra, B 6 octahedra, linear atomic chains, and/or atomic clusters in a three-dimensional network [ 4 , 5 , 6 , 7 ]. There are multiple possible arrangements of icosahedra, together with additional structural elements, that can form during material processing routes [ 3 , 8 , 9 ].…”

Selective Deposition of Hard Boron-Carbon Microstructures on Silicon

“…In addition to these two bands, the two broad bands centered around 1340 cm −1 and 1570 cm −1 , commonly known as “D” and “G” bands, reveal the presence of disordered carbon (bottom row). The presence of these disordered carbon bands has also been attributed to carbon in boron carbide materials in literature [ 4 , 6 , 21 ]. Combined with the similarity in XPS results from the thin-film counterparts of these B-C microstructures, they can indeed be characterized as B 50 C 2 .…”

“…The characteristic broad peaks indicating the presence of amorphous structures were observed from the sample in the top row of Figure 6 . These are the bands centered around 800 cm −1 and 1100 cm −1 which have been attributed to the B 4 C structural framework [ 21 ]. In addition to these two bands, the two broad bands centered around 1340 cm −1 and 1570 cm −1 , commonly known as “D” and “G” bands, reveal the presence of disordered carbon (bottom row).…”