Boron-rich boron carbide from soot: a low-temperature green synthesis approach
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ORIGINAL ARTICLE
Boron‑rich boron carbide from soot: a low‑temperature green synthesis approach M. S. Swapna1 · H. V. Saritha Devi1 · S. Sankararaman1 Received: 3 April 2020 / Revised: 1 July 2020 / Accepted: 13 July 2020 © The Korean Ceramic Society 2020
Abstract Boron carbide is a promising super-hard semiconducting material for refractory applications ranging from the nuclear industry to spacecraft. The present work is the first report of not only turning futile soot, containing carbon allotropes in varying composition, into boron-rich boron carbide (BC), but also developing it by a low-cost, low-temperature, and green synthesis method. The BC synthesised from gingelly oil soot is subjected to structural, morphological, and optical characterisations. The field emission scanning electron microscope shows beautiful flower-like morphology, and the thermogravimetric analysis reveals the high-temperature stability of the sample synthesised. The Tauc plot of the sample indicates a 2.38 eV direct bandgap. The formation of BC and boron-rich carbide evidenced by X-ray diffraction studies is confirmed through Raman and Fourier transform infrared spectroscopic signatures of B–C and C–B–C bonds. The fluorescence, power spectrum, and CIE analyses carried out suggest the blue light emission for excitation at 350 nm. Keyword Boron carbide · Soot · Carbon nanoparticle · Refractory · Allotropes · Green synthesis Abbreviations BC Boron carbide CNP Carbon nanoparticle CNT Carbon nanotubes EDS Energy-dispersive spectroscopy XRD X-ray powder diffraction FE Field emission SEM Scanning electron microscope TGA Thermogravimetric analysis UV–Vis Ultraviolet–visible PL Photoluminescence FT Fourier Transform IR Infrared CIE International Commission on Illumination
1 Introduction Boron carbide, also known as black diamond, is one among the hardest ceramic materials that finds a wide range of applications due to its exceptional electrical, structural, and * S. Sankararaman [email protected] 1
Department of Optoelectronics, University of Kerala, Trivandrum, Kerala 695581, India
optical properties [1–4]. Its diamond-like hardness makes it a potential material for applications in making thermal shock-resistant walls of nuclear reactors [5], abrasive powder in cutting, polishing, bulletproof vests, and in aerospace industries [6]. The BC, a covalent carbide, is said to have a complex structure existing in different stoichiometric compositions [2, 7]. The bonds boron (B)–carbon (C) or boron–boron play a significant role in deciding the structure and properties exhibited by them. The literature tells about the existence of carbon-rich as well as boron-rich carbides, having specific applications [2, 3, 8–10]. The content of boron and carbon in the precursor materials used for the synthesis decide the product formed [11–13]. The most common phase of boron carbide is the rhombohedral B4C consisting of 12-atom icosahedra with 3-atom C–B–C chains [2, 14]. The other structural forms of boron carbide include orthorhombic boron-
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