Effect of carbon coating on spontaneous C12A7 whisker formation

A carbon nanoreactor concept was applied to study the stabilization effect of carbon shell on phase composition and morphology of dodecacalcium hepta-aluminate Ca₁₂Al₁₄O₃₃. The starting C12A7 powder was obtained using aluminum and calcium hydroxides as precursors. Carbon shell was formed by a chemical vapor deposition of divinyl at 550 °C. After the calcination at 1400 °C, the product was characterized by X-ray diffraction analysis (XRD) and high resolution transmission electron microscopy (HRTEM). It was observed for a first time that spontaneous formation of calcium aluminate whiskers take place under the conditions described. Each whisker consists of a ‘head’ (globular particle of 0.5 microns in diameter) and a ‘tail’ (prolonged whisker of few microns in length and 0.1–0.2 microns in diameter). According to HRTEM, the ‘head’ is characterized with microcrystal lattice of Ca₁₂Al₁₄O₃₃ compound. XRD data show the presence of CaAl₂O₄ phase traces. The ‘head’ and ‘tail’ of the whisker are covered with structured graphene layers of 10 nm and 3 nm, correspondingly.