Surface structure and topology in surface stabilized Co-nanoparticles with a thin Al2O3 amorphous layer
Surface structure and topology in surface stabilized Co-nanoparticles with a thin Al2O3 amorphous layer
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DOI：
10.1016/j.apsusc.2004.04.014
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发表时间：
2004-09
影响因子：
6.7
通讯作者：
S. Rana;S. Ram;S. Seal;S. Roy
中科院分区：
文献类型：
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作者：
S. Rana;S. Ram;S. Seal;S. Roy
在700-850°C的温度下，在纯H2还原气氛中加热非晶态Co2+：AlO（OH）·αH2O凝胶，得到表面稳定的Co金属纳米颗粒，其表面具有薄的Al 2 O3陶瓷层。在加热过程中的早期温度下，凝胶分解并通过Al 2 O3（无定形）基质以精细结构分散在分开的Co2+组中。Co ~（2+）+H ~（2+）→Co ~（2+）+H ~+反应在分离的基团中进行，产生孤立的Co粒子。Al_2O_3层的形成和存在（在有限的厚度t≤ R_0范围内，R_0 ≤ 4.28nm是Al_2O_3作为稳定微晶生长的临界尺寸）控制着高能亚稳fcc或bcc Co同素异形体结构的生长过程。因此，平均微晶尺寸几乎不生长到41 nm那么大。Al_2O_3的表面能σ=0.790J/m_2，比fcc和hcp Co的表面能σ = 0.234J/m_2和0.279J/m_2大，抑制了表面原子的适度扩散，从而控制了小Co粒子的形核和生长。另外，纯Co金属颗粒在hcp体结构中快速生长。用X射线光电子能谱（XPS）对Al 2 O3表面改性fcc和bcc Co的结果进行了分析，并与X射线衍射和显微结构进行了关联。
Heating an amorphous Co2+:AlO(OH)·αH2O gel under a reducing atmosphere of pure H2gas at 700–850°C temperature results in surface stabilized Co-metal nanoparticles with a thin Al2O3ceramic surface layer. At early temperatures during heating, the gel decomposes and disperses in a refined structure in divided Co2+groups through a matrix of Al2O3(amorphous). A reconstructive Co2++H2→Co+2H+reaction operates in the divided groups to result in isolated Co-particles. Formation and existence of Al2O3layer (in a limited thickness t≤R0, with R0∼4.28nm the critical Al2O3dimension 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/m2in Al2O3, in comparison to 0.234J/m2in fcc or 0.279J/m2in 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 Al2O3surface modified fcc and bcc Co are analyzed with X-ray photoelectron spectroscopy in correlation of X-ray diffraction and microstructure.