Carbothermal Reduction Nitridation of Fly Ash, Diatomite and Raw Illite: Formation of Nitride Powders with Different Morphology and Photoluminescence Properties

Abstract

Rare-earth-doped SiAlON and Si3N4 materials from aluminosilicate starting materials have been reported to show superior photoluminescence (PL) properties. Three different starting materials, including pulverized coal furnace fly ash, diatomite and raw illite, were used for synthesis of nitride materials. The phase and morphology evolution of these products were carefully monitored at the low temperature range of 1350 °C to 1450 °C by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR). The PL properties of Eu-doped nitride products were also comparatively characterized. The results show that the type of starting material affects the phase composition and the photoluminescence properties of products. The existence of aluminum and alkali metals could effectively promote nitridation reactions. Aluminum in the starting materials led to the formation of different aluminum-rich nitride phases. Thus, β-SiAlON could be achieved at a much lower temperature (1350 °C) using raw illite or fly ash containing the proper amount of aluminum. Additionally, excess aluminum led to the formation of corundum and 15R-SiAlON. The products from pulverized coal furnace fly ash had more prismatic particles, and the products from diatomite had more fibrous particles. With the progress of the nitridation process, the fibers were increased, becoming longer and straighter, and the prismatic particles were more obvious. The presence of aluminum in the starting materials led to a blue shift in the photoluminescence spectrum.