Characterization of the Near-Eutectic Al2O3–40 wt% ZrO2 Composite Coating Fabricated by Atmospheric Plasma Spray. Part I: Preparation and Characterization of Nano Al2O3–ZrO2 Powder Using Sol–Gel Method

Abstract

Al(NO3)3·9H2O, ZrOCl2·8H2O, and NH4OH solution were used as starting materials to synthesize Al2O3-40 wt% ZrO2 nano composite powder for plasma spraying by sol–gel method. The results showed that δ-Al2O3 and θ-Al2O3 transformed to α-Al2O3 gradually with the heating temperature rising from 900°C to 1200°C, and only α-Al2O3 existed when the temperature reached 1200°C, while m-ZrO2 and t-ZrO2 coexisted in the system. Meanwhile, the content of m-ZrO2 went up dramatically with the rise of heating temperature and holding time. When the xerogel was heated below 1100°C with the holding time lower than 8 h, the grain size of obtained powder was less than 100 nm. In addition, the grain size of composite powder was more than 100 nm and the growth rate of α-Al2O3 was much larger than that of t-ZrO2 when the heating temperature was raised to 1200°C.