本文第一部份將磷灰石單晶礦物垂直或平行c軸切割，並且於30°C，pH值=0-3之緩衝溶液中，做靜態基底面(0001)及側面(11 0)的溶解實驗，以評估軸向及差排露頭處的溶解行為。於pH=0-3 範圍內，且經過一段孕核期之後，均出現六邊形之溶蝕坑及溶蝕丘，隨時間長大，並碰撞合併在一起。但是在pH=0所得之溶蝕坑，有較明顯的台地(terrace)。一般而言，形成溶蝕丘的地方是屬於較抗腐蝕的地方。而(0001)面上的溶蝕坑，則是[0001]方向差排的露頭處，因雜質偏析，造成鄰近溶液未飽和而孕核與成長，是一個原子從紐結(kink)位置離開的過程，其臨界核的大小取決於溶液的pH值和溶液的不飽和程度。在pH=0-1條件下，[0001]方向的溶解速率大於<11 0>方向的溶解速率，而<11-20>方向大於<10-10>方向之溶解速率。在pH=0-3之情況下，其異向溶解速率為
rate(mole / m2h)＝kaH+n
對[0001]方向及<11-20>方向其k分別為2.15、1.61；n分別為1.44、1.30。並且其溶解速率在不同pH值下的關係為
[0001] > <11-20> > <10-10> for pH=0-1
但在大於pH=3時則為反轉的關係。另外，氫氧基磷灰石針狀奈米顆粒在熱水溶液的靜態浸泡，其尖端部份經擴散控制而變成棒狀(nanorods)，側邊則是界面擴散控制的溶解機制。熱水溶液溶解之氫氧基磷灰石針狀奈米顆粒的比表面積、孔洞大小分佈以及在77K下的氮氣等溫吸附/脫附曲線也在此論文中探討。
第二部分，利用Nd-YAG雷射融蝕金屬錫鈀材，通入氧，藉著高加熱/高冷卻速率，並且經歷特殊的相變化途徑，合成高密度的立方晶相(fluorite-type)、類二氧化鋯單斜晶相(baddeleyite-type)、

This thesis is about the kinetics of anisotropic acidic/hydrothermal dissolution of apatite bulk single crystal vs. nanorods, and the kinetic phase change of dense nanocondensates of SnO2 vs. Ni-dissolved SnO2 prepared by laser ablation condensation technique.

In the first regard, directional dissolution of a natural (OH,F,Cl)-bearing apatite has been studied at various solution pH values (0~3) and 30 oC. This apatite showed abnormally high O-H stretching frequencies due to the substitution of Cl for OH. The advance of dissolution front indicated that steady-state directional dissolution for pH = 0-2 followed an apparent rate law of
rate(mole / m2h)＝kaH+n,
where the rate constants (k) are 2.15 and 1.61; and the rate orders (n) are 1.44 and 1.30 for [0001] and <11 0> directions, respectively. Previous study, however, indicated a smaller n value (n = 0.55~0.70) for fluorapatite powders at higher pHs. A nonlinear pH dependence of logarithmic dissolution rate at a wide pH range implied that the surface active sites and/or rate-determining steps have changed when the acidity of solution and/or the composition of the apatite were changed. The opening of etch pits on basal planes further indicated that the dissolution rates along the three principal directions have the following relationship:
[0001] > <11-20> > <10-10> for pH=0-1,
but the order was reversed for pH > 3.

As a comparison, static immersion of needle-like hydroxyapatite nanoparticles in neutral hydrothermal solution at 100oC caused preferential dissolution along the crystallographic c-axis to form nanorods with a lower aspect ratio. The anisotropic dissolution behavior is due to diffusion-controlled rapid dissolution at the sharp tip, and interface-controlled dissolution at side surfaces in terms of active sites. Extensive dissolution was accompanied with amorphization via explosive generation of dislocations, forming corrugated surface with both negative and positive curvature regions. The amorphous residue was significantly Ca and OH depleted when treated in the hydrothermal solution at pH=3. The BET specific surface area of the apatite nanoparticles remained 45±1 m2/g after immersion in neutral solution at 100oC for 36 h, but drastically decreased to 24.5 m2/g in acidic (pH =3) solution at 100oC for 8 h due to coalescence of the partially amorphized apatite powders. The specific surface area and average pore size also remained nearly unchanged for the dry pressed powders subject to firing at 100oC, but decreased and increased, respectively when sintered shortly at 600oC in air. BJH measurements at 77 K indicated the N2 adsorption/desorption hysteresis loops shift toward high relative pressure for sintered/hydrothermally etched powders indicating a higher activation energy of forming overlain liquid-like nitrogen layers. This can be attributed to a lower surface energy of the powders due to their shape change and/or partial amorphization. Alternatively, desorption through cavitation via the small voids could occur, in particular for such treated samples with characteristic bimodal pore size distribution.

