Formation of β-alumina in CuO. Al2O3. Na2O System

Abstract

The effect of doping by varying amounts of sodium ions (as sodium hydroxide) being 2, 5 and 10% on previousiy heated CuO.Al₂O₃ mixtures having molar ratios of 0.25 : 1, 0.5 : 1 and 1 : 1 was studied. The nine CuO.Al₂O₃.Na₂O mixtures were calcined at 900ºC. Their structural characteristics were assessed through XRD analysis and complemented by IR spectral data. Accompanying morphological changes were followed through scanning electron microscopy. The calcination of the mixes produced powders with α-alumina, copper aluminate and/or copper oxide, depending on the copper content, beside the formation of abundant β-alumina. Fibrous β-alumina was obtained with the lowest CuO : Al₂O₃ molar ratio (0.25 : 1) with the 5% Na⁺ doping corresponding to 1 : 10 Na₂O : Al₂O₃. With higher sodium content (10%), corresponding to 1 : 3–5 Na₂O : Al₂O₃ as well as higher molar ratio of CuO : Al₂O₃ (0.5 : 1), (1 : 1) platy ,β-alumina was obtained. Such changes were correlated with coordination number of aluminium and the number of coordinated water species in the lattice.