Large-scale synthesis of mullite nanowires by molten salt method.

Single-crystalline mullite (3Al2O3 2SiO2) nanowires have been produced in large quantities by a low cost and environmentally benign molten salt synthesis (MSS) method. The raw materials, Al2(SO4)3 and SiO2 powders, react in molten Na2SO4 at 1000 degrees C to produce mullite nanowires without the use of surfactants or templates. After the synthesis, the remaining salts can be easily separated from the products by washing with water. The final products are characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, selected-area electron diffraction, and inductively coupled plasma-atomic emission spectrometry. The thermal and chemical behavior of the raw materials is investigated by heating at a rate of 10 degrees C/min up to 1200 degrees C in air followed by thermogravimetric and differential scanning calorimetry analyses. The single-crystalline mullite nanowires have diameters of 30-80 nm and lengths from several hundreds of nanometers to micrometers and the growth mechanism is discussed.