use of metal templates for microcavity formation in alumina

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2.2. Properties and Applications of Alumina (Al2O3) Alumina is a widespread component of siliceous minerals. It often occurs as single crystal in the form of sapphire and ruby and in large deposits as the hydrated oxide bauxite (Al2O3· H2O) (McColm, 1983). The Bayer process is the main technique used for the industrial production of α- alumina. Bauxite, naturally contaminated with other oxides, is used as a starting material in the Bayer process (Moulson and Herbert, 1990). This involves raw material preparation, digestion, clarification, precipitation and calcination. Practically all the powder for the fabrication of alumina ceramics is prepared using this technique. A purer alumina product can be made by preparing ammonium alum (NH4Al(SO4)2) · 12H2O) (Liu, 2011). Among the aluminium oxide, -alumina is thermally the most stable phase. For example, ɣ-alumina will convert to α-alumina above 1000ºC. α-alumina has a hexagonal structure and two alumina molecules per unit, as shown schematically in Figure 2.1. Three oxygens form an equilateral triangle with aluminiums above and below the centre of the triangle. One of these groups is placed at each corner of a cube while another is placed at the centre of the cube. Figure 2.1. Schematic illustration of oxygen arrangement around Al 3+ ion in alumina (Source: McColm, 1983). 4
Alumina ceramic is one of the most widely studied and used advanced ceramic materials. Table 2.1 shows properties of alumina. Some selected properties of sintered α-alumina are shown in Table 2.2 (The purity of listed α- alumina is at least 99.5% and the density is at least 98% of the theoretical density. The nominal grain size is normally 5 µm). The crystal structure of corundum is illustrated in Figure 2.2. Structures and lattice parameters of stable alumina (corundum) and unstable aluminas are listed in Table 2.3. Table 2.1. Properties of alumina (Source: Insaco Inc., 2006) Property Value Density (g/cm 3 ) 3.9 Hardness (Rockwell 45N) 82 Melting Point ( o C) 2050 Tensile Strength (Kpsi) 54 Modulus of Elasticity (psi x 10 6 ) 46 Fracture Toughness (MPa m 1/2 ) 4.3 Coefficient of thermal expansion (x10 -6 / o C) 7.2 Thermal conductivity (W/m o K) 30.3 Volume resistivity (Ω-cm 2 /cm) >10 14 Table 2.2. Some properties of sintered α-alumina (Source: Claussen, 1976). 5
Page 1 and 2: USE OF METAL TEMPLATES FOR MICROCAV
Page 3 and 4: ACKNOWLEDGEMENTS I would like to ex
Page 5 and 6: ÖZET ALÜMİNA İÇİNDE MİKROBO
Page 7 and 8: 4.3.1. Alumina ....................
Page 9 and 10: Figure 3.4. Pressed samples: (a) be
Page 11 and 12: Figure 4.35. Phase equilibrium diag
Page 13 and 14: CHAPTER 1 INTRODUCTION Porous oxide
Page 15: 2.1. Porous Materials CHAPTER 2 LIT
Page 19 and 20: 2.3. Properties and Applications of
Page 21 and 22: Selection of stainless steels based
Page 23 and 24: Some physical properties of copper
Page 25 and 26: of some of the oxygen from the air
Page 27 and 28: not occupied by the flow of Cu from
Page 29 and 30: During the 4 hours soaking time at
Page 31 and 32: y the technique of dilatometry (Rah
Page 33 and 34: CHAPTER 3 EXPERIMENTAL In this chap
Page 35 and 36: Table 3.1. Properties of alumina po
Page 37 and 38: 3.2.1. Co-Pressing with Single-acti
Page 39 and 40: 3.3. Density Measurements The final
Page 41 and 42: Figures 4.3 and 4.4 show relative d
Page 43 and 44: Densification Rate (1/ o C) 0,005 0
Page 45 and 46: Densification Rate (1/ o C) 0,009 0
Page 47 and 48: (a) (b) (c) (d) (e) Figure 4.8. SEM
Page 49 and 50: Figure 4.10. EDS analysis of the Ti
Page 51 and 52: 4.3.3. Ti Diffusion into Alumina In
Page 53 and 54: Titanium advanced through alumina a
Page 55 and 56: Wt (%) Wt (%) 100 80 60 40 20 0 100
Page 57 and 58: Figure 4.22. EDS line analysis of t
Page 59 and 60: Densification Rate (1/ o C) 0,0069
Page 61 and 62: Figure 4.27, 28 and 29 belong to ED
Page 63 and 64: 4.3.5. Stainless Steel Diffusion in
Page 65 and 66: Wt (%) 50 45 40 35 30 25 20 15 10 5
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Wt (%) 70 60 50 40 30 20 10 0 Al (w
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4.3.7. Results of Sintering of Alum
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Wt (%) 40 35 30 25 20 15 10 5 0 Al
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CHAPTER 5 CONCLUSIONS Densification
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REFERENCES Alcoa, Inc., 2010, Alumi
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Isobe, T., Tomital, T., Kameshima,
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Yalamaç, E., 2010, Sintering, Co-S
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