Au based multicomponent alloys was recently discovered, showing a large glass forming ability, so that bulk amorphous materials can he obtained by copper mould casting. Bulk glassy alloys display an increased corrosion resistance and improved mechanical properties with respect to the conventional crystalline alloys. In this work, structural changes of the surface of amorphous gold based alloys were studied after corrosion resistance tests in order to relate surface morphology to tarnishing of these materials. Au gold alloys showing a large glass forming ability (Au(44)Cu(36)Ti(2)Si(18), Au(44)Cu(37)Ti(1)Si(18), Au(42)Cu(29)Ti(8)Si(21), Au(49)Cu(26.9)Ag(5.5)Pd(2.3)Si(16.3)) were produced in ribbon form by melt spinning. The surface structure of the as quenched ribbons was determined by parallel beam X ray diffraction (parallel beam XRD) and the presence of a single amorphous phase was evidenced for all samples. An incubation in artificial sweat was carried out for 7 days at 30 degrees C, following the European Standard EN 1811. The composition of the artificial sweat was 0.5% NaCl, 0.1 % lactic acid and 0.1 % urea. The pH was adjusted to 6.5 by adding an aqueous solution of ammonia. The incubation in artificial sweat produced changes of the surface that were studied by means of parallel beam XRD, scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS). The amount of ion released during incubation vias determined by Inductive Coupling Plasma - Atomic Emission Spectroscopy (ICP-AES) on the sweat solution after incubation. The Au(49)CU(26.9)Ag(5.5)Pd(2.3)Si(16.3) alloy after incubation forms, on the ribbon surface, Au nanocrystals that aggregate with SiO(2) forming particles of about 100 nm. Au(44)Cu(36)Ti(2)Si(18), Au(44)Cu(37)Ti(1)Si(18) and Au(42)Cu(29)Ti(8)Si(21) have different corrosion behaviours. Density and dimension of particles formed on the surface strictly depends on the alloy composition, so that for Au(42)Cu(29)Ti(8)Si(21) alloy a limited amount of agglomerates is formed. When particles are formed on the surface, a correspondent tarnishing of the material is observed that is more evident when larger amounts of particles are formed on the surface.
Effetto dell'attacco chimico su leghe amorfe a base Au con formazione di fasi nano cristalline
S Kaciulis;
2011
Abstract
Au based multicomponent alloys was recently discovered, showing a large glass forming ability, so that bulk amorphous materials can he obtained by copper mould casting. Bulk glassy alloys display an increased corrosion resistance and improved mechanical properties with respect to the conventional crystalline alloys. In this work, structural changes of the surface of amorphous gold based alloys were studied after corrosion resistance tests in order to relate surface morphology to tarnishing of these materials. Au gold alloys showing a large glass forming ability (Au(44)Cu(36)Ti(2)Si(18), Au(44)Cu(37)Ti(1)Si(18), Au(42)Cu(29)Ti(8)Si(21), Au(49)Cu(26.9)Ag(5.5)Pd(2.3)Si(16.3)) were produced in ribbon form by melt spinning. The surface structure of the as quenched ribbons was determined by parallel beam X ray diffraction (parallel beam XRD) and the presence of a single amorphous phase was evidenced for all samples. An incubation in artificial sweat was carried out for 7 days at 30 degrees C, following the European Standard EN 1811. The composition of the artificial sweat was 0.5% NaCl, 0.1 % lactic acid and 0.1 % urea. The pH was adjusted to 6.5 by adding an aqueous solution of ammonia. The incubation in artificial sweat produced changes of the surface that were studied by means of parallel beam XRD, scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS). The amount of ion released during incubation vias determined by Inductive Coupling Plasma - Atomic Emission Spectroscopy (ICP-AES) on the sweat solution after incubation. The Au(49)CU(26.9)Ag(5.5)Pd(2.3)Si(16.3) alloy after incubation forms, on the ribbon surface, Au nanocrystals that aggregate with SiO(2) forming particles of about 100 nm. Au(44)Cu(36)Ti(2)Si(18), Au(44)Cu(37)Ti(1)Si(18) and Au(42)Cu(29)Ti(8)Si(21) have different corrosion behaviours. Density and dimension of particles formed on the surface strictly depends on the alloy composition, so that for Au(42)Cu(29)Ti(8)Si(21) alloy a limited amount of agglomerates is formed. When particles are formed on the surface, a correspondent tarnishing of the material is observed that is more evident when larger amounts of particles are formed on the surface.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
