臺灣博碩士論文加值系統

本論文主要是研究東大石(又名六方水鋁石, tohdite)與氧化鋁的合成與相變化。在高溫下，利用靜態加壓的方式合成六方水鋁石;另外，在通入氧氣的條件下，以雷射剝蝕(laser ablation)金屬鋁靶形成氧化鋁凝聚物。

在第一部分裡，將含水之Al2O3 -TiO2 (莫耳比78:22)凝膠在各種的溫度壓力條件下燒結，並以XRD、 FTIR、光學顯微鏡和電子顯微鏡來進行鑑定。 當溫度低於 675oC時, 樣品在常壓下仍保持非晶質的相，但當壓力在1.5 kbar時則變成含鈦的六方水鋁石，並沿結晶的c軸伸長，形成發達的(0001)基部與{ }面。 六方水鋁石因含有羥(氫氧)基，所以在電子束的照射下易形成平行基層(basal layer)的孔洞。六方水鋁石可含Ti4+至3% 原子百分比，且Ti4+可取代在四面體或八面體位置上的Al3+ , 形成超晶格和缺陷微結構。在另一更高的溫度壓力條件下(高於675oC 和8 kbar)則形成更穩定之含鈦的剛玉(corundum) 結構，形貌介於六角形-菱形(hexagonal- rhombohedral)之間，並與金紅石(rutile)核種形成磊晶關係。含鈦的六方水鋁石和剛玉的合成可用來闡明以溶凝膠方式形成含過量氧化鋁變質岩(peraluminous metamorphic)之機制。而含奈米孔洞和細層的六方水鋁石可能具有催化應用上的價值。

第二部分是利用Nd-YAG 脈衝雷射在通入氧氣的情形下剝蝕金屬鋁靶，在快速的加熱/冷卻的效應下合成非晶質的Al2O3 奈米凝聚物。 在電子束的照射下，高於臨界粒徑20nm的奈米凝聚物會發生相分離並形成

Abstract
The present thesis focused on the synthesis and phase transformation of tohdite and alumina via static compression of gels at high temperature-pressures and dynamic laser ablation condensation of metal target under oxygen background gas.

In part I, hydrous Al2O3-TiO2 (78:22 in molar ratio) gel was fired at various PT conditions using a piston-cylinder apparatus and identified by XRD, FTIR, optical microscopy and electron microscopy. Below 675oC, the sample remained amorphous at ambient pressure, yet transformed at 1.5 kbar to Ti-doped tohdite, which is elongated along the crystallographic c-axis, with well-developed (0001) base and {10 0} faces. Tohdite has a significant water/hydroxy content and is therefore susceptible to pore coalescence parallel to the basal layer upon electron dosage. Tohdite also contains Ti4+ up to 3 at.%, which replaces Al3+ in tetrahedral and/or octahedral sites to form superstructures and defect microstructures. In contrast, a higher T-P condition (above 675oC and 8 kbar) caused the formation of more stable Ti-doped corundum, which is hexagonal-rhombohedral crystal form and in epitaxial association with rutile nuclei. Ti-doped tohdite and corundum shed light on a sol-gel route for their occurrence in peraluminous metamorphic rock. The nanoporous and nanodelaminated tohdite may have potential catalytic applications (Part I).

In part II, amorphous Al2O3 nanocondensates were synthesized via very energetic Nd-YAG laser pulse irradiation of oxygen-purged Al target for a very rapid heating/cooling effect. The nanocondensates above a critical diameter of 20 nm were phase separated as

Contents
致謝………… ………….……………..………..…..…….….I
中文摘要……………………….……………..………..………III
Abstract……………………….…………..………..…...…...VI
Contents…….………………………………..…………..…...VIII
List of Tables …………………………..………………..…...XI
List of Figures………………………………….…………………XII

Part I The synthesis and phase transformation of Tohdite

Abstract…………………………………… …….….……………..1
1. Introduction…………………… ……….……...….…..…...1
2 Experimental procedure…….…… ……….………..….………2
2.1. Materials
2.2. Methods
3. Results……………….…..…………….…….…………….……4
3.1. XRD
3.2. FT-IR spectrum
3.3. Optical polarized microscopy
3.4. SEM
3.5. TEM
4. Discussion…………………………………. ……….. ……….8
4.1. Catalytic nuclei and energetics for tohdite and corundum
4.2. Transient phases at specific TP path
4.3. Superstructure and defects of Ti-doped tohdite
4.4. Industrial and geological implications of Ti-doped tohdite and

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