Title

Surface Structure And Topology In Surface Stabilized Co-Nanoparticles With A Thin Al 2 O 3 Amorphous Layer

Keywords

Microstructure; Nanocermets; Phase transformation; Surface modified Co-nanoparticles; Surface topology; X-ray diffraction; XPS analysis

Abstract

Heating an amorphous Co 2+ :AlO(OH)·αH 2 O gel under a reducing atmosphere of pure H 2 gas at 700-850°C temperature results in surface stabilized Co-metal nanoparticles with a thin Al 2 O 3 ceramic surface layer. At early temperatures during heating, the gel decomposes and disperses in a refined structure in divided Co 2+ groups through a matrix of Al 2 O 3 (amorphous). A reconstructive Co 2+ +H 2 →Co+2H + reaction operates in the divided groups to result in isolated Co-particles. Formation and existence of Al 2 O 3 layer (in a limited thickness t≤R 0 , with R 0 ∼4.28nm the critical Al 2 O 3 dimension to grow as a stable crystallite) over growing Co-particles control the process in a high-energy metastable fcc or bcc Co allotrope structure. Average crystallite size thus hardly grows to be as big as 41nm. A large value of surface energy σ = 0.790J/m 2 in Al 2 O 3 , in comparison to 0.234J/m 2 in fcc or 0.279J/m 2 in hcp Co, inhibits a moderate diffusion of surface atoms and in turn controls the nucleation and growth in small Co-particles. Otherwise, a particle of pure Co metal grows rapidly in the hcp bulk structure. The results of the Al 2 O 3 surface modified fcc and bcc Co are analyzed with X-ray photoelectron spectroscopy in correlation of X-ray diffraction and microstructure. © 2004 Published by Elsevier B.V.

Publication Date

9-15-2004

Publication Title

Applied Surface Science

Volume

236

Issue

1-4

Number of Pages

141-154

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1016/j.apsusc.2004.04.014

Socpus ID

4043153465 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/4043153465

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