A new blue-coloured ceramic pigment has been designed within the Al2O3-MoO3 system and characterised from the structural, spectroscopic and technological viewpoints. The Al2O3-MoO3 system has been thoroughly investigated in the last decade for its well-known catalytic activity. Alumina-supported molybdena changes its structure from isolated polyhedra (tetrahedrically- to octahedrically-coordinated) to crystalline oxide of Mo(VI), Mo(V) or Mo(IV) depending on increasing loading, oxidising/reducing conditions, with a partial molybdenum sublimation at higher firing temperature. The MoO3 loading (8-15% wt) was designed in order to get different molybdena structures. Synthesis was carried out at 1300-1470°C in H2-nitrogen 5-95% atmosphere and the pigments were characterised by SR-XRD, XRPD-Rietveld, DRS, XPS, BET. The XRPD results show that the no Mo for Al substitution into the bulk ?-Al2O3 structure occurs: alumina cell parameters corresponds to those of pure corundum. For the lower loadings, no evidence for any molybdenum phase was observed in the XRD patterns, while for increasing loading some tugarinovite (MoO2) was found. These findings are in fairly good agreement with early reports for molybdena-alumina catalysts (Chung & Massoth, 1980). The presence of molybdenum in alumina has been interpreted as due to both Mo in tetrahedral sites on or near the surface of Al2O3 particles and Mo octahedral species, the former being almost irreducible and the latter, more reducible, increasing with loading. The colour does not change much for increasing loading. Being Mo(VI) the only valence detected by XPS in the lower loadings, the colouring mechanism is thought to be a metal-ligand charge transfer. The Al2O3-MoO3 exhibits a surprisingly good technological behaviour for a chemi-adsorbed pigment, being stable in a wide range of ceramic applications, including glazes, frits and bodies from 1000 to 1250°C. The dark blue colour is rather stable even in presence of aggressive components, such as CaO, ZnO, MgO or PbO.
Gray-blue Al2O3-MoOx ceramic pigments: crystal structure, colouring mechanism and technological performance
Dondi M;
2005
Abstract
A new blue-coloured ceramic pigment has been designed within the Al2O3-MoO3 system and characterised from the structural, spectroscopic and technological viewpoints. The Al2O3-MoO3 system has been thoroughly investigated in the last decade for its well-known catalytic activity. Alumina-supported molybdena changes its structure from isolated polyhedra (tetrahedrically- to octahedrically-coordinated) to crystalline oxide of Mo(VI), Mo(V) or Mo(IV) depending on increasing loading, oxidising/reducing conditions, with a partial molybdenum sublimation at higher firing temperature. The MoO3 loading (8-15% wt) was designed in order to get different molybdena structures. Synthesis was carried out at 1300-1470°C in H2-nitrogen 5-95% atmosphere and the pigments were characterised by SR-XRD, XRPD-Rietveld, DRS, XPS, BET. The XRPD results show that the no Mo for Al substitution into the bulk ?-Al2O3 structure occurs: alumina cell parameters corresponds to those of pure corundum. For the lower loadings, no evidence for any molybdenum phase was observed in the XRD patterns, while for increasing loading some tugarinovite (MoO2) was found. These findings are in fairly good agreement with early reports for molybdena-alumina catalysts (Chung & Massoth, 1980). The presence of molybdenum in alumina has been interpreted as due to both Mo in tetrahedral sites on or near the surface of Al2O3 particles and Mo octahedral species, the former being almost irreducible and the latter, more reducible, increasing with loading. The colour does not change much for increasing loading. Being Mo(VI) the only valence detected by XPS in the lower loadings, the colouring mechanism is thought to be a metal-ligand charge transfer. The Al2O3-MoO3 exhibits a surprisingly good technological behaviour for a chemi-adsorbed pigment, being stable in a wide range of ceramic applications, including glazes, frits and bodies from 1000 to 1250°C. The dark blue colour is rather stable even in presence of aggressive components, such as CaO, ZnO, MgO or PbO.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
