use of metal templates for microcavity formation in alumina

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ABSTRACT USE OF METAL TEMPLATES FOR MICROCAVITY FORMATION IN ALUMINA Alumina ceramics with microtunnels are produced by compressing submicron sized alumina powder and Ti, Cu or stainless steel wires in a metal die before firing the compacts at 1350 o C for 4 hours. Diameters of wires ranged from 50 to 125 micrometers. Copper was found to completely melt and flow away from the compact leaving no trace of copper in alumina. Stainless steel diffused out into the alumina leaving few pores behind. Titanium, on the other hand, diffused into alumina at 20 to 30micrometers/hour and left plenty of Kirkendal porosity behind. The amount of porosity could have been increased further by applying intensive milling to the powder. But no milling was done in this study and hence a complete micro-tunnel was not obtained. The Kirkendal effect was observed to be effective in producing pores in the ceramic. Densification behavior of the ceramic was also investigated with a vertical dilatometer. Densities up to 93% were achieved in the ceramics. In some tests Ti metal plates were used as diffusion couples with alumina compacts. Similar diffusion behavior was observed with plates and wires. iv
ÖZET ALÜMİNA İÇİNDE MİKROBOŞLUK OLUŞTURULMASI İÇİN METAL ŞABLONLAR KULLANILMASI Mikro tüneller içeren alümina seramikler, mikron altı boyutlu alümina tozu ile titanyum, bakır ya da paslanmaz çelik tellerin metal bir kalıp ile sıkıştırılarak 1350 o C sıcaklıkta 4 saat pişirilmesi ile üretilmiştir. Tellerin çapları 50 ile 125 mikrometre arasında değişmektedir. Bakır, tamamen eriyik halde bulunmuş ve alümina içerisinde hiçbir iz bırakmadan akıp gitmiştir. Paslanmaz çelik ise gerisinde biraz gözenek bırakarak alümina içine difüze olmuştur. Öte yandan titanyum, alümina içine 20-30 mikrometre/saat hızla difüze olmakta ve arkasında fazlaca Kirkendall porozite kalıntısı bırakmaktadır. Gözeneklilik miktarı, tozlara yoğun öğütme uygulanarak daha da arttırılabilir. Fakat bu çalışmada öğütme kullanılmamıştır ve bu yüzden tam bir mikro tünel gözlenmemiştir. Seramiklerde oluşan gözeneklerde Kirkendall etkisi yoğun bir biçimde gözlenmiştir. Ayrıca seramiğin yoğunlaşma davranışı dikey dilatometre ile incelenmiştir. Seramiklerde % 93'e varan yoğunluk elde edilmiştir. Bazı testlerde, metal Ti plakalar, yoğunlaştırılmış alümina ile difüzyon çifti olarak kullanılmaktadır. Benzer difüzyon davranışı plaka ve teller kullanılarak da gözlenir. v
Page 1 and 2: USE OF METAL TEMPLATES FOR MICROCAV
Page 3: ACKNOWLEDGEMENTS I would like to ex
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 and 16: 2.1. Porous Materials CHAPTER 2 LIT
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
Page 73 and 74:
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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