Abstract:
Experimental studies were carried out to develop mullite-zircon-zirconia refractory ceramic composites from some selected clays in southwest, Nigeria. Raw clay materials were sourced from three locations. The raw clays were first characterized to determine their chemical compositions, mineralogical phases and microstructural morphology, phase analysis and phase composition. The results obtained were used to select the most appropriate clay for further processing. Measurements were made of the mechanical properties of ceramic bodies produced from the selected clay in accordance with ASTM specifications. Microstructural morphology as well as phases developed by the ceramic bodies was also determined. Additives such as zirconia, niobium oxide and yttria in pre-determined proportions were made to the selected clay. Test samples were fabricated from the homogenous mixtures of the selected clay and additives. The compacted sintered samples were subjected to various tests and analytical methods to determine the mechanical properties. Phase compositions and microstructural morphology studies were also determined. The mechanical properties of the samples were then compared using a table of numerical indicators. The comparative cost of production per kilogram of monolith of each of the samples investigated was determined. The results obtained showed that the addition of zirconia and yttria favour the formation of mullite fibers phase as reinforcement in the ceramic matrix thereby forming toughened refractory ceramic composite at a temperature range of 1400oC to 1500oC. The presence of mullite and zirconia phases in some samples, coupled with the process of stress-induced transformation toughening give them a superior mechanical property compared to the other samples which did not contain mullite. The sample ET3/1 [30% (vol.) ZrO2, 70% (vol.) clay system fired at 1400oC and held for 1 hour] was considered to be very suitable while samples DT3/3 [40% (vol.) ZrO2, 60% (vol.) clay system fired at 1400oC and held for 3 hours] and DT4/2 [40% (vol.) ZrO2, 60% (vol.) clay system fired at 1500oC and held for 2 hours] were considered suitable. It was then concluded that mullite-zircon-zirconia refractory composite of optimum mechanical property was achieved with the composition 30% (vol.) ZrO2, 70% (vol.) clay system fired at 1400oC and held for 1 hour.
