Abstract

Nanosized copper oxide–zirconia particles containing 10–30 mol% of copper were prepared by using a precipitation technique in aqueous tetramethylammonium hydroxide solutions. Two methods, in situ (INS) and step-by-step (SBS), which differed in the time when the copper salt was introduced to the synthesis procedure, were used, and this allowed a comparison of the properties of the final powders produced using the two modes of preparation. The surface areas and phase compositions were different for the samples prepared from the two different methods after calcination at 500 °C. A surface area of 168 m² g⁻¹ was obtained for the sample prepared with the SBS method and 121 m² g⁻¹ for the INS method, both contain 30 mol% copper. Tetragonal ZrO₂ was observed from X-ray diffraction patterns for all samples prepared with the SBS method, however, no separate phase of copper or copper oxide was observed. It is proposed that all of the copper is finely distributed on the surface of the ZrO₂ particles with the SBS method. For the samples prepared from the INS method, tetragonal ZrO₂ was obtained at a low copper content and the peaks indexed to tetragonal ZrO₂ shifted to higher angle with the increase of copper content, indicating copper ions being incorporated into the lattice. An amorphous compound was obtained at high copper content (30 mol%). The phase change with the calcination temperature was also investigated for the INS sample containing 30 mol% copper. The studies show that tetragonal ZrO₂ and copper oxide were present after calcination at 400 °C, and tetragonal ZrO₂ with a small amount of monoclinic ZrO₂, as well as copper oxide, formed after calcination at 700 °C. However, after heating at 500 °C, amorphous compounds were obtained, suggesting that 500 °C could be a phase transition point. The incorporation of copper in the ZrO₂ lattice resulted in a loss of order in the ZrO₂ structure when calcined at 500 °C, with a further increase in the calcination temperature leading to the phase change.