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EN
We have studied the effect of leaching treatments on the surface microstructure and chemical composition on the two different twofold surfaces, (10000) and (101̅00), and the tenfold surface (00001) of a decagonal (d-) Al-Ni-Co quasicrystal. A sample exposing the three surfaces was leached with NaOH solution and then studied using atomic force microscopy and scanning electron microscopy combined with energy dispersive X-ray analysis. The leaching treatment preferentially removes the Al present in the crystal surface leaving a mixture of transition metal and their associated oxides. The high symmetry, tenfold axis was found to be less resistant to leaching than either of the twofold axes, providing further information regarding the effect of crystallographic direction on leaching kinetic.
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EN
Scanning tunneling microscopy is employed to characterise the structure and morphology of the (100) surface of the Ag-In-Gd 1/1 approximant. The surface prepared by the usual method of sputter-annealing produces step-terrace structure. Observed step heights are consistent with the lattice constant of the bulk. Scanning tunneling microscopy on terraces reveals cluster-like protrusions arranged with a square unit cell as expected from the bulk. It has not been possible to assign the terraces to the specific bulk planes because of lack of atomic resolution on terraces.
EN
In the present investigation, we have studied leaching on polygrain Al-based quasicrystalline (i-Al_{63}Cu_{25}Fe_{12}) as well as crystalline (B2 phase; Al_{55}Cu_{30}Fe_{15}) alloy surfaces using a 10 mole NaOH solution. The surface was leached at varying times from 30 min to 8 h and subsequently characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. Leaching of the samples for 30 min generated a homogeneous layer. However further leaching for 1-8 h yielded nano-size particles on the surface. Spherical microstructure has been observed on the Al-Cu-Fe crystalline surface whereas on the quasicrystalline surface a petal-like microstructure appeared. The implications of the evolution of different microstructures in the context of structure, stability and activity are discussed. The results are compared with the microstructure of leached polygrained samples containing a mixture of different surface orientations.
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