A novel synthesis of nano-sized mullite from aluminosilicate precursors

A novel method was proposed for the preparation of aluminosilicate-based ceramic materials by temperature induced transformation of amorphous aluminosilicates (zeolite precursors) as an alternative to conventional methods based on the thermal treatment of kaolin, feldspar and other silicate, aluminosilicate and/or oxide mixtures, or by sol–gel method.Amorphous aluminosilicate gels that are usually used as precursors for the crystallization of zeolites after exchanging their host's cations (sodium) with ammonium cations from solution were thermally treated (at 1263 K for 3 h) and yielded a mixture of mullite and amorphous silica. Further chemical treatment of the mixture with sodium hydroxide solution yielded a pure mullite phase having particle size below 100 nm.

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► A: Gel: (NH4)2O·Al2O3·2.6 SiO2·2.3 H2O.
► Heated isothermally at 1263 K for 3 h.
► Transforms to B: a mixture of mullite and amorphous SiO2.
► Further chemical treatment of the mixture with sodium hydroxide solution yielded to C: pure mullite.