Structure and infrared radiation properties of substituted cordierites

Abstract

Zn²⁺-or Ti⁴⁺-substituted cordierites with the nominal compositions of Mg_1,6Zn_0.4Al₄Si₅O₁₈ and Mg_1.8Ti_0.2Al_4.4Si_4.6O₁₈ respectively, were prepared by a conventional solid state reaction method. The structure of the substituted cordierites was characterized by X-ray diffraction (XRD), infrared (IR) spectroscopy and²⁹Si magic angle spinning (MAS) nuclear magnetic resonance (NMR). The infrared radiation properties were investigated in the bands within 2. 5–25 μm. Compared with the un-substituted cordierite composition (Mg₂Al₄Si₅O₁₈), Zn²⁺-or Ti⁴⁺-substituted cordierites show superior infrared properties. XRD and IR results confirm the formation of hexagonal α-cordierite as the main crystal phase for the substituted cordierites.²⁹Si MAS NMR result indicates that Zn²⁺ or Ti⁴⁺ substitutions for partial Mg²⁺ of α-cordierite promoted the ordering of the distribution of Al and Si atoms in T₁ (tetrahedra connecting six-membered rings together with [MgO₆] octahedra) and T₂ (tetraheda forming six-membered rings) tetrahedral sites. This resulted in a lattice deformation and increased the anharmonicity of polarization vibration, which is responsible for the improvement of infrared radiation properties of the substituted cordierites.

Keywords

α-cordierite / infrared radiation properties / substitution / ²⁹Si MAS NMR

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