Quanli Jia

Tunable Synthesis of SiC/SiO2 Heterojunctions via Temperature Modulation

A large-scale production of necklace-like SiC/SiO2 heterojunctions was obtained by a molten salt-mediated chemical vapor reaction technique without a metallic catalyst or flowing gas. The effect of the firing temperature on the evolution of the phase composition, microstructure, and morphology of the SiC/SiO2 heterojunctions was studied. The necklace-like SiC/SiO2 nanochains, several centimeters in length, were composed of SiC/SiO2 core-shell chains and amorphous SiO2 beans. The morphologies of the as-prepared products could be tuned by adjusting the firing temperature. In fact, the diameter of the SiO2 beans decreased, whereas the diameter of the SiC fibers and the thickness of the SiO2 shell increased as the temperature increased. The growth mechanism of the necklace-like structure was controlled by the vapor-solid growth procedure and the modulation procedure via a molten salt-mediated chemical vapor reaction process.

Effect of Temperature and Additives on the Hydration Behaviour of MgO Powders

High performance MgO-based castables have many advantages for refining clean steel. However, hydration of MgO powder limits the application of MgO-based castables. The effects of temperature, hydration time and additives (calcium aluminate cement and microsilica) on the hydration behaviour of MgO powders are investigated in this paper. The results show that the hydration content of MgO powders increases noticeably with an increase of hydration time and temperature, indicating that the intensity of brucite (Mg(OH)2) diffraction peaks and the brucite amount increase. With 5 mass-% microsilica or cement addition, the amount of hydrated product Mg(OH)2 decreases noticeably from 26 to 11 mass-% and 19 mass-%. Microsilica has a retarding influence on the hydration of magnesia.