use of metal templates for microcavity formation in alumina

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at around 1350 o C the metal oxidizes and the metal ions diffuse out into the alumina matrix. A counterdiffusion of Al +3 ions occurs in reverse direction. But the former is faster due to higher ionic mobility of the Ti +4 ions. The misbalance in the diffusion rates of the two components leads to the formation of pores behind Ti +4 ions. This effect was first recognized by Smigelkas and Kirkendal in 1947 and hence is named the Kirkendal effect (Kirkendall et al., 1947). In the late 1940s, Kirkendall explored that the interface between copper and zinc in brass moved at an elevated temperature due to their different diffusion rates. This rare occurence was later called as the Kirkendall effect. Porous materials, which contain micro-pores, can be created with combination of metal templates-Al2O3 in the alumina structure. In this case, the importance of the diffusion is great with Kirkendall effect. The Kirkendall effect derives from the difference in exclusive diffusional movability between the two elements of a binary diffusion couple. As a result of diffusion with Kirkendall effect at high temperatures, the formation of new phases (such as Al2TiO5) are most likely to occur in the material interface. Goodshaw and his research team (Goodshaw et al., 2009) investigated the microcavity formation conditions, mechanism and kinetics in alumina using Ti templates. They emphasized the importance of sintering temperature and diffusion for the creation of microcavity. Buscaglia and Carry (Buscaglia et al., 1993) examined reaction sintering of aluminium titanate (Al2TiO5). The mechanism of Al2TiO5 formation from the starting oxides Al2O3 and TiO2 has been carefully investigated by Freudenburg and Mocellin (Freudenburg and Mocellin, 1987-1988), who have underlined the importance of the nucleation and growth process microstructure in the temperature range 1280-1400 o C. In this thesis, densification behavior and specific surface area (BET) of different alumina powders and SEM observations of the alumina samples, that contain metal templates were investigated. Ceramic materials are inert and resistant to corrosion. In Chapter 2 of this thesis, a description of the porous materials, properties and applications of materials, biomedical materials and the Kirkendall effect, its scope and a theory of BET, Archimedes density measurement and densification rate will be presented. The experimental procedure and the results of this study are given and discussed in Chapters 3 and 4, while the conclusions are stated in the last chapter. 2
2.1. Porous Materials CHAPTER 2 LITERATURE REVIEW Porous materials refer to solids possessing pores. The porosity is the fraction of the pore volume to the total volume. Pores inside the solids can be classified into open pores and closed pores. Open pores are connected to the outside of the material surface and can be penetrated by fluids; closed pores are isolated holes. Porous ceramics are used for many special engineering applications. Their specific structural properties make them perfect materials for some applications. Especially thier high separation efficiency, non-corrosive structures and thermal resistance as well as mechanical strength and structural stability makes them very efficient materials for engineering applications (Dong and Diwu, 2007). Moreover porous ceramics have low mass density, high chemical saturation and resistance to abrasion. The other causes of preference for porous ceramics for engineering ceramics are the abundance of low-cost source of raw materials (Erol, 2008). Characteristic properties of porous ceramics make them suitable for different applications like: filters for molten metals and hot gases, refractory linings for furnaces, and porous implants in the area of biomaterials (Sepulveda and Binner, 1999), thermal coatings, human bone substrates. (Sadowski and Samborski, 2007). And also porous ceramics are widely used as catalyst carriers, separation membranes and diffusers (Isobe and Tomita1, 2006). 3
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: CHAPTER 1 INTRODUCTION Porous oxide
Page 17 and 18: Alumina ceramic is one of the most
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
Page 67 and 68:
Wt (%) 70 60 50 40 30 20 10 0 Al (w
Page 69 and 70:
4.3.7. Results of Sintering of Alum
Page 71 and 72:
Wt (%) 40 35 30 25 20 15 10 5 0 Al
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CHAPTER 5 CONCLUSIONS Densification
Page 75 and 76:
REFERENCES Alcoa, Inc., 2010, Alumi
Page 77 and 78:
Isobe, T., Tomital, T., Kameshima,
Page 79:
Yalamaç, E., 2010, Sintering, Co-S
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