Colloidal filtration of alumina-zirconia with solid oxide additives / Hakimeh Wakily

Homogeneous ceramic composites of alumina and zirconia (3 mol % yttria stabilized zirconia) with small amount of solid oxides were prepared using colloidal filtration method. The purpose of using zirconia was to provide zirconia toughened alumina (ZTA) including 15wt% zirconia. And to improve the microstructure and density of ZTA, less than 0.5 wt% of magnesia was added. Solid oxide lubricant (CuO) was doped in small quantities (≤1 wt %) to provide a self-lubrication action and thereby to decrease the coefficient of dry friction. Suspension of alumina as well as the second phase materials was prepared with various solid loadings and various concentrations of surfactant. Dolapix CE64 and Tiron were used as surfactant and their influence on the stability of solid oxide particles in suspension was investigated. The rheological properties of suspension were studied by measuring zeta-potential and viscosity. The satisfactory mixtures were made into sample pallets using colloidal filtration. The process was completed with pressurless sintering in 1550 ºC. Phase, grain size and qualitative compositional analysis were done using X-ray diffraction (XRD) and scanning electron microscopy (SEM) images. Density of green and sintered compounds was measured using Archimedes method. The mechanical properties evaluated by hardness and fracture toughness measurements (Vickers indentation method). The tribological properties of composites were investigated by wearing test and coefficient of friction procured for different compound against the zirconia ball. Densification studies show that near full density (>99%) was obtained. ZTA composite with MgO shows high value of hardness (up to 20 GPs) and enhanced fracture toughness (3.7 MPa.m-1/2). MgO-CuO doped ZTA also presents high value for hardness and fracture toughness (19.7 GPs and 4 MPa.m-1/2 respectively). Wearing resistant of CuO-doped ZTA was improved and coefficient of friction for CuO-doped composite against zirconia shows slightly decreases with distance