Microscopic Examination Of Nanosized Mixed Ni-ai Hydroxide Surface Precipitates On Pyrophyllite

摘要

The nature of Ni-hydroxide precipitates on pyrophyllite were re-examined by analytical electron microscopy (AEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), powder X-ray diffraction (PXRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy. Chemical analysis of precipitates showed that the precipitate contains about 20% Al. HRTEM imaging showed that the precipitate was amorphous and PXRD failed to find any crystalline peaks associated with crystalline Ni-AI layered double-hydroxide (LDH) or α-Ni(0H)_2. These results confirmed the conclusion from EXAFS spectroscopic data that Al coprecipitated with Ni on Al-rich substrates to form Ni-AI LDH surface precipitates. However, the HRTEM data clarifies that although the bonding environment of the precipitate is like that of Ni-AI LDH, no long-range ordering of the structure exists. The study illustrates the need for TEM observations to complement EXAFS data and the potential importance of amorphous materials in environmental settings.