In the second subject, dense SnO2 with fluorite-type related structures were synthesized via very energetic Nd-YAG laser pulse irradiation of oxygen-purged Sn target. Combined effects of rapid heating to very high temperatures, nanophase effect, and dense surfaces account for the condensation of fluorite-type structure which transformed martensitically to baddeleyite-type accompanied with twinning, commensurate shearing and shape change. Alternatively Pa-3-modified fluorite-type hardly survived transformation to a-PbO2 type and rutile type in the dynamic process analogous to the case of static decompression. In addition, the rutile-type SnO2 nanocondensates have {110}, {100} and {101} facets, which are beneficial for {~hkl} vicinal attachment to form edge dislocations, faults and twinned bicrystals. The {011}-interface relaxation, by shearing along <011> directions, accounts for a rather high density of edge dislocations near the twin boundary thus formed. The rutile-type SnO2 could be alternatively transformed from orthorhombic CaCl2-type structure (denoted as o) following parallel crystallographic relationship, (0 1)r//(0 1)o; [111]r//[111]o, and full of commensurate superstructures and twins parallel to (011) of both phases. Furthermore, SnO2-NiO solid solution (ss) condensates were fabricated by laser ablation on Ni-Sn target at 1.1 J/pulse and oxygen flow of 50 L/min. AEM observations indicated that the particles were more or less coalesced/agglomerated as nano chain aggregate or in close packed manner. The Ni-rich condensates have rock salt structure with defect clusters not in paracrystalline distribution as would otherwise develop into the spinel phase. The Sn-rich condensates are predominantly rutile-type with minor baddeleyite-type, which are vulnerable to martensitic transformation/relaxation to form {101} incommensuare faults as well as epitaxial twin variants of rutile upon rapid cooling and/or electron irradiation. Islands of metallic Ni-Sn-NiSn were partially oxidized/solidified when deposited on silica glass.

Abstract………………………………………………………………………………..I
Table of contents IV
List of Tables VII
List of Figures VIII
List of Appendix XVIII

Chapter 1 Directional acidic dissolution kinetics of (OH,F,Cl)-bearing apatite

1.1 Introduction 1
1.2 Experimental 2
1.2.1 Preparation and characterization of apatite specimens 2
1.2.2 Dissolution experiments 4
1.3 Result 5
1.3.1 Characterization of the natural apatite 5
1.3.2 pH-dependent dissolution 7
1.3.3 Morphology of the dissolved surfaces 9
1.4 Discussion 9
1.4.1 The OH-related vibrations 10
1.4.2 Formation of etch pits and etch hillocks 12
1.4.3 Anisotropic dissolution 14
1.4.4 The n exponent and rate constant k 15
1.5 Conclusion 17

Chapter 2 Microstructural and surface development of needle-like hydroxy- apatite nanoparticles upon dissolution in hydrothermal solution

2.1 Introduction 28
2.2 Experimental 29
2.3 Results 30
2.3.1 Starting material 30
2.3.2 Hydrothermal dissolution 30
2.3.3 Hydrothermal acidic dissolution 31
2.3.4 IR spectrum 31
2.3.5 BET and BJH measurements 32


2.4 Discussion 33
2.4.1 Diffusion- vs. interface-controlled dissolution 33
2.4.2 Amorphization 34
2.4.3 Surface area and pore size distribution 35
2.4.4 Bioactive implant and hyperthermophiles implications 36

Chapter 3 Laser Ablation Condensation and Transformation of Dense SnO2

3.1 Introduction 52
3.2 Experimental 53
3.3 Results 54
3.3.1 TEM and EDX observations 54
3.4 Dissusion 57
3.4.1 Formation and stabilization of fluorite-type structure 57
3.4.2 Fluorite- vs. Pa -type structure for SnO2 and analogue dioxides 59
3.4.3 Martensitic transformation of fluorite-type SnO2 condensates 60
3.5 Conclusions 61

Chapter 4 Defect generation of rutile-type SnO2 nanocondensates: Imperfect oriented attachment and phase transformation

4.1 Introduction 68
4.2 Experimental 69
4.3 Results 70
4.3.1 Structure and composition of the condensates 70
4.3.2 Shape and defects of the condensates 71
4.3.3 Size distribution of the condensates 72
4.4 Discussion 73
4.4.1 Effect of radiant heating on condensates coagulation 73
4.4.2 Coalescence twin 74
4.4.3 Deformation and transformation induced defects 75
4.5 Conclusions 76

Chapter 5 SnO2-NiO solid solution condensates prepared by laser ablation route

5.1 Introduction 86
5.2 Experimental 88

5.3 Results 89
5.3.1 NiO-SnO2 and Ni-Sn deposits on silica glass 89
5.3.2 AEM of NiO-SnO2 nanocondensates on carbon-coated collodion film 90
5.4 Discussion 92
5.4.1 Defect chemistry and defect clusters of Sn-dissolved NiO 92
5.4.2 Defect chemistry and defect clusters of Ni-dissolved SnO2 93
5.4.3 Formation of Ni-dissolved SnO2 condensates with dense crystal structure vs. amorphous and rutile-type structure 93
5.4.4 Ni-Sn and NiO-SnO2 solid solution condensates: Implications for catalytic applications 94
5.5 Conclusions 95
References 112

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