Steam reforming of methanol (CH 3 OH+H 2 O→3H 2 +CO 2 ) has been performed on a stable AlCuFe quasicrystal for the first time. The AlCuFe quasicrystal reveals excellent activity, after leaching treatment. The production rate of H 2 reaches 235 l/kg min at 573 K for steam reforming of methanol. The activity is due to Cu nanoparticles at the surfaces of quasicrystalline grains which are generated by the leaching treatment. The quasicrystals have two advantages: one is their brittle nature, which allows them to be crushed efficiently; the other is the involvement of Fe, which suppresses the sintering of Cu particles.

Highly active quasicrystalline Al-Cu-Fe catalyst for steam reforming of methanol

We report the preparation of the quasicrystalline particle-dispersed Al base composite alloys for the first time. Icosahedral AlCuFe quasicrystalline (i-AlCuFe) particles were homogeneously dispersed in a crystalline Al matrix using a novel process which combined mechanical alloying and hot press techniques. Hardness of the composite alloy increases with increasing volume fraction of the i-AlCuFe particle, i.e., increases from 25 kg/mm2 for pure Al to about 120 kg/mm2 for a 25 vol. % i-AlCuFe particle dispersed alloy.

Synthesis of stable quasicrystalline particle-dispersed Al base composite alloys

The coefficient of thermal expansion (α), Young's and rigid moduli (E and G), Poisson's ratio (v), compressive yield and fracture strengths (σ y and σ f ), fracture toughness (K), Vickers hardness (H v ) and cleavage fracture mode were examined along two-, three- and five-fold symmetry axes for an Al 70 Pd 20 Mn 10 single-quasicrystal prepared by the Czochralski method. In the temperature range below 600 K, α is 1.3×10 -5 K -1 which is about 50% as high as that for conventional Al-based alloys

Mechanical properties, fracture mode and deformation behavior of Al70Pd20Mn10 single-quasicrystal

Quasicrystal application on catalyst

Quasicrystals (QCs) exhibit unusual physical properties that are significantly different from those of crystalline materials and are not expected for alloys consisting of normal metallic elements. Opposite to conventional metallic alloys, their thermal conductivity and diffusivity are unusually low (with a positive temperature coefficient)—practically that of an insulator—which is atypical for materials containing about 70-at.% aluminum. Moreover the thermal conductivity decreases when the structural perfection is improved. One observes a low, if any, electronic contribution to the heat capacity and thus a vanishing density of electronic states at the Fermi level.The origin of this unexpected behavior was first attributed to the existence of a deep pseudogap at the Fermi level with a localization tendency of electrons near the Fermi level.However experimental evidence led to an alternative approach related to the structure of quasicrystals. In QCs, well-defined atomic clusters form self-similar subsets of the structure over which electronic and vibrational states are expected to extend. According to the inflation symmetry of the icosahedral structure, the so-called recurrent localization effects may then explain the conduction behavior and other striking features of quasicrystals (e.g., brittleductile transition at high temperature, corrosion resistance, low friction, high hardness).In the following, we first present the main thermal properties of quasicrystalline alloys compared to those of conventional materials with an emphasis on the variation of the thermal conductivity with temperature. The combination of such peculiar conduction, mechanical, and tribological properties gives the quasicrystalline alloys a technological interest for applications where superficial thermal and mechanical conditions are of prime importance. This is illustrated with two examples involving a QC coating on a base Al substrate: (1) thermal insulation for which a low conductivity is needed and (2) quenching heat-transfer modification due to a low-effusivity superficial effect. These processes are then explained in the third part of this article in terms of the cluster-modes delocalization mechanism responsible for the low conductivity of the quasicrystals.

Thermal Conductivity of Quasicrystals and Associated Processes

Temperature dependence of hardness and expansion in icosahedral Al72Pd20Mn8 alloy (i-AlPdMn) are examined in comparison with a cubic Al60Pd25Mn15 alloy (c-AlPdMn). The hardness at room temperature is about 780 kg/mm2 for i-AlPdMn, much greater than that for c-AlPdMn of 420 kg/mm2, and decreases to about 200 kg/mm2 at 973 K. The thermal expansion of i-AlPdMn is found to be linear versus temperature and the thermal expansion coefficient is estimated to be ~14.6×10-6 K-1.

Hiroshi Suenaga

Papers

Temperature Dependence of Hardness and Expansion in an Icosahedral Al-Pd-Mn Alloy