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Properties And Preparation Of Al2O3-ZrO2 Composite Nanopwders By Novel Co-precipitation Method

Posted on:2017-02-06Degree:MasterType:Thesis
Country:ChinaCandidate:L XiaoFull Text:PDF
GTID:2271330503485427Subject:Materials science
Abstract/Summary:PDF Full Text Request
Nano-composite ceramics have become a research hotspot among high performance ceramics due to their high temperature resistance, corrosion resistance,high hardness and high toughness etc. Al2O3-ZrO2 composite ceramic is a new type of ceramic with great development potential, because of its excellent mechanical properties, low thermal conductivity and good chemical stability. Preparation of Al2O3-ZrO2 composite powders with excellent properties is very important in the preparation of Al2O3-ZrO2 composite ceramics. The key of the composite powder preparation is to solve the problems of powder agglomeration and chemical composition nonuniformity, i.e., the preparation of Al2O3-ZrO2 composite powders with less agglomeration, small particle size and uniform chemical composition is necessary.Uniform Al2O3-ZrO2 composite ceramic nanopowders were prepared by a novel co-precipitation method using ZrOCl2·8H2O,Al(NO33·9H2O,Y(NO33 as raw materials, ammonium carbonate hydroxide(AHC)as complex agent.The effects of precipitants and processing on the composite nanopowders were characterized systematically by X-ray diffraction analysis(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM) and laser particle size analyzer.The results showed that in the complexation reaction when we used AHC as the complex agent,zirconium salts were firstly dissolved in a solution of carbonate(AHC),formed a dissolvable complex ion in form of [Zr(CO3x(OH)4-x]x-. In the process of co-precipitation,EDA not only was the pH regulator but cationic complex agent,it could react with the Al3+ and Y3+ salt to form the chelate, finally a complex precipitate contained Zr4+, Al3+ and Y3+ evenly was obtained.The effects of the pH and mole ratio of AHC/Zr on the Al2O3-ZrO2 nanopowders were examined in detail,The precursor was prepared in the condition of pH7.0,AHC/Zr molar ratio was 5:1,Homogeneous,nanosized and high purity Al2O3-ZrO2(Y2O3) composite powders could be obtained.ZTA composite ceramics with uniform distribution of Al2O3 and ZrO2 grainswere prepared using self-made nanopowders as raw materials.The effects of Zr/Al mole ratio on the mechanical properties and microstructure were investigated, and the reinforced and toughening mechanism were discussed.The results showed that in the condition of Zr/Al mole ratio was 2:1 and calcined at 1550℃,the relatively density of the composite ceramic can reach to 96%,and the composite ceramics had the best mechanical properties,the bending strength, hardness and fracture toughness were 510 MPa,12GPa,6.5MPa·m1/2.The fracture mode of the composites was mainly intergranular fracture.Toughening mechanism of ZTA ceramics were zirconia phase-transformation toughening and second phase particle toughening because of the strong grain boundary cohesion when the Zr/Al mole ratio was 2:1.So the mechanical properties of the composites were improved.
Keywords/Search Tags:Al2O3-ZrO2 nanopowders, Co-precipitation method, Toughening mechanism, Phase transformation, Mechanical properties
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