NICKEL-OXIDE ZIRCONIUM-OXIDE - NI2-TRANSITION AND SINTERING OF ZIRCONIA( INCORPORATION AND ITS INFLUENCE ON THE PHASE)

Nickel-containing zirconia samples (Ni less than or equal to 16.85%), prepared by contacting hydrous zirconium oxide with an Ni2+ solution t o a given pH were studied by various techniques (XRD, DTA, TG, XPS) to investigate the incorporation of Ni2+ in the zirconia structure in re lation to the dispersion degree of the transition-metal ions. Both dri ed (383 K) 'as prepared' and thermally treated (773 K, air) samples we re investigated. The as-prepared samples were a mixture of amorphous p articles of hydrous zirconium oxide and nickel basic nitrate crystalli tes, some very small in size, Heating at 773 K caused crystallization of the hydrous zirconium oxide and transformation of the nickel compou nd into nickel oxide. Concomitantly the nickel in the dispersed state entered the solid solution in the zirconia structure. The incorporatio n took place substitutionally in sites with trigonally distorted eight fold cubic symmetry. The presence of nickel favoured the formation of metastable tetragonal zirconia and affected the sintering process. The stability of the incorporated Ni2+ against reduction by hydrogen was also investigated.