Solid-phase combustion synthesis of calcium aluminate with CaAl2O4 nanofiber structures

Calcium aluminate with CaAl2O4 (CA) nanofiber structures was fabricated through a facile solid-phase combustion synthesis method with raw materials of CaO2, CaCO3, Al, and Al2O3 in Ar atomosphere at a pressure of 0.1 MPa. The results indicated that the relative content of CA decreased, but that of Ca12Al14O33 (C12A7) increased with the increase of r-value from 0 to 0.5 (r is molar substitution coefficient of CaCO3 for CaO2). Interestingly, CA nanofibers with tens of micrometers in length and about 200 nm in diameter were observed in the combustion products with r = 0.2, 0.3, 0.4, respectively. The more nanofibers can be found in the products, as the content of CaCO3 in raw material ratios increased. And the yield of nanofibers in the combustion product with r = 0.4 is the highest. The typical round droplet on head of nanofiber indicated that the growth process of nanofibers was governed by vapor-liquid-solid (VLS) mechanism with base growth mode. It is proposed that both higher reaction temperature and reducing atmosphere are requirements for the growth of CA nanofiber during the process of combustion synthesis. The nanofiber cannot be generated in the samples r0, and r5, because the gaseous Ca is absent due to oxidizing atmosphere and lower reaction temperature, respectively.