臺灣博碩士論文加值系統

本研究探討Al2O3/Ni及Al2O3/(ZrO2+Ni)複合材的氧化行為，而這些複合材是在CO氣氛下，以無壓燒結方式製備。在Al2O3/Ni 複合材氧化過程中，鎳不斷的向外擴散累積，形成一連續且緻密的氧化層。其氧化機制包含：(1) 低溫 (1000-1100oC)時，鎳在氧化鋁基地中擴散的擴散控制機構，(2)高溫(1100-1300oC)時，氧在NiAl2O4中擴散的擴散控制機構。低溫時，氧化活化能為267±32 kJ/mole；高溫時，氧化活化能為578±24 kJ/mole。添加氧化鋯於複合材中會增加其氧化速率。在Al2O3/(ZrO2+Ni)複合材中，當氧化鋯含量低於10vol.%以下時，低溫為鎳在氧化鋁基地中擴散的擴散控制機構，高溫為氧在NiAl2O4中擴散的擴散控制機構。當氧化鋯添加量超過10vol.%以上時，複合材的氧化過程傾向為反應控制機構。此現象可用Percolation Theory來解釋。在Al2O3/(ZrO2+Ni)複合材中的氧化活化能會隨著氧化鋯添加量的增加而降低，而氧化鋯中是否含有Y2O3，對於氧化速率的增加亦有影響。

In the present study, the oxidation behavior of Al2O3/Ni and Al2O3/(ZrO2+Ni) composites are investigated. The composites are prepared by pressureless sintering in CO. For the oxidation of Al2O3/Ni composites, nickel diffuses outward and oxygen diffuses inward, a dense spinel layer is formed inside surface. The oxidation is divided into two stages: (1) the diffusion of nickel in the alumina grain boundary to control the oxidation at lower temperature (1000-1100oC). (2) The diffusion of oxygen in NiAl2O4 layer to control the oxidation at higher temperature (1100-1300oC). The activation energy of oxidation at lower temperature is 267±32 kJ/mole, at higher temperature 578±24 kJ/mole. For Al2O3/(ZrO2+Ni) composites, the present of zirconia enhances the oxidation rate of the composites. When the zirconia content is lower than 10vol.%, nickel diffusion tends to control oxidation at lower temperature and oxygen diffusion to control oxidation at higher temperature. When the zirconia content is higher than 10vol.%, the oxidation may be controlled by the reaction control mechanism. The critical zirconia content forms the percolation threshold. The stabilizer, such as Y2O3, in the tetragonal phase zirconia raises the amount of oxygen vacancies and increases the oxygen diffusion rate in zirconia.

Chapter 1 Introduction........................................1
Chapter 2 Literature Survey...................................3
2-1 The characteristics of Al2O3, ZrO2, and Ni................3
2-2 Oxidation.................................................3
2-2-1 Reactions of oxidation..................................3
2-2-2 Oxidation mechanism.....................................5
2-2-3 Oxidation of Al2O3/Ni composites........................6
2-2-3-1 Oxidation of nickel...................................7
2-2-3-2 Formation of NiAl2O4 spinel phase.....................8
2-2-4 Effect of ZrO2 on oxidation behavior....................9
Chapter 3 Experimental Procedures............................15
3-1 Preparation of Al2O3/Ni, Al2O3/(t-ZrO2+Ni), and Al2O3/(m-ZrO2+Ni) composites..........................................15
3-1-1 Starting materials.....................................15
3-1-2 Preparation of specimens...............................15
3-1-3 Phase identification...................................16
3-1-4 Density measurement....................................16
3-2 The oxidation behaviors of Al2O3/Ni、Al2O3/(tZrO2+Ni)、and Al2O3/(mZrO2+Ni).............................................22
3-2-1 The preparation of oxidation specimens.................22
3-2-2 Measurement of electrical resistivity..................22
3-2-3 Oxidation..............................................22
3-2-4 Analysis of the oxidation rate.........................23
3-2-5 X-ray diffraction analysis.............................23
3-2-6 SEM observation........................................23
3-2-6-1 Observation of oxidation surface.....................23
3-2-6-2 Observation of oxidation layer.......................23
Chapter 4 Results and Discussion.............................25
4-1 The characteristics of Al2O3/Ni, Al2O3/(t-ZrO2+Ni), and Al2O3/(m-ZrO2+Ni) composites.................................25
4-1-1 Thermodynamic analysis.................................25
4-1-2 The properties of the composites.......................26
4-1-3 Connectivity of Ni inclusions..........................27
4-2 Oxidation................................................27
4-2-1 The oxidation of Al2O3/Ni composites...................27
4-2-1-1 X-ray diffraction analyses...........................27
4-2-1-2 The oxidation behavior analysis......................30
4-2-1-2-1 Oxidation rate.....................................30
4-2-1-2-2 Microstructure observation.........................35
4-2-1-3 Oxidation mechanism..................................43
4-2-1-4 Activation energy of oxidation.......................46
4-2-2 Oxidation of Al2O3/(t-ZrO2+Ni) composites..............56
4-2-2-1 X-ray diffraction analysis...........................56
4-2-2-2 Oxidation behavior analyses..........................56
4-2-2-2-1 Oxidation rate.....................................56
4-2-2-2-2 Microstructure observation.........................56
4-2-2-3 Oxidation mechanism..................................66
4-2-2-4 Activation energy of oxidation.......................69
4-2-3 The oxidation of Al2O3/(m-ZrO2+Ni) composites..........75
4-2-3-1 X-ray diffraction analyses...........................75
4-2-3-2 Oxidation behavior analyses..........................75
4-2-3-2-1 Oxidation rate.....................................75
4-2-3-2-2 Microstructure observation.........................75
4-3 General discussion.......................................80
4-3-1 The oxidation of Al2O3/Ni and of Al2O3/(t-ZrO2+Ni) composites...................................................80
4-3-2 The oxidation of Al2O3/(t-ZrO2+Ni) and of Al2O3/(m-ZrO2+Ni) composites..........................................83
Chapter 5 Conclusions........................................85
References...................................................87
APPEXDIX....................................................A-1

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