The effect of niobium oxide additives and sintering temperature on the phase developments and physico-mechanical properties of zirconia-clay ceramic composite was investigated. The clay of known mineralogical composition was source from a large deposit in Ile-Ife, in Osun State Nigeria. The beneficiated clay, was milled to a particle size of 300 μm. The milled clay was blended with varied percentages of yttria stabilized zirconia and niobium oxide powders in a tubular mixer for 18 hours at a speed of 72 rev/min. From the blended powders, standard samples were produced by uniaxial compression. This was followed by sintering in an electric furnace at 1200 oC and 1300 oC for one hour. The sintered samples were characterized for various physical and mechanical properties. The phases developed in the sample during sintering were also investigated using X-ray diffractometer (XRD). Morphology and microanalysis of the sintered ceramic composite samples were determined using ultrahigh resolution field emission scanning electron microscope (UHR-FESEM) equipped with energy dispersive spectroscopy (EDS). It was observed that at 1200 oC the presence of niobium oxide in the samples favours the decomposition of zircon to silica phases and zirconia. It was also observed that the combined effects of increased sintering temperature to 1300 oC and addition of niobium oxide favour the formation of more sillimanite in preference to mullite. At 1200 oC niobium oxide additive inhibits the formation of mullite in preference to the formation of aluminum niobate and sillimanite. It also favours decomposition of zircon to the silica phases and zirconia. Increase in the niobium oxide content lead to increased bulk density at 1300 oC. It was concluded that the sample with optimum physico-mechanical properties is considered to be sample FT2 with 10% ZrO2, 0% Nb2O5, 90% clay and sintered at 1300 oC held at the sintering temperature for 60 minutes

Keywords: Niobium oxide additives, sintering temperature, phase developments, physico-mechanical properties, zirconia-clay, ceramic composite.