Study On Preparation,Characterization And Properties Of Aluminum Niobium Oxide

This dissertation has conducted systemic research of aluminum niobium oxide?AlNbO₄?material preparation,microstructure observation,property estimation,preparation and property estimation of corresponding thermal barrier coatings,and the electrochemical performances.Some conclusions were obtained as follows.AlNbO₄ powder was prepared by solid-state reaction method.The forming mechanism of AlNbO₄ ceramic synthesized by solid state reaction was investigated through calculation and experiments.The results reveal that Al³⁺cation firstly diffuses into Nb₂O₅ crystal lattice and Al₂O₃-Nb₂O₅ solid solution is formed,then it transforms into AlNbO₄.The mixed powders of Al₂O₃ and Nb₂O₅ were calcined at 1350?for 1h,AlNbO₄ powder was synthesized.The crystal structure of AlNbO₄ was refined by Rietveld refinement using X-raypowder diffraction data.The equilibrium crystal structure of AlNbO₄ was investigated by using the first principle calculations and it had a good agreement with the experiment result.With the theory of elasticity,the elastic constants and elasticmoduli of AlNbO₄ was analyzed and predicted.The calculated Deby temperature was distributed at 651K.AlNbO₄ ceramic bulks were prepared using pressure less sintering and hot pressing sintering method.The phase composition,relative density,microstructure,and mechanical properties of as-prepared samples were studied.In view of the properties of AlNbO₄ceramic bulks,the best synthesis parameter pressure less sintering was calcined at 1450?for 6h when the relative density bigger than 90%.Dense AlNbO₄ ceramics were successfully synthesized by hot pressing sintering method.The best synthesis parameter was calcining at 1400?for 90min.The relative density is 99.31%and higher than the pressureless sintering sample.The bending strength was 326MPa and the fracture toughness was 4.997MPa·m^1/2.Then,the mechanical properties and thermal physical properties of dense AlNbO₄ ceramic were tested.The Vickers hardness was 6.1GPa.The elastic constants obtained by experiment are in good agreement with the calculation results.The average linear thermal expansion coefficient?CTE?in temperature range 773¹473K is?4.8⁶.2?×10^-6K^-1,while the expansion coefficient along crystal axisin temperature are:?_a=?6.97±0.30?×10^-6K^-1,?_b=?0.93±0.05?×10^-6K^-1,?_c=?9.72±0.24?×10^-6K^-1.The calculated minimum lattice thermal conductivity of AlNbO₄ was distributed at 1.95W/m·K.The thermal conductivity of AlNb O₄ is 2.06W/m·K at 1400?which had a good agreement with the calculation result.The phase stability results reveal that the AlNb O₄ceramic was phase-stable up to at least 1400?,which was better than that of YSZ?about1200??.The result showed that AlNbO₄ could be suitable for thermal barrier coating.The agglomerated AlNbO₄ powders were prepared by ball-milling,and spray drying technology separately.Their process parameters are studied respectively.The powders produced by the spray drying method are more suitable for the atmospheric plasma spraying?APS?.The AlNbO₄ thermal barrier coatings were prepared by APS method.The classic spraying technologies were decided by the way of experiments.The phase compositions of AlNbO₄ before and after thermal spraying have no change.The thermal conductivity of the coating was 1.36W·m^-1·K^-1.The cohesion strength was 21MPa.Niobium-based oxides have been considered as interesting candidates for anode material in advanced lithium ion batteries.Because Nb⁵⁺/Nb⁴⁺and Nb⁴⁺/Nb³⁺redox couples in niobium-based oxides are located between 1.0 and 2.0V and it is two-electron transfer reaction per niobium,leading to a higher storage capacity.As a lithium-ion batteries anode,AlNbO₄ delivers a good reversible capacity and rate capability.The discharge capacity was as high as 141.4 mAh·g^–1 after 50 charge.and the capacity retentions for AlNbO₄ was 90.7%compared to the fifth cycle.When the current density increases to 5C,AlNbO₄ anode displays 73.6mAh·g^–1 of reversible discharge capacity at the 50th cycle.