Structure and Infrared Radiation Properties of Substituted Cordierites

摘要

Zn 2+ -or Ti 4+ -substituted cordierites with the nominal compositions of Mg 1.6 Zn 0.4 Al4Si5O 18 and Mg 1.8 Ti 0.2 Al 4.4 Si 4.6 O 18 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 and 29 Si 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 （Mg2Al4Si5O 18 ）, Zn 2+ -or Ti 4+ -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. 29 Si MAS NMR result indicates that Zn 2+ or Ti 4+ substitutions for partial Mg 2+ 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.