Study On Structure And Properities Of Solution Plasma Spray Nano-ZrO₂/Y₂O₃ Coatings

In this paper, ZrOCl2·8H2O and Y2O3 were used as raw materials to prepare zirconium hydroxide sol which employ by positive titration method of NH3-H2O. Solution Precursor Plasma Spray (SPPS) had been used for the formation of yttria partially stabilized zirconia (ZrO2/Y2O3) nanostructured coatings from the solution precursor feedstock instead of conventional reconstituted nanopowder feedstock. The structures and properties of sol and coatings were characterized by TEM, SEM, EDS, XRD, TG-DSC, VIDAS imagine analyzer, granulometer, TH310 rockwell hardness tester etc.ZrOCl2·8H2O and Y2O3 were dissolved in water or absolute ethyl alcohol to occur hydrolyzation reaction and polymerization reaction simultaneously under the precipitator of NH3-H2O:In dilute solution the main existed form of Zr was mononuclear ZrO22+; when the ion concentration of Zr4+ was greater than 10-3mol/L and the ion concentration of H+ was in the range of 0.75～1 mol/L, the polymerization reaction begined resulting in [Zr3(OH)4]8+ trimer; when the ion concentration of Zr4+ set up to 1.6×10-1mol/L, the existed form of Zr was multinuclear complex whole; in the case of the ion concentration of H+ less than 0.75mol/L, the trimer transform into hexamer. When the ion concentration of Zr4+ or H+ were high relatively, the main existed form of Zr was tetramer [Zr4(OH)8 (H2O) 16]8+, the tetramer contain Zr (Ⅳ), two bridged linkage hydroxyl and tetrahydrate. The sol transformed into gel [Zr4(OH)8-x (H2O) 2x·yH2O]n after solation.The experiments analysis:the sol which the molar concentration was 0.8 mol/L, pH was in the range of 4-6 and the size of colloidal particle was in the range of 80～100nm were be suit for the feedstock in SPPS. The coatings result in melted particles in the technological parameter of the precusor molar concentration was 0.8 mol/L, the jet distance was 80 mm, the current intensity was 500 A, the voltage was 80 V, the pressur of atomization was 0.4 MPa, the rate of feed was 120 g/min, and the TEM analysis showing the grain size was in the range of 20-30 nm. SEM micrograph show the SPPS coatings's structure was quite uniform which different from TBC resulting from conventional reconstituted nanopowder feedstock. The new type SPPS coatings not have lamellar structure, and the main factor which most influence coating's structures and properties were the precusor molar concentration, the mixture ratio of solvent, the pressur of atomization and the rate of feed.The coatings which prepared by different precusor or in different technological parameter would have different porosity, different hardness, different bond strength and different thermal shock resistance. The SPPS coatings have excellent thermal shock resistance, which was better than conventional coatings. The SPPS coatings's excellent thermal shock resistance were related to the microstructure of themselves. For SPPS, the power were 40 KW(500 A×80 V), the precusor molar concentration was 0.8 mol/L, the jet distance was 80 mm, the pressur of atomization was 0.4 MPa, the rate of feed was 120 g/min, the prepared coatings would have better microstructure and better properties.