A porous (La, Sm) co-doped Sialon-polytypoid ceramic with colour and structure differences in multilayers

Abstract

In this paper, a porous Sialon polytypoid material with multilayered structure was in situ synthesized at 1700 °C for 3 h in a nitrogen atmosphere via a nitriding process. The plate-like Sialon grains were observed using a scanning electron microscope (SEM), and the chemical composition, structure, chemical state and optical absorption of this material were characterized by energy dispersive X-ray spectroscopy (EDX), synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (DRS). There are four layers with two ranges of grain sizes. The grains with sizes of 18–35 μm are in the inner layer (layer-4) and light-grey, while those grains with bigger sizes of 60–80 μm are present in the outer layers in green colour. These two types of grains have a slight difference in chemical composition, i.e. (La,Sm)_0.1Si₈Al₁₄O₅N_21.1 and (La,Sm)_0.33Si₆Al₁₂O₁N₂₁, respectively. They are polytypoids with different structures, which precipitated from the lanthanide-rich Sialon glass. The chemical states of the elements were different as indicated from XPS data. It is believed that the colour and size differences within layers resulted from the intrinsic differences of chemical composition, structure and chemical state of the two types of grains. This porous ceramic might be of potential applications in water treatment, building and automotive industries as a functionally gradient material (FGM) or ceramic filter.