Multiple-Quantum and Cross-Polarized 27Al MAS NMR of Mechanically-Treated Mixtures of Kaolinite and Gibbsite

Mixtures of the clay mineral kaolinite with gibbsite, when heated, form mullite, a high-temperature ceramic. The Al-27 multiple-quantum magic angle spinning (MQMAS) NMR technique is used to study the local Al environment in mixtures of kaolinite and gibbsite that have been ground together for varying amounts of time. This mechanical treatment forms new chemical species that are amorphous in nature and, therefore, unsuited to analysis by X-ray diffraction. Both novel and established cross-polarization techniques are employed to characterize the starting materials and mixtures, confirm the spatial proximity of H-1 and Al-27 nuclei, and "edit" the two-dimensional Al-27 MQMAS NMR spectra, thereby allowing overlapping peaks corresponding to octahedral Al sites to be studied.