Substitution of silicon within the rhombohedral boron carbide (B₄C) crystal lattice through high-energy ball-milling

Abstract

Boron carbide (B 4 C) is a ceramic with a structure composed of B 12 or B 11 C icosahedra bonded to each other and to three(C and/or B)-atom chains. Despite its excellent hardness, B 4 C fails catastrophically under shock loading, but substituting other elements into lattice sites may change and possibly improve its mechanical properties. Density functional theory calculations of elemental inclusions in the most abundant polytypes of boron carbide, B 12 -CCC, B 12 -CBC, and B 11 C p -CBC, predict that the preferential substitution site for metallic elements (Be, Mg and Al) is the center atom and that for non-metallic elements (N, P and S) it is generally the end of the three-atom chain in B 4 C's rhombohedral crystal lattice. However, Si, a semi-metal, seems to prefer the chain center in B 12 -CCC and icosahedral polar sites in both B 12 -CBC and B 11 C p -CBC. As a first step to testing the feasibility of elemental substitutions experimentally, Si atoms were incorporated into B 4 C at low temperatures (~200-400 o C) by high-energy ball-milling. High-resolution transmission electron microscopy showed that the Si atoms were uniformly dispersed in the product, and the magnitude of the lattice expansion and Rietveld analysis of the X-ray diffraction data were analyzed to determine the likely sites of Si substitution in B 4 C. Further corroborative evidence was obtained from electron spin resonance spectroscopy, magic-angle spinning nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy characterizations of the samples. Thus, a simple, top-down approach to manipulating the chemistry of B 4 C is presented with potential for generating materials with tailored properties for a broad range of applications.

Intramolecular O‐arylation using nano‐magnetite supportedN‐heterocyclic carbene‐copper complex with wingtip ferrocene

“…The peak at 283.1 eV shows bonding interactions of carbon and silicon. This fact is again confirmed by a peak around 100.6 eV in the Si 2p region (Figure g) . The peaks exhibited with binding energies at 284.4 and 286.6 eV are assigned to ferrocenyl carbons and carbenic carbon (C 2 carbon of benzimidazolium ring) bonded with Cu respectively .…”

Locating Si atoms in Si-doped boron carbide: A route to understand amorphization mitigation mechanism

“…Silicon has never been successfully incorporated to such a large extent despite multiple attempts [8][9][10][11][12][13]. The maximum solubility of Si in boron carbide, experimentally achieved, is reported to be 2.5 ±0.5 at.…”

In search of amorphization-resistant boron carbide

“…Efforts to minimize amorphization have mostly been focused on doping boron carbide with foreign atoms and forming composites. DFT analyses [39] for (B 12 )CBC and (B 12 )CCC revealed that Be, Mg, Al and Si preferred chain centers for substitution while N, P and S preferred chain ends; for (B 11 C p )CBC, Si favored polar icosahedral sites. Experimentally, doping with silicon in the icosahedra has roughly doubled the pressure required for amorphization to 67 GPa [40].…”