Experimental Design Applied to the Chemical Durability of Sol–Gel-Derived Zirconias

A statistical design was used to investigate the effects of various processing conditions on the chemical durability of sol–gel-derived zirconias. Eight processing variables were investigated: water:alkoxide molar ratio, alcohol:alkoxide molar ratio, nitric acid:alkoxide molar ratio, mixing temperature during hydrolysis, firing temperature, heating rate, soak at firing temperature, and firing atmosphere. Processing variables were set at high and low limits in a main-effects statistical design. The design identified four critical processing variables (listed in descending order of significance): firing temperature, firing atmosphere, water:alkoxide ratio, and nitric acid:alkoxide ratio. Sol–gel-derived zirconias were characterized by differential scanning calorimetry, X-ray diffractometry, and mercury intrusion. Suggestions are offered that may help to explain why these particular processing conditions influenced the chemical durability of sol–gel-derived zirconias.