FORMATION, TRANSFORMATION AND SINTERING OF ZRO2-MGO COMPOSITIONS PREPARED FROM ALKOXIDES

In the ZrO2-MgO system, c-ZrO2 solid solutions containing between 5 and almost-equal-to 23 mol.-% MgO were found to crystallise at low temperatures from amorphous materials prepared by the simultaneous hydrolysis of zirconium and magnesium alkoxides. The values of the lattice parameter a decreased linearly from 0.5091 to 0.5062 nm with increasing MgO content. At higher temperatures, transformation of the solid solutions proceeded in the following way: c --> c + t + MgO --> t + MgO --> t + m + MgO --> m + MgO. Pure ZrO2 crystallised in the tetragonal form at 415-440-degrees-C. Dense ZrO2(m)-MgO composite ceramics fabricated by hot pressing for 2 h at 1350-degrees-C and 35 MPa showed increasing bend strength with increasing MgO content. A composite containing 5 mol.-% MgO gave a fracture toughness of 4.5 MPa m1/2. (C) 1993 The Institute of Materials.