Influence of the pH on Al2O3:CuO pigments prepared by a polymeric precursor method

Copper (II) aluminate, CuAl2O4, which is known to be an inverse spinel, contains a d9 metal ion and has interesting electronic, magnetic and catalytic properties. It is used in industry in ceramic pigments, coatings and catalysts. Al2O3 with 10 mol% Cu (AlCu10) was synthesised by the polymeric precursor method (Pechini method), varying the pH of the precursor solution with the addition of ammonium hydroxide and ethylenediamine. The pyrolysis of the polymeric chain was shown to occur at higher temperatures for samples prepared at higher pH values. The colorimetric coordinates depended on pH and on increasing annealing temperature. Samples heat treated at 600 and 800 C presented blue and green colours, while those at 1000 C presented brown colours. AlCu10 samples prepared with higher values of pH had lower values of colorimetric coordinates, indicating alterations in their colour. The luminosity parameters L* also increased as a function of pH.