Microscopic examination of nanosized mixed Ni-Al hydroxide surface precipitates on pyrophyllite.
The nature of Ni-hydroxide precipitates on pyrophyllite were reexamined 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 cnrystalline Ni-Al layered double-hydroxide (LDH) or alpha-Ni(OH)2. These results confirmed the conclusion from EXAFS spectroscopic data that Al coprecipitated with Ni on Al-rich substrates to form Ni-Al 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.
Livi
Kenneth J T
KJ
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA. klivi@jhu.edu
Senesi
Giorgio S
GS
Scheinost
Andreas C
AC
Sparks
Donald L
DL
D000535:Aluminum / Q000737:chemistry*; D000538:Aluminum Silicates / Q000737:chemistry*; D011232:Chemical Precipitation; D006878:Hydroxides / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D009532:Nickel / Q000737:chemistry*; D010316:Particle Size; D013057:Spectrum Analysis; D013499:Surface Properties; D014961:X-Ray Diffraction
D000538:Aluminum Silicates; D006878:Hydroxides; C049037:aluminosilicate; D009532:Nickel; C031356:hydroxide ion; D000535:Aluminum