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.
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA. klivi@jhu.edu
Kenneth J T
KJ
Livi
Giorgio S
GS
Senesi
Andreas C
AC
Scheinost
Donald L
DL
Sparks
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